Occasional condom use and HIV risk reduction.

Model-based estimates indicate that even occasional condom use can substantially reduce the probability of human immunodeficiency virus transmission. For many realistic parameter values, an essentially linear relationship exists between the proportion of sexual contacts in which a condom is used and the resultant reduction in the risk of infection. Thus, in many cases, the use of condoms for half of all sexual contacts reduces the probability of transmission by about half the maximum possible reduction obtained through consistent use. These results suggest that occasional condom use should be reconceptualized within a harm-reduction paradigm in which increased use is stressed for those individuals who are either unable or unwilling to use condoms consistently.