Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.
2 min synopsisUK scopeSources checked 27 Aug 2026Clinical review pending
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Escalate
In shock, suspected sepsis or rapidly progressive pneumonia, collect feasible cultures without delaying resuscitation and time-critical antimicrobials. Start indicated transmission precautions immediately, and urgently involve infection, microbiology and health protection for a suspected outbreak, Legionnaires’ disease or high-consequence respiratory pathogen.
Synopsis
Identify the likely infectious cause of community-acquired pneumonia, obtain useful specimens, select proportionate empirical antibiotics, interpret microbiology safely and narrow, switch or stop treatment at a defined review point.
Begin with host, exposure and resistance risk: recent antibiotics, previous resistant isolates, influenza, aspiration, immune suppression, travel, water-system exposure and clusters can change the pathogen hypothesis.
Do not routinely request microbiology for uncomplicated low-severity adult CAP; in moderate or high severity, choose tests only when the result can refine treatment, detect a complication or trigger public-health action.
When bacteraemia or sepsis is plausible, obtain at least two adult blood-culture sets using two aerobic and two anaerobic bottles, filling each with 8–10 mL and sending them promptly for incubation.
Key red flags
Post-influenza deterioration
New fever, shock, haemoptysis, cavitation or rapid decline after apparent influenza improvement raises concern for bacterial coinfection, including Staphylococcus aureus, and needs urgent reassessment.
Investigation priorities
01
Microbiology triage by severityFirst step
Avoid low-yield testing while identifying patients whose results could change treatment.
Management branches
Sample, isolate and notifySecure actionable evidence without delaying treatment
CAP severity, sepsis physiology, host factors or an epidemiological clue makes microbiology or public-health action useful.
Before antimicrobials when safe, collect only specimens that answer a defined question; record prior exposure, anatomical source, collection time and the clinician who owns each result.
Institute pathogen-appropriate respiratory precautions immediately when influenza, COVID-19, measles, tuberculosis or another transmissible infection is plausible; do not wait for laboratory confirmation to protect others.
First-line empirical therapyMatch initial spectrum to severity and resistance risk
A clinical diagnosis of CAP has been established and treatment must begin before definitive microbiology.
Key medicines
AmoxicillinNICE first-line treatment for low-severity adult CAP is 500 mg orally three times daily for 5 days; higher doses may be selected from the BNF for severe infection.
DoxycyclineWhen amoxicillin is unsuitable in low or moderate severity, NICE lists 200 mg orally on day 1 followed by 100 mg once daily for 4 further days.
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
RCPath UK SMI S 2: Pneumonia, issue 1.3Current UK Standards for Microbiology Investigations pneumonia algorithm, issued April 2025, with linked respiratory and sterile-site laboratory standards.