History and Disease Patterns

History

Although we now know that Chlamydia pneumoniae is not associated with eye infections, this bacterium was first discovered in the 1960s during vaccine studies to prevent a type of bacterial eye infection called trachoma. It wasn’t until 1983, when the bacterium was isolated from a respiratory culture, that scientists understood how C. pneumoniae causes illness in people.

C. pneumoniae was first thought to be a virus. Eventually scientists learned that it is a bacterium and classified it as “atypical” because it is different from many other bacteria that cause pneumonia. It is also considered “atypical” because antibiotics commonly used to treat pneumonia caused by other types of bacteria do not work against C. pneumoniae infections. Only one serotype (type) of C. pneumoniae has been identified.

Disease Patterns

Since C. pneumoniae infection is likely underdiagnosed, the actual number of cases each is unknown. However it is estimated 300,000 cases of C. pneumoniae infection occur each year in the United States.¹ The number of people who get sick from a C. pneumoniae infection does not change a lot by season, but studies have shown that the number of infections varies over time, with peaks of disease about every 4 years.

Footnotes

¹ Kuo CC, Jackson LA, Campbell LA, Grayston JT. Chlamydia pneumoniae (TWAR). Clin Microbiol Reviews. 1995;8(4):451–61.