Community-Acquired Pneumonia (CAP)

• Defined as an acute infection of the pulmonary parenchyma acquired outside hospital or healthcare settings.
  
  

Classification of Pneumonia by Site of Acquisition

1. Community-Acquired Pneumonia (CAP):
   • Acute infection acquired outside hospital settings.
2. Nosocomial Pneumonia:
   • Includes:
     • Hospital-Acquired Pneumonia (HAP): Occurring ≥48 hours after hospital admission.
     • Ventilator-Associated Pneumonia (VAP): Occurring ≥48 hours after endotracheal intubation
       
       

Typical Pathogens

1. Gram-Positive Bacteria:
   • Streptococcus pneumoniae (S. pneumoniae):
     • The most common bacterial cause of CAP worldwide, accounting for 30–35% of cases in Europe and the United States.
     • Incidence has declined in some regions due to pneumococcal vaccination.
   • Staphylococcus aureus (including MRSA):
     • Typically associated with severe CAP, often following influenza infection.
     • Community-acquired MRSA is linked with necrotising pneumonia and has a high mortality rate.
   • Group A Streptococci:
     • Less frequent but can cause severe presentations of CAP.
2. Gram-Negative Bacteria:
   • Haemophilus influenzae:
     • Common in patients with chronic respiratory conditions like COPD.
   • Moraxella catarrhalis:
     • Frequently implicated in patients with pre-existing lung disease.
   • Enterobacteriaceae (e.g., Klebsiella pneumoniae):
     • Often associated with patients with chronic alcoholism or diabetes.
   • Pseudomonas aeruginosa:
     • Rare in healthy hosts but prevalent in those with underlying lung conditions such as bronchiectasis or cystic fibrosis.
       
       

Atypical Pathogens

1. Bacteria:
   • Mycoplasma pneumoniae:
     • A leading cause of CAP in younger adults, often presenting in epidemic cycles.
     • Accounts for up to 37% of outpatient CAP cases.
   • Chlamydia pneumoniae:
     • Responsible for 5–15% of CAP cases, particularly in older adults.
   • Legionella pneumophila:
     • Associated with outbreaks and severe CAP.
     • Often linked to exposure to contaminated water systems.
   • Chlamydia psittaci and Coxiella burnetii:
     • Zoonotic pathogens causing psittacosis and Q fever, respectively.
2. Viruses:
   • Respiratory Viruses:
     • Include influenza virus (A/B), rhinovirus, adenovirus, respiratory syncytial virus, and parainfluenza virus.
     • SARS-CoV-2 and human metapneumovirus are notable recent additions.
   • Polymicrobial Infections:
     • Mixed bacterial and viral etiologies occur in 5.7–13% of CAP cases and are associated with poorer outcomes.

Fungi

Risk Factors for Community-Acquired Pneumonia (CAP)

Primary Risk Factors

1. Living in Healthcare or Residential Settings:
   • Residents of nursing homes or long-term care facilities account for 10–18% of pneumonia hospitalisations.
   • Mortality rates in this group can reach up to 55%.
2. Advanced Age (>65 Years):
   • The risk of CAP increases with age, driven by age-related immune decline and the prevalence of comorbidities.
   • Older adults experience more severe disease and higher mortality rates.
3. Tobacco Exposure:
   • Smoking, both active and passive, significantly raises the risk of respiratory infections, including pneumococcal pneumonia.
   • Smokers are more likely to develop CAP-related complications, such as sepsis, at younger ages.
4. Excessive Alcohol Use:
   • Alcohol abuse impairs immune function and increases aspiration risks.
   • Daily alcohol intake of ≥24 g markedly raises the risk of CAP.
5. Medications Affecting Gastric Acidity:
   • Proton pump inhibitors and H2-receptor antagonists reduce stomach acid, promoting bacterial colonisation and increasing CAP risk.
6. Chronic Respiratory Diseases:
   • COPD increases CAP risk by 2- to 4-fold and is associated with worse outcomes and higher mortality in CAP patients.
7. Frequent Interaction with Children:
   • Adults living in households with children, especially three or more, face a higher likelihood of developing CAP.
     
