Pneumonia is an acute inflammatory condition of the lung tissue, primarily affecting the , the tiny air sacs in the lungs where gas exchange occurs between oxygen and carbon dioxide [1]. This inflammation leads to the alveoli filling with fluid, pus, or mucus, impairing normal respiration and resulting in symptoms such as cough, fever, and difficulty breathing [2]. The condition is most commonly caused by infectious agents, including bacteria such as pneumococcus, viruses like , , and , as well as fungi including and . Non-infectious causes, such as or radiation exposure, also exist but are less frequent. Pneumonia can affect individuals of all ages, though it poses a higher risk for and , particularly those with underlying health conditions like , , or compromised function. Diagnosis typically involves clinical evaluation, , and laboratory tests such as or . Treatment depends on the etiology, with used for bacterial pneumonia and for viral forms, while severe cases may require hospitalization and . Preventive strategies include vaccination with the and , along with public health measures like and to combat rising . The global burden of pneumonia remains significant, making it a leading cause of morbidity and mortality, especially in vulnerable populations.

Definition and Pathophysiology

Pneumonia is an acute inflammatory condition affecting the lung parenchyma, primarily involving the , the microscopic air sacs responsible for gas exchange between oxygen and carbon dioxide [1]. This inflammation leads to the alveoli filling with fluid, pus, or mucus, impairing normal respiration and resulting in symptoms such as cough, fever, and difficulty breathing [2]. The pathophysiological process begins when infectious or non-infectious agents trigger an immune response in the lower respiratory tract, leading to increased vascular permeability, infiltration of inflammatory cells such as neutrophils and macrophages, and the accumulation of exudate within the alveolar spaces [5]. This consolidation of lung tissue reduces compliance and disrupts ventilation-perfusion matching, causing hypoxemia and, in severe cases, respiratory failure.

Infectious Pathogens and Mechanisms of Infection

The majority of pneumonia cases are caused by infectious agents, including bacteria, viruses, fungi, and, less commonly, parasites [6]. These pathogens typically gain access to the lungs through inhalation of airborne droplets from infected individuals during coughing or sneezing, or via aspiration of oropharyngeal secretions [7]. Once in the alveoli, they overcome local defense mechanisms such as mucociliary clearance and alveolar macrophages, initiating an inflammatory cascade.

Bacterial pneumonia, particularly in adults, is most commonly caused by pneumococcus, which accounts for the majority of community-acquired cases [8]. This pathogen adheres to respiratory epithelial cells, evades phagocytosis through its polysaccharide capsule, and releases toxins that damage host tissues. Other bacterial causes include , , , and , each with distinct virulence factors and mechanisms of lung invasion [5].

Viral pneumonia, especially prevalent in children and during seasonal epidemics, is frequently caused by respiratory viruses such as A and B, , , and adenoviruses [10]. Viruses infect respiratory epithelial cells, leading to cell lysis, disruption of the mucosal barrier, and secondary bacterial superinfection. Viral infections often precede or predispose individuals to more severe bacterial pneumonia, exacerbating the clinical picture.

Fungal causes of pneumonia, such as , , and , are less common and primarily affect individuals with compromised function, including those with HIV, patients undergoing immunosuppressive therapy, or individuals with diabetes [11]. These fungi can establish chronic or disseminated infections due to impaired host defenses.

Non-Infectious Causes and Pathophysiological Pathways

In rare instances, pneumonia may arise from non-infectious etiologies, which do not involve microbial agents and are therefore not contagious [5]. These include aspiration of gastric contents or foreign substances, leading to chemical pneumonitis, also known as . Radiation therapy for thoracic malignancies can induce lung injury and fibrosis, resulting in radiation pneumonitis. Additionally, exposure to toxic chemicals, autoimmune disorders, and adverse drug reactions may trigger inflammatory responses in the lung parenchyma, mimicking infectious pneumonia [5].

The pathophysiology of non-infectious pneumonia often involves direct tissue injury, oxidative stress, and activation of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) and interleukin-1 (IL-1), leading to alveolar damage and impaired gas exchange. Unlike infectious forms, these conditions require targeted diagnostic evaluation and specific therapeutic interventions tailored to the underlying cause rather than antimicrobial agents.

Impact on Gas Exchange and Respiratory Function

The hallmark of pneumonia's pathophysiology is the disruption of normal gas exchange due to alveolar filling and interstitial inflammation. As the alveoli become consolidated with exudate, their ability to participate in oxygen and carbon dioxide diffusion is severely compromised. This results in ventilation-perfusion (V/Q) mismatch, intrapulmonary shunting, and ultimately, hypoxemia. The degree of respiratory impairment correlates with the extent and location of lung involvement, with multilobar or bilateral disease posing a higher risk of acute respiratory failure.

Reduced lung compliance increases the work of breathing, leading to tachypnea and use of accessory muscles. In severe cases, this can progress to acute respiratory distress syndrome (ARDS), characterized by diffuse alveolar damage, widespread infiltrates on imaging, and refractory hypoxemia [14]. Additionally, systemic inflammation may contribute to sepsis and multi-organ dysfunction, particularly in vulnerable populations such as the elderly or those with pre-existing comorbidities like or [5]. Early recognition of these pathophysiological changes is critical for timely intervention and improved clinical outcomes.

Causes and Types of Pneumonia

Pneumonia is a heterogeneous condition arising from a variety of infectious and non-infectious agents, which can be classified based on the causative pathogen and the clinical context in which the infection is acquired. The primary categories include bacterial, viral, fungal, and non-infectious forms, each with distinct etiologies, risk factors, and implications for diagnosis and treatment. Understanding the specific cause is critical for guiding appropriate therapy and improving patient outcomes.

Bacterial Causes

Bacterial pneumonia is the most common form in adults, particularly in community-acquired cases. The leading pathogen is pneumococcus, a Gram-positive bacterium responsible for the majority of community-acquired pneumonia (CAP) cases [8]. This organism typically causes a rapid-onset illness characterized by high fever, productive cough with purulent or blood-tinged sputum, pleuritic chest pain, and signs of pulmonary consolidation.

