4 Pneumonia
Learn how pneumonia is classified, assessed, treated, and monitored, including severity indicators and important complications.
Understanding
is an infection of lung tissue, especially the alveoli. Inflammatory fluid may fill the alveoli and impair oxygen exchange. Causes include bacteria, viruses, and, less often, fungi or parasites; the responsible organism is not always identified.
Classification and causes
is commonly classified by where it was acquired, its cause, or the circumstances that led to infection.
develops outside a hospital or healthcare facility. Common causes include pneumococcus and respiratory viruses.
develops at least hours after hospital admission and was not incubating at admission.
develops more than hours after endotracheal intubation. HAP and VAP matter because likely organisms and antibiotic-resistance risks can differ from those in CAP.
follows inhalation of material from the mouth or stomach into the lower airways. Risk rises with impaired swallowing or consciousness.
By cause, may be bacterial, viral, fungal, or a mixed infection. A positive viral test does not by itself rule out bacterial coinfection.
Clinical assessment
Ask about cough, sputum, breathlessness, fever or chills, pleuritic chest pain, and recent respiratory illness. Also ask about aspiration risk, travel or outbreak exposures, chronic disease, immune status, recent hospitalization or antibiotic use, and prior cultures showing resistant organisms.
Older adults may present with confusion, weakness, or functional decline rather than prominent fever. Assess temperature, heart and respiratory rates, blood pressure, mental status, hydration, work of breathing, and oxygen saturation. Listen for crackles, reduced breath sounds, or other focal findings.
, cyanosis, inability to speak comfortably, confusion, and low blood pressure are concerning signs.
Diagnostic evaluation and severity
In adults, suspected CAP is generally confirmed by a new pulmonary infiltrate on imaging together with compatible symptoms and signs. Chest radiography is commonly used; lung ultrasound may be an alternative when an experienced clinician and suitable equipment are available. If suspicion remains high despite a negative radiograph, additional imaging may be considered.
Use pulse oximetry to assess oxygenation. Depending on severity and context, evaluation may include blood tests, blood or sputum cultures, viral testing, and other targeted tests. Cultures are especially important in severe disease or when resistant pathogens are a concern, but are not routinely needed for every mild outpatient case.
Using severity to guide care
The Severity Index and CURB-65 can support, but do not replace, clinical judgment about outpatient care, hospital admission, or intensive monitoring. Severe CAP is suggested by either a major criterion or at least three minor criteria.
A major criterion is septic shock requiring vasopressors or respiratory failure requiring mechanical ventilation. Minor criteria include respiratory rate , confusion, multilobar infiltrates, or low blood pressure requiring aggressive fluids.
Treatment principles
Treatment depends on the likely cause, severity, patient risk factors, local resistance patterns, and test results.
Stabilize and support. Provide oxygen for , fluids when appropriate, relief of fever or pain, and respiratory support if needed. Escalate care promptly for worsening work of breathing, oxygenation, circulation, or mental status.
Treat the cause. Use antibiotics when bacterial is suspected or cannot safely be excluded in a patient requiring hospital care. Select empiric therapy according to setting, severity, allergies, comorbidities, prior microbiology, and local guidance. Narrow or stop antibiotics when test results and clinical progress make that appropriate. Antibiotics do not treat viruses; pathogen-specific antiviral treatment may be indicated for some viral infections.
Reassess regularly. Check clinical stability, treatment response, adverse effects, and whether the diagnosis or plan needs revision. For adults hospitalized with CAP, current ATS guidance supports daily review of stability and microbiology to guide de-escalation or early discontinuation when appropriate. The 2025 ATS CAP update was not endorsed by IDSA; antibiotic choices should follow applicable current guidance and local protocols.
Complications
Important complications include respiratory failure and acute respiratory distress syndrome (ARDS); sepsis or septic shock; parapneumonic pleural effusion or ; lung abscess or tissue destruction; and bacteremia or infection spreading beyond the lungs.
Consider complications or an alternative diagnosis when the patient deteriorates or fails to improve as expected.
Monitoring and reassessment
Trend respiratory rate, oxygen saturation and oxygen requirement, work of breathing, temperature, heart rate, blood pressure, mental status, hydration, and ability to eat or take medication. In hospitalized patients, review test results, antimicrobial response, and potential drug adverse effects. Reassess daily for clinical stability and opportunities to narrow therapy.
Worsening oxygen needs, new confusion or hypotension, or persistent deterioration warrants prompt escalation and evaluation for complications.