Updated

Frequent testing alone can't prevent the spread of HIV, researchers stress in a CDC report on a few cases centered in the porn industry. Researchers say a 25-year-old male porn actor, labeled "Patient A," tested negative for HIV in 2014 and over the next 22 days had unprotected sex with at least 17 people who hailed from seven US states and four countries.

Then an HIV test came back positive, and further tests showed he likely transmitted the virus to two men: Another adult-film actor and a non-work-related partner tested HIV positive less than a month after their encounters with Patient A and showed a similar strain of the virus, reports Live Science.

Some porn companies require that actors have a negative HIV test within two weeks of filming. But MD Magazine reports tests can't detect the virus within the first 14 days of infection.

"Adult film performers and production companies, medical providers, and all persons at risk for HIV should be aware that testing alone is not sufficient to prevent HIV transmission," the CDC states.

It suggests the industry promote the use of condoms, regular HIV testing, and the use of antiviral drugs, like pre-exposure prophylaxis (PrEP), for performers at risk of HIV.

In a release, the president of the AIDS Healthcare Foundation says the porn industry's HIV and STD testing protocol "failed" in this case, as the CDC confirmed "this HIV infection did, in fact, occur on set." (Here's good news in the fight against HIV.)

This article originally appeared on Newser: CDC: Porn Actor Spread HIV After Testing Negative for It

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