Fastidious organism that does not Gram stain - an "atypical".
Also known as Chlamydia pneumoniae, transmitted from close person-to-person contact.
Long incubation period of 3-4 weeks.
Upper respiratory tract infections
Testing available using culture, serology, or molecular methods. PCR is the preferred method of diagnostic testing for acute C. pneumoniae infection. Difficult to culture.
CDC. Chlamydia pneumoniae Infection. January 10, 2019. https://www.cdc.gov/pneumonia/atypical/cpneumoniae/hcp/disease.html