Many HIV positive women’s troubles may now be behind them—literally. Studying positive women across the U.S., Brown University Medical School researchers recently found more instances of anal infections from a common sexually transmitted virus than cervical ones.

The human papillomavirus (HPV) is so common that 40 million Americans have it (those who don’t can cut risk with faithful condom use). It’s especially widespread among positive people. Most strains, or forms, of HPV are not serious; others can lead to cancer.

Over time, the dangerous strains can cause abnormal cell growth in the cervix or anus. Some cells return to normal; others turn precancerous, possibly becoming cervical or anal cancer years later. Regular testing can catch growths early, and treating them can prevent cancer, so women are accustomed to having cervical Pap smears periodically (frequency depends on your risk factors). Now, you’re on notice: Get anal smears too.

Anal sex doesn’t seem to be the culprit. In Brown’s “SUN study,” all HPV strains were more frequent anally than cervically—whether or not the women reported having had anal sex.

Lead investigator Erna Kojic, MD, theorizes, “HPV is very infectious; it may be that the anus is simply more exposed and vulnerable to casual contact.” Whether more anal HPV will mean an overall increase in anal cancers, Kojic adds, remains unclear. “Cancer takes years to develop,” she says, “and the time to study it is now.” Meanwhile, watch your back.