People who don’t tell their partners about their sexual pasts could be forced to pay damages for negligently transmitting AIDS or other sexually communicated diseases, the California Supreme Court ruled in a groundbreaking decision.

In a 4-3 ruling yesterday, the state’s highest court held that a man accused of infecting his wife with HIV, the virus that causes AIDS, must disclose in pretrial proceedings some of his previous sexual activity.

Although the California Supreme Court had never ruled on the issue, Justice Marvin Baxter, writing for the majority, said state appeals courts around the country “have long imposed liability on individuals who have harmed others by transmitting communicable diseases.”

“We agree with these courts that to be stricken with disease through another’s negligence is … no different from being struck with an automobile through another’s negligence,” Judge Baxter wrote.

The case pitted the rights of a woman infected with a deadly disease – apparently unintentionally – against her husband’s right of privacy. Under the ruling, people can be held liable even if they do not know they are infectious.

“This is a sad case,” Judge Baxter wrote, noting that both the plaintiff Bridget B and the defendant John B are infected with HIV and that each has blamed the other