Can HIV transmission be amplified?
The probability of HIV transmission depends on the infectiousness of the index case and the susceptibility of the exposed subject (2). Considerable progress has been made regarding infectiousness, with far less progress in understanding susceptibility. Infectiousness is determined by the concentration of HIV during exposure and viral phenotypic factors. The inoculum required for HIV transmission has been estimated from a series of studies. The largest and most compelling work was conducted in the Rakai district of Uganda, where HIV transmission was directly related to the blood HIV concentration (3). Transmission was not observed when the blood viral burden was less than 3,500 copies/ml, whereas about 50% of transmission events were observed in subjects with the greatest blood viral burden. Neither this nor other transmission studies examined the genital tract viral burden directly, which can differ from that in the blood. Nor is it clear whether HIV is transmitted by cell-free or cell
