In January, the city of Los Angeles passed a law requiring actors to wear condoms. A measure to do the same for the whole county is on the ballot on Tuesday.

Producers say the condom requirement will drive them out of business since consumers will not buy such films. Local newspapers like The Los Angeles Times oppose the ballot measure, calling it well-intentioned but unenforceable, and warning that it could drive up to 10,000 jobs out of state.

Very frequent testing makes it almost impossible for an actor to stay infected without being caught, said Dr. Jacques Pepin, the author of “The Origins of AIDS” and an expert on transmission rates. “And if you are having sex mostly with people who themselves are tested all the time, this must further reduce the risk.”

When the virus first enters a high-risk group like heroin users, urban prostitutes or habitués of gay bathhouses, it usually infects 30 to 60 percent of the cohort within a few years, studies have shown. The same would be expected in pornography, where performers can have more than a dozen partners a month, but the industry says self-policing has prevented it.

“Our talent base has sex exponentially more than other people, but we’re all on the same page about keeping it out,” said Steven Hirsch, the founder of Vivid Entertainment, one of the biggest studios.

Performers have to test negative every 28 days, although some studios recently switched to every 14.

If a test is positive, all the studios across the country that adhere to standards set by the Free Speech Coalition, an industry trade group, are obliged to stop filming until all the on-screen partners of that performer, all their partners, and all their partners’ partners, are found and retested. In 2004, the industry shut down for three months to do that.