It has been recently advocated that avoiding partners who may be at high risk of carrying HIV provides 5000-fold better protection against HIV infection than usage of condoms . In this paper, it is demonstrated that this guideline is largely based on unrealistic assumptions. If the sensitivity of identifying high-risk partners, realistic estimates of the efficiency of mechanical and chemical barrier methods, and the compliance in following either strategy are taken into account, use of condoms and/or suppositories containing nonoxynol-9 might be more effective than the attempt to avoid high-risk partners. Thus, both barrier methods should be strongly recommended for casual sexual heterosexual contacts.
PIP: Generalizing the results of Fienberg, the effects of optimistic assumptions on prevalence and infectivity and pessimistic assumptions about the effectiveness of barrier methods on estimates of the risk of HIV infection are demonstrated. Using the Pearl index as a basis for estimating the efficiency of a barrier method, it is shown that condoms -- preferably used together with spermicides -- and suppositories containing the spermicide nonoxynol-9 should be recommended for casual contacts among heterosexuals, The risk of HIV infection depends on the prevalence of HIV and its infectivity, the compliance of the individual to the strategy, i.e., the probability that the guidelines are followed, and the effectiveness of the strategy. It is misleading to conclude that "choosing a partner who is not in any high-risk group provides almost 4 orders of magnitude (5000-fold) of protection, compared with choosing a partner who is in the highest-risk category (with a prevalence of 5%.) With realistic assumptions, the protection cannot be in excess of 230-fold -- prevalence among randomly selected partners divided by prevalence among low-risk partners. Further, one cannot ignore the sensitivity of identifying high-risk partners. Finally, the influence of emotions or alcohol may even lead to sexual encounters with identified high-risk partners. Avoiding high risk partners with a compliance of 90% cannot provide more than 5-fold protection. For a given sensitivity and compliance rate, the use of barrier methods provides more protection than choice of low-risk partners. Due to the fact that barrier methods also provide protection against other sexually transmitted diseases which might be cofactors for HIV infection, the actual protective effect of these methods most likely will be even higher.