Other significant bacterial agents include:

  • Haemophilus influenzae, often associated with chronic respiratory conditions such as .
  • Mycoplasma pneumoniae, which causes atypical pneumonia with milder, more insidious symptoms such as dry cough, headache, and malaise. This pathogen has been increasingly reported, especially during influenza seasons [17].
  • Legionella pneumophila, which can cause severe pneumonia, particularly in immunocompromised individuals or those with underlying health conditions, and may present with gastrointestinal or neurological symptoms.
  • Staphylococcus aureus, including methicillin-resistant strains (MRSA), which are more commonly associated with hospital-acquired pneumonia (HAP) or post-influenza superinfections.
  • Pseudomonas aeruginosa, a Gram-negative bacillus frequently implicated in nosocomial and ventilator-associated pneumonia (VAP), especially in patients with structural lung disease or prolonged hospitalization [18].

Viral Causes

Viral pneumonia is a frequent cause of respiratory infection, particularly in children and during seasonal epidemics. Common viral agents include:

  • Influenza viruses (types A and B), which can cause severe lower respiratory tract infections and predispose to secondary bacterial pneumonia [10].
  • respiratory syncytial virus (RSV), a major cause of bronchiolitis and pneumonia in infants and young children.
  • SARS-CoV-2, the virus responsible for COVID-19, which can lead to severe viral pneumonia and acute respiratory distress syndrome (ARDS) [5].
  • adenovirus and metapneumovirus, which can also cause lower respiratory tract infections, particularly in immunocompromised hosts.

Viral pneumonia often presents with a more gradual onset than bacterial forms, featuring fever, dry cough, fatigue, and systemic symptoms like myalgia and headache. Radiologically, it may show bilateral interstitial or ground-glass opacities rather than lobar consolidation.

Fungal and Parasitic Causes

Fungal pneumonia is less common and typically affects individuals with compromised function. Key fungal pathogens include:

  • Pneumocystis jirovecii, which causes life-threatening pneumonia in patients with HIV/AIDS, organ transplant recipients, or those on immunosuppressive therapy.
  • Aspergillus species, which can lead to invasive aspergillosis, particularly in neutropenic patients or those with structural lung disease.
  • Cryptococcus neoformans, Histoplasma capsulatum, Coccidioides immitis, and Blastomyces dermatitidis, which are endemic in certain geographic regions and can cause pulmonary disease in both immunocompetent and immunocompromised individuals [21].

Fungal infections may present with chronic cough, weight loss, night sweats, and progressive dyspnea. Imaging often reveals nodules, cavities, or diffuse infiltrates, and diagnosis frequently requires specialized microbiological testing or biopsy.

Non-Infectious Causes

In rare instances, pneumonia can result from non-infectious mechanisms, which are not transmissible and require distinct diagnostic and therapeutic approaches. These include:

  • , caused by the inhalation of gastric contents, food, or oropharyngeal secretions, leading to chemical pneumonitis or secondary infection.
  • Radiation-induced lung injury (radiation pneumonitis), which can occur after thoracic radiotherapy for cancers such as .
  • Inhalation of toxic chemicals or irritants, such as chlorine or ammonia, resulting in acute lung inflammation.
  • Autoimmune or drug-induced lung disease, where medications or systemic conditions trigger an inflammatory response in the lung parenchyma [5].

These forms of lung inflammation may mimic infectious pneumonia clinically and radiologically but require management focused on removing the offending agent, supportive care, and sometimes immunosuppressive therapy.

Classification by Clinical Context

Pneumonia can also be classified based on the setting in which it is acquired:

  • Community-acquired pneumonia (CAP): Occurs outside of healthcare facilities and is most commonly caused by Streptococcus pneumoniae, Haemophilus influenzae, and atypical bacteria like Mycoplasma pneumoniae.
  • Hospital-acquired pneumonia (HAP): Develops 48 hours or more after hospital admission and is often due to multidrug-resistant (MDR) organisms such as Pseudomonas aeruginosa and MRSA.
  • Ventilator-associated pneumonia (VAP): A subset of HAP occurring in patients on mechanical ventilation, with similar pathogens and higher mortality [23].

Understanding the type and cause of pneumonia is essential for selecting appropriate empiric antimicrobial therapy, preventing complications, and implementing effective public health measures such as and .

Symptoms and Clinical Presentation

Pneumonia presents with a range of clinical manifestations that vary in severity and specificity depending on the causative agent, the patient’s age, and underlying health status. The hallmark symptoms arise from the inflammatory response in the lung parenchyma, particularly the alveoli, leading to impaired gas exchange and respiratory distress [1]. The clinical picture can be categorized into typical symptoms, atypical presentations, and age-specific variations, particularly in vulnerable populations such as infants and the elderly.

Common Symptoms in Adults

The most frequent symptoms of pneumonia in adults include a persistent , often productive with yellow, green, or blood-tinged sputum, high accompanied by chills, and (difficulty breathing) [25]. The cough may be dry in viral or atypical forms but is typically productive in bacterial pneumonia. Patients frequently experience that worsens with deep breaths or coughing due to inflammation of the pleura. Additional systemic signs include , malaise, excessive sweating, tachypnea (rapid breathing), and tachycardia [26]. In severe cases, especially among the elderly or those with comorbidities, symptoms may escalate to include confusion, cyanosis (bluish discoloration of lips or nails indicating hypoxia), and signs of septic shock such as hypotension [27].

Clinical Differences by Etiology

The clinical presentation of pneumonia varies significantly based on its cause—bacterial, viral, or fungal—reflecting differences in pathogen virulence and host immune response.

Bacterial Pneumonia

Bacterial pneumonia, most commonly caused by pneumococcus, typically presents with an acute onset and severe symptoms. Patients often exhibit high fever (often >38.5°C), chills, productive cough with purulent or “rusty” sputum, and clear signs of consolidation on physical examination such as bronchial breath sounds, dullness to percussion, and tactile fremitus [28]. Laboratory findings may show leukocytosis and elevated inflammatory markers like (CRP). This form is more prevalent in older adults and those with or other comorbidities [5].

Viral Pneumonia

Viral pneumonia, caused by pathogens such as virus, (RSV), or , tends to have a more gradual onset with milder initial symptoms. Patients often present with moderate fever, dry cough, myalgia, headache, and nasal congestion, resembling a severe upper respiratory infection [30]. Dyspnea may develop later, especially in immunocompromised individuals. Radiologically, viral pneumonia often shows bilateral interstitial or ground-glass opacities rather than lobar consolidation [31].

Fungal Pneumonia

Fungal pneumonia, seen primarily in immunocompromised individuals such as those with or on immunosuppressive therapy, presents with a subacute or chronic course. Symptoms include chronic cough, persistent fever, night sweats, weight loss, and progressive dyspnea [21]. Invasive forms, such as those caused by , may lead to hemoptysis and cavitary lesions on imaging. These infections require specific antifungal therapies and are often diagnosed through microbiological cultures or serological testing [33].

