This is the first study to investigate HIV prevalence in a large, diverse community sample of gay men in New Zealand. Overall this was 6.5%, and higher among older men and those living outside New Zealand. Prevalence was markedly elevated among those with more sexual partners in the previous 6 months, those who had had unprotected anal sex with a casual partner, who had met a sexual partner online or who had injected drugs in that period. About one fifth (20.9%) of infected men were unaware of their infection. A lower proportion of ethnically European men were undiagnosed compared to other respondents. The vast majority of undiagnosed men thought they were HIV negative. Diagnosed HIV positive men were more likely to report more than 20 sexual partners, unprotected anal sex with casual partners, sex with a man they met online, and injecting drugs in the previous 6 months compared to HIV negative respondents. Uninfected men were more likely to exhibit attitudes conducive to HIV control.
We have demonstrated the acceptability of adding an anonymous oral fluid collection component into HIV behavioural surveillance undertaken at a large gay community event as well as gay bars and sex-on-site venues. The overall high specimen provision rate (80.4%) with little variation across enrolment sites, age and ethnicity suggest that the HIV prevalence estimates will be representative of those men taking part in the behavioural survey. As the survey is repeated in a consistent manner over time this will enable a comparable measure of HIV prevalence to be obtained in the future.
There are several limitations to the study. It is not possible to be certain of the actual response rate to the questionnaire as those who initially refused might have completed it subsequently, but it is probably in the order of half invited. The recruitment occurred in a number of community settings in Auckland so the findings may not be generalised to all gay men in New Zealand, to MSM in Auckland who do not attend these settings, or who only seek sexual partners through the Internet. Specimen provision was higher among men who had recently engaged in unprotected anal intercourse which may have resulted in slightly overestimating HIV prevalence among all study participants. While behavioural data rely on self-report that cannot be verified, the anonymity of the questionnaire and study protocols present little incentive to misreport. A small number of responses and biological data were inconsistent, with four respondents whose specimens were HIV negative on Western blot indicating they had tested HIV positive in their questionnaire. Two of the latter were deemed positive on the basis of them having relatively high optical densities on the original GACELISA test and reporting being on ART.
A prevalence of 6.5% in this Auckland study of MSM is consistent with past New Zealand clinic studies. In the most recent 2005/6 unlinked anonymous study of HIV among sexual health clinic attenders, the prevalence among MSM in Auckland was 6.1% [11
]. Those who attend sexual health clinics would be expected to have a higher prevalence than those in a community sample as they have self identified as having STI risk. However, HIV prevalence in the latter is likely to have increased in recent years, with more infections having occurred coupled with prolonged survival.
Table summarises the results from a number of prevalence studies among MSM in community settings internationally, with a wide range of findings. When placed alongside these, our data on HIV prevalence show that HIV remains relatively well controlled among Auckland MSM, despite having a mature epidemic that has existed since the early 1980s. This is consistent with the rate of new HIV diagnoses among MSM being lower in New Zealand than that in Australia, the United Kingdom and the USA [1
]. As the rate of HIV diagnosis is higher in Auckland than elsewhere in New Zealand this conclusion will be valid for the whole country.
HIV antibody prevalence and undiagnosed infection in community samples of MSM in selected countries
The proportion of HIV infected MSM who were undiagnosed (20.9%) in Auckland is considerably lower than found previously in Melbourne [12
], five UK cities [13
] and 21 US cities [17
] (Table ). This is somewhat surprising as behavioural surveillance shows that HIV testing rates among gay men in Auckland [10
] are not higher than in those cities [14
]. This may indicate that testing in Auckland is targeting MSM at highest risk, which since 2006 has included rapid HIV testing services [21
], or the incidence is lower in Auckland.
