Comparisons of Three Methods to Estimate Incidence Rates of HIV Infection among Persons Seeking Voluntary, Anonymous Counseling and Testing Services

Introduction: The annual case number of persons who are newly diagnosed with human immunodeficiency virus (HIV) infection continues to increase in Taiwan after successful control of HIV outbreak among injecting drug users. Whether the increasing case number is related to increased awareness and HIV testing activities or increasing incidence in high-risk populations, such as men who have sex with men (MSM), remains to be investigated.

Objectives: In this study, we aimed to compare three methods to estimate the incidence rates of HIV infection among persons seeking voluntary, anonymous counseling and testing services (VCT) at a university hospital and the difference incidence rates among risk populations.

Methods: Between 1 April 2006 and 30 September, 2010, 10198 persons sought VCT services for HIV testing at the National Taiwan University Hospital, which was sponsored by the Taiwan Centers for Disease Control (CDC).Anti-HIV antibody was tested using particle agglutination (SFD HIV 1/2 PA, Bio-Rad FUJIREBIO, Japan) and HIV infection was confirmed using Western blot. Demographics and behavioral data were obtained at the time of counseling. Three methods were used to estimate HIV incidence: first, based on self-reported dates of prior tests (SR); second, based on linking prior records with an unique testing code (UTC); and third, based on the BED IgG-Capture Enzyme Immunoassay (BED assay) for recent HIV infection (within 153 days). Trends in HIV incidence were analyzed by Poisson regression and weighted linear regression. The incidence rate ratios or odds ratios between risk populations were analyzed by Poisson regression and conditional logistic regression in the case-control study.

Results: During the study period, 360 individuals (3.5%) were test positive for HIV infection (3.5%). Comparable overall seroconversion rate was found by the three methods, 5.24, 5.76, and 3.83 per 100 person-years [PY], respectively. The incidence rate of recent HIV infections in MSM was significantly higher than that in heterosexuals in the case-control study (odds ratio, 9.31; 95% CI, 4.77-18.20). Five behaviors/characteristics: “ever use illicit drug”, “ the baseline RPR≧4”, “condom use in anal sex <100%” , “confirmed sexual partner to be HIV-positive”, or “having anal sex” were risk factors for both recent HIV infection and new HIV cases among either all clients or MSM (SR and BED, all p values <0.05). There was a trend of increase in new HIV cases incidence in MSM from 2006 to 2010 by the SR method (p=0.0025, Poisson regression), but the trend in the incidence rate of recent HIV infection in MSM was not significant during the study period by the BED assay (p=0.6388, weighted linear regression).

Conclusions: From 2006 to 2010, the incidence rates of HIV infections among clients of this VCT program did not decrease. MSM had a significantly higher incidence rate of recent HIV infections than heterosexuals, especially those with illicit drug use or other high risk behaviors.