Atypical Pneumonia

Atypical pneumonia, often caused by , , or , presents with less specific symptoms compared to typical bacterial pneumonia. Patients may have a persistent dry cough, low-grade fever, malaise, headache, and myalgias, with minimal physical findings despite significant radiological abnormalities [34]. infections can be more severe, with gastrointestinal symptoms like diarrhea and neurological manifestations such as confusion. Radiologically, atypical pneumonia shows diffuse, bilateral interstitial infiltrates rather than focal consolidation, and the bronchogram air sign is less prominent [35].

Age-Specific Presentations

In Infants and Young Children

In neonates and infants (0–12 months), pneumonia may present with non-specific signs such as feeding difficulties, tachypnea, irritability, lethargy, or apnea, with fever sometimes absent or mild [36]. The diagnosis can be delayed due to this atypical presentation. In children aged 1–5 years, symptoms become more recognizable, including high fever, productive cough, tachypnea, and respiratory distress with retractions [37]. School-aged children (>5 years) often present similarly to adults, with pleuritic chest pain and persistent cough, though some may experience extrapulmonary symptoms like rash or joint pain in cases of Mycoplasma infection [38].

In the Elderly

Older adults, particularly those over 65, may not exhibit classic symptoms. Instead, they may present with confusion, altered mental status, or falls, with minimal respiratory complaints [39]. This atypical presentation increases the risk of delayed diagnosis and severe outcomes, including sepsis and multi-organ failure [40].

The timely recognition of these diverse clinical presentations is essential for prompt diagnosis and appropriate management, particularly in high-risk groups. A high index of suspicion, especially in the presence of tachypnea, hypoxia, or systemic symptoms, should prompt further evaluation with and laboratory testing to confirm the diagnosis and guide treatment [41].

Diagnosis and Imaging Techniques

The diagnosis of pneumonia relies on a combination of clinical evaluation, imaging techniques, and laboratory tests to confirm the presence of pulmonary inflammation, identify the likely etiological agent, and assess disease severity. Among these, imaging—particularly chest radiography—plays a central role in establishing the diagnosis and guiding clinical management. Accurate interpretation of radiological findings allows clinicians to differentiate pneumonia from other respiratory conditions and detect potential complications early.

Radiographic and Computed Tomography Findings

The chest X-ray is the primary imaging modality used to diagnose pneumonia and remains essential for confirming clinical suspicion [42]. It enables visualization of pulmonary infiltrates, areas of consolidation, and fluid accumulation within the alveoli, all characteristic of infectious or inflammatory lung processes [43]. In typical bacterial pneumonia, often caused by , the radiograph typically shows lobar or segmental consolidation with well-defined opacities that respect anatomical boundaries [35]. A hallmark sign is the air bronchogram, where air-filled bronchi are visible within consolidated lung tissue, indicating alveolar filling with exudate while airways remain patent [45].

In contrast, atypical pneumonia, commonly due to pathogens like or , presents with different radiological patterns. These include bilateral, diffuse, or peribronchial opacities, often described as ground-glass opacities or interstitial infiltrates, which may be disproportionate to the patient’s clinical symptoms [31]. Viral pneumonias, including those caused by or , frequently show bilateral ground-glass changes and can mimic interstitial lung diseases [30].

When the chest X-ray is inconclusive or complications are suspected, computed tomography (CT) of the thorax provides superior detail and is particularly valuable in complex cases [48]. CT scans can reveal subtle consolidations, nodules, cavitations, and early signs of complications such as abscess formation or pleural involvement [49]. In critically ill patients or those with immunocompromise, CT is often used to exclude alternative diagnoses such as or [50].

Detection of Complications on Imaging

Imaging is critical for identifying complications that may require urgent intervention. The presence of pleural effusion, a common complication of bacterial pneumonia, appears on chest X-ray as a meniscus-shaped opacity at the lung base, often obscuring the diaphragmatic contour [51]. In upright films, larger effusions cause blunting of the costophrenic angles, while decubitus views can detect smaller, free-flowing fluid. When infection spreads to the pleural space, it results in empyema, which may show loculations or septations on CT, necessitating drainage [52].

Another serious complication is lung necrosis leading to pulmonary abscess, typically associated with pathogens like or anaerobes. Radiologically, this appears as a thick-walled cavity containing an air-fluid level, often in the upper lobes or dependent lung segments, particularly in cases of [53]. CT imaging enhances the characterization of such cavities and helps differentiate abscesses from other cavitary lung lesions such as tumors or fungal infections [54].

Role of Other Diagnostic Imaging and Functional Assessments

While chest imaging is central, other tools support the diagnostic process. Lung ultrasound has gained prominence, especially in pediatric and critical care settings, due to its portability and lack of ionizing radiation. It can detect consolidations, pleural effusions, and dynamic air bronchograms, making it useful for bedside evaluation [55]. In neonates and infants, where clinical signs may be subtle, lung ultrasound improves early detection of pneumonia even in the absence of fever or cough [56].

Additionally, pulmonary function tests (PFTs) may be used during follow-up to assess residual functional impairment after pneumonia. Although not used acutely, spirometry and measurement of diffusing capacity for carbon monoxide (DLCO) can reveal restrictive patterns or reduced gas exchange, particularly in cases of severe or recurrent pneumonia [57]. These tests are especially relevant in patients with pre-existing or those who experience persistent symptoms post-recovery [58].

Integration with Clinical and Laboratory Findings

Imaging must always be interpreted in conjunction with clinical and laboratory data. Biomarkers such as and help distinguish bacterial from viral etiologies and guide antibiotic use [14]. Similarly, microbiological investigations—including , , and molecular testing—are essential for identifying the causative pathogen, especially in severe or hospital-acquired cases [60]. In immunocompromised patients, advanced diagnostics such as bronchoalveolar lavage via may be required to obtain samples for culture and cytology [61].

Ultimately, the integration of imaging with clinical assessment and laboratory results enables accurate diagnosis, appropriate classification of pneumonia severity using tools like the CURB-65 score or Pneumonia Severity Index (PSI), and timely initiation of targeted therapy [41]. Early and precise diagnosis not only improves outcomes but also supports antimicrobial stewardship by minimizing unnecessary antibiotic use.

