The majority of people who have chlamydia aren't aware of any signs or symptoms, even after several months or years with infection. Nonetheless the impact of untreated chlamydia can be serious for women, causing significant damage to the reproductive organs.
Researchers don't know exactly how long it takes for such effects to occur or exactly what proportion of women with untreated chlamydia suffer such consequences. It is probably only a minority of women who have these serious complications.
In men, serious consequences are rare. Occasionally, men can experience epididymitis, which is an inflammation of the coiled tube (epididymis) at the back of the testicle that stores and carries sperm.
Treatment for chlamydia is simple, requiring a short course of antibiotics. However if the infection is left untreated in women it can spread into the uterus or fallopian tubes and cause pelvic inflammatory disease (PID). Pelvic inflammatory disease can result in serious complications, including infertility, ectopic pregnancy and long-term abdominal pain.
Researchers are not sure of what proportion of cases of untreated chlamydia progress to PID and of how long this takes. Now that treatments are available, it would be unethical for researchers to identify women with chlamydia, withhold treatment and simply observe the damage the infection causes.
Research suggests that if treatment is not provided immediately after diagnosis of chlamydia, a small proportion of women (less than 5%) develop PID within a few weeks. It's not known how many more women would have PID if treatment was withheld for a full year. But we do know that around one in seven women who have pelvic inflammatory disease become infertile.
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