Validation of Performance of the Gen-Probe Human Immunodeficiency Virus Type 1 Viral Load Assay with Genital Swabs and Breast Milk Samples

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Abstract
Human immunodeficiency type 1 (HIV-1) continues to spread at an alarming rate. The virus may be transmitted through blood, genital secretions, and breast milk, and higher levels of systemic virus in the index case, as measured by plasma RNA viral load, have been shown to correlate with increased risk of transmitting HIV-1 both vertically and sexually. Less is known about the correlation between transmission and HIV-1 levels in breast milk or genital secretions, in part because reliable quantitative assays to detect HIV-1 in these fluids are not available. Here we show that the Gen-Probe HIV-1 viral load assay can be used to accurately quantify viral load in expressed breast milk and in cervical and vaginal samples collected on swabs. Virus could be quantified from breast milk and swab samples spiked with known amounts of virus, including HIV-1 subtypes A, C, and D. As few as 10 copies of HIV-1 RNA could be detected above background threshold levels in ≥77% of assays performed with spiked breast milk supernatants and mock swabs. In genital swab samples from HIV-1-infected women, similar levels of HIV-1 RNA were consistently detected in duplicate swabs taken from the same woman on the same clinic visit, suggesting that the RNA values from a single swab sample can be used to measure genital viral load.