The rate of severe complications associated with chlamydia, the most commonly reported sexually transmitted disease, might be lower than commonly thought.

Infection with chlamydia trachomatis is the most common preventable cause of pelvic inflammatory disease (PID) in young women. PID, in turn, can lead to ectopic pregnancy and infertility.

Some sources have claimed that up to 40 percent of untreated chlamydia will progress to PID, and that 20 percent to 25 percent of women with PID will have an ectopic pregnancy or become infertile. It's been unclear, however, if these numbers apply to all women.

The researchers wanted to estimate the incidence of severe complications from genital chlamydia infection in women. They focused on close to 44,000 women aged 15 to 24 where chlamydia screening is recommended for women aged 15 to 29 who attend family planning clinics, who are pregnant or who frequent youth clinics.

By the time they were 35, only 5.6 percent of women with chlamydia infection had developed PID, while 3.9 percent of all women had PID. The rate was 4 percent in women who had ever tested negative for chlamydia, and 2.9 percent in those who were never tested.

Overall, 2.3 percent of women had an ectopic pregnancy, 2.7 percent of those testing positive for chlamydia, 2 percent of those testing negative and 1.9 percent for those never screened.

Four percent of the entire group and 6.7 percent of those testing positive for chlamydia became infertile. For those testing negative, the rate was 4.7 percent and 3 percent for those who had never been screened.