Community-Acquired Pneumonia (CAP)

Classification of Pneumonia by Site of Acquisition

Categories of Pneumonia

• Community-Acquired Pneumonia (CAP):
  • Acute infection acquired outside hospital settings.

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

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.

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

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.

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

• While rare, fungal pathogens like Histoplasma capsulatum and Coccidioides immitis can cause CAP in immunocompromised individuals or those with specific environmental exposures.

Risk Factors for Community-Acquired Pneumonia (CAP)

Primary Risk Factors

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%.

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.

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.

Excessive Alcohol Use

• Alcohol abuse impairs immune function and increases aspiration risks.
• Daily alcohol intake of ≥24 g markedly raises the risk of CAP.

Medications Affecting Gastric Acidity

• Proton pump inhibitors and H2-receptor antagonists reduce stomach acid, promoting bacterial colonisation and increasing CAP risk.

Chronic Respiratory Diseases

• COPD increases CAP risk by 2- to 4-fold and is associated with worse outcomes and higher mortality in CAP patients.

Frequent Interaction with Children

• Adults living in households with children, especially three or more, face a higher likelihood of developing CAP.

Secondary Risk Factors

Poor Oral Hygiene

• Aspiration of bacteria from dental plaque contributes to infection, particularly in older adults.

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.

Chronic Liver Disease

• Cirrhosis and other liver conditions increase susceptibility to bacterial infections, including pneumonia, often leading to severe outcomes.

Chronic Kidney Disease

• Patients with renal dysfunction are at significantly higher risk for severe CAP and associated mortality.

Opioid Use

• High doses or immunosuppressive opioids elevate CAP risk, affecting both HIV-positive and HIV-negative individuals.

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.

Immunocompromised States

• Conditions such as HIV, malignancies, or immunosuppressive therapy increase susceptibility to severe and atypical CAP pathogens.

Neurological or Swallowing Disorders

• Impaired airway protection from stroke, seizures, or dysphagia raises the risk of aspiration pneumonia.

Pathogen Entry Mechanisms

Microaspiration of Oropharyngeal Secretions:

•  The most common route for bacterial pneumonia, allowing upper airway flora to enter the lower airways.

Inhalation of Infectious Aerosols

•  A key mechanism for viral and atypical pathogens, such as Legionella or Mycoplasma pneumoniae.

Hematogenous Spread

•  Pathogens can disseminate via the bloodstream from distant infected sites, such as right-sided endocarditis.

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

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.

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

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

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.

Dyspnea

• A frequent and predictive symptom of CAP.
• Associated with hypoxemia and impaired alveolar gas exchange.

Pleuritic Chest Pain

• Present in approximately 30% of cases.
• Often reported alongside other respiratory symptoms like dyspnea and cough.

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.

Fatigue and Malaise

• Systemic symptoms like fatigue and malaise are common, reflecting the body's inflammatory response.

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

Legionella Pneumonia

• Presents with diarrhoea, headache, confusion (linked to hyponatremia), and constitutional upset.

Mycoplasma Pneumonia

• Symptoms may include otitis media, hemolytic anemia, Stevens-Johnson syndrome, and sore throat.

Aspiration Pneumonia

• Often associated with impaired swallowing, poor oral hygiene, or conditions like stroke and chronic alcoholism.

Risk Factors Worsening Symptoms or Disease Severity

Advanced Age (>65 Years)

• Increases susceptibility and mortality risk.
• Higher prevalence of comorbidities contributes to severe presentations.

Chronic Respiratory Diseases

• COPD, asthma, and bronchitis are linked to a 2- to 4-fold increase in CAP risk.

Comorbidities

• Diabetes, heart disease, chronic kidney or liver disease increase the risk of severe disease.

Substance Use

• Smoking, alcohol misuse, and opioid use impair respiratory defenses and predispose to CAP.

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

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.

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

Pleural Effusion

• Manifests as decreased tactile fremitus, diminished breath sounds, and dullness to percussion.
• Large effusions may present with dyspnea due to mechanical compression.

Empyema

• Findings mimic pleural effusion.
• Confirmatory diagnosis involves thoracentesis and analysis of pleural fluid for pH, cell counts, and microbiological studies.

Systemic Findings

Vital Signs

• Fever (>38°C or 100°F) is typical but may be absent in elderly or immunocompromised individuals.
• Tachycardia and tachypnea are common.

General Appearance

• Patients may appear acutely ill with increased work of breathing.
• Cyanosis or hypoxemia may indicate severe disease or respiratory failure.

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

Legionella Pneumonia

• May present with diarrhea, confusion (due to hyponatremia), and constitutional symptoms.
• Consolidation may still be evident on examination.

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

Atypical Presentations

• Confusion, lethargy, or worsening of underlying chronic conditions may predominate.
• Fever and focal chest signs may be absent, necessitating heightened clinical suspicion.

Imaging Correlation

• In immunosuppressed patients, pulmonary infiltrates may not be apparent on chest radiographs and may require advanced imaging like CT.

Diagnostic Insights

Purulent Sputum

• Indicates typical bacterial pathogens.
• Blood-tinged sputum may be seen in S. pneumoniae or Klebsiella pneumoniae infections.

