One in 10 high school students in northern Japan has chlamydia, a curable sexually transmitted disease, a study showed Thursday.

The study tested 3,190 Japanese students aged 16 to 18 at more than a dozen high schools, and found that 11.4 percent of them were infected, said Dr. Hirohisa Imai at Asahikawa Medical College in Hokkaido.

Most of the students who tested positive weren't aware they had chlamydia, and those who knew they were infected weren't getting treatment, he said.

Chlamydia can cause infertility and is often called the silent infection because it can have no symptoms. Infection rates in the United States and Europe are generally estimated at 1 percent to 2 percent of the population.

Imai, who was to announce his findings at a conference this week, said his study was the first conducted on a large scale in Japan. Previous government statistics were drawn from patients who had received treatment at hospitals and clinics, he said.

"This shows that infections in Japan are the worst among the world's advanced countries," Imai said.

He blamed Japan's inadequate sex education in schools, and said the numbers suggest Japanese teens might be extremely vulnerable to infections of other sexually transmitted diseases, including HIV/AIDS. Chlamydia can be prevented by using a condom when having sex. It is caused by a bacteria, and can be treated with antibiotics.

Among girls tested, the average infection rate was 13.9 percent -- higher than the rate for boys, at 7.3 percent -- Imai said.

Imai led a team of health care workers who visited 13 high schools from October to December 2003.