ATLANTA -It may seem axiomatic that porn films carry an HIV risk to the actors, but the industry has relied on a voluntary screening program. Now the CDC says the program failed, with a male actor’s infection spreading to three female co-workers.

The male actor probably became infected with HIV during a working trip to Brazil, according to a CDC investigation of the Los Angeles industry recounted today in Morbidity and Mortality Weekly Report.

The investigation “identified important and remediable gaps in the prevention of HIV and other sexually transmitted diseases (STDs) in the adult film industry,” said the CDC.

In Los Angeles County, there are an estimated 200 adult production companies, employing 6,000 workers, of whom 1,200 take part in what the report called “direct work-related sexual contact.”

Many of them participate in a screening program for HIV and other STDs, the CDC said, but it is “not adequate to prevent transmission” for several reasons:

* It is voluntary. * Workers have to pay for it themselves, which may mean they get tested less often. * And people can become infected and transmit disease for a period of time before testing can pick it up.

The CDC report said exposure to disease is associated with “basic practices” in the industry, in that workers have sex — often prolonged and frequent — with multiple partners and, on the heterosexual side, do not customarily use condoms.

In this case, a 40-year-old man tested positive for HIV on April 9, 2004, after being negative on previous tests on Feb. 12 and March 17. Between the two negative tests, he had traveled to Brazil to work and had engaged in unprotected sex acts.

While in Brazil, the investigators found, the man had suffered a flu-like illness that passed before he returned to California.

Back in Los Angeles — and before he tested positive — the man had unprotected sex with 13 female partners, three of whom subsequently tested HIV-positive, after having been negative the month before. The so-called “attack rate” — the number of people who were infected divided by the number exposed — was 23%.

The man and two of the three women provided whole blood samples; sequencing showed that key sections of the HIV genome were identical in all the samples, supporting the conclusion that the man was the source of infection.

The investigation also looked at 61 first- and second-generation sexual contacts of the four outbreak patients and found that 59 of them remained HIV-negative. Data for the other two wasn’t available.

The first-generation contacts are those who had direct sexual contact with one of the four; the second-generation contacts are those who had sex with the first generation.

The four cases “underscore the hazards associated with unprotected sex among workers” in the adult film industry, the CDC said.

What’s needed is “an effective health and safety program” that would ensure workers are protected against transmission, aware of their rights under the law, and vaccinated if possible against sexually transmitted diseases, including hepatitis B.

The California department of industrial relations eventually cited two of the employers for failing to comply with the state’s blood-borne pathogens standard, failing to report a serious work-related illness, and failing to prepare and follow a written occupational injury and illness prevention program.

The citations are being appealed, the CDC report said.

Other STDs are also an issue, the CDC said.

The most recent prevalence data for adult film workers — taken between June, 2000 and December, 2001 — show that:

* 5.5% of men and 7.7% of women had chlamydial infection. * 2% of men and women had gonorrhea.

The data were taken before the voluntary screening program was instituted, the CDC says.

By comparison, a nationally representative sample of young adults 18 to 26 years, between April, 2001 and May, 2002 showed that:

* 3.7% of men and 4.7% of women had chlamydial infection. * And 0.4% of men and women had gonorrhea.