LOS ANGELES – Health officials confirmed on Thursday a third case of H.I.V. infection among actors in the pornography industry.

Sharon Mitchell, the director of a clinic that is testing hundreds of performers for H.I.V., the virus that causes AIDS, said the latest infection had been detected in a 26-year-old woman from the Czech Republic who had worked on a sex-video on March 23 with Darren James, the first actor here known to have been infected in the outbreak. Ms. Mitchell, who informed the Czech actress of her condition on Thursday morning, did not identify her, but confirmed a report on the Adult Video News Web site that her stage name is Jessica Dee. Four tests were used to establish the presence of the virus.

“She’s been counseled,” said Ms. Mitchell, the director of the Adult Industry Medical Health Care Foundation. “No one is ever very happy about getting H.I.V., but she’s taking to counseling very well and she is already on anti-retroviral therapy – early H.I.V. meds.”

Another actress who had worked with Mr. James, Lara Roxx, a Canadian, was found to have the virus two weeks ago.

The outbreak, which involves the first known cases of H.I.V. in the San Fernando Valley adult-video industry since 1999, has forced a 60-day halt to filming while performers are tested and re-tested for the virus. It is believed to have been brought in by Mr. James from Brazil, where he was working on a film in early March.

Ms. Mitchell said on Thursday that she had contacted Brazilian health officials to try to trace the virus on the São Paulo film location. She said she believed it was linked to a young actress who had sex with Mr. James in the film. She declined to name that actress, and said her identity had been provided not by Mr. James but by “an outside source.”

Ms. Mitchell said she had yet to ascertain whether the Brazilian actress knew that she had the virus at the time she worked with Mr. James.

Health department investigators in Los Angeles have obtained the legal names and medical files of about 60 performers here who were known to have had sexual contact with Mr. James and Ms. Roxx, or with someone else who had sex with the two. The investigation will presumably now be expanded to include anyone who had sexual contact with Ms. Dee.