     

Secondary Risk Factors

1. Poor Oral Hygiene:
   • Aspiration of bacteria from dental plaque contributes to infection, particularly in older adults.
2. Diabetes Mellitus:
   • Diabetes predisposes individuals to CAP through mechanisms like hyperglycemia, immune dysfunction, and aspiration risks.
   • It also increases the likelihood of severe bacterial pneumonia.
3. Chronic Liver Disease:
   • Cirrhosis and other liver conditions increase susceptibility to bacterial infections, including pneumonia, often leading to severe outcomes.
4. Chronic Kidney Disease:
   • Patients with renal dysfunction are at significantly higher risk for severe CAP and associated mortality.
5. Opioid Use:
   • High doses or immunosuppressive opioids elevate CAP risk, affecting both HIV-positive and HIV-negative individuals.
6. Lifestyle and Environmental Factors:
   • Crowded living conditions (e.g., prisons, shelters) and exposure to environmental toxins like fumes and solvents increase susceptibility.
   • Contact with zoonotic pathogens (e.g., Chlamydia psittaci from birds or Coxiella burnetii from livestock) can lead to atypical pneumonia.
7. Immunocompromised States:
   • Conditions such as HIV, malignancies, or immunosuppressive therapy increase susceptibility to severe and atypical CAP pathogens.
8. Neurological or Swallowing Disorders:
   • Impaired airway protection from stroke, seizures, or dysphagia raises the risk of aspiration pneumonia.
     
     

Pathogen Entry Mechanisms

1. Microaspiration of Oropharyngeal Secretions:
   • The most common route for bacterial pneumonia, allowing upper airway flora to enter the lower airways.
2. Inhalation of Infectious Aerosols:
   • A key mechanism for viral and atypical pathogens, such as Legionella or Mycoplasma pneumoniae.
3. Hematogenous Spread:
   • Pathogens can disseminate via the bloodstream from distant infected sites, such as right-sided endocarditis.
4. Direct Contiguous Spread:
   • Rarely, infections can extend from adjacent structures, e.g., tuberculosis spreading from lymph nodes to the lung.
     
     

Defensive Breakdown

• Under normal conditions, the lung's innate and adaptive immune systems maintain a sterile lower respiratory tract.
• Pneumonia indicates:
  • Compromised host defenses (e.g., due to smoking, COPD, immunosuppression, or aspiration).
  • High pathogen virulence or inoculum size, overwhelming the immune response.
    
    

Host Response to Infection

1. Local Inflammatory Reaction:
   • Pathogens elicit an immune response within the alveoli, leading to the recruitment of neutrophils and macrophages, cytokine release, and alveolar exudate formation.
2. Systemic Response:
   • In some cases, systemic inflammation ensues to contain the infection, which can lead to complications such as:
     • Bacteremia
     • Sepsis
     • Acute Respiratory Distress Syndrome (ARDS)
     • Multiorgan Dysfunction Syndrome (MODS)
       
       

Emerging Concepts: The Lung Microbiome

• Traditional models of CAP considered the alveoli sterile until pathogenic invasion. However, newer research highlights the role of the lung microbiome.
  • Dysbiosis Hypothesis:
    • Alterations in the resident microbial community (e.g., due to viral infection or smoking) may lead to overgrowth of specific bacteria or secondary infections.
    • The alveolar microbiome resembles oral flora, predominantly anaerobes like Prevotella and Veillonella, and may influence disease progression.
  • Dysbiosis might explain the low detection rates of pathogens in some CAP cases using conventional culture methods.
    
    

Implications of Microbial Interactions

• Microbial competition between invading pathogens and resident lung flora can modulate disease severity.
• The extent of the host immune response—ranging from localised control to systemic dysregulation—largely determines outcomes.
  
  

Global and Regional Incidence

• CAP is one of the most prevalent infectious diseases, with a worldwide incidence ranging from 1.5 to 14 cases per 1000 person-years, depending on geography, season, and population demographics.
• In the United States:
  • Annual incidence: 248 per 10,000 adults, rising to 2000 per 100,000 among those aged ≥65 years.
  • CAP accounts for over 4.5 million outpatient visits annually and 1.5 million hospitalisations.
  • It is the eighth leading cause of death and the most common infectious cause of mortality.
• In Europe:
  • Incidence varies from 1.07 to 1.7 per 1000 person-years, with the highest rates observed in older populations.
  • Mortality ranges widely from <1% to 48%, depending on the country and healthcare setting.

Mortality

• Mortality rates for CAP vary by severity and care setting:
  • 1–5% in outpatients.
  • 5.7–14% in hospitalised general ward patients.
  • 34–50% in intensive care unit patients, particularly among those requiring ventilation.
• Pneumococcal pneumonia has a mortality rate of 5%, increasing to 30% in cases with associated bacteremia.
  