Tachypnoea

• A highly predictive symptom for CAP when combined with fever and focal chest findings.

Hypoxemia

• SpO₂ <95% on room air correlates with disease severity and is a marker for hospitalisation.

Severity Assessment (CURB-65 Score)

CURB-65 Criteria

• Each criterion scores 1 point:
  • Confusion: Abbreviated Mental Test score ≤8 or new onset of disorientation.
  • Urea Level: Serum blood urea nitrogen >7 mmol/L.
  • Respiratory Rate: ≥30 breaths per minute.
  • Blood Pressure: Diastolic ≤60 mmHg or systolic <90 mmHg.
  • 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

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.

Pulse Oximetry

• Assess oxygen saturation at presentation.
• Saturation <94% indicates a worse prognosis and may necessitate oxygen therapy or urgent referral.

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.

Full Blood Count (FBC)

• Leukocytosis is common and suggests bacterial pneumonia.
• A WBC count >15 x10⁹/L is associated with Streptococcus pneumoniae.

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.

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

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.

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.

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.

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.

Liver Function Tests (LFTs)

• Provide baseline data.
• Abnormal results may suggest Legionella or underlying liver disease.

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

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.

Chest Ultrasound

• Useful for pleural effusions and guiding thoracentesis.

Thoracentesis

• Analyse pleural fluid to differentiate parapneumonic effusion, empyema, or other causes.
• Positive Gram stain or pH <7.2 indicates empyema.

Bronchoscopy

• Consider in unresolved CAP or immunocompromised patients to obtain respiratory samples for culture or PCR.

Direct Fluorescent Antibody (DFA) Testing

• Can assist with detecting Legionella or atypical pathogens but has limited sensitivity.

Respiratory Conditions

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.

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.

Asthma Exacerbation

• Symptoms: Acute bronchospasm, wheezing, and worsening of underlying symptoms.
• Investigations: Chest X-ray typically unremarkable.

Bronchiectasis Exacerbation

• Symptoms: Increased sputum production and recurrent infections.
• Investigations: Chest imaging may show airway dilation and mucus plugging.

Empyema

• Symptoms: Fever, chest pain, and systemic signs.
• Investigations: Pleural effusion on chest X-ray; confirmed by pleural fluid analysis.

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

Congestive Heart Failure (CHF)

• Symptoms: Dyspnea, orthopnea, and peripheral edema.
• Investigations: Bilateral interstitial infiltrates or pleural effusion on chest X-ray; cardiomegaly often present.

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.

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

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.

Hypersensitivity Pneumonitis

• Symptoms: Acute dyspnea and cough following antigen exposure.
• Investigations: Positive immunologic tests; imaging shows diffuse ground-glass opacities.

Systemic Lupus Erythematosus (SLE) Pneumonitis

• Symptoms: Dyspnea, fever, and pleuritic chest pain.
• Investigations: Diffuse pulmonary infiltrates on imaging; supportive serology findings.

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

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.

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

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.

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

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.

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%.

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.

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

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.

Criteria for Home Treatment

• Stable comorbidities.
• Reliable ability to take oral medications.
• Supportive social circumstances.

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

Persistent Symptoms

• Reassess for potential complications (e.g., pleural effusion, empyema, lung abscess).
• Repeat chest X-ray and consider advanced imaging or bronchoscopy.

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

Clinical and Pathogen-Related Factors

• Presence of bacteraemia.
• Infections with multidrug-resistant organisms (Staphylococcus aureus, Pseudomonas aeruginosa, Enterobacteriaceae).

Comorbidities

• Neurological diseases, cardiovascular disease, and advanced chronic obstructive pulmonary disease (COPD).

Severe Disease Presentations

• ICU admission or respiratory failure.
• Overwhelming sepsis.

Long-Term Outcomes

Mortality Beyond Hospitalisation

• 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.

Cardiovascular Complications

• CAP is associated with increased risk of acute and chronic cardiac complications, including:
  • Myocardial infarctions.
  • Arrhythmias.
  • Heart failure exacerbations.

Respiratory Sequelae

• Long-term pulmonary effects include reduced lung function and exacerbations of underlying respiratory diseases (e.g., asthma, COPD).

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

• Emerging evidence suggests potential utility of biomarkers for predicting outcomes, including:
  • 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

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.

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.

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.

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.

Acute Coronary Syndrome (ACS)

• Prevalence: Reported in 5.3% of hospitalised patients with CAP.
• Mechanism: Systemic inflammation and hypoxia can exacerbate coronary ischemia.

Cardiac Arrhythmias

• Prevalence: Occurs in 4.7% of hospitalised CAP patients.
• Management: Monitor and treat according to arrhythmia type and severity.

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.

Lung Abscess

• Prevalence: Rare.
• Pathophysiology: Localized necrosis of lung tissue.
• Management: Prolonged antibiotics and potential surgical drainage.

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.

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

Chronic Pulmonary Effects

• Persistent reduction in lung function and increased susceptibility to future infections.

Cardiovascular Sequelae

• Increased risk of myocardial infarctions, arrhythmias, and heart failure.

Systemic Inflammation

• Ongoing inflammation post-infection can exacerbate comorbidities like diabetes or COPD.

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.

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