Two adult film actors have tested positive for HIV, with one most likely infecting the other during unprotected sex at a film shoot in Nevada, California health officials said.

One of the actors had previously tested negative for the virus that causes AIDS before a pair of film shoots but then began showing symptoms during the second shoot and was later found to be HIV-positive, the California Department of Public Health said Monday in a statement.

"In this case, the actor and production company thought he was HIV-negative during filming," the statement said. "Shortly after his negative test, HIV levels in his body rose rapidly to where he could infect other actors through unprotected sex."

The other infected actor also participated in the shoots, and health officials said the virus was probably transmitted by the actor who previously tested negative. California health officials would not give further details about the patients or cases, citing privacy restrictions. A message left with public health officials in Nevada was not immediately returned.

The infections came amid a major decline in porn filming in Los Angeles County, once the center of porn production in the country, where a 2012 law requires actors to use condoms. The number of porn filmmakers applying for filming permits in the county declined from 485 in 2012 to 40 in 2013. The last confirmed on-set HIV infection was in 2004.

— The Associated Press