To the Editor:
Reports of increases in unprotected anal intercourse and in sexually transmitted infections among men who have sex with men (MSM) in North America and Europe are widespread.1-5 In contrast, there have been relatively few reports of increases in HIV-1 incidence.6,7 Sentinel indicators of increasing unprotected sex among MSM may no longer reliably herald increases in HIV-1 incidence4 in part because a very large proportion of unprotected anal intercourse involves partners who are concordant for HIV-1 infection.8-10 Continued, direct surveillance of HIV-1 incidence among MSM is therefore critically important.
We previously reported an increase in HIV-1 incidence density in calendar year 2000 in an open cohort of young community-recruited MSM in Vancouver.11 In this report, we extend that analysis by examining trends in HIV-1 incidence density through 2003 in a stable subset of this cohort. As well, we present complementary trends in the number of new HIV-1 diagnoses among MSM undergoing HIV-1 serologic testing in the province of British Columbia.
The Vanguard Project is a prospective study of MSM who at enrollment are 18-35 years of age and living in the greater Vancouver region.11 Since May 1995, men who tested HIV-1 seronegative at their baseline visit have been followed prospectively for seroconversion. We restricted the present trends analysis to that stable cohort of men who had at least 1 HIV-1 serologic test in each of the 3 calendar periods 1998-1999, 2000-2001, and 2002-2993, excluding men who reported injection drug use during follow-up (n = 35). This fixed cohort analysis precluded an influence of changes in cohort composition on observed HIV seroincidence over the 7-year study period.
HIV-1 incidence density was calculated for each calendar year as the number of new infections divided by the total number of person-years of observation. Person-time accrued either to the midpoint between the last and next-to-last study visit or date of seroconversion, which we assumed to be the midpoint between the last seronegative and first seropositive visit. Ninety-five percent CIs assumed a Poisson distribution.
As of December 31, 2003, 247 MSM completed at least 1 follow-up study visit in each of the 3 calendar periods. Table 1 summarizes the seroconversion experience of this stable cohort. Overall HIV-1 incidence density between 1997 and 2003 was 0.87% (95% CI: 0.38% to 1.37% per person-year). Annual incidence density remained <1.00 per person-year between 1997 and 2001, then increased 2- to 3-fold in 2002 and 2003. Although based on a small number of events, the HIV-1 incidence density for 2002-2003 combined (1.78, 95% CI: 0 to 3.33 per person-year) was almost 3 times that observed during the period 1997-2001 (0.64, 95% CI: 0 to 1.12) (P = 0.14). Inclusion of data from 211 men excluded from the present analysis did not alter our finding of increased seroincidence in 2002 and 2003.
To examine trends in the proportion of MSM testing positive, we estimated the total number of tests performed annually among non-injecting drug user (IDU) MSM. Between 1997 and 2001, the annual percentage of tests with non-IDU MSM risk remained stable (ranging between 15.1% and 16.8% of tests for which transmission risk was reported). For each of these calendar years, we assumed that this percentage also applied to tests performed in men for whom no transmission risk factor was reported. Then, because transmission risk data were no longer collected for seronegative tests thereafter, we applied the average from the previous 5 years (16.4%) to estimate the percentage of male tests with non-IDU MSM risk in 2002 and 2003. We used χ2 statistics to compare groups and to test the significance of trends.
A sustained increase since calendar year 2000 in the number of new HIV-1 diagnoses among all non-IDU MSM seeking HIV-1 counseling and testing in British Columbia was observed (Table 1). Following a significant decline between 1997 and 1999 in the percentage of HIV-1 serologic tests that were reactive in non-IDU MSM (trend χ2 7.754, P = 0.005), this percentage increased significantly in calendar year 2000, compared with the previous year (χ2 5.811, P = 0.016). Since 2000, this percentage has not declined (trend χ2 0.052, P = 0.819).
In summary, both available sources of HIV-1 surveillance data suggest a sustained increase in HIV-1 incidence among MSM in British Columbia since 2000. Several factors may be contributing to this increase, including a significant rise in the proportion of MSM engaging in unprotected anal intercourse with casual partners who are potentially serodiscordant for HIV-1 infection,12 an increase in sexually transmitted coinfections that facilitate HIV transmission, and clinically indicated interruptions and delays in the administration of antiretroviral therapy. The latter appears to have produced a net increase in the number of highly viremic MSM in British Columbia and, thus, an increase in the potential for sexual transmission of HIV-1 in this population.13,14
We conclude that there is an immediate need to develop and deliver effective, targeted interventions to address this new risk among MSM in British Columbia. Further, our mathematical transmission models do not predict any decrease in HIV-1 seroincidence among MSM through the remainder of the decade, suggesting a need to sustain such efforts.14 As well, additional research into the determinants of recent increases in risky behavior among MSM is warranted.
Thomas M. Lampinen, PhD*†
Gina Ogilvie, MD, MSc‡§
Keith Chan, MS*
Mary Lou Miller, RN*
Darrel Cook, MSc‡
Martin T. Schechter, MD, PhD†
Robert S. Hogg, PhD*†
*British Columbia Centre for Excellence in HIV/AIDS †Department of Health Care and Epidemiology University of British Columbia ‡British Columbia Centre for Disease Control §Department of Family Practice University of British Columbia Vancouver, British Columbia, Canada
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