COLUMBIA, Mo. -- A 20-year-old Columbia woman has been charged with knowingly exposing people to HIV while working as a prostitute after being caught in an undercover sting last month.

Antionette L. Clark was one of five people arrested in June as part of a joint effort between Columbia police and the FBI to crack down on prostitution.

Clark was arrested at a hotel in east Columbia on June 19 after agreeing to have sex with an undercover officer in exchange for cash after the officer responded to an online ad, the Columbia Daily Tribune reported.

A probable-cause statement says Clark admitted being HIV-positive after she was arrested. She initially was charged with misdemeanor prostitution before prosecutors amended the case last week to charging her with knowingly being infected with HIV while performing the act of prostitution, a felony.

It wasn't known whether anyone has been assigned to represent Clark.

There are 221 people in Boone County living with HIV, according to the most recent statewide statistics from about a year ago, said Dustin Hampton, an HIV health educator at the Columbia/Boone County Department of Public Health and Human Services.

Andrea Waner, spokeswoman for the Columbia/Boone County Department of Public Health and Human Services, said people who are sexually active or have concerns shouldn't hesitate to get tested, because symptoms can take years before they become apparent.

"We definitely recommend you not wait for symptoms to show up," Waner said.

While there occasionally are cases in which people knowingly expose others to the virus, the accusations against Clark aren't the norm for people who have HIV, Hampton said.

"I think that overall people living with HIV are responsible and are taking precautions to protect their own health from other issues and also to protect the health of people around them," he said.

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Information from: Columbia Daily Tribune, http://www.columbiatribune.com