Mycoplasma are the smallest of the free-living organisms; unlike viruses, mycoplasma can reproduce outside of living cells. Many species within the genus Mycoplasma thrive as parasites in human, bird, and animal hosts. Some species can cause disease in humans.

Mycoplasma are found most often on the surfaces of mucous membranes. They can cause chronic inflammatory diseases of the respiratory system, urogenital tract, and joints. The most common human illnesses caused by mycoplasma are due to infection with M. pneumoniae, which is responsible for 10-20% of all pneumonias.

Pneumonia caused by mycoplasma is also called atypical pneumonia, walking pneumonia, or community-acquired pneumonia. Infection moves easily among people in close contact because it is spread primarily when infected droplets from the respiratory system circulate in the air due to coughing, spitting, or sneezing.

Atypical pneumonias can affect otherwise healthy people who have close contact with one another. Pneumonia...