LONDON (Reuters) - Chlamydia infection, a known cause of infertility in women, can also reduce a man's chance of fathering a child, Swedish researchers said on Thursday.

"Men should be aware that they can (contract) the infection and they should get tested and treated for it," said Dr. Jan Olofsson of the Scandinavian Fertility Center in Gothenburg.

In a collaborative study with scientists at Sweden's Umea University Hospital of 244 couples treated for infertility, Dr. Olofsson discovered that a quarter of the women and a fifth of the men tested positive for chlamydia antibodies.

"We found that quite a high number of the couples with antibodies had an ongoing infection," Dr. Olofsson added in a telephone interview.

After following the couples for an average 3 years, the researchers found that chlamydia antibody levels were inversely associated to the overall pregnancy rate. Men with the antibodies had a 33% lower rate of fertility than those without them.

"It is quite a high figure," Dr. Olofsson said.

About 92 million new cases of chlamydia were diagnosed in 1999, according to the World Health Organization. But because the infection is often asymptomatic, about 70% of women and 50% of men do not know they have it.

Dr. Olofsson, who reported the findings in the journal Human Reproduction, said it is not known how chlamydia causes male infertility. Researchers believe it may have an impact on sperm but other mechanisms, and infections, could also be involved.

He advised men with fertility problems to be checked for the infection and get treatment if they have it. "I think men should be very worried about this. Men do not go for testing easily," said Dr. Olofsson.

He also suggested routine testing for men and women undergoing fertility treatment. An estimated one in six couples suffers from infertility, and in about half of cases it is due to a male problem.

Hum Reprod 2004;19:1121-1126.

Copyright © 2003 Reuters Limited. All rights reserved. Republication or redistribution of Reuters Limited content, including by framing or similar means, is expressly prohibited without the prior written consent of Reuters Limited. Reuters Limited shall not be liable for any errors or delays in the content, or for any actions taken in reliance thereon.