  

Common Symptoms

1. Cough:
   • Often productive, with mucopurulent sputum indicative of bacterial etiology.
   • Scant or watery sputum is more suggestive of atypical pathogens.
   • Older adults may not present with a cough, instead showing non-specific symptoms.
2. Dyspnea:
   • A frequent and predictive symptom of CAP.
   • Associated with hypoxemia and impaired alveolar gas exchange.
3. Pleuritic Chest Pain:
   • Present in approximately 30% of cases.
   • Often reported alongside other respiratory symptoms like dyspnea and cough.
4. Fever and Chills:
   • Fever (>38ºC or >100ºF) is a common finding but may be absent in older or immunocompromised individuals.
   • Rigors and night sweats are also frequently reported, although less so in the elderly.
5. Fatigue and Malaise:
   • Systemic symptoms like fatigue and malaise are common, reflecting the body's inflammatory response.
6. Abnormal Chest Examination Findings:
   • Signs include crackles, diminished breath sounds, dullness to percussion, and wheezing.
   • Tachypnea and adventitious sounds (e.g., rales, rhonchi) are predictive of CAP.
     
     

Atypical Presentations

• In Older Adults:
  • Symptoms such as confusion, lethargy, or worsening of pre-existing conditions often predominate.
  • Fever and respiratory symptoms may be absent, necessitating a higher index of suspicion.
• In Immunocompromised Patients:
  • Symptoms can be subtle, with pulmonary infiltrates often detected only on imaging.
    
    

Specific Aetiological Presentation

1. Legionella Pneumonia:
   • Presents with diarrhoea, headache, confusion (linked to hyponatremia), and constitutional upset.
2. Mycoplasma Pneumonia:
   • Symptoms may include otitis media, hemolytic anemia, Stevens-Johnson syndrome, and sore throat.
3. Aspiration Pneumonia:
   • Often associated with impaired swallowing, poor oral hygiene, or conditions like stroke and chronic alcoholism.
     
     

Risk Factors Worsening Symptoms or Disease Severity

1. Advanced Age (>65 Years):
   • Increases susceptibility and mortality risk.
   • Higher prevalence of comorbidities contributes to severe presentations.
2. Chronic Respiratory Diseases:
   • COPD, asthma, and bronchitis are linked to a 2- to 4-fold increase in CAP risk.
3. Comorbidities:
   • Diabetes, heart disease, chronic kidney or liver disease increase the risk of severe disease.
4. Substance Use:
   • Smoking, alcohol misuse, and opioid use impair respiratory defenses and predispose to CAP.
5. Medications:
   • Use of proton pump inhibitors, H2 blockers, and immunosuppressive drugs increases CAP risk.
     
     

Other Notable Symptoms

• Myalgia and Anorexia:
  • Common systemic features, particularly in severe cases.
• Nausea and Abdominal Pain:
  • Often linked to atypical pathogens like Mycoplasma or Legionella.
• Headache and Diarrhea:
  • Frequently seen in infections caused by atypical bacteria.
    
    

Diagnostic Considerations

• Chest Imaging:
  • Symptoms alone are insufficient for a definitive diagnosis; a chest radiograph is required to confirm CAP.
• Severity Markers:
  • Tachycardia, leukocytosis, or leukopenia are indicative of a systemic inflammatory response.
  • Hypoxemia (SpO₂ <95%) correlates with disease severity.
    
    

Pulmonary Examination Findings

1. Auscultatory Changes:
   • Crackles (Rales): Commonly heard over affected lung segments, indicative of alveolar involvement.
   • Decreased Breath Sounds: Suggestive of consolidation or pleural effusion.
   • Dullness to Percussion: Associated with lobar consolidation or effusion.
   • Wheezing: May occur, particularly in atypical or viral pneumonia.
2. Signs of Consolidation:
   • Increased Tactile Fremitus and Egophony: Indicative of airspace consolidation.
   • Often present in bacterial pneumonia caused by pathogens such as Streptococcus pneumoniae or Klebsiella pneumoniae.
   • Consolidation is less common in atypical pneumonias caused by Mycoplasma pneumoniae or Chlamydia pneumoniae.
     
     

Pleural Involvement

1. Pleural Effusion:
   • Manifests as decreased tactile fremitus, diminished breath sounds, and dullness to percussion.
   • Large effusions may present with dyspnea due to mechanical compression.
2. Empyema:
   • Findings mimic pleural effusion.
   • Confirmatory diagnosis involves thoracentesis and analysis of pleural fluid for pH, cell counts, and microbiological studies.
     
     

Systemic Findings

1. Vital Signs:
   • Fever (>38°C or 100°F) is typical but may be absent in elderly or immunocompromised individuals.
   • Tachycardia and tachypnea are common.
2. General Appearance:
   • Patients may appear acutely ill with increased work of breathing.
   • Cyanosis or hypoxemia may indicate severe disease or respiratory failure.
3. Severe Presentations:
   • Hypotension, altered mental status, or signs of sepsis suggest systemic involvement.
   • These findings necessitate immediate evaluation for complications such as septic shock or multiorgan dysfunction.
     