Treatment and Antibiotic Protocols

The treatment of pneumonia is tailored to the underlying cause, severity of illness, and patient-specific risk factors. Antibiotic therapy is the cornerstone of management for bacterial pneumonia, while viral and fungal forms require distinct therapeutic approaches. The selection of antibiotics follows established protocols based on the setting of acquisition—whether community-acquired (CAP) or hospital-acquired (HAP)—and the patient's comorbidities, which influence the likelihood of infection by multidrug-resistant (MDR) organisms [41].

Antibiotic Therapy for Community-Acquired Pneumonia (CAP)

For adults with mild to moderate community-acquired pneumonia, the first-line antibiotic is high-dose , effective against Streptococcus pneumoniae, the most common bacterial pathogen [64]. In patients with comorbidities such as , diabetes, or recent antibiotic use, combination therapy is recommended. This typically includes a (such as amoxicillin/clavulanic acid or a third-generation ) plus a (e.g., ) to cover atypical pathogens like Mycoplasma pneumoniae and Legionella pneumophila [41]. Alternatively, a respiratory such as or may be used as monotherapy in these higher-risk patients [66].

Hospitalized patients with moderate to severe CAP are typically treated with intravenous antibiotics, often combining a (e.g., ceftriaxone) with a or using a fluoroquinolone alone. This dual approach enhances coverage against both typical and atypical bacteria and has been associated with improved outcomes, including reduced mortality [41]. The duration of antibiotic therapy is generally 5 to 7 days for uncomplicated cases, but may be extended in the presence of complications or slow clinical response [68].

Antibiotic Therapy for Hospital-Acquired and Ventilator-Associated Pneumonia (HAP/VAP)

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) require broader-spectrum empiric therapy due to the high risk of infection by MDR pathogens. Common causative agents include Gram-negative bacilli such as Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii, as well as [23]. Initial empiric treatment should include an antipseudomonal (e.g., piperacillin/tazobactam, ceftazidime, cefepime, or ) combined with either an or an antipseudomonal [70].

In cases where MRSA is suspected—such as in patients with recent hospitalization, indwelling devices, or prior MRSA infection—additional coverage with or is essential [71]. However, it is critical to de-escalate therapy within 48 to 72 hours based on microbiological results and clinical improvement to minimize the development of further resistance and reduce adverse effects [70]. This principle is a key component of programs, which aim to optimize antibiotic use and combat the growing threat of resistance [73].

Management of Atypical and Resistant Pneumonia

Atypical pneumonia, caused by pathogens such as Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella pneumophila, does not respond to standard beta-lactam antibiotics like . Instead, treatment relies on antibiotics effective against intracellular organisms, including , (e.g., doxycycline), and respiratory fluoroquinolones [5]. For severe Legionella infections, fluoroquinolones are preferred due to their superior intracellular penetration and bactericidal activity [70].

In cases of antibiotic-resistant pneumonia, precise microbiological diagnosis is paramount. This includes blood cultures, sputum Gram staining and culture, and bronchoscopic sampling when necessary [70]. Targeted therapy for resistant organisms may involve newer agents such as , , or , particularly for carbapenem-resistant Enterobacterales (CRE) or MDR Pseudomonas aeruginosa [77]. Inhaled antibiotics are also emerging as adjunctive therapy, especially in chronic lung infections, to achieve high local concentrations while minimizing systemic toxicity [78].

Emerging Therapeutic Strategies

In the face of rising antibiotic resistance, novel approaches are being explored. , using viruses that specifically target bacteria, has shown promise in compassionate-use cases of MDR Pseudomonas aeruginosa pneumonia, with reports of clinical and microbiological improvement [79]. Additionally, aim to modulate the immune response—such as enhancing phagocytic clearance or reducing damaging inflammation—rather than directly targeting the pathogen [80]. Long-term, low-dose macrolides are also used in chronic conditions like for their immunomodulatory effects, reducing exacerbation frequency [81].

Supportive and Adjunctive Therapies

Beyond antimicrobial treatment, supportive care is vital. is indicated when oxygen saturation falls below 90–92%, with delivery via nasal cannula or mask to maintain target saturation between 92% and 96% [82]. In severe cases, high-flow nasal oxygen (HFNO) or mechanical ventilation may be required. Antiviral agents such as are used for influenza-related pneumonia, while supportive measures like hydration, antipyretics, and rest are essential for viral forms [83].

The integration of clinical, radiological, and laboratory findings ensures appropriate treatment selection and duration. Biomarkers such as can help distinguish bacterial from viral etiology, guiding antibiotic initiation and discontinuation [14]. Ultimately, the success of pneumonia treatment depends on timely diagnosis, rational antibiotic use, and adherence to evidence-based protocols to improve outcomes and curb the spread of resistance.

Prevention and Vaccination Strategies

Preventing pneumonia involves a multifaceted approach that combines vaccination, infection control measures, and lifestyle modifications. These strategies are especially critical for high-risk populations, including , , and individuals with chronic health conditions such as or compromised function [85].

Vaccination Against Pneumococcal Disease

Vaccination is one of the most effective methods for preventing bacterial pneumonia, particularly that caused by Streptococcus pneumoniae, also known as . In Italy, the national immunization schedule includes the pneumococcal conjugate vaccine (PCV), with formulations such as PCV13, PCV15, and PCV20, which are recommended for infants and older adults [86]. The standard pediatric schedule involves doses at 3, 5, and 11–13 months of age [87].

For adults aged 65 and over, the conjugate pneumococcal vaccine (e.g., PCV15 or PCV20) is preferred due to its ability to induce a more durable immune response compared to the older polysaccharide vaccine (PPSV23) [88]. Individuals with chronic diseases such as , heart disease, or immunodeficiencies, as well as those without a functioning spleen, are also prioritized for vaccination [89]. Studies have shown that pneumococcal vaccination reduces the incidence of invasive pneumococcal disease by over 80% in vaccinated children and contributes to herd immunity, thereby protecting unvaccinated populations [90].

Influenza and SARS-CoV-2 Vaccination

Viral infections such as and are common precursors to secondary bacterial pneumonia. The is recommended annually, especially for high-risk groups, as it significantly reduces the risk of influenza-related complications, including pneumonia [91]. High-dose influenza vaccines (HD-IIV4) have demonstrated superior efficacy in reducing hospitalizations among older adults [92].

Similarly, vaccination against has proven highly effective in preventing severe forms of , including viral pneumonia, acute respiratory distress syndrome (ARDS), and respiratory failure [93]. Updated bivalent or monovalent boosters targeting circulating variants are recommended for individuals aged six months and older, with particular emphasis on vaccinating older adults and those with comorbidities [94]. These vaccines have contributed to a notable decline in pneumonia cases during winter seasons [39].

