Fast Facts

• Chlamydia pneumoniae is a type of bacteria that can infect the lungs.
• C. pneumoniae is spread from person to person when people who are sick cough or sneeze while in close contact with others, who then breathe in the bacteria.
• Most people with C. pneumoniae infection are asymptomatic (meaning they do not show signs or symptoms of illness) or have mild symptoms, although a serious lung infection (pneumonia) can develop, particularly in older adults.
• C. pneumoniae infection is characterized by a gradual onset of symptoms and long incubation period (the time between first catching the bacteria from an ill person and development of symptoms) of 3 to 4 weeks.
• After gradual onset, symptoms (like coughing and a general sense of illness) due to C. pneumoniae infection may continue for several weeks or months despite appropriate antibiotic treatment (medicines that kill bacteria in the body).
• Pneumonia caused by C. pneumoniae is considered atypical because antibiotics commonly used to treat pneumonia caused by other types of bacteria do not work against C. pneumoniae infections.
• Unlike Mycoplasma pneumoniae infection, another common cause of atypical pneumonia, symptoms of C. pneumoniae infection can also include swelling of the voice box and hoarseness (laryngitis); however, not all patients with C. pneumoniae infection show signs of laryngitis.
• Since C. pneumoniae infection is likely underdiagnosed, the actual number of cases each is unknown. However it is estimated that there are about 300,000 cases of C. pneumoniae infection each year in the United States.¹

Footnotes

¹ Kuo CC, Jackson LA, Campbell LA, Grayston JT. Chlamydia pneumoniae (TWAR). Clin Microbiol Reviews. 1995;8(4):451–461.