We conducted a five-step process of literature search and review. First, we established what was already known, starting with a series of recent systematic reviews and meta-analyses that were identified through a comprehensive literature review conducted for a related project that also examined per-act HIV transmission risk and provided estimates of pooled per-act HIV transmission probabilities for blood transfusion [5 (link)], parenteral exposures [5 (link)], receptive anal intercourse [6 (link)], receptive penile–vaginal intercourse [7 (link)], insertive penile–vaginal intercourse [7 (link)], and mother-to-child transmission [8 (link)]. Each of these peer-reviewed studies included a comprehensive literature review and employed accepted and robust meta-analytic methods. We then reviewed the 2011 British Pre-exposure Prophylaxis Guidelines [9 (link)], which provided a summary table of per-act HIV transmission risks using estimated medians and ranges based largely on the results of the meta-analyses noted above.
Second, we conducted a literature search to identify data published after the publications noted above. We searched for human studies published in English language only between 1 January 2008 and 22 February 2012 within the following databases: Medline (Ovid), Embase (Ovid), CINAHL (EbscoHost), Web of Science, Global Health, and the Cochrane Library. We used the following search string: [‘HIV’ or ‘HIV infections’ or ‘human immunodeficiency virus’ or ‘AIDS’] and [’disease transmission’ or ‘infectious/infectivity/infectiousness’ or ‘transmissibility’ or ‘contact/contacts/per-contact’ or ‘per-act’] and [’sexual’ or ‘heterosexual’ or ‘homosexual’ or ‘coital’ or ‘intercourse’ or ‘anal’ or ‘oral’ or ‘blood transfusion’ or ‘needle-sharing’ or ‘needle stick’ or ‘perinatal’ or ‘mother to child’]. We highlighted data from developed regions to more closely reflect the US epidemic; this strategy was consistent with that used for the relevant meta-analyses, which did not pool data from developed and developing countries due to heterogeneity among studies, except for the per-act HIV-transmission risk from parenteral exposures, which is less geographically dependent. We used the results of this literature search to ensure that the above-mentioned meta-analyses were up to date. For the exposures for which there were no recent reviews or meta-analyses, we reviewed the literature cited in CDC’s last summary [1 ] and the 2011 British Pre-exposure Prophylaxis Guidelines [9 (link)]. We also contacted subject matter experts to ascertain whether other studies or unpublished data of which we were unaware existed.
Third, we reviewed the resulting abstracts to identify articles that mentioned HIV transmission or any type of transmission risk estimate, or described models that were used to generate these estimates, both among serodiscordant couples and MSM. Fourth, we reviewed the text and bibliographies of all those publications that met these criteria to identify additional sources of transmission-risk data. We synthesized the information from these first four steps to generate updated per-act transmission risk estimates. We favored pooled estimates with 95% confidence intervals (CIs) reported from the meta-analyses that either used fixed-effects models or that used random-effects models that adjusted for the heterogeneity between studies, because such models provide more robust transmission risk estimates than simple medians and ranges.
Lastly, we conducted a literature search of human studies in PubMed to identify articles about factors known to modify sexual HIV transmission risk published between 1 January 2008 and 13 May 2013. We used the following search strings: ‘HIV transmission’ and each of the following separately: ‘genital ulcer disease’, ‘circumcision’, ‘condom use’, ‘pre-exposure prophylaxis’, ‘acute HIV infection’, ‘acute stage of disease’, ‘viral load’, ‘treatment’, ‘early antiretroviral therapy’.
Second, we conducted a literature search to identify data published after the publications noted above. We searched for human studies published in English language only between 1 January 2008 and 22 February 2012 within the following databases: Medline (Ovid), Embase (Ovid), CINAHL (EbscoHost), Web of Science, Global Health, and the Cochrane Library. We used the following search string: [‘HIV’ or ‘HIV infections’ or ‘human immunodeficiency virus’ or ‘AIDS’] and [’disease transmission’ or ‘infectious/infectivity/infectiousness’ or ‘transmissibility’ or ‘contact/contacts/per-contact’ or ‘per-act’] and [’sexual’ or ‘heterosexual’ or ‘homosexual’ or ‘coital’ or ‘intercourse’ or ‘anal’ or ‘oral’ or ‘blood transfusion’ or ‘needle-sharing’ or ‘needle stick’ or ‘perinatal’ or ‘mother to child’]. We highlighted data from developed regions to more closely reflect the US epidemic; this strategy was consistent with that used for the relevant meta-analyses, which did not pool data from developed and developing countries due to heterogeneity among studies, except for the per-act HIV-transmission risk from parenteral exposures, which is less geographically dependent. We used the results of this literature search to ensure that the above-mentioned meta-analyses were up to date. For the exposures for which there were no recent reviews or meta-analyses, we reviewed the literature cited in CDC’s last summary [1 ] and the 2011 British Pre-exposure Prophylaxis Guidelines [9 (link)]. We also contacted subject matter experts to ascertain whether other studies or unpublished data of which we were unaware existed.
Third, we reviewed the resulting abstracts to identify articles that mentioned HIV transmission or any type of transmission risk estimate, or described models that were used to generate these estimates, both among serodiscordant couples and MSM. Fourth, we reviewed the text and bibliographies of all those publications that met these criteria to identify additional sources of transmission-risk data. We synthesized the information from these first four steps to generate updated per-act transmission risk estimates. We favored pooled estimates with 95% confidence intervals (CIs) reported from the meta-analyses that either used fixed-effects models or that used random-effects models that adjusted for the heterogeneity between studies, because such models provide more robust transmission risk estimates than simple medians and ranges.
Lastly, we conducted a literature search of human studies in PubMed to identify articles about factors known to modify sexual HIV transmission risk published between 1 January 2008 and 13 May 2013. We used the following search strings: ‘HIV transmission’ and each of the following separately: ‘genital ulcer disease’, ‘circumcision’, ‘condom use’, ‘pre-exposure prophylaxis’, ‘acute HIV infection’, ‘acute stage of disease’, ‘viral load’, ‘treatment’, ‘early antiretroviral therapy’.