Vaccination Against Other Respiratory Pathogens

In addition to pneumococcal and influenza vaccines, immunization against Haemophilus influenzae type b (Hib) plays a crucial role in preventing bacterial pneumonia in children. The Hib vaccine, typically administered as part of a hexavalent formulation (combined with diphtheria, tetanus, pertussis, polio, and hepatitis B), is given at 2, 4, and 6 months, with a booster between 11 and 13 months [96]. Its introduction has led to a dramatic decline in invasive Hib diseases, including meningitis and pneumonia [97].

Public Health Surveillance and Immunization Programs

Italy’s public health system employs integrated surveillance through the RespiVirNet program, coordinated by the and the Ministry of Health. This system monitors acute respiratory infections (ARI) and circulating respiratory viruses, including influenza, SARS-CoV-2, respiratory syncytial virus (RSV), and metapneumovirus [98]. Data from general practitioners and pediatricians in the InfluNet network, along with virological testing from regional laboratories, inform public health decisions and vaccine formulation [99].

Despite these efforts, vaccination coverage in Italy remains below the World Health Organization’s target of 95%. As of 2023, pneumococcal vaccine coverage among children was approximately 90–92%, while influenza vaccination among adults over 65 reached only 52.5% in the 2024–2025 season [100][101]. Regional disparities and socioeconomic barriers contribute to these gaps, particularly in Southern regions [102].

Hygiene and Infection Control

Good hygiene practices are essential for limiting the spread of respiratory pathogens. Key measures include regular handwashing with soap and water, covering the mouth and nose when coughing or sneezing, and avoiding close contact with infected individuals [103]. In healthcare settings, preventing hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) requires strict adherence to protocols such as oral hygiene for intubated patients and proper ventilator management [104].

Lifestyle and Environmental Modifications

Lifestyle factors significantly influence pneumonia risk. Smoking damages the mucociliary clearance system and impairs immune defenses in the lungs, increasing susceptibility to both bacterial and viral pneumonia [105]. Quitting smoking is one of the most effective ways to reduce this risk. Similarly, excessive alcohol consumption and poor oral hygiene are associated with higher rates of aspiration pneumonia and respiratory infections [106].

Environmental exposures, such as indoor air pollution from cooking with biomass fuels or exposure to mold and dampness, also contribute to respiratory vulnerability [107]. Reducing exposure to outdoor air pollutants like PM2.5 and NO2 is crucial, as these have been linked to increased hospital admissions for respiratory conditions, including pneumonia [108].

Targeted Prevention in High-Risk Populations

Prevention strategies must be tailored to vulnerable groups. For older adults, the combination of pneumococcal and influenza vaccination, along with early recognition of respiratory symptoms, is vital due to age-related immune decline (immunosenescence) [109]. In individuals with chronic lung diseases like or , vaccination and pulmonary rehabilitation can reduce exacerbations and hospitalizations [110].

For immunocompromised individuals, including those with HIV, post-transplant patients, or those on immunosuppressive therapy, vaccination is even more critical. However, live vaccines may be contraindicated, necessitating careful planning with healthcare providers [111].

In conclusion, preventing pneumonia requires a comprehensive strategy that integrates vaccination, public health surveillance, hygiene practices, and lifestyle changes. High vaccination coverage, especially among at-risk populations, remains a cornerstone of effective prevention, supported by robust healthcare infrastructure and targeted public health campaigns [112].

Complications and Prognosis

Pneumonia, while often treatable, can lead to severe and potentially life-threatening complications, particularly in vulnerable populations such as the elderly, young children, and individuals with compromised function or chronic health conditions like or . The prognosis of pneumonia varies significantly based on the patient's age, underlying health status, the causative pathogen, and the timeliness and appropriateness of treatment. Early diagnosis and intervention are crucial to prevent progression to serious complications and improve survival rates.

Common Complications of Pneumonia

The most frequent complications of pneumonia arise from the spread of infection or the body's intense inflammatory response. These include:

  • Pleural complications: Inflammation of the pleura (pleuritis) can lead to a pleural effusion, where fluid accumulates in the pleural space. If the infection spreads to this fluid, it can result in an empyema, characterized by the presence of pus. Empyema often requires chest tube drainage and targeted antibiotic therapy [113].
  • Lung abscess: This occurs when a localized area of the lung tissue undergoes necrosis, forming a cavity filled with pus. It is more commonly associated with infections by anaerobic bacteria or Staphylococcus aureus. Treatment typically involves prolonged courses of broad-spectrum antibiotics and, in some cases, percutaneous or surgical drainage [114].
  • Acute respiratory distress syndrome (ARDS): ARDS is a severe complication marked by acute respiratory failure, refractory hypoxemia, and diffuse bilateral infiltrates on chest imaging. It results from a massive systemic inflammatory response, often triggered by pathogens like Streptococcus pneumoniae or influenza viruses. Management requires mechanical ventilation in an intensive care unit (ICU) [14].
  • Sepsis and septic shock: The dissemination of the infection into the bloodstream can lead to sepsis, a dysregulated systemic response that may progress to septic shock, characterized by refractory hypotension and organ dysfunction. This carries a high mortality risk, especially in elderly patients and those with comorbidities [40].

Prognosis and Mortality

The prognosis for pneumonia is generally favorable for otherwise healthy individuals receiving prompt treatment. However, mortality rates increase dramatically in severe cases and among high-risk groups. Hospitalized patients, particularly those requiring ICU admission, face a mortality rate estimated between 15% and 30% [117]. The overall burden in Italy is significant, with approximately 9,000 deaths attributed to pneumonia annually [118]. Mortality is especially high among individuals over 80 years of age, where pneumonia is a leading cause of death [119].

Long-Term Pulmonary and Systemic Effects

Even after clinical recovery, pneumonia can have lasting consequences on lung function and overall health.

  • Pulmonary function alterations: During the acute phase, pneumonia causes reduced lung compliance and impaired gas exchange, leading to hypoxemia. In the post-infectious period, some patients develop restrictive lung disease, characterized by a reduction in total lung capacity (TLC) and forced vital capacity (FVC), often due to post-inflammatory fibrosis or scarring [120]. Studies indicate that a reduction in lung volume of up to 10% can persist, even in the absence of clear radiological abnormalities [121].
  • Exacerbation of chronic respiratory diseases: Pneumonia is a major trigger for acute exacerbations of , accelerating the decline in lung function, measured by forced expiratory volume in one second (FEV1). Each exacerbation is associated with an incomplete recovery, contributing to a faster progression of the disease and increased risk of hospitalization and mortality [122].
  • Development of chronic conditions: In severe or recurrent cases, the inflammatory process can lead to irreversible structural changes, such as bronchiolitis obliterans, where fibrosis obliterates the terminal bronchioles, resulting in permanent airflow obstruction [123].

