Mycoplasma pneumoniae is a very small bacterium which lacks a cell wall. It is sensitive to macrolides, tetracyclines and fluoroquinolones. It is a common cause of community-acquired pneumonia in children and young adults, but the infection may also produce extrapulmonary symptoms. The incubation period is 1 to 4 weeks. The infection occurs as widespread epidemics every few years, but it is also present every year as an endemic infection regardless of the season. Consider atypical mycobacterial infection in patients with - persistent pulmonary infection and chronic pulmonary disease or immunosuppression - suspected pulmonary tuberculosis that responds poorly to treatment.