The number of sexually-transmitted diseases in Minnesota rose to an all-time high in 2011, with most cases occurring among young adults, a development that prompted state health officials to urge preventive measures and regular testing for people who are sexually active.

Chlamydia was the most common reported disease, with 16,898 cases statewide and about one in three cases occurring in rural Minnesota.

Gonorrhea remained second, with 2,283 cases. Nearly two-thirds of cases occurred among people aged 15 to 24 and cases were concentrated in the Twin Cities metropolitan area.

Syphilis ranked third, with 366 cases. The state Health Department said new infections were concentrated in the Twin Cities and among males, particularly among men who reported having sex with men.

Untreated chlamydia and gonorrhea can lead to infertility in men and women, and can be passed from an infected woman to her newborn child, causing premature delivery, infant pneumonia and blindness, the state Health Department noted.

Overall, cases rose more than 8 percent from 2010.

"STDs remain a serious health threat if not detected and treated early,'' said Dr. Edward Ehlinger, the state health commissioner.

African-American infection rates for gonorrhea and chlamydia were much higher than for white Minnesotans. Rates for American Indians and Latinos were somewhat higher.

Health officials urged anyone who is sexually active to be tested annually, even if they don't show symptoms.