STD Quarterly
How to stem chlamydia’s silent spread? Look at nucleic acid amplification tests
Developments in nucleic acid amplification tests now give health care providers unprecedented opportunity to attack chlamydial infections, says Julius Schachter, PhD, professor of laboratory medicine at the University of California at San Francisco (UCSF) and director of the World Health Organization International Reference Center for Chlamydia.
"The issue is now that physicians have access to broad-base screening," says Schachter. "We have the HEDIS [Health Plan Employer Data and Information Set] guidelines that say that all young sexually active women should be routinely tested for chlamydia, and this is a way to do it." (The National Committee for Quality Assurance in Washington, DC, a nationwide organization charged with measuring and reporting on managed care quality, began assessing the percentage of sexually active women ages 15 to 25 screened for chlamydia in its HEDIS 2000 information set. See Contraceptive Technology Update, February 2000, for more information.)
Chlamydia is the most frequently reported infectious disease in the United States, according to the National Center for HIV, STD, and TB Prevention in the Centers for Disease Control and Prevention (CDC) in Atlanta.1
Caused by the bacterium Chlamydia trachomatis, chlamydia is a chief contributor to what has been termed "the hidden epidemic" of STD infection in the United States. Since 75% of women and 50% of men have no symptoms, most people infected with chlamydia are not aware of their infections and might not seek health care, according to the CDC.
Though 526,653 cases of chlamydia were reported in 1997, an estimated 3 million cases occur annually, according to the CDC.1 Severe underreporting is largely a result of substantial numbers of asymptomatic persons whose infections are not identified because screening is not available, the agency states.
STD impacts teens
Chlamydia is widespread among adolescents, particularly among teen-age girls, CDC estimates reflect. One of every 10 adolescent girls tested for chlamydia is infected with the disease, states the CDC. Based on reports to CDC provided by states that collect age-specific data, teen-age girls have the highest rates of chlamydial infection. In these states, 15- to 19-year-old girls represent 46% of infections, and 20- to 24-year-old women represent another 33%.1 These high percentages are consistent with high rates of other STDs among teen-agers.
If chlamydia is left unchecked, up to 40% of women with the STD will develop pelvic inflammatory disease (PID), according to the CDC. Of those with PID, 20% will become infertile, 18% will experience debilitating, chronic pelvic pain, and 9% will have a tubal pregnancy, the leading cause of first-trimester, pregnancy-related deaths in U.S. women.1
Chlamydia might also result in adverse outcomes of pregnancy, including neonatal conjunctivitis and pneumonia. Research has shown that women infected with chlamydia have a 3-5 fold increased risk of acquiring HIV, if exposed.2
Chlamydia also is common among young men, who are seldom offered screening. Untreated chlamydia in men typically causes urethral infection, but might also result in complications such as swollen and tender testicles, according to the CDC.
"A quarter of men who acquire the infection do not get symptoms; and over time, that means that the majority of prevalent infections are asymptomatic," notes Schachter.
Four nucleic acid amplification tests are now available in the United States, says Schachter. These include:
• Amplicor polymerase chain reaction (PCR) test (Roche Diagnostics Corp., Indianapolis);
• ligase chain reaction (LCR) LCx Chlamydia trachomatis Assay (Abbott Laboratories, Abbott Park, IL);
• transcription-mediated amplification (TMA) TMA- Amplified Chlamydia trachomatis Assay (Gen-Probe, San Diego);
• BDProbeTec strand displacement amplification test (Becton, Dickinson, and Co., Franklin Lakes, NJ).
Because nucleic acid amplification is exquisitely sensitive and highly specific, it offers the opportunity to use noninvasive sampling, such as urine testing, to screen for infection in asymptomatic persons.3 It also can be used to detect gonorrhea, another prevalent STD.
"Suddenly, we are in the best position we have ever been for diagnosing the infection," says Schachter.
A 1999 cost-effectiveness decision analysis compared pelvic examination with cervical screening, the current national standard, with a model of urine screening with ligase chain reaction testing for Chlamydia trachomatis and Neisseria gonorrhoeae. The analysis, published by Schachter and colleagues at UCSF, showed that the nucleic acid amplification test is the most cost-effective strategy to detect chlamydial and gonococcal genital infection in asymptomatic sexually active adolescent females.4 Due to its ease of implementation, such testing is the most likely to prevent the greatest number of cases of PID, the authors conclude.
