History and Disease Patterns


As early as the 1930s, scientists were reporting pneumonias that were “atypical” compared to characteristics usually seen with pneumonia. Patients with atypical pneumonia tended to

  • Have symptoms for longer
  • Not be as sick
  • Not respond to some antibiotics used for treating “typical” pneumonia

In 1944, scientists discovered an agent that causes “atypical” pneumonia and later named it Mycoplasma pneumoniae. They first thought it was a virus or fungus, so they chose the name “mycoplasma,” which is Greek for “fungus-formed.” Eventually, scientists learned that it is a bacterium with many unique characteristics. It does not have a rigid cell wall, which affects the types of antibiotics that work well against it. It is also the smallest organism capable of living and reproducing on its own. Smaller germs, like viruses, have to live and reproduce inside cells.

Disease patterns

M. pneumoniae infections are common in the United States. The number of infections varies over time, with peaks of disease every 3 to 7 years. An estimated 2 million cases of M. pneumoniae infections occur each year in the United States. However, many infections are not diagnosed, so the actual number is likely higher. This illness can happen any time during the year but may be more common in summer and early fall.