In this study of HIV infected patients in care, we used individual level data to inform an attributable risk model to describe the effect TV infection may have on HIV transmissibility. Our model estimates that this range is from 0% to 28% and the base model estimate is that 22% of projected HIV transmissions from women are attributable to TV infections and up to 2% of all HIV transmission in the USA may be related to TV infection. The estimates of transmission risk in a previous study are approximately 2 to 4-fold higher of that reported here 21
. Two differences in the studies may explain this. First, the number of MSM recruited was very different (50% vs. 33% in our study). Second, the inclusion of HIV RNA values varied. In the prior study, the transmission risk was estimated as the standard risk if a person was receiving antiretroviral therapy, otherwise the transmission risk per act was not adjusted for the viral load. In our study we adjusted the standard per act transmission risk based on the actual difference between the subject’s HIV RNA value and the usual untreated population HIV RNA of 38,000 copies/ml. The model showed that estimates of new HIV infections were very sensitive to estimates of transmission probabilities associated with viral load. These results support the recently proposed use of antiretroviral therapy as a component of an HIV epidemic control strategy 33, 34
The prevalence of TV infection was far greater than either gonorrheal or chlamydial infections. This is quite consistent with other studies of TV prevalence in HIV infected women15
where TV infection is reported in 22% HIV + women when culture or PCR are used as the detection methods. This difference is likely to be due to the relative sensitivity of screening for NG and CT compared with traditional methods of screening for TV. Screening for TV has been a manual assay previously and therefore not as readily used for screening due to the labor involved and the low sensitivity of microscopy. The prevalence is only 11% if of wet mounts are used as the detection method. It is also possible that co-infection with HIV allows a more persistent infection with TV but not NG or CT, explaining the increased prevalence. NAAT screening for TV was easily implemented and allowed an unrecognized infection present in more than 10% of the study population to be identified and treated.
TV infection was associated with high HIV viral loads. HIV RNA was higher in TV-infected participants when examined by either the proportion of participants with less than 400 copies/ml or by mean HIV copies/ml. The association between high viral loads and TV infection suggests that TV occurs more often in women who are receiving less than adequate care whether they are new to care or only marginally engaged in care. Improved entry and retention in care will prevent complications of both TV and HIV infection and avoid the human and economic costs associated with small, but significant numbers of HIV infections. Other previously described variables associated with TV infection were vaginal intercourse low socioeconomic status (low educational attainment, unemployment, lack of private insurance), and non-white race. Poverty has been consistently associated with TV infection with a 3-fold increase in TV when income was <1.85 of the federal poverty level6
. An association of TV with educational status has been previously reported, but the 5-fold increased risk with low education reported in the present study is much greater6
. The association between low educational attainment and TV suggests that inadequate health literacy may be an important element in the pathway to TV-infection21, 22
. In data presented here, a 3-fold difference in TV prevalence was seen between whites and non-whites. However, in multivariable analysis, race remained associated with TV infection but not statistically, perhaps due to sample size or a lack of the racial association within a cohort of HIV- infected people.
The limitations of this study include the self-reported nature of some of the data on which risk estimates are based, however ACASI technology was used to minimize this. The study was conducted at one site, which may limit the applicability to other populations. However, the study site draws patients from a wide geographic area within NC. Demographics of the STI sub-study are similar to the demographics of the population of newly HIV diagnosed persons in North Carolina; therefore, the study findings may be applicable to HIV-infected individuals receiving medical care in North Carolina. Our TV effect estimate of 1.8 is based on HIV acquisition and limited HIV transmission studies. Although these estimates are based on limited data and our analyses would be strengthened by more robust data, there are no other direct data. Moreover, our sensitivity analyses took into account changes in these assumptions. Third, a conversion method was needed to the estimations we used to convert three month data to six-month data did not include adjustment for changes in sex behavior over time or an adjustment the possibility of more than one main partner. However in the subset of patients who were enrolled in both studies, the calculation was able to predict the number of partners subjects reported in 6 months by using data from the 3-month data collection. Fourth, models are based on estimates and not observations. A full discussion of the strengths and weaknesses of HIV transmission risk models are beyond the scope of this paper but have been recently discussed 35
. Finally, the findings, we report here are only based on NAAT testing of urine specimens, other detection methods and use of vaginal specimens instead are likely to influence the findings.
An incidence of TV infection of 2% –3% for HIV-infected women, as reported here, suggests that more than 5000 new TV infections are occurring in the 290,000 HIV infected US women annually and potentially contributing to HIV transmission events. Medical care settings provide the opportunity to address both behavioral and biologic aspects of HIV transmission. Biological factors, such as TV, that enhance HIV transmission may be addressed with STI and HIV medical treatments. TV diagnostic assays are appropriate when clinical history and exam support use of GC and CT testing. However, due to the often-asymptomatic nature of TV, the limited use of nucleic acid amplification assays, the insensitivity of cytology, and requirement for a pelvic examination for collection, TV is frequently overlooked. Examination of the synergistic effects of medical care, education and counseling, combined with STI treatment and antiretroviral use, should provide more insights into effective HIV epidemic control.