A substantial number of HIV infections are likely attributable to pre-existing infection with the herpes simplex virus type 2 (HSV-2), according to a study published in The Lancet Infectious Diseases.

Researchers intended to estimate the percentage of incident HIV infections attributable to HSV-2 infection, using the classic epidemiologic formula known as the population attributable fraction (PAF). The relative risk for HIV acquisition in people with and without established HSV-2 infection, as well as the relative risk for HIV acquisition in people with and without recently acquired HSV-2 infection, were used for the PAF calculation. The study researchers reviewed global populations and data based on World Health Organization (WHO) regional areas (Americas, African, Eastern Mediterranean, European, South-East Asian, and Western Pacific). Population data was obtained from official studies and the Joint United Nations Programme on HIV/AIDS estimates.

In 2016, of the 1.4 million incident HIV infections obtained through sexual transmission in people between the ages of 15 and 49 years, HSV-2 infection contributed to approximately 420,000 of those cases. Globally, the PAF of incident HIV infection attributable to HSV-2 infections was 29.6% among people aged 15 to 49 years. Based on WHO regional areas, the PAF breakdown for HIV infection attributable to HSV-2 was highest in Africa (37.1%), followed by the Americas (21.3%), Western Pacific (13.0%), South-East Asia (12.4%), Eastern Mediterranean (12.3%), and Europe (11.6%). 

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Investigators also showed that the PAF of incident HIV infections attributable to HSV-2 infection via sexual transmission was higher in women (age 15-24 years, 30.8%; 25-49 years, 36.4%; 15-49 years; 34.8%) than men (17.9%, 30.2%, 26.2%, respectively); higher in people aged 25 to 49 years (32.4%) than those aged 15 to 24 years (23.2%); and higher in women sex workers (26.7%) than men who have sex with men (19.9%). 

Limitations of the study included a possible underestimation of recently acquired HSV-2 infections as well as a built-in causal link in PAF estimates by definition. 

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The study researchers noted that “the contribution of HSV-2 infection to HIV acquisition is substantial given the high prevalence of HSV-2 infection globally.” They call for “interventions targeted against HSV-2, such as new vaccines or microbicides,” noting that these interventions “have the potential to improve the lives of millions of people by reducing recurrent genital herpetic symptoms. In addition, in the presence of an effect of HSV-2 infection on HIV acquisition, prevention measures against HSV-2 transmission could have a further, indirect benefit on HIV.”

Disclosures: One study author declared an affiliation with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.


Looker KJ, Welton NJ, Sabin KM, et al. Global and regional estimates of the contribution of herpes simplex virus type 2 infection to HIV incidence: a population attributable fraction analysis using published epidemiological data [published online November 18, 2019]. Lancet Infect Dis. doi: 10.1016/S1473-3099(19)30470-0

This article originally appeared on Infectious Disease Advisor