NAAT identified chlamydial infections: Enhanced sensitivity, reduced transmissibility?

Estimates of C. trachomatis (Ct) have been facilitated by the development of non-invasive nucleic acid amplification tests (NAATs). Given the high sensitivity and low limit of detection, NAAT as compared to culture, increases the yield of infections detected by 20-40 percent. However, the public health significance and transmissibility of NAAT-identified infections are not known.

We conducted a cross-sectional study with follow-up of participants with chlamydial infection and their sexual partners. 6,094 participants aged 18 to 35 attending an urban Emergency Department from November 2002 through February 2005 provided specimens for Ct screening using NAAT. Participants testing positive and their sexual partners were offered follow-up including re-testing for Ct using NAAT and traditional assay, e.g., culture, and treated. 90 Ct-positive participants had one or more sexual partners enrolled.

Evidence of transmission, defined by concordance within partnerships, was observed among 75% of partners of index cases testing positive by both NAAT and traditional assay but only 45% of partners of index cases testing positive by NAAT only (prevalence ratio 1.7, 95% CI 1.1, 2.5). Among index participants returning for follow-up who had not received antibiotics during the ED visit, 17% had no evidence of Ct infection (median follow-up = 3 weeks).

Our results suggest that up to 20% of positive NAAT results for Ct may be of lower transmissibility and less public health significance. Guidelines for testing, patient counseling and management should be formulated so that physicians, patients, and researchers are aware of not only NAAT's advantages, but also its limitations.