     

Special Considerations in Atypical CAP

1. Legionella Pneumonia:
   • May present with diarrhea, confusion (due to hyponatremia), and constitutional symptoms.
   • Consolidation may still be evident on examination.
2. Mycoplasma Pneumonia:
   • Less pronounced pulmonary findings but may include anemia, rash, or otitis media.
   • Extrapulmonary symptoms like headache, sore throat, and gastrointestinal complaints are common.
     
     

Elderly and Immunocompromised Patients

1. Atypical Presentations:
   • Confusion, lethargy, or worsening of underlying chronic conditions may predominate.
   • Fever and focal chest signs may be absent, necessitating heightened clinical suspicion.
2. Imaging Correlation:
   • In immunosuppressed patients, pulmonary infiltrates may not be apparent on chest radiographs and may require advanced imaging like CT.
     
     

Diagnostic Insights

1. Purulent Sputum:
   • Indicates typical bacterial pathogens.
   • Blood-tinged sputum may be seen in S. pneumoniae or Klebsiella pneumoniae infections.
2. Tachyponea:
   • A highly predictive symptom for CAP when combined with fever and focal chest findings.
3. Hypoxemia:
   • SpO₂ <95% on room air correlates with disease severity and is a marker for hospitalisation.

Severity Assessment (CURB-65 Score)

CURB-65 Criteria

1. Confusion: Abbreviated Mental Test score ≤8 or new onset of disorientation.
2. Urea Level: Serum blood urea nitrogen >7 mmol/L.
3. Respiratory Rate: ≥30 breaths per minute.
4. Blood Pressure: Diastolic ≤60 mmHg or systolic <90 mmHg.
5. Age: ≥65 years.
   
   

Risk Stratification

• Score 0–1: Low risk (mortality <3%).
  • Management: Consider home-based care.
• Score 2: Intermediate risk (mortality 3–15%).
  • Management: Hospital-based care is recommended.
• Score 3–5: High risk (mortality >15%).
  • Management: Evaluate for intensive care admission.
    
    

Initial Investigations

1. Chest X-Ray:
   • A definitive diagnosis of CAP requires evidence of new consolidation on a chest X-ray.
   • Perform a chest X-ray for all patients presenting to the hospital as soon as possible, ideally within 4 hours of admission.
   • Consider further imaging (e.g., CT scan) if the X-ray shows atypical changes (e.g., cavitation, pleural effusion, multifocal consolidation).
   • Avoid routine X-rays in community-managed patients unless:
     • Diagnosis is uncertain.
     • There is concern about poor treatment response.
     • There is a risk of underlying lung pathology, such as cancer.
2. Pulse Oximetry:
   • Assess oxygen saturation at presentation.
   • Saturation <94% indicates a worse prognosis and may necessitate oxygen therapy or urgent referral.
3. Arterial Blood Gas (ABG):
   • Measure ABG in patients:
     • Receiving oxygen with an SpO₂ <94%.
     • At risk for hypercapnic ventilatory failure.
     • With high-severity CAP.
   • Document inspired oxygen concentration for accurate interpretation.
4. Full Blood Count (FBC):
   • Leukocytosis is common and suggests bacterial pneumonia.
   • A WBC count >15 x10⁹/L is associated with Streptococcus pneumoniae.
5. C-Reactive Protein (CRP):
   • Elevated CRP (>100 mg/L) supports the diagnosis of bacterial pneumonia.
   • Levels <20 mg/L make bacterial pneumonia unlikely.
   • Persistent elevation may indicate treatment failure or complications.
6. Urea and Electrolytes (U&E):
   • Inform severity and assess renal function.
   • Urea >7 mmol/L contributes to CURB-65 scoring for severity assessment.
     
     

Further Investigations

1. Blood Cultures:
   • Obtain prior to antibiotics in moderate or severe CAP.
   • Identify pathogens such as S. pneumoniae or H. influenzae.
   • Bacteraemia is a marker of disease severity.
2. Sputum Culture and Gram Stain:
   • Recommended in patients with moderate to severe CAP, or when treatment response is inadequate.
   • Limitations include contamination with upper respiratory flora and low sensitivity.
3. Urinary Antigen Tests:
   • Detect antigens for Legionella pneumophila and S. pneumoniae.
   • Highly specific, rapid, and less affected by prior antibiotic use.
   • Indicated in severe CAP or when epidemiological factors suggest Legionella.
4. Polymerase Chain Reaction (PCR):
   • Detects respiratory viruses and atypical pathogens (Mycoplasma pneumoniae, Chlamydia pneumoniae).
   • Use in severe CAP or outbreaks (e.g., Legionnaires’ disease).
   • Preferred during the COVID-19 pandemic for SARS-CoV-2 testing.
5. Liver Function Tests (LFTs):
   • Provide baseline data.
   • Abnormal results may suggest Legionella or underlying liver disease.
6. Procalcitonin (PCT):
   • Helps distinguish bacterial from viral pneumonia.
   • Elevated in bacterial CAP, particularly pneumococcal infections.
   • Supports antibiotic stewardship by guiding initiation or discontinuation of therapy.
     
