If not detected and treated, chlamydia, which usually has no symptoms, can cause pelvic inflammatory disease, ectopic pregnancy and infertility.
The prevalence of chlamydial infection was higher than expected, especially among men. The infection was present in all races but six times greater in young black adults than in young whites, researchers found. Almost 14 percent of young black women and more than 11 percent of black men of comparable ages carried the bug.
Analysis of urine specimens of 12,548 study participants from across the country showed U.S. Asian men to have the lowest infection rates, scientists said. The highest infection rate occurred in the South (5.4 percent); the lowest was in the Northeast (2.4 percent).
Overall, the prevalence of gonorrhea was far lower -- 0.43 percent, the scientists discovered. Among black men and women, however, the prevalence was 2.13 percent.
"Asymptomatic young adult men clearly account for a large reservoir of infection in the general population, but screening recommendations have largely excluded men," said lead author Dr. William C. Miller, assistant professor of medicine and epidemiology.
"The marked differences in these sexually transmitted infections across racial and ethnic groups are disturbing," Miler said. "Our results provide compelling evidence that nationwide disparities in chlamydial and gonococcal infections are real rather than the result of biased estimates."
The differences may be partially responsible for considerable variations in reproductive health among whites, blacks and other racial and ethnic groups, he said. For example, black women have a 33 percent higher incidence of ectopic pregnancy compared with whites, and in many areas, including New York City, black women and infants face a greater risk of childbirth-related death, he said.
A report on the research, based on data collected during the third wave of Add Health, appears in the May 12 issue of the Journal of the American Medical Association. The new work is the most comprehensive assessment ever of the prevalence of chlamydial and gonococcal infections in the general population of young U.S. adults.
Besides Miller, UNC schools of medicine and public health authors are Drs. Carol A. Ford, associate professor of pediatrics; John L. Schmitz, assistant professor of pathology and laboratory medicine; Marcia M. Hobbs, research assistant professor of medicine; Myron S. Cohen, J. Herbert Bate professor of medicine and chief of the infectious diseases division; Kathleen Mullan Harris, professor of sociology; and J. Richard Udry, professor of maternal and child health and of sociology.
Drs. Martina Morris and Mark S. Handcock, both sociologists and statisticians at the University of Washington at Seattle, also participated in the study.
"We found the prevalence of untreated asymptomatic chlamydial infection to be high in young adults in the United States," Miller and colleagues wrote. "The high prevalence of chlamydial infection in both men and women suggests that current screening approaches that focus primarily on clinic-based testing of young women are inadequate. The reduction of disparities in the prevalence of both chlamydial and gonococcal infections across racial and ethnic groups must also be a priority."
Other findings were that:
- Men and women of the same race did not differ markedly in infections.
- Native Americans and Latinos also carried the Chlamydia trachomatis bacterium at high rates.
- By comparison with chlamydia, gonococcal infections, also known as gonorrhea, were low as expected because that illness usually causes painful or unsightly symptoms for which most patients seek treatment.
Support for the infection study came from the UNC Sexually Transmitted Diseases Cooperative Research Center, the National Institutes of Health and the Robert Wood Johnson Foundation.
The National Institute of Child Health and Human Development and 17 other agencies have supported Add Health, a program project designed by Udry, Harris and Dr. Peter S. Bearman, now of Columbia University. It has carefully followed close to 20,000 U.S. adolescents into adulthood to uncover behaviors that promote or damage young people's health such as smoking, drug use and sexual activity and attitudes