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Meth Use May Account for 1 in 5 of New HIV Infections in Seattle MSM
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IAS 2015, July 19-22, 2015, Vancouver
Mark Mascolini
Methamphetamine use could explain 20% of new HIV infections among men who have sex with men (MSM) in Seattle and surrounding King County, Washington [1]. Because MSM account for 80% of all new HIV infections in King County, meth use could explain 16% of all new HIV infections in the county.
Seattle/King County public health epidemiologists who conducted this study noted that two factors drive the impact of risk factors on HIV acquisition--the size of the population at risk and the strength of the association between the risk factor and HIV acquisition (relative risk). Because population-attributable risk percent (PAR%) takes both measures into account, these investigators used that metric to explore the impact of meth use on HIV risk in King County MSM.
The King County team used multiple national and regional sources to determine the number of new HIV infections among MSM from 2009 through 2013, and they used 2013 data to estimate PAR%. They estimated the number of MSM at risk of acquiring HIV as male King County residents at least 15 years old times 0.054 minus the number of MSM living with HIV. The investigators calculated PAR% as (estimated population HIV incidence minus estimated incidence in non-meth users) divided by estimated population HIV incidence. (Incidence is the new-diagnosis rate.)
Among MSM diagnosed with HIV from 2009 through 2013, 28% used meth. MSM proved significantly more likely to use meth than other people with HIV (28% versus 13%, P < 0.001). MSM who used meth were less likely to have a late HIV diagnosis (AIDS within 6 months of testing positive) than MSM who did not use meth (18% versus 25%, P = 0.04). And meth-using MSM had a shorter time from their last negative HIV test than did MSM who did not use meth (median 242 versus 334 days, P < 0.001). But meth-using MSM were less likely to be linked to care within 3 months of HIV diagnosis than non-meth users (93% versus 97%, P = 0.05) and less likely to reach an undetectable viral load once in treatment (71% versus 79%, P = 0.09).
Overall HIV incidence among King County MSM in 2013 was 553 infections per 100,000 MSM at risk. Among MSM who did not use meth in the last year, estimated HIV incidence measured 441 per 100,000. Estimated HIV incidence among all meth users came to 2305 per 100,000. MSM who used meth proved 5 times more likely to get diagnosed with HIV than MSM who did not use meth (relative risk 5.2, 95% confidence interval 3.7 to 7.3).
Among HIV-negative MSM in King County, reported meth use ranged from 3% in a 2014 Gay Pride survey, to 6% on an STD clinic intake form, up to 10% in a National HIV Behavioral Survey. Reported meth use in MSM newly diagnosed with HIV proved even higher, ranging from 23% to 28%.
These numbers led to a PAR% of 20% (range 15% to 26%) for the impact of meth on HIV incidence among MSM. Because MSM account for 80% of all HIV diagnoses in King County, the researchers estimated that meth use among MSM may account for 16% of all HIV infections.
The researchers concluded that "meth is an important driver of the HIV epidemic in MSM in King County." They stressed that meth use in the year before HIV diagnosis led to delayed linkage to HIV care and lack of viral suppression. They advised health departments to collect data on meth use in people with newly diagnosed HIV to monitor the impact of this risk factor.
Reference
1. Buskin S, Hood J, Katz D, et al. Estimating the population-level impact of methamphetamine use on HIV acquisition among men who have sex with men using population attributable risk percent: a powerful and underused planning tool. IAS 2015. 8th Conference on HIV Pathogenesis, Treatment and Prevention. July 19-22, 2015. Vancouver. Abstract MOPEC491.
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