     

Advanced Imaging and Procedures

1. CT Scan:
   • Recommended when:
     • Diagnostic uncertainty persists despite X-ray.
     • Atypical findings like cavitation or multifocal consolidation are present.
     • Underlying malignancy or structural lung disease is suspected.
2. Chest Ultrasound:
   • Useful for pleural effusions and guiding thoracentesis.
3. Thoracentesis:
   • Analyse pleural fluid to differentiate parapneumonic effusion, empyema, or other causes.
   • Positive Gram stain or pH <7.2 indicates empyema.
4. Bronchoscopy:
   • Consider in unresolved CAP or immunocompromised patients to obtain respiratory samples for culture or PCR.
5. Direct Fluorescent Antibody (DFA) Testing:
   • Can assist with detecting Legionella or atypical pathogens but has limited sensitivity.
     
     

Respiratory Conditions

1. Acute Bronchitis:
   • Symptoms: Cough without dyspnea or fever; often follows a viral upper respiratory tract infection.
   • Investigations: Chest X-ray shows no evidence of consolidation.
2. Chronic Obstructive Pulmonary Disease (COPD) Exacerbation:
   • Symptoms: Worsening dyspnea and sputum production in a patient with a history of COPD.
   • Investigations: Hyperinflation on chest X-ray; absence of consolidation.
3. Asthma Exacerbation:
   • Symptoms: Acute bronchospasm, wheezing, and worsening of underlying symptoms.
   • Investigations: Chest X-ray typically unremarkable.
4. Bronchiectasis Exacerbation:
   • Symptoms: Increased sputum production and recurrent infections.
   • Investigations: Chest imaging may show airway dilation and mucus plugging.
5. Empyema:
   • Symptoms: Fever, chest pain, and systemic signs.
   • Investigations: Pleural effusion on chest X-ray; confirmed by pleural fluid analysis.
6. Tuberculosis:
   • Symptoms: Chronic cough, weight loss, and night sweats, often in patients from endemic areas.
   • Investigations: Cavitary lesions or lymphadenopathy on chest imaging; positive tuberculosis skin test or IGRA.
     
     

Cardiovascular Conditions

1. Congestive Heart Failure (CHF):
   • Symptoms: Dyspnea, orthopnea, and peripheral edema.
   • Investigations: Bilateral interstitial infiltrates or pleural effusion on chest X-ray; cardiomegaly often present.
2. Pulmonary Embolism (PE):
   • Symptoms: Acute dyspnea, pleuritic chest pain, and features of deep vein thrombosis.
   • Investigations: Chest X-ray may show nonspecific findings; CTPA confirms pulmonary artery thrombus.
3. Myocardial Infarction (MI):
   • Symptoms: Chest pain and dyspnea; may mimic respiratory symptoms.
   • Investigations: ECG and cardiac biomarkers critical for diagnosis; chest imaging normal.
     
     

Infectious and Autoimmune Conditions

1. Coronavirus Disease 2019 (COVID-19):
   • Symptoms: Fever, cough, anosmia, and gradual symptom progression.
   • Investigations: RT-PCR for SARS-CoV-2 and bilateral ground-glass opacities on chest imaging.
2. Hypersensitivity Pneumonitis:
   • Symptoms: Acute dyspnea and cough following antigen exposure.
   • Investigations: Positive immunologic tests; imaging shows diffuse ground-glass opacities.
3. Systemic Lupus Erythematosus (SLE) Pneumonitis:
   • Symptoms: Dyspnea, fever, and pleuritic chest pain.
   • Investigations: Diffuse pulmonary infiltrates on imaging; supportive serology findings.
4. Granulomatosis with Polyangiitis (Wegener’s Granulomatosis):
   • Symptoms: Hemoptysis, cough, and constitutional symptoms.
   • Investigations: Nodules or cavitary lesions on imaging; positive ANCA antibodies.
     
     

Structural and Neoplastic Conditions

1. Lung Cancer or Metastases:
   • Symptoms: Chronic cough, hemoptysis, and weight loss.
   • Investigations: Focal or diffuse consolidation on chest X-ray; further defined by CT or biopsy.
2. Pneumothorax:
   • Symptoms: Sudden-onset dyspnea and pleuritic chest pain.
   • Investigations: Chest X-ray shows visible pleural line with absent lung markings.
     