Another study, which examined use of such tests in family-planning clinics, found that nucleic acid amplification chlamydia tests are cost-effective if prevalence is greater than 3%.5
Move tests beyond walls
The new tests offer promise in expanding venues for chlamydia testing outside STD clinic walls. Researchers are evaluating use of nucleic acid amplification tests in such areas as juvenile detention centers, emergency departments, high schools, general medicine clinics, drug rehab centers, homeless clinics, and military induction centers.6
Danish researchers recently compared the efficacy of a screening program for urogenital chlamydial infections based on home sampling with that of a screening program based on conventional swab sampling performed at a physician’s office.7 The study examined adolescent females’ use of in-home samples in comparison with physician office-based screening.
"We have shown that when a home-sampling screening program is offered to the population, there is a lower risk of PID when compared with use of the current test facilities," says Lars Ostergaard, MD, PhD, DMSc, Department of Infectious Diseases, Aarhus (Denmark) University Hospital. "We also showed that the use of home-sampling screening could reduce the prevalence in the population."
The challenges of home-sampling strategies are to make sure that as many people as possible use the screening and that education on sexual health also is provided, says Ostergaard, who examined in-home screening among women ages 18-25 in a previous study.8
"Although home sampling has proven to be an effective strategy, I do not think it can stand alone," he notes. "Education is still needed, but the two things can easily be combined."
Researchers are looking at the benefits of using vaginal swabs in the nucleic acid amplification tests. When used for chlamydia testing, vaginal swabs perform comparably to other specimen types, and patients can be trained to collect their own samples.9 Vaginal swabs also require less laboratory processing.
Vaginal swabs are not approved by the Food and Drug Administration for any of the nucleic acid amplification tests, notes Schachter. In research settings, vaginal swabs perform comparably to other specimen types.
The ultimate goal of the screening studies is to prevent transmission, reduce prevalence, and prevent the costly and serious complications of chlamydia, says Schachter.
"It has been shown that introduction of screening in family planning clinics prevents PID,"10 says Schachter. "Screening and treatment of pregnant women also prevents newborns from being infected.11 Here are two obvious target populations, and the hope is that better tests will produce more effective prevention."
References
1. Centers for Disease Control and Prevention. Some Facts About Chlamydia. August 7, 2000. Web: www.cdc.gov/nchstp/dstd/chlamydia_facts.htm.
2. Wasserheit JN. Epidemiological synergy. Interrelation-ships between human immunodeficiency virus infection and other sexually transmitted diseases. Sex Transm Dis 1992; 19:61-77.
3. Hammerschlag MR. Is urine testing for sexually transmitted diseases as accurate as swabs? Infect Med 2000; 16:574-578, 581.
4. Shafer MA, Pantell RH, Schachter J. Is the routine pelvic examination needed with the advent of urine-based screening for sexually transmitted diseases? Arch Pediatr Adolesc Med 1999; 153:119-125.
5. Howell MR, Quinn TC, Brathwaite W, et al. Screening women for Chlamydia trachomatis in family planning clinics. Sex Transm Dis 1998; 25:108-117.
6. Martin DH. The diagnosis and treatment of STDs in non-clinic based settings. Program and abstracts of the 38th Annual Meeting of the Infectious Diseases Society of America; Sept. 7-10, 2000; New Orleans, LA. Abstract S58.
7. Ostergaard L, Andersen B, Moller JK, et al. Home sampling versus conventional swab sampling for screening of chlamydia trachomatis in women: a cluster-randomized 1-year follow-up study. Clin Infect Dis 2000; 31:951-957.
8. Ostergaard L, Moller JK, Andersen B, et al. Diagnosis of urogenital Chlamydia trachomatis infection in women based on mailed samples obtained at home: Multipractice comparative study. BMJ 1996; 313:1,186-1,189.
9. Schachter J. New techniques and specimen acquisition for population-based screening and diagnosis of STDs: advantages and concerns. Program and abstracts of the 38th Annual Meeting of the Infectious Diseases Society of America; Sept. 7-10, 2000; New Orleans, LA. Abstract S56.
10. Scholes D, Stergachis A, Heidrich FE, et al. Prevention of pelvic inflammatory disease by screening for cervical chlamydial infection. N Engl J Med 1996; 334:1,362-1,366.
11. Schachter J, Grossman M, Sweet RL, et al. Prospective study of perinatal transmission of Chlamydia trachomatis. JAMA 1986; 255:3,374-3,377.
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