Effectiveness of condoms in preventing HIV transmission

The consistent use of latex condoms continues to be advocated for primary prevention of HIV infection despite limited quantitative evidence regarding the effectiveness of condoms in blocking the sexual transmission of HIV. Although recent meta-analyses of condom effectiveness suggest that condoms are 60 to 70% effective when used for HIV prophylaxis, these studies do not isolate consistent condom use, and therefore provide only a lower bound on the true effectiveness of correct and consistent condom use. A reexamination of HIV seroconversion studies suggests that condoms are 90 to 95% effective when used consistently, i.e. consistent condom users are 10 to 20 times less likely to become infected when exposed to the virus than are inconsistent or non-users. Similar results are obtained utilizing model-based estimation techniques, which indicate that condoms decrease the per-contact probability of male-to-female transmission of HIV by about 95%. Though imperfect, condoms provide substantial protection against HIV infection. Condom promotion therefore remains an important international priority in the fight against AIDS.

Cost-effectiveness of HIV-prevention skills training for men who have sex with men

OBJECTIVE

A previous study empirically compared the effects of two HIV-prevention interventions for men who have sex with men: (i) a safer sex lecture, and (ii) the same lecture coupled with a 1.5 h skills-training group session. The skills-training intervention led to a significant increase in condom use at 12-month follow-up, compared with the lecture-only condition. The current study retrospectively assesses the incremental cost-effectiveness of skills training to determine whether it is worth the extra cost to add this component to an HIV-prevention intervention that would otherwise consist of a safer sex lecture only.

DESIGN

Standard techniques of incremental cost-utility analysis were employed.

METHODS

A societal perspective and a 5% discount rate were used. Cost categories assessed included: staff salary, fringe benefits, quality assurance, session materials, client transportation, client time valuation, and costs shared with other programs. A Bernoulli-process model of HIV transmission was used to estimate the number of HIV infections averted by the skills-training intervention component. For each infection averted, the discounted medical costs and quality-adjusted life years (QALY) saved were estimated. One- and multi-way sensitivity analyses were performed to assess the robustness of base-case results to changes in modeling assumptions.

RESULTS

Under base-case assumptions, the incremental cost of the skills training was less than $13,000 (or about $40 per person). The discounted medical costs averted by incrementally preventing HIV infections were over $170,000; more than 21 discounted QALY were saved. The cost per QALY saved was negative, indicating cost-savings. These results are robust to changes in most modeling assumptions. However, the model is moderately sensitive to changes in the per-contact risk of HIV transmission.

CONCLUSIONS

Under most reasonable assumptions, the incremental costs of the skills training were outweighed by the medical costs saved. Thus, not only is skills training effective in reducing risky behavior, it is also cost-saving.

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.

Implications of increased infectivity in early-stage HIV infection. Application of a Bernoulli-process model of HIV transmission

Recent reports suggest that the infectivity of sexually transmitted HIV (i.e., the probability of transmission on a single sexual contact) may be up to 1,000 times greater during the first few months of infection than during the long asymptomatic period that precedes the development of AIDS. Assuming the validity of this estimate, a simple Bernoulli-process model of HIV transmission indicates that, in some cases, the expected number of secondary infections is greater for the brief period of primary infection than for the much longer asymptomatic phase. The implications of these findings for current HIV/AIDS prevention practices are analyzed with particular attention to the role of condom use in preventing HIV transmission.