     

Drug and Radiation-Induced Lung Disease

1. Pulmonary Drug Hypersensitivity or Toxicity:
   • Drugs: Common culprits include nitrofurantoin, daptomycin, and bleomycin.
   • Symptoms: Dyspnea, fever, and nonproductive cough.
   • Investigations: Diffuse infiltrates on chest imaging; reversible upon discontinuation of the drug.
2. Radiation Pneumonitis:
   • Symptoms: Subacute respiratory symptoms post-radiotherapy.
   • Investigations: Pulmonary infiltrates confined to the irradiated field.
     
     

Initial Assessment and Risk Stratification

• Use CRB-65 for patients in the community and CURB-65 in hospital settings to assess CAP severity and guide management:
  • Score 0–1 (low severity): Treat most patients at home with oral antibiotics.
  • Score 2 (moderate severity): Consider hospital admission or short-stay inpatient care.
  • Score 3–5 (high severity): Hospitalize immediately, and for scores of 4 or 5, arrange for intensive care unit (ICU) evaluation.
    
    

Urgent Management in Suspected Sepsis

• Identify sepsis early by assessing for signs of systemic infection, multi-organ dysfunction, or acute deterioration.
• Utilise scoring systems such as NEWS2 (National Early Warning Score 2) to quantify illness severity.
• Immediate Actions:
  • Administer empirical antibiotics within 1 hour of identifying sepsis.
  • Provide intravenous fluid resuscitation for volume depletion.
  • Consider vasopressors to maintain a mean arterial pressure of ≥65 mmHg if hypotension persists.
    
    

In-Hospital Management

1. Empirical Antibiotics:
   • Administer antibiotics as soon as a clinical diagnosis is made and within 4 hours of presentation.
   • High-severity CAP: Start broad-spectrum IV antibiotics, such as a beta-lactamase inhibitor (e.g., amoxicillin/clavulanate) combined with a macrolide (e.g., clarithromycin). For penicillin-allergic patients, consider cephalosporins or fluoroquinolones.
   • Moderate-severity CAP: Begin with oral antibiotics, typically amoxicillin plus clarithromycin. For penicillin-allergic patients, alternatives include doxycycline or fluoroquinolones.
   • Low-severity CAP: Treat with oral amoxicillin; for penicillin allergy, use clarithromycin or doxycycline.
2. Oxygen Therapy:
   • Maintain oxygen saturation ≥94% in most patients.
   • Target oxygen saturation at 88–92% for patients at risk of hypercapnic respiratory failure (e.g., chronic respiratory diseases).
   • Regularly monitor arterial blood gases in severe cases or when oxygen saturation falls below 94%.
3. Supportive Care:
   • IV Fluids: Address hypovolemia, particularly in septic patients.
   • VTE Prophylaxis: Initiate low molecular weight heparin for immobile patients.
   • Pain Management: Use simple analgesics (e.g., paracetamol) for symptoms like pleuritic chest pain.
   • Nutritional Support: Provide enteral or parenteral nutrition for prolonged hospital stays or severe CAP.
4. Monitoring:
   • Record vital signs at least twice daily; increase frequency in critically ill patients.
   • For patients with high-severity CAP, perform senior clinician reviews at least every 12 hours.
     
     

Community Management

1. Antibiotics:
   • Prescribe oral amoxicillin as the first-line treatment. Alternatives for penicillin-allergic patients include clarithromycin or doxycycline.
   • Add or switch to a macrolide if symptoms do not improve with initial therapy.
2. Criteria for Home Treatment:
   • Stable comorbidities.
   • Reliable ability to take oral medications.
   • Supportive social circumstances.
3. Hospital Referral:
   • Refer patients with CRB-65 scores ≥3 or rapidly worsening symptoms to hospital immediately, preferably by ambulance.
     
     

Antibiotic Duration and Review

• The recommended duration of treatment is 5 days, extended only if:
  • Clinical stability has not been achieved.
  • Microbiological results suggest prolonged therapy.
• Switch from IV to oral antibiotics when:
  • Fever resolves for >24 hours.
  • Heart rate normalises (<100 beats/min).
  • No hypoxia or hypotension is present.
    
    

Management of Complications or Poor Response

1. Persistent Symptoms:
   • Reassess for potential complications (e.g., pleural effusion, empyema, lung abscess).
   • Repeat chest X-ray and consider advanced imaging or bronchoscopy.
2. Referral:
   • Engage respiratory or infectious disease specialists for unresolved cases or those with complex comorbidities.

Follow-Up

• Repeat chest X-rays at 6 weeks post-treatment for:
  • Smokers.
  • Patients >50 years of age.
  • Those with persistent symptoms or abnormal physical findings.

Prognosis

• Mortality rates:
  • Hospitalised patients: 5–15%, rising to 20–50% for ICU-admitted patients.
  • Community-managed patients: Generally favorable outcomes with appropriate treatment.
    
