Evaluating Diagnostic Tools for Sexually Transmitted Infections
The development of nucleic acid amplification tests (NAAT) for detecting gonorrhea (GC) and chlamydial (CT) infections has broadened our understanding of the epidemiology of these infections within the general population. NAAT is used with urine specimens, which can easily be obtained in large-scale public health programs or population surveys. Compared to the performance of traditional methods for the diagnosis of GC and CT, urine-based NAAT has improved sensitivity for enhanced detection of infected individuals and has eliminated the need for collection of urethral swabs or pelvic examinations.
Results of studies of the general population using these methods indicate that NAAT typically detects substantially more infected persons than traditional assays, that the majority of NAAT-detectable infections are asymptomatic, and that infected individuals do not exhibit the same high-risk behavioral profile of subjects identified in studies of clinic populations.
These results could indicate the presence of asymptomatic infections that are unlikely to be detected and treated without major public health interventions that encourage widespread screening. However, it is also possible that NAAT is identifying clinically inconsequential infections because of the assay's ability to detect low levels of viable organisms or amplifiable DNA from past infections that have not yet cleared. The lack of current symptoms and the insignificant correlation between detectable infection and current risk behaviors support this latter interpretation.
RTI is exploring this issue by testing a sample of 8,000 adults ages 18-35 attending a large urban emergency department. We will evaluate (and treat) subjects who test NAAT-positive for GC and CT using traditional diagnostic methods for these infections, and we will test and treat recent sexual partners of infected subjects. This research will allow us to
- Evaluate whether the probabilities of GC and CT transmission, as estimated by concordance of infection between partners, are equivalent for infections that are detectable only by NAAT versus infections that are detectable by traditional testing procedures
- Determine whether asymptomatic infections have an equivalent probability of transmission as symptomatic infections
- Examine correlates (individual sexual and health-seeking behaviors, symptomology, partner characteristics, clinical characteristics, and organism genotype) of infections detected by NAAT versus infections detected by traditional diagnostic tests.
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