3: Community-acquired pneumonia.

Community-acquired pneumonia is caused by a range of organisms, most commonly Streptococcus pneumoniae, Mycoplasma pneumoniae, Chlamydia pneumoniae and respiratory viruses. Chest x-ray is required for diagnosis. A risk score based on patient age, coexisting illness, physical signs and results of investigations can aid management decisions. Patients at low risk can usually be managed with oral antibiotics at home, while those at higher risk should be further assessed, and may need admission to hospital and intravenous therapy. For S. pneumoniae infection, amoxycillin is the recommended oral drug, while benzylpenicillin is recommended for intravenous use; all patients should also receive a tetracycline (eg, doxycycline) or macrolide (eg, roxithromycin) as part of initial therapy. Flucloxacillin or dicloxacillin should be added if staphylococcal pneumonia is suspected, and gentamicin or other specific therapy if gram-negative pneumonia is suspected; a third-generation cephalosporin plus intravenous erythromycin is recommended as initial therapy for severe cases. Infections that require special therapy should be considered (eg, tuberculosis, melioidosis, Legionella, Acinetobacter baumanii and Pneumocystis carinii infection).