ATLANTA?Nearly 30 percent of people deemed at risk for HIV have never been tested, the government said Thursday in warning they could be unknowingly spreading the virus that causes AIDS.

The study by the Centers for Disease Control and Prevention involved more than 30,000 people in the United States.

Some 73 percent of those considered at risk for HIV said they had been tested, but only 30 percent said they had been tested in the previous year.

The results underscore a problem that has concerned health officials for years: A substantial segment of people with the virus don’t realize they have it and are probably spreading it.

The study cited lack of access to testing centers and a perceived lack of confidentiality as reasons some people don’t get tested.

The 1999 study was released in advance of World AIDS Day, which is Saturday.