Whilst the BTS community acquired pneumonia guidelines acknowledge that certain features occur more frequently with particular organisms (see below), they consider none to be specific enough to influence the initial choice of antibiotic.
Increasing age, co-morbidity, acute onset, high fever and pleuritic chest pain.
Younger patients, smokers, absence of co-morbidity, diarrhoea, neurological symptoms, more severe infection, evidence of multisystem involvement (e.g. abnormal liver function tests, elevated serum creatinine kinase).
Legionella infection peaks in autumn in the UK, and in 50% of cases is related to travel abroad. Less frequently, cases occur in clusters due to contaminated water cooling systems.
Younger patients, less multisystem involvement. Epidemics occur in UK spanning three winters every four years.
Incidence peaks in winter and occurs more commonly in intravenous drug users or debilitated patients, particularly those with influenza. It is relatively more prevalent in patients on intensive care but even in this setting strep. pneumoniae remains the most common cause of pneumonia.