Last month, actor Charlie Sheen announced that he’s been HIV positive for about four years.

He told Today’s Matt Lauer that it was “impossible” he transmitted the disease to others, despite having unprotected sex with two people since his diagnoses. Both were informed ahead of time, Sheen said.

Under California Health and Safety Code 120290, Sheen could be charged with a misdemeanor offense and sentenced to six months in jail under a vague law regarding transmission of any disease. But had he not disclosed his HIV status with his sexual partners, he could be charged with a felony punishable up to 8 years behind bars.

These are only two of five of California’s laws that can be used to prosecute people who know they’re HIV-positive and potentially expose others.

While federal mandates began the criminalization of HIV infection, federal agencies have asked states to review their laws to reflect the scientific knowledge that has been gleaned since 1981 when the U.S. Centers for Disease Control and Prevention (CDC) published its first report on immune system failures in previously healthy gay men.

A major contention surrounding these laws is how they target only one infectious disease while other infectious diseases don’t carry the same stigma. Opponents of those laws say they don’t reflect realistic scientific data, violate patient rights, and don’t decrease infection rates.

“It’d be nice to think these laws were passed in the wrong-headed hysteria from the late ’80s and early ’90s, but that’s not precisely true.” Catherine Hanssens, founder and executive director of the Center for HIV Law & Policy (CHLP), told Healthline.

Other activists groups, including the American Civil Liberties Union (ACLU), have also supported federal legislative efforts to repeal laws “rooted in misconceptions and prejudices against people living with HIV/AIDS.”

Read More: The History of HIV »

The Foundation of HIV Laws

In 1987, President Ronald Reagan issued an executive order to investigate the HIV virus epidemic. An advisory commission recommended health departments aggressively advocate HIV testing and make sure those results remained confidential. It also recommended HIV-specific criminal laws.

This created an inherent conflict. Many public health officials have said fewer people would get tested if their results could be used against them in criminal proceedings.

In 1990, the federal Ryan White Act was passed. It provided states the funding to combat the growing AIDS crisis and states had to certify they had laws adequate to prosecute someone who intentionally infected another person with HIV.

A 2007 study examining New York and Illinois found that despite the states’ laws regarding HIV status, few people knew them and the laws had little measurable effect on safer sex.

More than two-thirds of the states in the U.S. have some kind of HIV-specific criminal law, some of which do not require the transmission of HIV to another person for a conviction.

“There’s a disconnect between what public health officials are saying and what the law says,” Mayo Schreiber, Jr., deputy director of the CHLP, told Healthline.

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California: A Single-State Snapshot

All of California’s HIV-specific laws are felonies and none require transmission.

A study by researchers at the Williams Institute at UCLA and the California HIV/AIDS Research Program found from 1988 to June 2014, 800 people came into contact with the criminal justice system because of their HIV status. Use of the law peaked in 2000, but in 2013 — the last year with complete data — only 17 people were in the system for HIV-related charges, the lowest since 1991.

The Williams study provides a snapshot of how these laws are being used when federal agencies are asking states to review those statutes. The researchers in that study found few clues to how the laws are being enforced and who they’re being used against.

Of those 800 cases, 95 percent of them involved people in sex work. Only 31 percent of those cases resulted in charges for an HIV-specific offense, and all but one of the 390 charges resulted in a conviction, the Williams researchers found.

The study showed that laws are disproportionately used agains blacks, Latinos, and women. Black men are more likely to be convicted and given a larger sentence than any other group.

“That’s what happens to African American men in our justice system regardless,” Hanssens said.

White men, on the other hand, account for 40 percent of the HIV population in California, but only make up 16 percent of people in court for their HIV status.

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HIV Laws Don’t Have Intended Effect

The National HIV/AIDS Strategy of the United States, revised in July and effective through 2020, acknowledges HIV laws do little to deter behavior and so encourages prosecutors to use their discretion in “dismissing blatantly stigmatizing and discriminatory cases against people living with HIV.”

“In too many instances, the existence and enforcement of these types of laws run counter to scientific evidence about routes of HIV transmission and effective measures of HIV prevention, and undermine the public health goals of promoting HIV screening and treatment,” the policy states.

As noted by a CDC and the Department of Justice study, most state laws do not account for preventative measures, such as condom use or pre-exposure prophylaxis (PrEP).

The majority of the laws on the books in 2011 — 67 in 33 states — were passed before studies showed that antiretroviral therapy (ART) reduces the risk of HIV transmission by 96 percent, according to the CDC. Used with a condom, that risk drops to 99 percent, although early- and late-stage patients may be more infectious.

On sexual exposure, receptive anal intercourse poses a risk of 138 per 10,000 exposures, or 0.014 percent. Penile and vaginal sex averages a 0.006 percent exposure risk, even without PrEP or condoms, according to the CDC.

Some laws in different states also have enhanced punishments for HIV-positive people regarding biting or spitting, which the CDC rates as “negligible,” even after 10,000 exposures.

Still, in 2010, a Michigan man was initially charged under anti-terrorism laws. Authorities said his HIV was a “harmful biological substance” when he bit his neighbor during an altercation. That charge was later dropped.

Read More: PrEP Seen as Big Part of White House’s New HIV Strategy »

HIV Laws, Use Vary by State

In September 2014, an Alabama pastor confessed during a sermon that he had sex with multiple women who didn’t know he had been HIV-positive since 2003.

Although the pastor wasn’t charged under the state’s existing HIV laws, state representative Juandalynn Givan introduced H.B. 50 in March. It would change the law from a class C misdemeanor to a class C felony. The maximum allowed punishment would increase from three months to 10 years.

According to the CHLP, as of April 2014, there have been nearly 200 HIV-related prosecutions within the last six years. But that figure, they warn, is illustrative. There is no uniform system to track them, and laws vary from state to state, so it’s difficult to get a definitive count.

According to CHLP figures, 30 states have HIV-specific statutes with at least one prosecution within the past two years, nine have prosecuted HIV cases without a specific statute, and three have HIV laws but haven’t invoked them recently.

Iowa recently removed a law provision that required a person convicted of an HIV-related offense to register as a sex offender. Ten other states, however, still require the convicted to register.

The latest case involved a 31-year-old black Hispanic Indiana man accused of “knowingly spreading HIV for more than a decade.” All but four of the 16 charges filed in June are felonies. The prosecution contends he never disclosed his HIV status or only joked about it with nine women, who have since tested positive for HIV.

Besides sexual activity, some states have laws that enhance sentencing for biting and spitting, despite research that shows a low likelihood of transmission.

“There’s not one good thing that can be said about the state of these laws,” Hanssens said. “We do know the laws have never been justified.”