Factors associated with declining to report the number of sexual partners using computer-assisted self-interviewing: a cross-sectional study among individuals attending a sexual health centre in Melbourne, Australia.

Background The number of sexual partners is one of the most important risk factors for sexually transmissible infections (STIs), including HIV. The aim of the present study was to examine the association between declining to report the number of partners using computer-assisted self-interviewing (CASI) and HIV or STI positivity at a public sexual health centre in Melbourne, Australia, in 2016.
METHODS: Individuals were categorised into three risk populations: women, men who have sex with women only (MSW) and men who have sex with men (MSM). Logistic regression analysis was used to examine the association between declining to report the number of sexual partners in the past 12 months and HIV or STI positivity for women and MSW, with generalised estimating equations (GEE) used for estimation in MSM to address repeated-measures within individuals.
RESULTS: In all, 18085 individuals (5579 women, 6013 MSW, 6493 MSM) were included in the final analysis. There was no association between chlamydia positivity and declining to respond among women and MSW. MSM who declined to respond were more likely to be chlamydia positive (adjusted odds ratio1.21; 95% confidence interval (CI) 1.01-1.43). Known HIV-positive MSM and MSM newly diagnosed with HIV had 3.31-fold (95% CI 2.48-4.42) and 2.82-fold (95% CI 1.84-4.32) greater odds respectively of declining to respond compared with HIV-negative MSM. Gonorrhoea and syphilis positivity in MSM were not associated with declining to respond.
CONCLUSIONS: There was no association between declining to report the number of partners and chlamydia positivity among women and MSW. However, MSM who declined to report the number of partners were slightly more likely to have chlamydia and substantially more likely to be HIV positive.