Unlike the experience in other countries [22
], we found no statistically significant differences in overall HIV prevalence by ethnicity in our sample. In particular, HIV prevalence was the same in European (6.7%) and in Māori (6.4%) MSM. This is consistent with previously reported epidemiological data suggesting no overrepresentation of HIV in this group, but it is different to the experience of indigenous individuals within MSM communities elsewhere [25
]. We did on the other hand find that HIV positive MSM of non-European ethnicity were less likely to have had been diagnosed. This finding is consistent with a recent analysis that non-European MSM are more likely to present late in the course of infection in New Zealand [26
] and warrants further investigation.
In spite of this favourable position internationally, the number of new diagnoses among MSM in New Zealand continues at a higher level than in the late 1990s [1
]. Findings from this study add to our understanding of HIV transmission and acquisition risks, and have implications for ongoing prevention. We believe four issues should be highlighted.
First, we have shown high prevalence of HIV among MSM who had recently engaged in certain behaviours, including having over 20 recent sexual partners, having unprotected anal intercourse with casual partners, meeting sexual partners online, and injecting drugs. Men with these behaviours can act as ongoing reservoirs of infection especially if condoms are not used for anal sex, creating clusters of transmission if sexual contact is assortative (sexual mixing occurs with similar men), or dispersing HIV through sexual networks if contact patterns are dissortative. As most individuals will have imperfect information about the past behaviour of a prospective sexual partner, choosing to have unprotected anal intercourse may entail more risk than anticipated if this decision is based on an assumption that HIV prevalence is relatively low among all MSM.
Secondly, the majority of the men with undiagnosed HIV infection believed themselves to be HIV negative. Many had had a quite recent HIV test, and may consequently have held strong but incorrect convictions about their absence of HIV infection. These findings challenge safe sex strategies based on disclosure of HIV status alone. This is emphasised by our result that most of the diagnosed positive men would not expect a man who knew he had HIV to disclose this before sex; possibly a reflection of their own experience. Conversely the vast majority of all participants reported that condoms were "OK as part of sex", although the proportion disagreeing with this was higher (9.4%) among the known positive respondents. As condoms are a verifiable intervention by all participants during sex, they should continue to be strongly promoted.
Thirdly, the proportion undiagnosed varied among those with HIV. This was higher among men of non-European ethnicity, and also - although chance could not be excluded as the explanation for this finding - among those aged under 30 years. The reason for this needs to be explored further. Promotion of HIV testing should continue, and the responsiveness of testing services to diverse groups of MSM encouraged. All MSM with HIV infection should be able to access treatment as early as appropriate, which will not only be to their own benefit but also potentially reduce ongoing spread. More HIV testing, in terms of both coverage and frequency, should not however be considered the panacea for HIV control. The benefits of earlier diagnosis on ongoing transmission can only be expected if behaviour changes, and/or treatment that reduces infectivity is begun. HIV is particularly infectious in the weeks after infection, and modelling has shown that individuals in this primary stage of infection transmit disproportionately to their number in the community, but even very frequent routine testing would pick up few individuals at this stage. A negative HIV test should be seen as an opportunity to discuss HIV risk-taking, and how this could be reduced. To diagnose HIV infection after a number of negative tests should be seen as a failure to make full use of these opportunities.
Fourthly, recent behaviour that increases the probability of HIV transmission was more common among MSM with diagnosed HIV than among respondents who were uninfected. Risk of transmission exists, especially if individuals are not on ART [6
], as was the case with 35.4% of diagnosed men in this study, or if HIV positive men have another STI [27
], as was reported by 10% of our respondents in the previous year. We do not know if the behaviour of these individuals has changed since their HIV diagnosis, as would be suggested from previous overseas studies [28
], but it does raise concern about ongoing spread by some diagnosed men in New Zealand. As ART was not reported universally among those with known HIV it is unlikely these men had all engaged in unprotected anal intercourse believing themselves to be uninfectious. Further research is needed to better understand these experiences. Overall, these findings suggest that the risk of onward transmission of HIV should continue to be emphasised by those providing care to MSM with HIV, and by their support communities.