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BACKGROUND: Women represent 12% of the annual HIV diagnoses in Los Angeles County (LAC). Nearly all women in LAC report heterosexual sex (HET) or injecting drug use (IDU) as their primary risk factor for HIV infection. To better understand the current distribution of HIV infections in LAC women, we used HIV Incidence Surveillance data to examine HIV incidence estimates by mode of transmission.
METHODS: We used data from the HIV Incidence Surveillance system in LAC to estimate the number of new HIV infections among HET and IDU women aged 15-60 during 2008-2010. HIV Incidence Surveillance relies on the Serologic Testing Algorithm for Recent HIV Seroconversion (STARHS) methodology, which uses the BED HIV-1 capture enzyme immunoassay, to identify recent HIV infections by testing remnant diagnostic serum. This population-based incidence method uses HIV testing data from newly diagnosed HIV cases and imputes testing history and STARHS results for persons who are unaware of infection.
RESULTS: We estimate that 774 women, ages 15 to 60 years, were infected with HIV during 2008-2010. While only 0.2% of women in LAC are estimated to be IDU, 26% (n=197) of all the female incident HIV cases were IDU during this three-year period. In comparison, HET women make up over 99% of the women at risk of HIV in LAC and were estimated to account for 566 (74%) of the new infections among women. We observed a higher proportion of new female HIV infections attributable to IDU transmission using HIV Incidence Surveillance compared with HIV case surveillance where 20% of new diagnoses were female IDU.
CONCLUSIONS: Among women in LAC, the difference between HIV case diagnoses and HIV incidence estimates for IDU and HET show the importance of continued HIV incidence surveillance data for examining trends in new infections. Due to the relatively small population size of female IDU in LAC, numbers of new infections are relatively low, which potentially leads women to perceive their risk of becoming HIV infected is low. However, the HIV incidence estimate provides evidence that women who inject drugs are disproportionately impacted by new HIV infections among women.