Causes, How It Spreads, and People at Increased Risk

Chlamydia pneumoniae is a type of bacteria that causes lung infections, such as pneumonia. The bacteria cause illness by damaging the lining of the respiratory tract (throat, windpipe, and lungs).

How It Spreads

A person who is sick with C. pneumoniae infection has the bacteria in their nose, throat, windpipe, and 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. If someone who is infected coughs into their hands, they can spread the bacteria to others, by shaking hands for example, who can also become infected if they touch their nose or mouth while the bacteria are on their hands.

Most people who are exposed for a short amount of time to someone with C. pneumoniae infection do not get sick. However, it is common for this illness to spread between family members who live together. C. pneumoniae infections are known to have long incubation periods (the time between first catching the bacteria from an ill person and development of symptoms), with symptoms beginning 3 to 4 weeks after exposure. ^{1, 2, 3, 4, 5, 6, 7}

People at Increased Risk

People of all ages can get sick from C. pneumoniae. It most commonly infects people for the first time when they are school-aged children or young adults; however, reinfection is most common in older adults.

People at increased risk include those who live or work in crowded settings where outbreaks most commonly occur⁸, such as:
• Schools
• College residence halls (dormitories)
• Military barracks
• Nursing homes
• Hospitals
• Prisons

Older adults are at increased risk for severe disease caused by C. pneumoniae infection, including pneumonia.

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Footnotes

¹ Csango PA, Haraldstad S, Pedersen JE, Jagars G, Foreland I. Respiratory tract infection due to Chlamydia pneumoniae in military personnel. Scand J Infect Dis Suppl. 1997;104:26–9.

² Dawood FS, Ambrose JF, Russell BP et al. Outbreak of pneumonia in the setting of fatal pneumococcal meningitis among US Army trainees:  potential role of Chlamydia pneumoniae infection. BMC Infect Dis. 2011;11:157.

³ Oktem IM, Ellidokuz H, Sevinc C, et al. PCR and serology were effective for identifying Chlamydophila pneumoniae in a lower respiratory infection outbreak among military recruits. Jpn J Infect Dis. 2007;60:97–101.

⁴ Schmidt SM, Muller CE, Mahner B, Wiersbitzky SK. Prevalence, rate of persistence and respiratory tract symptoms of Chlamydia pneumoniae infection in 1211 kindergarten and school age children. Pediatr Infect Dis J. 2002;21:758–62.

⁵Conklin L, Adjemian J, Loo J, et al. Investigation of a Chlamydia pneumoniae outbreak in a federal correctional facility in Texas. Clin Infect Dis. 2013;57:639–47.

⁶Mylotte J. Nursing home-acquired pneumonia. Clin Infect Dis. 2002;35:1205–11.

⁷Kuo C, Jackson LA, Campbell LA, Grayston JT. Chlamydia pneumoniae (TWAR). Clin Microbiol Rev. 1995;8:451–61.

⁸Fajardo KA, Zorich SC, Voss JD, Thervil JW. Pneumonia outbreak caused by Chlamydophila pneumoniae among US air force academy cadets, Colorado, USA. EID. 2015;21.