Swedish study suggests Chlamydia the most common sexually transmitted infection might cause infertility in men as well as long-term health problems for women.
Pregnancy likelihood after fertility treatment may be cut by a third if the man is infected by chlamydia.
So far reasons for the infertility in men remain unknown, although it is thought that sperm motility is a possible factor being studied by the research team.
Although men can experience sharp burning and itching in their genitals, most evidence of infertility has so far been connected to women, because of the danger of their developing pelvic inflammatory diseases that can damage the fallopian tubes.
Chlamydia is diagnosed in 35,500 men and 45,500 women in England and Wales each year, doubling the figures from 1997.
Chlamydia is currently one of the most common sexually transmitted diseases - about 4 million cases of chlamydia occur in the USA each year. However, about half of all men and three-quarters of all women who have chlamydia have no symptoms and don't know that they have the disease. The disease is transmitted by the Chlamydia trachomatis bacterium. It can be serious but it is easily cured if detected in time.
Almost half of all women who get chlamydia and aren't treated by a doctor will get pelvic inflammatory disease (PID), a generic term for infection of the uterus, fallopian tubes, and/or ovaries. PID can cause scarring inside the reproductive organs, which can later cause serious complications, including chronic pelvic pain, difficulty becoming pregnant, ectopic (tubal) pregnancy, and other dangerous complications of pregnancy. Chlamydia causes 250,000 to 500,000 cases of PID every year in the U.S.