Management of Resistant and Atypical Pneumonia

The management of pneumonia that is resistant to initial treatment or follows an atypical course presents a significant clinical challenge.

  • Antibiotic-resistant pneumonia: The rise of multidrug-resistant (MDR) pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA), carbapenem-resistant Enterobacterales (CRE), and MDR Pseudomonas aeruginosa, complicates treatment [23]. A precise microbiological diagnosis through blood cultures, sputum analysis, or bronchoscopic samples is essential. Therapy must be tailored to sensitivity results, often requiring last-generation antibiotics like vancomycin, linezolid, or novel beta-lactam/beta-lactamase inhibitor combinations (e.g., ceftazidime-avibactam) [70]. Close monitoring and therapy de-escalation within 48-72 hours are critical to prevent further selective pressure and combat .
  • Atypical pneumonia: Caused by pathogens like Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella pneumophila, atypical pneumonia presents with a more insidious onset, featuring a dry cough, low-grade fever, and systemic symptoms like headache and myalgia [34]. These pathogens are insensitive to penicillin but respond to macrolides (e.g., azithromycin), tetracyclines (e.g., doxycycline), or respiratory fluoroquinolones (e.g., levofloxacin) [5].

Emerging Therapies and Future Directions

In response to the growing threat of antibiotic resistance, new therapeutic strategies are being explored.

  • Bacteriophage therapy: The use of bacteriophages—viruses that specifically target bacteria—has shown promise in treating chronic, MDR Pseudomonas aeruginosa pneumonia, with reported clinical and microbiological improvements in refractory cases [79].
  • Host-directed therapies: These innovative approaches aim to modulate the patient's immune response rather than directly targeting the pathogen, using anti-inflammatory or immunomodulatory agents to enhance bacterial clearance and reduce tissue damage [80].
  • Long-term macrolides: Despite concerns about resistance, low-dose, long-term macrolides are used in chronic conditions like bronchiectasis for their immunomodulatory properties, which help reduce the frequency of exacerbations [81].

Risk Factors and Vulnerable Populations

Pneumonia can affect individuals of all ages, but certain populations are at significantly higher risk due to a combination of biological, clinical, environmental, and socioeconomic factors. These risk factors increase susceptibility to infection, the likelihood of severe disease, and the risk of complications, hospitalization, and death. Understanding these vulnerabilities is essential for targeted prevention and early intervention strategies.

Age-Related Vulnerabilities

Age is one of the most significant determinants of pneumonia risk. Both the very young and the elderly have compromised immune defenses, making them particularly susceptible. , especially infants and toddlers under two years of age, are at high risk due to their immature immune systems and smaller airways, which are more easily obstructed by inflammation and secretions [39]. In this group, common pathogens include , , and . Conversely, adults over 65 are also at heightened risk due to immunosenescence, the age-related decline in immune function, and a higher prevalence of chronic diseases [39]. This demographic faces a significantly higher risk of severe complications, prolonged hospital stays, and mortality from pneumonia.

Underlying Health Conditions

The presence of chronic medical conditions dramatically increases the risk of developing pneumonia and experiencing a more severe course. Individuals with are particularly vulnerable, as the disease damages the lungs' natural defenses, including the mucociliary clearance system, and creates an environment conducive to bacterial colonization [133]. Pneumonia is a leading cause of exacerbation in COPD patients, accelerating lung function decline. Similarly, impairs the immune response, including neutrophil function, making it harder for the body to fight off infections. Other critical comorbidities include , which can lead to pulmonary congestion and impaired oxygenation, and . The risk is further amplified in individuals with a compromised , such as those living with , undergoing chemotherapy for , receiving immunosuppressive therapy after an , or taking long-term corticosteroids [111]. These individuals are not only more susceptible to common pathogens but also to opportunistic infections like pneumonia.

Lifestyle and Environmental Exposures

Several modifiable lifestyle and environmental factors significantly contribute to pneumonia risk. is a major risk factor, as it damages the cilia in the airways and impairs the function of alveolar macrophages, the primary immune cells in the lungs, thereby reducing the body's ability to clear inhaled pathogens [135]. This damage increases susceptibility to both bacterial and viral pneumonia. is another significant factor, as it can suppress the immune system and increase the risk of due to impaired consciousness and swallowing reflexes [106]. Poor has also been linked to a higher risk of pneumonia, particularly in hospitalized or elderly patients, as it allows pathogenic bacteria to colonize the oropharynx, which can then be aspirated into the lungs [106]. Environmental exposures, such as air pollution from traffic, industrial emissions, or indoor sources like biomass fuels, can irritate the lungs and weaken respiratory defenses. Living in crowded or poorly ventilated housing conditions, often associated with lower socioeconomic status, facilitates the transmission of respiratory pathogens.

Socioeconomic and Geographic Disparities

Socioeconomic and geographic factors create significant disparities in pneumonia risk and outcomes. In Italy, individuals from lower socioeconomic backgrounds face higher rates of pneumonia and mortality due to a combination of factors, including limited access to healthcare, delayed diagnosis, and higher rates of comorbidities and risk behaviors like smoking [138]. The "north-south divide" in Italy is evident, with regions in the south, such as Campania and Sicily, often reporting higher mortality and incidence rates for respiratory diseases compared to the more affluent north [102]. This disparity is exacerbated by differences in the quality and accessibility of healthcare services, including primary care and hospital facilities. Furthermore, exposure to environmental pollution, particularly in industrialized areas, is a well-documented risk factor. The SENTIERI study by the Istituto Superiore di Sanità has shown an excess of mortality from respiratory diseases, including pneumonia, in areas with high levels of environmental contamination [140]. These geographic and socioeconomic inequalities highlight the need for public health interventions that address the social determinants of health.

