Most wives around the world consider married sex to be safe sex. Why bother negotiating condom use or getting tested for STIs when marriage is supposed to be about love, commitment and monogamy? But the hard truth is that for married women, the greatest risk of HIV infection comes from their husbands having extramarital sex, according to research findings revealed in the book The Secret: Love, Marriage, and HIV, by Jennifer S. Hirsch, Holly Wardlow, Daniel Jordan Smith, Harriet M. Phinney, Shanti Parikh and Constance A. Nathanson.

“The fact that a lot of women around the world get HIV from their husbands gave me chills,” says Hirsch, a medical anthropologist at Columbia University. “But discussion about this type of HIV transmission has been silenced. We’ve really ignored that unilateral monogamy is not an effective prevention effort.”

For the study, sponsored by the U.S. National Institutes of Health, Hirsch and colleagues examined the social and economic dynamics driving extramarital affairs in five different countries: Mexico, Nigeria, Papua New Guinea, Uganda and Vietnam. The team found that in these countries, husbands most often had affairs when certain social situations were in place. For example, when husbands traveled for work they had more extramarital sex. Lone-li-ness motivated these men to find other women who could temporarily replace their wives. In addition, when men socialized together in the absence of their wives but in the presence of other women (and alcohol) they’d challenge each other to see who could “score.”

Concentrating HIV prevention efforts in these settings and circumstances, Hirsch says, could lower the number of husbands who transmit HIV to their wives. What’s more, she adds, the HIV prevention messages need to shift from promoting fidelity and supposedly monogamous safe sex. “We have to think about addressing extramarital sex at a social level,” Hirsch says. “It’s not our job to put condoms on penises one at a time.”

Successful public health interventions work within—as opposed to ignoring—the social structures and situations in which men cheat on their wives, Hirsch says. Examples of good prevention tactics include: making condoms available where men spend their leisure time; fighting for immigration reform so migrant workers aren’t geographically displaced and more prone to unprotected, extramarital sex; working to end stigma that causes gay or bisexual men to marry for convention but continue high risk sexual practices; and fighting the anti-condom messages from faith-based communities.

But Hirsch’s suggested game plan can also apply to HIV prevention efforts for married women right here in the United States. The best way to prevent husbands everywhere from transmitting HIV to their wives, she stresses, is having frank discussions about marital reality and not the dream.

As Hirsch sums up: “We should not be suggesting that marital sex is safe sex.”