Associations between herpes simplex virus type 2 and HCV With HIV among injecting drug users in New York City: the current importance of sexual transmission of HIV

Objectives. We examined relationships between herpes simplex virus type 2 (HSV-2), a biomarker for sexual risk, and HCV, a biomarker for injecting risk, with HIV among injecting drug users (IDUs) who began injecting after large-scale expansion of syringe exchange programs in New York City.Methods. We recruited 337 heroin and cocaine users who began injecting in 1995 or later from persons entering drug detoxification. We administered a structured interview covering drug use and HIV risk behavior and collected serum samples for HIV, HCV, and HSV-2 testing.Results. HIV prevalence was 8%, HSV-2 39%, and HCV 55%. We found a significant association between HSV-2 and HIV (odds ratio [OR] = 7.9; 95% confidence interval [CI] = 2.9, 21.4) and no association between HCV and HIV (OR = 1.14; 95% CI = 0.5, 2.6). Black IDUs had the highest prevalence of HSV-2 (76%) and HIV (24%) but the lowest prevalence of HCV (34%).Conclusions. Most HIV infections among these IDUs occurred through sexual transmission. The relative importance of injecting versus sexual transmission of HIV may be critical for understanding racial/ethnic disparities in HIV infection.Persons who inject drugs, or injecting drug users (IDUs), are at risk for HIV infection through both multiperson use (sharing) of needles and syringes and unprotected sex. Sharing needles and syringes is a considerably more efficient mode of HIV transmission than is heterosexual intercourse,^1,2 so in most epidemiological situations, injecting-related transmission is much more important than is sexual transmission. This relative efficiency of transmission is reflected in the current Centers for Disease Control and Prevention transmission classification system, in which persons with both injecting drug risk and heterosexual risk behavior are placed in the injecting drug use transmission category only.³However, several factors may change the relative importance of injecting versus sexual transmission of HIV among IDUs. First, programs to prevent injecting-related transmission can be quite effective. In areas where combined HIV prevention programs (including syringe exchange, drug abuse treatment, community outreach, and voluntary HIV counseling and testing)⁴ have been implemented, injecting-related transmission has been substantially reduced and sexual transmission can be more important among IDUs. This effect appears to have occurred in Amsterdam^5,6 and Chicago.⁷Second, use of certain drugs may be associated with unsafe sexual behaviors and thus increase the importance of sexual transmission of HIV in populations of injecting and noninjecting drug users. Crack cocaine^8,9 and, more recently, methamphetamine^10,11 are probably the 2 most important examples of this phenomenon.Third, some sexually transmitted diseases, such as syphilis and herpes simplex virus type 2 (HSV-2), may increase HIV transmission among both injecting and noninjecting drug users. There is considerable biological and epidemiological evidence that HSV-2 infection facilitates both acquiring and transmitting HIV. Two meta-analyses and a recent qualitative review have concluded that prevalent HSV-2 infection is associated with a two- to threefold increased likelihood of acquiring HIV.^12–14 Although most research on HSV-2 and HIV has been conducted in Africa, several studies indicate positive associations between HSV-2 and HIV among injecting and noninjecting drug users in the United States.¹⁵ Because HSV-2 is transmitted sexually but not through sharing drug injection equipment, it can be used as a biomarker for sexual risk among IDUs.¹⁶Assessing the relative importance of injecting versus sexual transmission of HIV among IDUs may also have great importance for understanding racial/ethnic differences in HIV infection among injecting and noninjecting drug users.We examined relationships between HSV-2 and HIV among IDUs who began injecting after arge-scale implementation of syringe exchange programs from 1992 to 1998 in New York City. The expanded programs included not only a much greater volume of syringes exchanged but also increases in services such as voluntary HIV counseling and testing and referrals to drug abuse treatment. Thus, the large-scale expansion of the syringe exchange programs can be seen as the beginning of combined HIV prevention programs for IDUs^17–19 in New York City. The expansion of the syringe exchange programs was followed by a reduction in HIV incidence from approximately 4/100 person-years to 1/100 person-years among IDUs in New York City.²⁰We chose the term “persons who inject drugs,” which emphasizes that these individuals should be considered persons first and that they are much more than the behavior of injecting drug use. However, we address official classification of HIV transmission routes, so we use the current standard terms “injecting drug use” and “injecting drug users” and the abbreviation “IDU.” We want to emphasize that HIV prevention for persons who inject drugs should fully consider their human rights.