Research eyes rapid testing of chlamydia
You have just examined a young woman who reports she has had recent multiple sexual partners and says she has used irregular protection against sexually transmitted disease (STD). You order lab tests, including a screen for chlamydia. When positive results return the next day, will she come back for treatment?
There is a good chance a treatment opportunity may be missed, because as many as one-fourth of patients diagnosed with chlamydia never return for care.1 This presents a challenge for clinicians, as chlamydia is the most frequently reported bacterial sexually transmitted infection in the United States, according to the Atlanta-based Centers for Disease Control and Prevention (CDC).2 In 2002, 834,555 chlamydial infections were reported to CDC from 50 states and the District of Columbia.2 On a global scale, chlamydia is even more prevalent. In 1999, about 92 million new cases of the illness were recorded, according to the Geneva-based World Health Organization (WHO).3
An international team of scientists is moving forward with research on a new dipstick test that is designed to give results in fewer than 25 minutes and cost as little as 70 cents.3 Funding for the Firstburst test comes from the Wellcome Trust, a London-based biomedical research charity, the WHO, and the federal National Institutes of Health. The Wellcome Trust is adding further funding to help set up a company to distribute the technology, initially for use in Africa and Asia.
"It is important to have a quick, simple-to-use test for chlamydia because seven out of 10 women who contract the disease have no idea they have been infected," says Helen Lee, PhD, a scientist in the University of Cambridge’s Department of Hematology and head of the Firstburst research team. "But once it has been diagnosed, it is easily treated with a one-off pill."
It is vital that the test is instant and not expensive, especially in developing countries where clinical care is not easily accessed and limited dollars preclude expensive diagnostics, says Lee. The Firstburst test is designed to work with noninvasive samples such as self-collected vaginal swabs or urine.
Rapid test may be key
No data have yet been published on the First-burst test, and its initial distribution is planned for foreign countries. However, if such a test were to undergo federal Food and Drug Administration review and approval, it definitely could be of use in U.S. clinics, says Julius Schachter, PhD, professor of laboratory medicine at the University of California San Francisco. While turnaround time for results from currently available nucleic acid amplification tests is shorter than with culture (most performed in four to five hours with results available within 24 hours), treatment opportunities still can be missed, he notes.
"A subset of women who test positive with nucleic acid amplification tests don’t get treated. Some of them never come back to the clinic, and about a quarter of them take a month or so to get treated," Schachter reports. "In that month, some of them develop pelvic inflammatory disease [PID], and some of them transmit the infection."
There is a need and a potential use for rapid tests in the United States, says Schachter. Rapid detection, paired with the single-dose therapy of azithromycin, would be an effective strategy in attacking the infection, he notes.
Chlamydia is known as a "silent" disease because about 75% of infected women and about half of infected men have no symptoms; if symptoms do occur, they usually appear within one to three weeks after exposure.2 Women may present with an abnormal vaginal discharge or report a burning sensation when urinating; men with signs or symptoms might have a penile discharge or notice a burning sensation when urinating.2
Untreated chlamydial infection in women can spread into the uterus or fallopian tubes and cause PID, which leads to permanent damage to the fallopian tubes, uterus, and surrounding tissues.2 Such damage can lead to chronic pelvic pain, infertility, and potentially fatal ectopic pregnancy.2
Check the specs
Look to sensitivity and specificity ratings when it comes to determining a test’s ability to detect infection. Sensitivity pertains to the percentage of patients with disease who test positive. It reflects the test’s ability to "rule in" or confirm a diagnosis. Specificity is the percentage of patients without disease who test negative. It gauges a test’s ability to "rule out" a diagnosis.
Screening tests for detection of chlamydia include those processed in laboratories and those designed to be used at the point of care. Point of care tests can yield results at the time of the initial patient visit, but most available lab-processed tests offer greater sensitivity. In clinics where a high proportion of patients do not return for treatment after positive test results, however, less-sensitive rapid tests could lead to the treatment of more patients and be more cost-effective.4
Sensitivity for such tests is 52-85% for endocervical swabs and 65-85% for male urethral swabs, with specificities of approximately 95%.5,6 Use of such tests may not be indicated in low-prevalence populations or for asymptomatic individuals due to their lower predictive value.7
Research may yet yield a fast, sensitive test, says Schachter.
"If the test were specific enough, if it didn’t give false positives, you could use it in a triage approach: Give people that test in the clinic, and if they are positive, treat them," he says. "If they are not and you are worried, give a more sensitive test like a nucleic acid amplification test."
References
1. Hook EW 3rd, Spitters C, Reichart CA, et al. Use of cell culture and a rapid diagnostic assay for Chlamydia trachomatis screening. JAMA 1994; 272:867-870.
2. Centers for Disease Control and Prevention. Chlamydia. December 2003. Accessed at: www.cdc.gov/std/Chlamydia/STDFact-Chlamydia.htm.
3. Reaney P. New rapid test developed to detect chlamydia. Dec. 16, 2003. Accessed at: www.reuters.com/newsArticle.jhtml?type=topNews&storyID=4004743.
4. Gift TL, Pate MS, Hook EW 3rd, et al. The rapid test paradox: When fewer cases detected lead to more cases treated: A decision analysis of tests for Chlamydia trachomatis. Sex Transm Dis 1999; 26:232-240.
5. Black CM. Current methods of laboratory diagnosis of Chlamydia trachomatis infections. Clin Microbiol Rev 1997; 10:160-184.
6. Thomas BJ, MacLeod EJ, Taylor-Robinson D. Evaluation of sensitivity of 10 diagnostic assays for Chlamydia trachomatis by use of a simple laboratory procedure. J Clin Pathol 1993; 46:912-914.
7. STD Control Branch, California Department of Health Services. Evaluation of Diagnostic Tests for Detection of Genitourinary Chlamydia Infections. San Francisco; March 2001.
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