Chlamydia Serology for Community-Acquired Pneumonia; Respiratory Pathogen Multiplex PCR (LAB7307)

Community-acquired pneumonia (CAP) is a common cause of morbidity and mortality in the United States, with many causal organisms. Given this diversity, diagnosis and treatment can be difficult, especially in cases of atypical pneumonia. One prime example of diagnostic complexity is Chlamydia (Chlamydophila) pneumoniae.

As an obligate intracellular bacteria, C. pneumoniae stains poorly via Gram stain. Serological testing for IgG and IgM immunofluorescence has been utilized in the past to augment the diagnostic yield, however, it comes with substantial disadvantages. These antibodies are often only detectable after a several-week delay, occur at low titers in infected patients, and lack specificity to distinguish pathogenic Chlamydia species from their non-pathogenic counterparts.

Nucleic acid amplification testing (NAAT), in the form of the Respiratory Pathogen Multiplex Panel (RP2.1), offers improved sensitivity, specificity, and turn-around time for detecting Chlamydia pneumoniae, and is the preferred test in most patients.

Note: In patients with pneumonia and exposures to exotic birds, serological testing for Chlamydia psittaci (psittacosis) may be warranted.

• Chlamydia antibodies are often present in low titers, and may only be detectable several weeks after infection.
• Available IgM and IgG assays cannot differentiate between pathogenic and non-pathogenic, environmental Chlamydia species.

• Molecular testing, or NAAT, has become the standard for detecting Chlamydia pneumoniae due to its superior sensitivity and specificity to serology.
• NAAT is available through the Respiratory Pathogen Multiplex Panel (RP2.1).

1. Petitjean J, Vincent F, Fretigny M, et al. Comparison of two serological methods and a polymerase chain reaction-enzyme immunoassay for the diagnosis of acute respiratory infections with Chlamydia pneumoniae in adults. J Med Microbiol. 1998;47(7):615-621. doi:10.1099/00222615-47-7-615.
2. Gnarpe J, Lindquist L. A new DIG-PCR-EIA method for the detection of Chlamydia pneumoniae DNA in clinical samples. APMIS. 2000;108(9):626-632. doi:10.1034/j.1600-0463.2000.d01-106.x