IgM. Culture and PCR are also useful early in disease. Community-wide M. pneumoniae epidemics occur every four to eight years. Although M. pneumoniae is not reportable in the U.S., the last year widespread epidemic activity was reported appears to have been 1993. M. pneumoniae is highly transmissible. Humans are the only known source of infection.
Acquisition is presumed to be by droplet spread from symptomatic patients.
The incubation period is one to four weeks. The unusually long incubation period complicates epidemiologic investigations and makes effective preventive treatment and cohorting less than optimally effective at interrupting transmission. Asymptomatic carriage after infection can occur for prolonged intervals even after treatment with antibiotics, but has not been associated with transmission. The most common clinical syndromes caused by M. pneumoniae are acute bronchitis and upper respiratory tract infections, including pharyngitis and occasionally otitis media or myringitis. Coryza, sinusitis and croup are infrequent.