Community Acquired Pneumonia Overview

Community Acquired Pneumonia (CAP)

• An acute infection of the lung affecting the parenchyma, accompanied by a constellation of suggestive features and acute infiltrate on chest x-ray
• Develops in a patient who is NOT hospitalized or residing in a long-term facility
• Incidence: 24.8 cases per 10,000
• Average length of stay: 5.2 days
• 13th leading cause of death in the US (combined with influenza)

CAP, HAP, VAP By Setting

• Community-acquired pneumonia develops in the outpatient setting
• Hospital-acquired pneumonia develops within 48 hours of admission to a hospital in a non-intubated patient
• Ventilator-associated pneumonia is HAP that begins within 48 hours after intubation

Atypical Pneumonia and Atypical Pathogens

• Atypical pneumonia refers to pneumonia presenting with symptoms or chest x-ray distinct from classic cases.
• Atypical pathogens include Mycoplasma pneumoniae, Chlamydophila (Chlamydia) pneumoniae, Legionella pneumophila
• Streptococcus pneumoniae is the most common pathogen

CAP Prevention

• Pneumococcal vaccinations prevent invasive disease like bacteremia
• Target groups: Elderly age 65+, immunocompromised, alcoholics, those with liver disease, chronic heart disease, sickle cell, asplenia
• PCV 15, PCV 20, PCV 21, PPSV23 are available

CAP Diagnosis

• Must have clinical features of pneumonia on history and physical examination
• Radiographic evidence- chest x-ray to be obtained when CAP is suspected
• Predominant symptoms: Cough, fevers, chills, dyspnea, pleuritic chest pain, purulent sputum

CAP Differential Diagnosis

• Bronchitis (acute or exacerbation of COPD)
• COVID-19
• Acute coronary syndrome
• Heart failure and pulmonary edema
• Pulmonary embolism
• Bronchogenic carcinomas
• Metastatic disease
• Radiation pneumonitis

Outpatient vs Inpatient Diagnostic Testing

• Outpatient- CXR is the only diagnostic test of value
• Inpatient- CXR, pre-treatment blood cultures, sputum cultures if a sample can be obtained, CBC, CMP, viral PCR
• Severe CAP/Critically Ill- CXR, blood and sputum cultures + PCR viral tests, CBC, CMP, coagulation studies, serum lactate, PCT, urine antigen tests for legionella and pneumococcus, ABG

Diagnostic Testing

• Chest x-ray is recommended to confirm the diagnosis
• CT scans have higher sensitivity but no evidence that outcomes are improved over CXR
• Chest ultrasound can assess for pleural effusion and guide thoracentesis
• Blood cultures are only recommended in severe CAP and patients with recent hospitalization or antibiotic therapy (within 90 days)
• Sputum cultures may be helpful in severe CAP

Urine Antigen Testing (UAT)

• Pneumococcal UAT is recommended for severe CAP specifically for streptococcus penumonia or legionella
• Legionella UAT is recommended for severe CAP/ICU admission and patients with recent travel or known outbreak
• Used for outpatient treatment failure
• Legionella is associated with travel (cruise ships, spas, hotels)

Influenza Testing

• Rapid influenza molecular assay is recommended over rapid influenza diagnostic tests (antigen testing) during flu season
• UCSF has specific testing guidelines during summer months

SARS-CoV-2 Testing

• Diagnostic testing for people with signs or symptoms of COVID-19, regardless of vaccination status
• Nucleic Acid Amplification Tests (NAATs) and Antigen tests

Biomarkers

• Procalcitonin is not recommended for guiding antibiotic therapy, but may be useful in de-escalating therapy
• May be helpful for assessing COVID-19 vs bacterial pneumonia
• C-reactive protein (CRP) may be elevated in both COVID-19 and bacterial pneumonia

Summary of Diagnostic Testing

• Extensive diagnostic testing is helpful for patients with risk factors for severe CAP requiring ICU admission
• Trend away from automatic blood cultures for non-severe CAP admitted to the floor