Chlamydia
| Numbers (% or LR) | |
|---|---|
| Incidence (annual) of infection | 0.55% (552.8 per 100,000) [1] |
| Risk Factor | |
| 1. Female | LR 1.3 [1] |
| 2. Age 15-24 | LR 10 [1] |
| 3. Men who have sex with men (MSM) | LR 1.8 [2,3] |
| 4. Human Immunodeficiency Virus (HIV) | LR 2 [4] | Symptoms/Syndrome |
| 1. Pelvic Inflammatory Disease (PID) | LR 2.5 [5] |
| 2. Cervicitis | LR 2.2 [6] |
| 3. Urethritis | LR 2.5 [7] |
| 4. Proctitis | LR 1.8 [8] |
| 5. No clinical symptoms or syndrome | LR 1.0 |
| Test | Clinical sensitivity | Clinical specificity |
| 1. NAAT | 97% | 98% [9] |
| 2. Antigen testing | 80% | 98% [10] |
| 3. DNA probes | 78% | 99% [9] |
| Other |
| Explanation for + test without disease: Asymptomatic disease (most likely scenario) vs false positive (rare) |
| Explanation for - test with disease: Poor testing technique, wrong site, wrong supplies, poor handling of specimen prior to analysis |
| Example of high value use: Sexually active women between 15 – 24 |
| Example of low value use: Prior to sexual activity, testing of site with no risk factors |
| Choosing wisely or other guidance: CW: Do not use serologic testing USPSTF: Test all sexually active women less than 24, and sexually active women greater than 24 who are at increased risk of infection |
Discussion
Incidence and risk factors:
Chlamydia remains an illness with mandatory reporting, tracked by the CDC. As such, incidence, including trends over time are publicly available. The incidence utilized was reported from the 2019 STD surveillance report.
The likelihood ratio for the risk factor of being female is calculated from CDC data from 2019 [1]. There is inherent bias, as young women are a population of patients who receive routine, asymptomatic STI testing while male patients in this age group are likely to be tested if they are asymptomatic and not seeking care, estimates have been adjusted to reflect this. The likelihood ratio for those aged 15 – 24 is also taken from CDC data from 2019 [1], and has the same limitations as mentioned above.
The likelihood ratio of chlamydia infections in MSM was determined by utilizing data from the San Francisco Department of Public health, which publishes an annual report of STIs in the city. San Francisco was selected as a well cited paper from Kent, et al. published in 2003 demonstrated the need for three site anatomic testing in the MSM population [2]. The most recent published report, utilizing data from 2018, demonstrated a rate of chlamydia diagnosis to be 11.3% in MSM and 6.5% in other men. This was used to calculate a likelihood ratio of 1.8.
Numerous studies have demonstrated that people living with HIV have higher rates of positive testing for chlamydia, yielding the LR as indicated above. Again, this brings a limitation in that this population likely is receiving more regular and asymptomatic testing.
Symptoms/Syndromes:
The likelihood ratio for pelvic inflammatory disese (PID) was determined PID based on data published by Price et al [5] demonstrating rates of chlamydia infections in those with PID. Similarly, the LR for cervicitis was determined based on rates as published by Sellors et al.[6]. Next, urethritis LR was determined based on rates published by Merchant et al.[7] And lastly, proctitis LR was determined based on rates published by Marcus et al.[8]
Test sensitivity & specificity:
Extensive comparison testing of NAAT diagnostics, antigen testing (DFA and EIA), and DNA probes have been undertaken, typically in comparison to culturing as the gold standard. Given advances in testing, the CDC has recommended utilizing NAAT testing on a stand-alone basis for diagnosis. As indicated above, NAAT testing caries very high clinical sensitivity and specificity on recent analysis.
References
Centers for Disease Control and Prevention. Sexually Transmitted Disease Surveillance 2019. Atlanta: U.S. Department of Health and Human Services; 2021.
Kent CK, Chaw JK, Wong W, et al. Prevalence of rectal, urethral, and pharyngeal chlamydia and gonorrhea detected in 2 clinical settings among men who have sex with men: San Francisco, California, 2003. Clin Infect Dis. 2005;41(1):67-74. doi:10.1086/430704
San Francisco Department of Public Health. San Francisco Sexually Transmitted Disease Annual Summary, 2018. San Francisco Department of Public Health, San Francisco, California. February, 2021; p113.
Scott KC, Philip S, Ahrens K, Kent CK, Klausner JD. High prevalence of gonococcal and chlamydial infection in men who have sex with men with newly diagnosed HIV infection: an opportunity for same-day presumptive treatment. J Acquir Immune Defic Syndr. 2008;48(1):109-112. doi:10.1097/QAI.0b013e318165dc0b
Price MJ, Ades AE, De Angelis D, et al. Risk of pelvic inflammatory disease following Chlamydia trachomatis infection: analysis of prospective studies with a multistate model. Am J Epidemiol. 2013;178(3):484-492. doi:10.1093/aje/kws583
Sellors J, Howard M, Pickard L, Jang D, Mahony J, Chernesky M. Chlamydial cervicitis: testing the practice guidelines for presumptive diagnosis. CMAJ. 1998;158(1):41-46.
Merchant RC, DePalo DM, Liu T, Rich JD, Stein MD. Developing a system to predict laboratory-confirmed chlamydial and/or gonococcal urethritis in adult male emergency department patients. Postgrad Med. 2010;122(1):52-60. doi:10.3810/pgm.2010.01.2099
Marcus JL, Bernstein KT, Stephens SC, et al. Sentinel surveillance of rectal chlamydia and gonorrhea among males--San Francisco, 2005-2008. Sex Transm Dis. 2010;37(1):59-61. doi:10.1097/OLQ.0b013e3181b76c42
Black CM, Marrazzo J, Johnson RE, et al. Head-to-head multicenter comparison of DNA probe and nucleic acid amplification tests for Chlamydia trachomatis infection in women performed with an improved reference standard. J Clin Microbiol. 2002;40(10):3757-3763. doi:10.1128/JCM.40.10.3757-3763.2002
Black CM. Current methods of laboratory diagnosis of Chlamydia trachomatis infections. Clin Microbiol Rev. 1997;10(1):160-184. doi:10.1128/CMR.10.1.160
Author: Ravi Tripathi