Atypical pneumonia is caused by bacteria not commonly associated with pneumonia. The clinical picture is less severe than that of typical pneumonia, hence it is also known as “walking pneumonia”
Etiology
- Mycoplasma pneumoniae
- Chlamydia pneumoniae + psittaci
- Legionella pneumophila
- Coxiella burnetti – presents as Q fever
- Viral – influenza A, SARS , RSV , coronavirus
Epidemiology
- Atypical organisms are implicated in ≈20% of CAP
- M.pneumoniae – person to person
- C.psittaci – contact with birds
- Legionella – water coolers, no person to person transmission
Clinical features
M.pneumoniae
- Vague + slow onset – constitutional symptoms
- Dry cough, fever, headache, pleuritic pain, usually presents with ear infection
- Hacking dry cough persists
- Extra-pulmonary features
- Rashes – erythema multiforme / nodosum , urticaria
- Neurological – guillain barre syndrome, cerebellar ataxia, aseptic meningitis
- Blood- cold agglutinin disease, haemolytic anemia
- Joints – arthralgia, arthritis
- Heart – pericarditis, Myocarditis
C.pneumoniae
- Gradual onset – may show improvement before worsening again
- Non-specific URT infection symptoms
- Cough + scanty sputum
- Hoarseness
- Headache
- Fever is UNUSUAL
- Symptoms can persist for months despite antibiotic course
- Diabetes mellitus can complicate infection
L.pneumophilia
- Most severe atypical pneumonia
- Initially mild headache, leads to high fever, chills, rigors – early on
- Dyspnea, pleuritic pain, haemoptysis
- GIT – nausea, vomit, diarrhoea
- Neurological – confusion, disorientation,
- Severe complications – pancreatitis, peritonitis, Myocarditis, GLN
Management
- Treated similarly to CAP
- Macrolides – azithromycin, clarithromycin, erythromycin (safe in pregnancy)
- Doxycycline
- Rifampicin + macrolide – legionella
- Fluroquinolones