LOS ANGELES, June 12 (Reuters) - There have been 16 unpublicized cases of HIV among porn actors since a 2004 outbreak made headlines, Los Angeles health officials said on Friday, a disclosure that was likely to raise new concerns about AIDS in the adult film industry.

The revelation came in response to a request for information by the Los Angeles Times, which reported that an unidentified actress had tested positive last week.

The adult film industry had said it was the first case since the 2004 outbreak, the Times reported.

In fact 22 performers have tested positive, including last week's case and five in 2004, according to the numbers released by the Los Angeles County Department of Public Health.

Since the 2004 outbreak, in which a male star infected three actresses and another performer also tested positive, the $12-billion-a-year U.S. adult film industry has required regular testing by porn actors.

Most of that testing is conducted by the Adult Industry Medical Healthcare Foundation, which issues work certificates to the performers who test negative.

The unnamed actress first tested positive for HIV on June 4 and worked the following day before taking second and third tests, according to the Times.

The second test was also positive and results of the third were pending, according to AIM Healthcare.

"AIM Healthcare has never been cooperative with us and our investigations," Dean Fryer, a spokesman for the state Division of Occupational Safety and Health, told the paper, adding that the clinic had refused to name the actress or her employer.

In a statement on its website, AIM Healthcare said it was still awaiting "final confirmation" that the actress was positive for HIV.

The porn industry, which is largely centered in the San Fernando Valley suburbs of Los Angeles, includes about 200 production companies that employ about 1,200 actors, the Times said.

Since 2004, 1,357 porn performers have tested positive for gonorrhea and 15 for syphilis, according to county health data cited by the Times.