New cases of HIV infection in Minnesota rose 13 percent in 2009, the biggest increase in 17 years, signaling the return of a scourge among young gay men that public health experts had hoped was under control.

The largest increase by far was among gay men ages 13 to 24.

Of the 95 new cases reported among 15- to 24-year-olds, 77 were among men, almost all gay and bisexual men, the Minnesota Department of Health reported. It released the preliminary data two months ahead of its usual annual report, a reflection of the public health urgency.

"This increase in cases tells us that HIV/AIDS remains a significant health threat in Minnesota, and we need to take steps to strengthen our prevention efforts," said Dr. Sanne Magnan, Minnesota Commissioner of Health.

"We haven't had numbers this high in 17 years," said Peter Carr, director of the HIV and sexually transmitted diseased department at the Health Department.

Carr said the increase does not reflect higher rates of testing but rather a true increase in the number of new cases.

Public health experts said that increases among gay men are the result of a number of factors. One is likely complacency - many young teenagers and adults view HIV as a treatable disease, and do not fear the consequences as do older adults. Also, the internet has exploded as a means of connecting gay men seeking casual sex, Carr said.

"It's way easier than connecting with someone in a bar," he said. "That high efficiency may be contributing to greater levels of anonymous sex," he said.

Safe sex education and public health interventions must go to the internet as well, he said. "We need to be taking a look at how we can use internet and social media sites to connect with people in that generation."

In all, there were 368 new HIV cases reported in 2009, compared with 326 in 2008.