One in 25 young Americans carry the organism that causes

the disease, and the rate of infection is particularly high among

young blacks and in the southern United States, researchers said.

The findings are based on the most comprehensive study of the

prevalence of chlamydia among Americans to date, and support

previous research that points to sharp regional differences in the

rate of infection.

In fact, the authors said the data may explain why black women

are at greater risk for chlamydia-related complications, such as

ectopic pregnancies, and childbirth-related death.

The infection was six times greater in young black adults than

in young whites, according to the study of more than 12,000

adults with an average age of 22.

Almost 14 percent of young black women and more than 11

percent of black men of comparable ages carried the bug.

The rates of infection were also higher among Native Americans

and Latinos than whites, according to the study in the Journal of

the American Medical Association.

"The marked differences in these sexually transmitted infections

across racial and ethnic groups are disturbing," said lead author

William Miller, assistant professor of medicine at the University

of North Carolina at Chapel Hill.

People infected with the bacteria that causes chlamydia often

exhibit no symptoms, but the disease can have serious conse-

quences for a woman's reproductive health and can result in

pelvic inflammatory disease, ectopic pregnancy and infertility

if untreated.

Public health guidelines typically call for young women to be

tested for the disease during clinical visits, but the results of

the study suggest that approach is "inadequate," Miller said.

"Asymptomatic young adult men clearly account for a large

reservoir of infection in the general population, but screening