    

Short-Term Mortality

• Mortality rates among hospitalised CAP patients range from 5–15%, with a significant increase to 20–50% for those requiring ICU admission.
• For community-treated patients, prognosis is generally favorable, with low mortality risk when managed appropriately.
  
  

Factors Associated with Increased 30-Day Mortality

1. Clinical and Pathogen-Related Factors:
   • Presence of bacteraemia.
   • Infections with multidrug-resistant organisms (Staphylococcus aureus, Pseudomonas aeruginosa, Enterobacteriaceae).
2. Comorbidities:
   • Neurological diseases, cardiovascular disease, and advanced chronic obstructive pulmonary disease (COPD).
3. Severe Disease Presentations:
   • ICU admission or respiratory failure.
   • Overwhelming sepsis.
     
     

Long-Term Outcomes

1. Mortality Beyond Hospitalization:
   • Studies indicate long-term mortality rates of:
     • 6.5% during hospitalisation.
     • 13% at 30 days.
     • 23% at six months.
     • 31% at one year.
   • Causes of long-term mortality often involve pre-existing comorbidities such as malignancies, cardiovascular diseases, and advanced respiratory conditions.
2. Cardiovascular Complications:
   • CAP is associated with increased risk of acute and chronic cardiac complications, including:
     • Myocardial infarctions.
     • Arrhythmias.
     • Heart failure exacerbations.
3. Respiratory Sequelae:
   • Long-term pulmonary effects include reduced lung function and exacerbations of underlying respiratory diseases (e.g., asthma, COPD).
4. Readmission Rates:
   • Approximately 7–12% of CAP patients are readmitted within 30 days, primarily due to:
     • Exacerbation of comorbidities.
     • Recurrence or progression of respiratory symptoms.
       
       

Prognostic Biomarkers

• Pro-adrenomedullin: Associated with disease severity and prognosis.
• Cortisol and C-reactive protein (CRP): Indicators of systemic inflammation and infection severity.
• Procalcitonin: May help differentiate bacterial from non-bacterial pneumonia and guide antibiotic therapy.
  
  

Chronic Implications of CAP

• CAP is increasingly viewed as a systemic illness with significant chronic health impacts.
• Long-term complications include:
  • Persistent systemic inflammation, which can exacerbate comorbidities.
  • Increased vulnerability to recurrent infections.
• These findings emphasise the importance of considering CAP as not only an acute condition but also a trigger for chronic health issues.
  
  

Short-Term Complications

1. Septic Shock:
   • Prevalence: Medium likelihood, particularly in severe CAP.
   • Clinical Features: Fever, tachypnea, tachycardia, and multi-organ failure.
   • Management: Follow sepsis protocols; initiate prompt treatment including antibiotics and supportive care.
2. Acute Respiratory Distress Syndrome (ARDS):
   • Prevalence: Medium likelihood in severe CAP.
   • Pathophysiology: Non-cardiogenic pulmonary edema and widespread lung inflammation.
   • Mortality: High, with rates between 30–50%.
   • Management: Low tidal volume ventilation and advanced respiratory support.
3. Antibiotic-Associated Clostridioides difficile Colitis:
   • Prevalence: Medium, related to disruptions in gut flora.
   • Clinical Features: Diarrhea, abdominal pain, and leukocytosis.
   • Management: Discontinue causative antibiotics; treat with oral metronidazole, vancomycin, or fidaxomicin.
4. Heart Failure:
   • Prevalence: Occurs in approximately 14% of hospitalised CAP patients.
   • Risk Factors: Older age, pre-existing heart disease, and severe pneumonia.
   • Management: Optimise fluid balance and treat underlying cardiac conditions.
5. Acute Coronary Syndrome (ACS):
   • Prevalence: Reported in 5.3% of hospitalised patients with CAP.
   • Mechanism: Systemic inflammation and hypoxia can exacerbate coronary ischemia.
6. Cardiac Arrhythmias:
   • Prevalence: Occurs in 4.7% of hospitalised CAP patients.
   • Management: Monitor and treat according to arrhythmia type and severity.
7. Pleural Effusion:
   • Prevalence: Seen in up to 57% of hospitalised CAP patients; 1–2% may develop empyema.
   • Significance: Indicator of severe disease; associated with treatment failure.
   • Management: Thoracentesis and appropriate antibiotic therapy.
8. Lung Abscess:
   • Prevalence: Rare.
   • Pathophysiology: Localized necrosis of lung tissue.
   • Management: Prolonged antibiotics and potential surgical drainage.
9. Necrotising Pneumonia:
   • Prevalence: Rare, associated with pathogens such as Staphylococcus aureus and Klebsiella pneumoniae.
   • Risk Factors: Smoking, diabetes, and chronic lung disease.
   • Management: High-dose antibiotics and surgical intervention if needed.
10. Pneumothorax:
    • Prevalence: Rare.
    • Mechanism: Rupture of lung tissue due to bacterial infection.
    • Management: Chest tube placement and supportive care.
      
