Presently about half of all cases of CAP which are admitted to a hospital are of unproven etiology. CAP often presents with fever, chills, and a cough with or without production of purulent sputum. The patient's exposure and medical histories are often more helpful in defining the most likely etiologic agent than are the presenting symptoms. Exposure to grocery store mist machines, air-conditioning cooling towers, or a recent stay in a hotel or hospital suggest L. pneumophilia . Mycobacterium tuberculosis is suggested by cough, fever, night sweats, and weight loss lasting for a month or more.
Aspiration suggests a polymicrobic infection and the presence of anaerobes.
Cultures of blood or pleural fluid are useful in identifying the etiologic agent. Routine sputum cultures are neither sensitive nor specific. When the etiologic agent and its susceptibilities are known, antimicrobial therapy should be narrow in spectrum. Clin Inf Dis.