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. Specific disease syndromes are age-related. M. pneumoniae is the leading cause of pneumonia in school-age children and young adults but is an uncommon cause of symptomatic illness in children younger than five years of age.
Initial symptoms are malaise, fever, and sometimes headache.
A nonproductive cough develops within a few days and lasts for three to four weeks during which time it may become productive. Chest film abnormalities are variable and characteristically are more extensive then the clinical picture would suggest. Acute bronchitis and upper respiratory tract illnesses caused by M. pneumoniae are generally mild and resolve without antibiotic therapy. Transmissibility is reduced when appropriate therapy is used early in the course of the infection. Erythromycin, clarithromycin and azithromycin are preferred for treatment of M. pneumoniae infections in children younger than eight years of age.