      

Non-Resolving Pneumonia

• Patients with no clinical improvement after at least seven days of appropriate antibiotics may have:
  • Delayed Response: Slower recovery in severe cases or comorbid patients.
  • Loculated Infections: Empyema or lung abscess requiring drainage.
  • Alternative Diagnoses: Conditions like bronchial obstruction or subacute infections (e.g., Mycobacterium tuberculosis, fungal infections).
    
    

Long-Term Complications

1. Chronic Pulmonary Effects:
   • Persistent reduction in lung function and increased susceptibility to future infections.
2. Cardiovascular Sequelae:
   • Increased risk of myocardial infarctions, arrhythmias, and heart failure.
3. Systemic Inflammation:
   • Ongoing inflammation post-infection can exacerbate comorbidities like diabetes or COPD.
4. Increased Mortality:
   • Long-term mortality rates following hospitalisation for CAP:
     • 6.5% during hospitalisation.
     • 13% at 30 days.
     • 31% at one year.
   • Deaths are often linked to underlying conditions, including malignancies and cardiovascular diseases.
     
     

1. Cilloniz C, Martin-Loeches I, Garcia-Vidal C, et al. Risk factors for mortality and complications in community-acquired pneumonia. Respiratory Research. 2016;17:105.
2. Cilloniz C, Martin-Loeches I, Garcia-Vidal C, et al. Microbial etiology of pneumonia: epidemiology and risk factors. Critical Care Clinics. 2021;37(4):677–694.
3. Chalmers JD, Aliberti S, Blasi F. Management of community-acquired pneumonia in adults: an update. European Respiratory Review. 2019;28(151):190043.
4. File TM Jr, Ramirez JA. Community-acquired pneumonia. New England Journal of Medicine. 2023;389(17):1633–1634.
5. Gadsby NJ, Musher DM. Evolving diagnostic challenges in community-acquired pneumonia. Clinical Microbiology Reviews. 2022;35(4):e0001522.
6. Gadsby NJ, Musher DM. The microbial etiology of community-acquired pneumonia in adults: from classical bacteriology to host transcriptional signatures. Clinical Microbiology Reviews. 2022;35(4):e0001522.
7. Jain S, Self WH, Wunderink RG, et al. Community-acquired pneumonia requiring hospitalization among U.S. adults. New England Journal of Medicine. 2015;373(5):415–427.
8. Jain S, Williams DJ, Arnold SR, et al. Etiology of community-acquired pneumonia among hospitalized children in the United States: the EPIC study. New England Journal of Medicine. 2015;372:835–846.
9. \Lim WS, van der Eerden MM, Laing R, et al. Defining community-acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003;58:377–382
10. Mandell LA, Wunderink RG, Anzueto A, et al. Infectious Diseases Society of America/American Thoracic Society Consensus Guidelines on the Management of Community-Acquired Pneumonia. Clinical Infectious Diseases. 2007;44(Suppl 2):S27–S72.
11. National Institute for Health and Care Excellence (NICE). Pneumonia in adults: diagnosis and management. National Institute for Health and Care Excellence. Updated 2023. Available at: www.nice.org.uk
12. Torres A, Chalmers JD, Dela Cruz CS, et al. Challenges in severe community-acquired pneumonia: a point-of-view review. Intensive Care Medicine. 2019;45(2):159–171.
13. Torres A, Cilloniz C, Polverino E, et al. Community-acquired pneumonia in critically ill patients. Intensive Care Medicine. 2016;42(12):2226–2235.
14. Torres A, Lee N, Cilloniz C, et al. Laboratory studies and imaging techniques in the diagnosis of pneumonia. Clinics in Chest Medicine. 2018;39(4):515–531.
15. Torres A, Polverino E, Cilloniz C, et al. Community-acquired pneumonia and cardiovascular complications. Chest. 2017;151(4):927–938.
16. Wunderink RG, Waterer GW. Advanced diagnostic testing and complications of CAP. Lancet Respiratory Medicine. 2021;9(8):1032–1044.
17. Wunderink RG, Waterer GW. Diagnostic differentiation in severe pneumonia. Lancet Infectious Diseases. 2021;21(8):1125–1133.
18. Wunderink RG, Waterer GW. Advanced diagnostic testing for community-acquired pneumonia. Lancet Respiratory Medicine. 2022;10(1):55–66.