Undetectable Blood Viral Load and HIV Transmission Risk: Results of a Systematic Review, James Wilton, CATIE (2013)

CATIE aims to provide people living with HIV (PLWH) or hepatitis C, at-risk communities, health care providers, and community organizations with up-to-date resources and expertise to reduce transmission and improve quality of life. This article provides an overview of a recent systematic review of studies focusing on viral load and transmission rates in serodiscordant couples conducted by one of Canada’s leading infectious disease specialists and her colleagues.

The review builds on HPTN 052 and other similar research studies by seeking a more nuanced view of viral load and transmission rates in serodiscordant couples. For example, “undetectable viral load,” which is based on the limit of detection for HIV per milliliter of blood, should be a controlled variable because limits of virus detection can vary among tests. Moreover, PLWH may have an undetectable blood viral load but still have a detectable viral load in their semen, vaginal fluid, or rectal fluid.

The systematic review also found significant limitations for the findings in the studies. For example, there was a high level of condom use, which may diminish some of the low transmission rates attributable simply to undetectable viral loads. The “majority of the couples enrolled in the studies were heterosexual and were (likely) having mostly vaginal sex,” so the findings may not be directly translatable to same-sex couples. Finally, low sexually transmitted infection (STI) rates among couples in the studies reviewed, attributable to stable monogamous couples and regular STI testing and treatment, may have decreased the risk of HIV transmission. Therefore, the findings may be limited to serodiscordant couples in the general population that fit those characteristics.