For the first time in 14 years, the number of new infections from sexually transmitted diseases in Minnesota has declined.

The Minnesota Department of Health said Tuesday that new cases of chlamydia, gonorrhea and syphilis dropped by 5 percent in 2009, a sudden reversal of a trend that has worried public health leaders for years.

Health officials said they could not explain the drop -- or predict whether it's a turning point or a one-year blip. "But we are encouraged by this apparent decrease," said Allison LaPointe, surveillance coordinator for the Minnesota Department of Health.

The decline also represented a puzzling contrast to the sudden 13 percent increase in new HIV cases that the Health Department reported in January. That was the biggest increase in 17 years.

By far the largest decrease was in new cases of gonorrhea. They declined 24 percent from a year ago to 2,302, continuing a trend that has been evident in Minnesota and nationally for a few years. The decrease in new cases was especially large among blacks -- 39 percent.

Peter Carr, head of the STD section for the Health Department, said that aggressive follow-up of sexual partners, testing and treatment might be making a difference.

Syphilis also declined substantially, with new cases dropping from 168 in 2008 to 117 last year. However, that change hides a more troubling problem that goes hand-in-hand with the increase in HIV; the number of people co-infected with syphilis and HIV increased. The presence of syphilis increases the likelihood of HIV infection by two to five times, and most of the new cases were among gay and bisexual men.

The 'silent' STD

New infections of chlamydia, by far the most widespread STD, remained essentially unchanged, with 14,186 new cases.

Chlamydia is generally a "silent'' disease with few symptoms, but if left untreated it can lead to infertility among women. For that reason, doctors are supposed to offer regular testing to all sexually active young women, but in Minnesota only about 40 percent are screened, health officials said.

Chlamydia has been increasing by 2 to 3 percent annually, and the rate is now twice as high as it was in 1996, LaPointe said.

Though the overall rate was flat, the number of new infections among 15- to 19-year-olds increased.

Health officials said they could not explain why the overall rates have declined, but some credited outreach and education programs. For the last six years the city of Minneapolis has operated an STD screening and education program called Seen on Da' Streets directed at teenagers and young men in neighborhoods with higher rates of infection. Outreach workers have contacted some 11,000 young men in those primarily black communities, and it might be paying off, city health officials said.

"That change in the pattern has to be attributed to something different," said Gretchen Musicant, director of the Department of Health and Family Services for Minneapolis.

Josephine Marcotty • 612-673-7394