Of the 18,430 participants in the final NHBS-HET pilot data set who completed an interview, 14,750 (80%) met our analysis criteria. Participants were excluded from the analysis if they ever reported injection drug use (N=2,241), had male-male sex (N=414), both injected drugs and had male-male sex (N=311), or if they refused to provide this information (N=5). Participants were also excluded if they did not consent to an HIV test (N=377), did not have a negative or confirmed positive HIV test result (N=212) or reported being HIV-positive but, when tested, were HIV-negative (N=5). Additionally, we excluded persons whose survey responses were invalid (N=120). Of the participants in the sample, 207 (1.4%) had newly diagnosed HIV infection. Characteristics of participants and those with newly diagnosed HIV infection are presented in Table . Of the 14,750 NHBS-Pilot Study participants who met the analysis criteria, 57% were female, nearly half were less than 30 years old, and most (73%) were black (Table ). Socioeconomic status was low. Few participants had a past-year risk behavior (traditionally) associated with HIV infection such as crack use (11%), exchange sex for money or drugs (12%) or STD diagnosis (14%).
Sample Characteristics, Pilot Study of National HIV Behavioral Surveillance System among Heterosexuals at Increased Risk, 2006-2007
Table shows the performance of the predictor variables, including the number and proportion of participants, HIV prevalence, sensitivity and specificity. For each of the five individual risk behavior variables, HIV prevalence was between 2.1% and 3.1%. However, because relatively small proportions of participants engaged in these behaviors (8-21%), and sensitivity was low for each (range: 13-32%), we removed these individual variables from consideration. Evaluation of combined predictor variables, in which persons reporting any or more than one of these five factors would meet the criteria, resulted in improved sensitivity and specificity but did not meet our threshold for further consideration.
Sensitivity and Specificity Performance of Potential Eligibility Criteria by HIV Prevalence, Pilot Study of National HIV
Behavioral Surveillance System Among Heterosexuals at Increased Risk, 2006-2007
Four predictor variables assessed sexual network risk. For each of these variables or combinations of variables, the HIV prevalence exceeded the overall sample prevalence of 1.4%. Two of these variables met sensitivity and specificity criteria for further evaluation: 1) reporting not knowing the HIV status of one’s most recent partner or that one’s most recent partner was an IDU, had been incarcerated, used crack or, for women, was MSM; and 2) sexual concurrency.
We also present data on several social/structural factors including living in an HRA: low income (participant’s household income did not exceed Department of Health and Human Services [HHS] poverty guidelines); and limited education (high school graduate or less). Each of these performed well with respect to HIV prevalence, sensitivity, and specificity. A combined variable including anyone with low income or limited education (which we termed low socioeconomic status [SES]) performed even better, with a sensitivity of 96% and specificity of 12%.
Practicality was assessed for variables meeting criteria for sensitivity >70% and specificity <40%. Use of sexual network measures as eligibility criteria would limit our ability to monitor partner HIV status and other characteristics over time. The use of these variables is also limited by the concern that a large proportion of people did not know the risk behaviors or HIV status of their partners. Use of questions based on characteristics of the most recent partner also might underestimate risk for persons with more than one partner. As a result of these limitations, sexual network risks were eliminated from consideration as potential ways to identify the target population eligibility criteria.
All social/structural factors presented met the threshold for further evaluation. Of these, living in an HRA and low SES performed best and were evaluated for practicality. Use of residency in an HRA was less optimal for several reasons. For instance, some participants had difficulty identifying their census tract of residence on a map; because NHBS is an anonymous survey, staff do not collect address or other detailed information that would make identifying census tract of residency easier. Furthermore, when performance of HRA residency as a predictor variable was assessed by region, it was determined that it performed poorly in the Midwest and the West because a smaller proportion of participants lived in HRAs (data not shown), which would have been problematic for a national surveillance system. The HRA criterion also performed worse in project sites that used RDS than those that used VBS; participants with newly diagnosed HIV infection recruited through the RDS method were less likely to live in an HRA than those recruited through the VBS method.
In contrast, the use of low SES as a method for defining the target population posed fewer concerns with respect to practicality. Measurement of self-reported income and education is less complicated than residency in an HRA. Moreover, it had excellent sensitivity in cities within all U.S. regions and territories and among all heterosexual sub-populations (data not shown).
The results of these analyses were presented at an NHBS principal investigators’ meeting in October 2009 and representatives from each NHBS project site were asked to weigh the evidence and make a recommendation about 1) the final definition of the target population and its operationalization through specific eligibility criteria, and 2) the sampling method that should be used. RDS was the recommended sampling method for NHBS-HET, endorsed by project areas that had used VBS as well as those that used RDS.
The final NHBS-HET definition incorporated the low SES criteria described above. Participants for NHBS-HET would be eligible if they met the general NHBS eligibility criteria (live in the MSA, not previously participated in current cycle, able to complete the interview in English or Spanish), are male or female, have had vaginal or anal sex with an opposite-sex partner in the previous 12 months, and are aged 18-60 years. The upper age limit was increased to 60 years based on the high prevalence of new diagnosis among those aged 40-50 years in the pilot study. The SES criteria were incorporated into the RDS method by offering only NHBS-HET participants who are low SES as measured by income and education (described above) and have not injected drugs in the previous 12 months an opportunity to recruit others into the study. By using low SES as recruitment criteria, but not as eligibility criteria, we sought to limit the potential inconvenience to participants traveling to a field site only to be found ineligible for the study, and the potential negative impact the study might suffer as a result. However, since only persons meeting the recruitment criteria may recruit others, the resulting sample would be comprised primarily of the low SES target population. The HRA concept is applied only for initial participants, who must be residents of an HRA; in addition, field sites must be located within HRAs. These HRA criteria make sure that the study starts in, and recruitment is maintained within, lower SES communities. This combination of eligibility and recruitment criteria, in conjunction with the RDS method, were selected to ensure that future cycles of NHBS-HET attain a sample of heterosexuals at increased risk for HIV infection.