Downs A M, De Vincenzi I
European Centre for the Epidemiological Monitoring of AIDS, Hôpital National de Saint-Maurice, Saint-Maurice, France.
J Acquir Immune Defic Syndr Hum Retrovirol. 1996 Apr 1;11(4):388-95. doi: 10.1097/00042560-199604010-00010.
The objective of this study was to investigate the relationship between the number of unprotected heterosexual contacts with an HIV-infected person and the probability of HIV transmission. Data from a European study involving 563 heterosexual partners of HIV-infected subjects were analyzed. The number of unprotected contacts could be estimated for 525 couples (377 with male index case, 148 with female index case) from the reported frequency of unprotected contacts and an estimate of the length of the period during which transmission could have occurred. Nonparametric (isotonic regression) and parametric (Bernoulli model) analyses were performed on data at study entry and on follow-up data (121 couples). The nonparametric analysis resulted in several exposure groups, with the proportion of infected partners increasing with the number of contacts. For example, the percentage of female partners infected ranged from 10%, among those with < 10 unprotected contacts with an infected male, to 23% after 2,000 unprotected contacts. The parametric estimates of (assumed constant) per-contact infectivity were higher for male-to-female than for female-to-male transmission, but not significantly so. However, in comparison with nonparametric estimates, the model assuming constant infectivity appears to seriously underestimate the risk after very few contacts and to seriously overestimate the risk associated with a large number of contacts. Our results suggest that the association between the number of unprotected sexual contacts and the probability of infection is weak and highly inconsistent with constant per-contact infectivity. Probable explanations for these findings include large variability in infectivity between couples and within individuals over time. Estimates based on partner study data under the hypothesis of constant infectivity can, therefore, be highly misleading at a public health level, particularly when extrapolated to multiple casual contacts.
本研究的目的是调查与艾滋病毒感染者发生无保护措施异性接触的次数与艾滋病毒传播概率之间的关系。分析了一项欧洲研究的数据，该研究涉及563名艾滋病毒感染者的异性伴侣。根据报告的无保护接触频率以及对可能发生传播的时间段的估计，可以估算出525对伴侣（377对以男性为索引病例，148对以女性为索引病例）的无保护接触次数。对研究开始时的数据以及随访数据（121对伴侣）进行了非参数（等渗回归）和参数（伯努利模型）分析。非参数分析得出了几个暴露组，感染伴侣的比例随着接触次数的增加而增加。例如，女性伴侣被感染的百分比范围从与感染男性发生少于10次无保护接触的人群中的10%，到发生2000次无保护接触后的23%。男性传染给女性的（假设为恒定的）每次接触感染性的参数估计值高于女性传染给男性的情况，但差异不显著。然而，与非参数估计相比，假设感染性恒定的模型似乎在接触次数很少后严重低估了风险，而在接触次数很多时又严重高估了相关风险。我们的结果表明，无保护性行为接触次数与感染概率之间的关联较弱，且与每次接触恒定的感染性高度不一致。这些发现的可能解释包括不同伴侣之间以及个体随时间的感染性存在很大差异。因此，在恒定感染性假设下基于伴侣研究数据的估计在公共卫生层面可能会产生极大的误导，尤其是在推断到多个偶然接触的情况时。
