Synopsis
Recognise pneumonia caused by intracellular or exposure-linked pathogens without relying on an unreliable 'atypical' phenotype, choose targeted microbiology, provide intracellular-active therapy, and trigger UK public-health action where required.
- Atypical pneumonia commonly refers to Legionella species, Mycoplasma pneumoniae, Chlamydia psittaci and Coxiella burnetii; clinical features overlap substantially with ordinary bacterial and viral pneumonia.
- Ask about hotel, hospital, spa or water-aerosol exposure for Legionella; birds for psittacosis; and sheep, cattle, goats or birthing products for Q fever.
- Legionella may cause severe pneumonia with diarrhoea, confusion, hyponatraemia, renal or liver disturbance, but none of these features is sufficiently specific to diagnose it.
Key red flags
High fever, cough and severe pneumonia after travel, hotel, healthcare, spa or aerosolised-water exposure, sometimes with diarrhoea, confusion, hyponatraemia or renal and hepatic disturbance.
Investigation priorities
Direct organism-specific testing and identify a reportable exposure or outbreak.
Management branches
Pneumonia with a possible atypical respiratory pathogen.
- Assess ABCDE, oxygen requirement, NEWS2 and CRB65/CURB65 where appropriate; manage shock or respiratory failure immediately and obtain chest imaging.
- Take a focused exposure history and send proportionate microbiology before antibiotics when this creates no harmful delay.
Key medicines
ClarithromycinA common adult CAP regimen is 500 mg orally or IV twice daily, usually within a 5-day uncomplicated CAP course; confirmed Legionella may require a specialist-defined longer course.
DoxycyclineA typical adult regimen begins with 200 mg on day 1 then 100 mg once daily, with dose and duration adjusted to organism, severity and current local guidance.