Populations at Risk for Chronic or Recurrent Pneumonia

Some individuals are predisposed to developing chronic or recurrent pneumonia, which often signals an underlying structural or functional problem. Patients with , a condition characterized by permanent dilation of the bronchi, are at high risk due to the pooling of mucus that provides a breeding ground for bacteria like and [141]. Recurrent pneumonia can also be a sign of an , either congenital or acquired, which must be investigated in patients with multiple episodes. Other structural issues, such as lung malformations or post-infectious scarring, can also predispose to recurrent infections. Occupational exposures to organic dusts or toxic chemicals can lead to chronic lung damage and increased susceptibility. In all these cases, the approach to diagnosis shifts from acute management to identifying and treating the underlying cause to prevent future episodes.

Pneumonia in Children and Special Populations

Pneumonia presents unique challenges in children and special populations, including the elderly, immunocompromised individuals, and those with chronic conditions. The clinical presentation, risk factors, treatment approaches, and outcomes differ significantly across these groups, necessitating tailored diagnostic and therapeutic strategies. The vulnerability of these populations stems from immature or weakened immune systems, comorbidities, and social determinants of health, making pneumonia a leading cause of morbidity and mortality in these demographics.

Pneumonia in Children: Age-Specific Clinical Presentation

The signs and symptoms of pneumonia in children vary widely depending on age, with younger children exhibiting more atypical and non-specific manifestations. In neonates and infants (0–12 months), pneumonia may present without classic respiratory symptoms like cough or fever. Instead, key indicators include tachypnea (respiratory rate >60 breaths per minute), feeding difficulties, irritability, lethargy, vomiting, and apnea [36]. Cough may be absent or minimal, and fever can be subfebrile or even absent, particularly in very young infants. These atypical presentations can delay diagnosis, as symptoms may be mistaken for gastrointestinal issues or general malaise [36].

In preschool-aged children (1–5 years), symptoms become more recognizable but still overlap with other respiratory infections. Common signs include high fever (>38.5°C), persistent cough (productive or dry), tachypnea (>40 breaths per minute), and signs of respiratory distress such as nasal flaring and intercostal retractions. Abdominal pain and vomiting may occur due to diaphragmatic irritation from lower lobe involvement [37]. Viral causes like the (RSV) are more common in this age group, often mimicking bronchiolitis.

In school-aged children (>5 years), the clinical picture resembles that of adults, with more specific symptoms such as pleuritic chest pain, productive cough, and high fever. However, atypical pneumonia caused by is particularly prevalent in this group, often presenting with a persistent dry cough, headache, and extrapulmonary manifestations like rash or arthritis [38]. Despite these differences, tachypnea remains a more reliable indicator of severity than fever in pediatric populations [56].

Diagnosis and Monitoring in Pediatric Pneumonia

Diagnosing pneumonia in children, especially infants, requires a high index of clinical suspicion. The pediatrician must be alert to subtle signs such as poor feeding, altered behavior, or increased work of breathing, even in the absence of fever or cough [36]. Physical examination should focus on respiratory rate, oxygen saturation (SpO₂), and signs of distress. A SpO₂ below 94% in room air is a critical indicator of hypoxemia and necessitates immediate intervention [37].

Imaging plays a crucial role, with chest X-ray being the standard for confirming pulmonary infiltrates or consolidation [36]. However, lung ultrasound is increasingly used in pediatric settings due to its lack of ionizing radiation and ability to detect consolidations and air bronchograms with high sensitivity [55]. This modality is particularly valuable for monitoring disease progression and response to treatment in hospitalized children.

Treatment Strategies in Pediatric Pneumonia

The treatment of pneumonia in children differs significantly from that in adults, particularly regarding antibiotic selection and duration. For community-acquired pneumonia (CAP) in children, high-dose amoxicillin (75–90 mg/kg/day) is the first-line antibiotic due to its efficacy against pneumococcus, the most common bacterial pathogen [151]. In cases of suspected atypical pneumonia (e.g., Mycoplasma pneumoniae), a such as azithromycin may be added, though its empirical use is discouraged in younger children due to concerns about resistance and side effects [152].

Unlike in adults, where broader-spectrum antibiotics like are sometimes used, these agents are generally avoided in children due to potential adverse effects on musculoskeletal development [153]. The duration of antibiotic therapy is also shorter, with evidence supporting a 5-day course for uncomplicated pneumonia in children aged 2–59 months, provided there is clinical improvement [154].

Hospitalization Criteria in Pediatric Patients

The decision to hospitalize a child with pneumonia depends on age, severity of illness, and presence of comorbidities. Indicators for hospitalization include hypoxemia (SpO₂ <90–92%), significant respiratory distress, altered mental status, inability to feed, and underlying conditions such as congenital heart disease or immunodeficiency [155]. Infants, especially those under 3 months, are at higher risk of rapid deterioration and often require inpatient monitoring even with mild symptoms [36].

Complications in Pediatric Pneumonia

Children, particularly the very young, are at increased risk for both respiratory and systemic complications. Respiratory complications include acute respiratory failure, pleural effusion, empyema, lung abscess, and necrotizing pneumonia, which can lead to permanent lung damage [157]. Systemic complications such as sepsis and septic shock are more common in immunologically immature infants and can progress rapidly [158]. The immature immune system also increases susceptibility to opportunistic pathogens like in immunocompromised children [111].

Special Populations: The Elderly and Immunocompromised

The elderly (≥65 years) are another high-risk group, with pneumonia often presenting with atypical symptoms such as confusion, lethargy, or falls, rather than classic respiratory signs [39]. Comorbidities such as , , and cardiac disease increase susceptibility and complicate management. Similarly, immunocompromised individuals, including those with HIV, organ transplants, or on immunosuppressive therapy, are prone to infections from atypical or opportunistic pathogens such as fungi (e.g., ) or [33].

Preventive Strategies in High-Risk Groups

Prevention is paramount in vulnerable populations. The pediatric vaccination schedule in Italy includes vaccines against Streptococcus pneumoniae (PCV13) and Haemophilus influenzae type b (Hib), both of which have dramatically reduced the incidence of invasive bacterial pneumonia in children [85]. The PCV13 vaccine, administered at 3, 5, and 11–13 months, has shown over 80% efficacy in preventing pneumococcal disease [90]. Despite these successes, vaccination coverage in Italy remains below the WHO-recommended 95%, with regional disparities posing a public health challenge [164].

For the elderly and those with chronic conditions, the and are strongly recommended. The high-dose influenza vaccine has demonstrated superior efficacy in reducing hospitalizations among older adults [92]. However, vaccination rates among adults with chronic diseases remain suboptimal, highlighting the need for targeted public health campaigns.

