Why such high HIV prevalence reported for non-injecting drug users who are predominantly heterosexual?  This reaches 37% in Porto Alegre, Brazil; 43% in China; 13% in Canada; 20% in Florida; 19% in New York City; 24% in Portugal; 29% in Russia?  Possible factors include impaired decision making under the influence of drugs or the exchange of sex for drugs.  Studies published in STI Journal also propose high prevalence of, amonst other STI infections,  HSV-2 as a particular risk for HIV amongst non-injecting drug users (STIs/Plitt & Taha), and comparable groups, e.g. Tanzanian female bar-workers (STIs/Riedner & Hayes).  HSV increases susceptibility to HIV through disruption of the epithelial surface, as well as increasing transmissibility from persons co-infected with HSV and HIV through raising levels of plasma HIV-1 RNA.

A recent study of non-injecting drug users (NIDU)  (Jarlais & Cooper) attending a New York drug detoxification centre and a methadone maintenance programme – 785 over the period 1995-1999 and 1,764 over the period 2005-2011 – claims that HSV-2 co-infection is the principal driver of HIV transmission, especially amongst female NIDUs.  Over both periods that latter group shows: very high levels of HSV-2 mono-infection (78% and 86% respectively), high levels of HIV/HSV-2 co-infection (10% and 21%, and negligible HIV mono-infection.  The pattern is similar though less pronounced in the case of males.  As between the two periods (1995-1999 & 2005-2011) there is a doubling in the prevalence of HIV (from 7% to 13% overall) which is represented more or less uniformly across all ethic and behavioural groups.  Though the specific quantitative contribution of HSV-2 to the HIV infection cannot be determined by this type of study, these results suggest that the rise in HIV among NIDUs should be considered an epidemic of HSV-2/HIV co-infection, and that HSV-2 is likely to be the driver of the increased HIV incidence.

So what should be done to minimize HIV transmission among non-injecting drug users?  The obvious response would be suppressive HSV-2 therapy.  Unfortunately, however, trials have not as yet shown this to be effective in reducing HIV transmission (STIs/Mujugira & Wald; Barnabas & Celum).  The authors recommend further research into the effectiveness of higher dosages of HSV-2 suppressive therapy: also of HSV-2 suppressive therapy prior to ART or in combination with ART – since a recent study found evidence of HIV in the semen of men who had reached viral suppression on ART (Politch & Anderson).  At all events, HIV/HSV-2 co-infected NIDUs would appear to be a priority for ART as prevention, and the authors recommend providing ART to this group at all CD4 cell counts.  (New York introduced in 2011 a new policy of offering ART to all HIV sero-positive persons in the city regardless of CD4 count).