Guidelines issued by the Centers for Disease Control and Prevention (CDC) to identify those who stand to benefit from Truvada (tenofovir/emtricitabine) as pre-exposure prophylaxis (PrEP) against HIV may overlook certain high-risk men who have sex with men (MSM).

Researchers at the Los Angeles LGBT Center used real-world data to develop their own risk calculator that they believe will fill this gap in the CDC guidelines.

The investigators gathered data between January 2009 and June 2014 on behavioral risk factors for HIV among initially HIV-negative clients visiting its clinic. They compared this data with HIV test results to determine any association between behaviors and eventually testing positive for the virus.

The researchers then used that data to construct an HIV-risk algorithm that the center now uses for recommending PrEP to its clients. Consisting of 13 questions, the calculator goes further than the CDC guidelines by asking about factors potentially associated with HIV risk among MSM, such as substance use, number of sex partners, age, race or ethnicity and other factors related to sexual partners.

Fifty-one percent of the study participants had a risk score of five—the threshold for recommending a PrEP consultation—or greater. If all of them had received daily Truvada, three quarters of the HIV infections seen during the study’s follow-up would have been avoided. This is assuming adequate adherence to the daily pill regimen.

A limitation of the calculator is that it may not be appropriate for transgender individuals or heterosexuals, injection drug users or those living outside Los Angeles. The calculator also does not take into account scenarios involving HIV-negative men in long-term partnerships with HIV-positive men.

The calculator is part of the “F*ck w/out Fear” prevention campaign. To read the POZ article about it, click here.

To read a press release about the study, click here.

To access the risk calculator, click here.

To read the study abstract, click here.