LOS ANGELES (AP) — Los Angeles County’s top health official says four more cases of syphilis have been found during their investigation of an outbreak among porn performers — and the discovery of more cases is likely.

Dr. Jonathan Fielding says the total number of syphilis cases among porn performers is up to nine on Tuesday. Five cases were reported last week, causing the multi-billion dollar industry to call for a halt in filming to prevent the spread of disease.

Fielding says the number is likely to rise, since the transmission of sexually transmitted diseases in the porn industry is common because performers often have unprotected sex with multiple actors.

He says the increase was discovered by testing the sexual partners of the earlier cases found. The investigation is ongoing.

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