Sampling irregularities, or why the present estimate for risk of HIV casual transmission is probably an underestimate

Abstract

Updating the list of casual transmission studies yielded a minor revision of the recently reported estimate of the risk of HIV casual household transmission, estimating it as 0.3% per year of contact. A meta-analysis of the studies used to calculate this risk indicated that the estimated risk is probably an underestimate for four main sampling irregularities: (a) The studies employed samples which were based on selective non-participation of subjects including refusals and unlocatable subjects at average rates of 36% and 14%, respectively; (b) only 17% of the studies reported full numerical details of the population studied; (c) the studies were based on unjustified exclusions of subjects by the investigators at an average rate of 31%; (d) the sampling of studies cited in the transmission studies is consistent with the hypothesis that the studies were biased against reporting cases of casual transmission. In the 13% of the studies that reported full details of exclusions, the average rate of all exclusions combined was 84%. Since it is likely that cases of casual transmission were mostly included among the exclusions, this may have resulted in an unrepresentatively low frequency of casual infection among the 16% that were left to be studied.