HIV epidemiology and behavioural surveillance among men who have sex with men in New Zealand

Abstract

AIMS: HIV diagnoses among men who have sex with men (MSM) in New Zealand increased from the year 2001. The aim of the thesis was to improve understandings of the causes of the increase, in order to inform HIV prevention and identify further research needs.

METHODS: Epidemiological data on HIV and AIDS diagnoses among MSM in New Zealand were examined using information from the AIDS Epidemiology Group. A programme of regular behavioural surveillance among MSM was also designed and conducted.

RESULTS: Between 1996-2005, HIV diagnoses among MSM by antibody testing where HIV infection was acquired in New Zealand revealed two distinct phases: A very low period between 1997 to 2000 in which around 21 diagnoses were recorded annually; and a resurgent period from 2001 to 2005 where annual HIV diagnoses experienced a sustained rise to 66 at the end of 2005.

New adjusted estimates indicated that known prevalent HIV cases among MSM in New Zealand increased from 437 to 588 between 1995 and 2000 (35%), and from 588 to 965 (64%) between 2000 and 2005. This reflected diverging trends from the mid-1990s: Ongoing new HIV infections among MSM which accelerated from the year 2000; and decreased deaths from AIDS due to improved antiretroviral treatments. Unless the growing number of MSM with HIV is counterbalanced by a decrease in the rate of secondary transmission from positive individuals, it will increase the number of new HIV infections. Contrary to this, when expressed as diagnosed incidence-to-prevalence pool ratios (IPRs), the average annual rate of secondary transmission was found to be increasing over time.

The behavioural surveillance programme in Auckland surveyed 812 MSM in 2002, 1220 in 2004, and 1228 in 2006. An online module in 2006 additionally surveyed 2141 MSM, 647 of whom lived in Auckland.

There were no overall changes in HIV testing over the three offline surveys, suggesting that the increase in HIV diagnoses was not an artefact of testing patterns. There were also no widespread changes in the rate of unprotected anal sex with casual sex partners, or partners described as a "fuckbuddy" or a "boyfriend", among the overall offline samples.

However, the proportion of MSM recruited offline who had recently engaged in sex with a man met through the Internet increased significantly from 2002 to 2004 (from 26.6% to 44.8%). When MSM surveyed online in 2006 were examined, they exhibited riskier behaviours compared to offline-recruited respondents. For example, rates of non-condom use and sexual partner concurrency were especially high, and testing rates were lower.

CONCLUSION: It is likely that moderate changes involving increases in unprotected sex for some MSM, and alterations to sexual networks and sexual connectivity, have combined to push the reproductive rate of HIV beyond the new epidemic threshold set by the increase in longevity from the mid-1990s. These changes need not have been great if the reproductive rate of HIV was already situated close to the epidemic tipping point. In this case, a resurgent outbreak of HIV may even have been triggered by apparently small and subtle shifts in factors influencing HIV spread.