Socioeconomic and Geographic Disparities

Significant regional disparities exist in pneumonia outcomes across Italy, with higher incidence and mortality in the South. These inequalities are driven by factors such as air pollution, poor housing conditions, and unequal access to healthcare [102]. Children in overcrowded or damp homes are at greater risk due to exposure to mold and indoor pollutants, which impair respiratory defenses [167]. Strengthening primary care, expanding community health programs, and investing in environmental health are essential to reducing these disparities.

Public Health Surveillance and Epidemiology

Pneumonia remains a significant public health burden globally and in Italy, with substantial morbidity, hospitalization, and mortality, particularly among vulnerable populations. Effective public health surveillance is critical for monitoring trends, guiding prevention strategies, and informing timely responses to outbreaks. In Italy, the epidemiological landscape of pneumonia is shaped by a combination of demographic, socioeconomic, and environmental factors, with notable regional disparities in incidence and outcomes.

National Surveillance Systems and Data Collection

The primary system for monitoring respiratory infections in Italy is RespiVirNet, the Integrated Surveillance System for Acute Respiratory Infections (ARI) and respiratory viruses, coordinated by the Istituto Superiore di Sanità (ISS) and the Ministry of Health [98]. This network integrates data from multiple sources to provide a comprehensive picture of respiratory pathogen circulation. Key components include:

  • InfluNet, a sentinel network of general practitioners and pediatricians who report weekly cases of influenza-like illness (ILI) and ARI, enabling real-time tracking of infection trends [99].
  • Regional virology laboratories that perform pathogen characterization on samples from severe cases, identifying circulating viruses such as influenza, SARS-CoV-2, respiratory syncytial virus (RSV), and other pathogens like rhinovirus and metapneumovirus [170].
  • Hospital-based surveillance that monitors severe cases, hospitalizations, and intensive care admissions, linked to the National Hospital Discharge Database (SDO) managed by the Ministry of Health [171].

These data are analyzed weekly and disseminated through public reports like the Influnet Report, which provides information on incidence, geographic spread, and the virological profile of circulating pathogens [172]. For instance, during the 2025-2026 season, RespiVirNet reported high ARI incidence, particularly among children aged 0-4 years, with a peak of 11.3 cases per 1,000 patients in a single week [173].

Epidemiological Burden and Key Statistics

Pneumonia imposes a heavy burden on the Italian healthcare system. Annually, approximately 150,000 hospitalizations occur due to pneumonia, with an incidence below 2 cases per 1,000 inhabitants [118]. Mortality is estimated at around 9,000 deaths per year, with a disproportionately high impact on the elderly and those with comorbidities [118]. In 2023, over 136,000 hospital admissions for pneumonia were recorded, and the disease is a leading cause of death among individuals over 80 years of age [176]. The case fatality rate for hospitalized patients ranges from 15% to 30%, highlighting the severity of the condition [117].

Demographic and Socioeconomic Risk Factors

Epidemiological data reveal stark disparities in pneumonia risk and outcomes. The most significant demographic risk factors are advanced age and early childhood. Individuals over 65, especially those over 80, are at high risk due to immunosenescence and the prevalence of comorbidities like and [39]. In 2022, pneumonia was a major contributor to the increased mortality observed in this age group [119]. Conversely, children under five, particularly infants, are also highly vulnerable, with pneumonia being a leading cause of pediatric mortality in this group [87].

Socioeconomic status plays a crucial role. Individuals from lower socioeconomic backgrounds face higher mortality rates from respiratory diseases, including pneumonia [138]. Factors such as lower educational attainment, limited access to healthcare, and poor housing conditions contribute to delayed diagnosis and treatment, increasing the risk of complications and hospitalization [182].

Geographic Disparities and Environmental Influences

Significant regional differences exist in pneumonia rates and outcomes within Italy. Regions in the South, such as Campania and Sicily, report higher mortality and incidence of respiratory diseases compared to regions in the North, like Tuscany, which has some of the lowest health disparities in the country [102]. These disparities are linked to environmental and structural factors.

Air pollution is a major environmental risk factor. The national epidemiological study SENTIERI has shown that environmental pollution is associated with increased respiratory disease and mortality [140]. The EpiAir2 project demonstrated that air pollution in 25 major Italian cities significantly increases emergency hospitalizations for respiratory conditions, including pneumonia [108]. Pollutants like PM2.5 and NO2 impair respiratory defenses, increasing susceptibility to bacterial and viral infections.

Poor housing conditions, such as dampness and mold, also contribute to respiratory vulnerability by irritating the airways and weakening lung defenses [167]. Indoor air pollution from tobacco smoke, cooking fuels, and chemicals further exacerbates the risk [107].

Challenges in Surveillance and Response

Despite the existence of robust systems like RespiVirNet, several challenges hinder effective surveillance and response. Surveillance is often fragmented, with inconsistent diagnostic criteria and reporting systems across regions [188]. Delays in diagnosis and reporting are common, especially in primary care settings, due to the nonspecific nature of symptoms and variable access to diagnostic tools like or [189]. Approximately 50% of severe pneumonias are acquired in hospitals (HAP) or are ventilator-associated (VAP), requiring specific surveillance systems for healthcare-associated infections (HAI) [190].

Another major challenge is the weakness of the territorial healthcare system, particularly in rural and southern areas. This limits timely access to care and the coordination between hospital and primary care, especially during epidemic peaks [191]. Efforts to strengthen territorial care, such as the establishment of Community Houses and Community Hospitals under the National Recovery and Resilience Plan (PNRR), aim to address these gaps [192].

Impact of Vaccination on Epidemiology

Vaccination is a cornerstone of pneumonia prevention and has significantly altered its epidemiology. The pneumococcal conjugate vaccine (PCV13) has led to a substantial reduction in invasive pneumococcal diseases, including pneumonia, in children under five, with an efficacy exceeding 80% [90]. This has also produced a herd immunity effect, reducing pneumococcal transmission in the adult population [85]. Similarly, the Haemophilus influenzae type b (Hib) vaccine has drastically reduced Hib-related pneumonia and meningitis, making these diseases rare in vaccinated populations [97].

Despite these successes, vaccination coverage in Italy faces challenges. For the pneumococcal vaccine, national coverage for the complete cycle by 24 months was around 90-92% in 2023, falling short of the WHO-recommended 95% threshold [164]. Influenza vaccine coverage among adults over 65 was only 52.5% in the 2024-2025 season, far below public health targets [101]. Increasing vaccine uptake, especially among high-risk groups, is essential to further reduce the burden of pneumonia.

References