Voluntary confidential HIV testing of STD patients in Switzerland, 1990-5: HIV test refusers cause different biases on HIV prevalences in heterosexuals and homo/bisexuals. Swiss Network of Dermatovenereology Policlinics.

OBJECTIVES: To monitor the prevalence of HIV infection among heterosexual and male homo/bisexual STD patients and assess the effect of HIV test refusers on the HIV prevalences.
METHODS: A voluntary confidential HIV test was offered to all people diagnosed with an STD at the Swiss Network of Dermatovenerology Policlinics (SNDP) between July 1990 and June 1995. Anonymous sociodemographic and behavioural information was collected for each patient regardless of whether s/he accepted or refused the HIV test.
RESULTS: The prevalence of HIV was 1.6% among heterosexuals and 22.4% homo/bisexual men and remained stable between July 1990 and June 1995. Refusal rates were 17.5% among heterosexuals and 16.0% among homo/bisexual men and did not change significantly over time. To assess the potential effect of HIV test refusers on the monitored HIV prevalences, we analysed test refusers by multivariate logistic regression. Among heterosexuals, refusal rates were significantly higher among patients with relatively low risk behaviours (patients reporting 0-1 sexual partners in the previous 6 months) while among homo/bisexual men they were significantly higher in those with high risk behaviours (patients reporting 10 or more sexual partners in the previous 6 months).
CONCLUSIONS: We found high and stable HIV prevalences among patients treated for an STD at the SNDP. It appears that HIV test refusers biased HIV prevalences among heterosexuals and homo/bisexual men in different directions: in heterosexuals HIV prevalences were overestimated and in homo/bisexuals they were underestimated. A regular analysis of the characteristics of HIV test refusers should be an integral part of surveillance systems which use voluntary confidential HIV testing.