Do criminal HIV exposure laws reduce transmission risk? A mathematical modeling analysis

Background: HIV-specific criminal laws in 23 US states prohibit HIV-positive persons from engaging in sexual activities without first disclosing their seropositive status to sex partners. The sexual behaviors addressed by these laws vary widely. While some exposure laws are very strict, criminalizing virtually all sexual behavior absent disclosure, others are more flexible, criminalizing only higher-risk activities, such as unprotected vaginal or anal intercourse. The effectiveness of these laws in reducing HIV transmission risk is not known.

Methods: A simple mathematical model was used to compare the risk reduction effectiveness of strict and flexible exposure laws, both to each other and to a “no-law” alternative. The model distinguished between high- and low-risk sex without disclosure, and sexual activities engaged in after disclosure, which could be more or less risky than low-risk sex.

Results: Compared to the no-law alternative, flexible exposure laws always decrease HIV transmission risk, but strict laws could fail to reduce risk in situations where post-disclosure sex is riskier than low-risk sex. Also, flexible laws are more effective than strict laws when post-disclosure sex is riskier than low-risk sex, but could be less effective if low-risk sex is the least risky alternative, depending on compliance rates. Given the right circumstances, both flexible and strict exposure laws could reduce HIV transmission risk up to 40 to 60%.

Conclusion: HIV exposure laws could prevent new HIV infections. Whether a flexible or strict law will produce a greater reduction in risk depends on legal compliance and the riskiness of post-disclosure sexual behavior.