A cluster of new HIV cases in southeast Idaho has led health district officials in the Magic Valley to make plans in case online hookups or other factors ease the disease's path west.

The state has recorded 37 new cases of HIV and AIDS so far this year, 23 percent more than this time last year, said Tom Shanahan, spokesman for the Idaho Department of Health and Welfare. Of those, 13 were in people under 25 years old, and 15 were in southeast Idaho - the health district just east of the South Central Public Health District. The numbers represent only those cases reported to state officials.

Many of the infections come from the usual sources: men having unprotected sex with other men, and drug users sharing needles or syringes. But one growing source is of particular concern to officials. The spike in the southeastern cases seemed largely driven by people who found their partners anonymously using the Internet.

Though the numbers are still small, the spike in activity was enough for SCPHD officials to send a health alert out to local physicians, said Tom Machala, director of communicable disease and prevention.

Most HIV cases still happen in larger areas like Boise, Machala said. But the ability to meet sexual partners online has made it easier for all sexually transmitted diseases to spread across the state, and harder to track how they spread, he said.

"It's very hard to trace people," Machala said, noting the number of Magic Valley residents who regularly travel to Boise or Pocatello.

Many who use the sites don't want to be identified, hiding behind vague usernames, he said. And officials have identified HIV-positive users of some sites who pose as HIV-negative.

That's assuming officials can access the sites. Web use policies at state agencies can sometimes block the sites, Machala said, making it impossible for health officials to send out warnings about STDs.

State officials have been aware for several years that such Web sites existed, said state epidemiologist Dr. Christine Hahn. But she acknowledged that the sites were probably used earlier than officials knew.

The concern, she said, isn't that sparse HIV numbers are increasing, but that more people in their 20s seem to be using the sites, spreading HIV and other STDs through unsafe sex. That age group is too young to remember when AIDS was far deadlier in the 1980s and early '90s and don't realize HIV is still a problem, she said.

"I think it seems far away and long ago," Hahn said. "They don't realize that this is a real risk now."

Exacerbating the problem is the fact that many young adults say they've learned about the need to use protection or abstain from sex, but don't believe that STDs actually exist in their area, Hahn said.

No one from south-central Idaho who had contact with the HIV-positive people in southeast Idaho has tested positive yet, Machala said. The district has not been able to reach every person.

HIV/AIDS cases are but a fraction of the STDs reported by Idaho doctors every year. Out of 2,008 STDs diagnosed between April and June of this year, for example, only 12 were HIV/AIDS. Only 1,000 STDs were reported for the same time period in 2007.

By the numbers: HIV/AIDS cases so far for 2008, by health district: District 1 (Hayden): 1 District 2 (Lewiston): 2 District 3 (Caldwell): 5 District 4 (Boise): 5 District 5 (Twin Falls): 4 District 6 (Pocatello): 15 District 7 (Idaho Falls): 5 One-third of cases were AIDS.