STD Quarterly: Research underscores need for increased STD screening

Testing only symptomatic patients may miss undetected infection

What is your facility’s policy on testing for sexually transmitted diseases (STDs)? If it is limited to symptomatic patients, significant amounts of undetected infection may be passing under your radar.

Just-published research conducted in Baltimore shows that between 1997 and 1998, undiagnosed gonorrhea and chlamydia infections occurred in a combined one in 12 (7.9%) of young adults ages 18-35 in the city.1 The number of undetected gonorrhea and chlamydia infections in the city may be as high as the number of cases that are diagnosed and treated, say researchers.

In response to the findings, the Baltimore City Health Department has mailed letters to more than 1,000 doctors and clinics urging them to screen all sexually active patients younger than 30 for gonorrhea and chlamydia, regardless of whether the patients report or exhibit any symptoms of infection.

"Clearly, as the most recent article in the Journal of the American Medical Association [JAMA] that actually used Baltimore as a site showed, there is a very significant amount of disease burden of asymptomatic chlamydia and gonorrhea in the community," says Peter Beilenson, MD, Baltimore City health commissioner. "The best way to pick that up is urine screening, and that’s why we are doing it."

Taking aim at STDs

The new research underscores what public health officials say is the "hidden epidemic" of STD infection in the United States.2

Look at the latest statistics presented at the March 2002 National STD Prevention Conference in San Diego. While the overall national gonorrhea rate remained stable, 13 of 20 cities with the highest rates in 1999 had even higher rates in 2000, according to the Centers for Disease Control and Prevention (CDC).3 In five of the top 20 1999 cities — Kansas City, MO; Buffalo, NY; Jacksonville, FL; Detroit; and Birmingham, AL — the gonorrhea rate rose by more than 20% in 2000. (To see chart, click here.) 

On a national level, the overall rate of gonorrhea appears to have stabilized, following a 9% increase between 1997 and 1999. In 2000, the rate of gonorrhea was 131.6 cases per 100,000 people, compared to 132 cases per 100,000 people in 1999. Prior to that upturn, national gonorrhea rates had declined each year since 1975.

In 2000, 702,093 chlamydial infections were reported to CDC. However, the CDC estimates that 3 million new cases of this largely asymptomatic infection occur in the United States each year.

New CDC figures show that chlamydia positivity among young women is lowest in areas with longstanding screening and treatment programs, but remains high in areas where programs are not as widely available. Since case reports do not provide a complete picture of the burden of disease, researchers look to studies of chlamydia prevalence in various groups, such as the percentage of women testing positive for chlamydia in family planning clinics.

In 2000, the 10 states with the highest level of chlamydia positivity among 15- to 24-year-old women in family planning clinics included Mississippi (15.8%), Rhode Island (11.9%), Louisiana (9.7%), Texas (9.3%), South Carolina (8.6%), Alabama (7.9%), North Carolina (7.5%), California (7.3%), Illinois (7.4%), and Wisconsin (7.2%). (To see map, click here.)

Chlamydia, caused by the bacterium Chlamydia trachomatis, is known as a "silent" disease because three-quarters of infected women and half of infected men have no symptoms. The infection is frequently not diagnosed or treated until complications develop. For women, the consequences are chilling: genital chlamydial infection is the leading cause of preventable infertility and ectopic pregnancy.4

Gonorrhea is caused by Neisseria gonorrhoeae, a bacterium that can grow and multiply easily in mucous membranes of the body. When initially infected, the majority of men have some signs or symptoms, such as a burning sensation when urinating and a yellowish-white discharge from the penis. However, the early symptoms of gonorrhea in women are often mild, and many who are infected have no symptoms of infection. When symptoms are present, they may include a painful or burning sensation when urinating and a vaginal discharge that is yellow or occasionally bloody.

Gonorrhea and chlamydia, when left untreated, cause pelvic inflammatory disease and have been linked to increased transmission of HIV, says Jonathan Zenilman, MD, associate professor of the infectious diseases division at the Baltimore-based Johns Hopkins University School of Medicine. Zenilman served as a co-author of the JAMA paper.

Why is it so important to screen for gonorrhea and chlamydia, regardless of whether the patients report or exhibit any symptoms of infection? Studies of asymptomatic STDs in a variety of settings have found that risk factor analysis is a poor tool in identifying a large proportion of gonorrhea and chlamydial infections, states Zenilman.

What prompted the JAMA research? STD surveillance traditionally has been based on cases reported to health departments, says Zenilman. Previous reports demonstrated that these estimates are biased toward ascertaining symptomatic cases presenting to public clinics, he states. No population-based estimates have been previously performed on a citywide scale, so the study provided researchers the opportunity to perform such an assessment and to estimate the number of cases of undiagnosed asymptomatic infection in the population.

The rise of new noninvasive nucleic acid amplification tests for gonorrhea and chlamydia made the study possible, he observes. The tests are noninvasive and can be performed on urine.

Researchers interviewed 728 young adults from a randomly selected cross section of Baltimore households and tested urine specimens from 579 participants. Analysis of results from urine specimens subjected to the nucleic acid amplification tests and comparisons with clinically diagnosed cases of gonorrhea and chlamydia showed the high percentages of hidden cases.

The high prevalence rate in the general public and the lack of symptoms suggests that screening programs and extending access to care are critical for reducing the prevalence of these infections, say researchers.

Urine-based screens are being done on a regular basis in most of the family planning and STD programs run by the city of Baltimore, Beilenson reports. However, due to the increased cost represented by the new tests, such screens have not yet been implemented across the board, he notes. The urine-based tests run about $15, as compared to about $3 for traditional tests.5

"We’ve gotten an additional $75,000 grant from the CDC, and we’ve rebudgeted some of our existing STD money from the federal government," says Beilenson.

Reluctance to discuss reproductive health matters is a more troublesome barrier to uncovering the hidden epidemic of STDs, say public health officials. Embarrassment among patients and clinicians when discussing sexual health is common, but it is not a good reason for avoiding health risk assessments, states J. Dennis Fortenberry, MD, associate professor of pediatrics and medicine at the Indiana University School of Medicine in Bloomington, in an accompanying editorial to the Baltimore research.6

"Societal willingness to stigmatize sexuality and STDs continues to hide issues that are central aspects of our lives," states Fortenberry in the editorial. "Given the morbidity and costs of STDs, including those due to human immunodeficiency virus infection, these are veils that no longer seem affordable."


1. Turner CF, Rogers SM, Miller HG, et al. Untreated gonococcal and chlamydial infection in a probability sample of adults. JAMA 2002; 287:726-733.

2. Institute of Medicine. The Hidden Epidemic: Confronting Sexually Transmitted Diseases. Washington, DC: National Academy Press; 1996.

3. Centers for Disease Control and Prevention. CDC: Gonorrhea Rates Increased in Two-Thirds of Hardest-Hit U.S. Cities. San Diego; March 5, 2002.

4. Kaiser Family Foundation. Questions & Answers. The Tip of the Iceberg: How Big is the STD Epidemic in the United States? Menlo Park, CA; December 1998.

5. Jones R. STD study. NPR Morning Edition, broadcast Feb. 13, 2002.

6. Fortenberry JD. Unveiling the hidden epidemic of sexually transmitted diseases. JAMA 2002; 287:768-769.