HIV cultured from pharynx: potential role in oral HIV transmission?

Whilst debate continues about exactly how risky oral sex really is, researchers from the University of Washington in Seattle and the Imapcta Salud y Educacion, Lima, Peru have successfully cultured infectious HIV from pharyngeal swabs from four men with high pharyngeal HIV RNA.

HIV-1 RNA can be detected in saliva, yet culture of HIV-1 from saliva is only successful in less than 1% of samples due to the inactivation of the virus by saliva. Tonsillar biopsy specimens have previously been shown to harbour both HIV-1 RNA and DNA. The researchers set about describing the predictors and variability of HIV-1 RNA in the pharynx and attempted to cultivate HIV-1 from oropharyngeal surfaces.

In total 64 HIV-positive men without bacterial STIs from Seattle, USA and Lima, Peru were evaluated prospectively at week 0, 2 and 4 to assess viral load in plasma and in swab specimens obtained from the pharynx. A subset of 17 men with high pharyngeal viral load were evaluated one year later for the recovery of infectious virus from blood, tonsil and buccal surfaces.

The median CD4 count of the 64 participants was 290 cells/ml and 45% were currently receiving antiretrovirals. The median baseline viral load was similar in plasma (4.24 log) and the pharynx (4.22 log). Each one log increase in plasma viral load was associated with a 0.323 log increase in pharyngeal viral load whilst both antiretroviral therapy and tonsillectomy were associated with reductions in pharyngeal viral load. There was a statistically significant study site effect between Seattle and Lima with respect to age, treatment, viral load and tonsillectomy; men were older in Seattle (median 39 vs 27 years), 24% in Seattle were using antiretroviral therapy compared with 5% in Lima, median viral in Seattle was 3.12 log compared to 4.75 log in Lima, and 42% of the men in Seattle had a tonsillectomy compared with 13% in Lima.

Infectious HIV was cultured from the pharynx of 4 of the subset of 17 men with high pharyngeal viral load but was not isolated from the buccal mucosa (the inside of the mouth) or the saliva of any of the men. The observation that the oropharynx appears to harbour higher levels of HIV than the buccal mucosa is likely due to the proximity of lymphoid tissue in the posterior oropharynx.

Three of the four men were not using antiretroviral therapy and the other was taking dual nucleoside therapy which was not fully suppressive.

Median mucosal RNA was 5.85 log in the culture positive men versus 4.69 log in culture negative men.

Both tonsillectomy and use of antiretroviral therapy were associated with a reduction in pharyngeal viral load. Pharyngeal HIV shedding was higher among persons with tonsils and detectable viral load.

Whilst the detection of culturable HIV RNA in the posterior pharynx may indicate the potential for the oral transmission of HIV further behavioural data are needed if we are to understand the role sex acts such as "deep throating" may play in the oral transmission of HIV.