Sexually Transmitted Infections (STIs): Advances in Testing Technology

Hook III, Edward W. "Ned", MD
Professor of Medicine
Director, Division of Infectious Disease
UAB School of Medicine
Birmingham, AL

Also by this Author 

Sexually Transmitted Infections (STIs) are a significant public health concern in the United States - chlamydia and gonorrhea are the two most commonly reported notifiable diseases in the country.1 Edward (Ned) Hook, M.D., Director, Division of Infectious Diseases, Department of Medicine, University of Alabama at Birmingham, reviews the key trends relating to three common bacterial STIs (chlamydia, gonorrhea, syphilis) and discusses how more widespread screening, facilitated by advances in testing technology, can significantly reduce the burden of these conditions and their associated complications.

Disease Prevalence

“Chlamydia and gonorrhea are very, very common diseases,” says Dr. Hook. “In 2010 over 300,000 cases of gonorrhea, and 1.3 million cases of chlamydia, were reported to the Centers for Disease Control and Prevention (CDC).1 Since reporting is far from complete, the actual number of cases is more like double those reported.” Syphilis is a less common disease, he notes, but it has very important health consequences and can present diagnostic challenges.

Screening Importance

“For chlamydial infections, it’s recommended that every sexually active woman in this country be tested on an annual basis until she’s age 25 or above,” notes Dr. Hook.2 “That recommendation is made irrespective of whether those women are married or not, whether or not they’re involved in a monogamous relationship, or whether they perceive themselves to be at risk or not.” Routine screening for gonorrhea is recommended for sexually active women at risk of infection, especially those below 25 years of age.2

The importance of screening for these infections, explains Dr. Hook, is that typically they are asymptomatic. “If clinicians think they can wait until patients are symptomatic, they're going to be missing infections. If undiagnosed, these can cause complications, particularly in women.” Women may develop Pelvic Inflammatory Disease (PID), which often leads to life-long problems of infertility, increased risk of ectopic pregnancy, and chronic pelvic pain. “In fact,” says Dr. Hook, “PID is the leading preventable cause of infertility on earth today.”

Increasing Screening with Improved Testing

“Unfortunately less than 50% of women for whom screening is recommended actually get it and that’s really most unfortunate,” notes Dr. Hook. ”All too frequently we see women with disease which has gone on to complications that could have been avoided if they’d been screened.”

Dr. Hook believes the availability of improved tests for chlamydia and gonorrhea has significantly lowered some of the barriers to increasing screening rates. “The nucleic acid amplification tests (NAATs) are not only the most sensitive diagnostics for these infections that we’ve ever had, but because of their remarkable sensitivity are quite easy tests for clinicians to perform.”3

“These tests can be obtained on both women and men without requiring a pelvic examination or uncomfortable testing,” explains Dr. Hook. “A simple urine test from patients of either sex or for women, a vaginal swab collected by herself in the privacy of the exam room will work just as well as a specimen collected through a formal pelvic examination. So that advance is a fabulous thing, making testing easier for women and reducing the barriers.”

Dr. Hook sees the need for greater awareness among physicians that a specimen collected following a routine examination can be used for screening these infections and that testing should be part of routine checkups and pregnancy evaluations. The availability of more convenient, less invasive testing has benefits for both clinicians and patients. “I would describe it as a win-win,” says Dr. Hook. “For the clinicians, it helps patient throughput, and it’s more convenient for patients who now don’t have to undergo pelvic examination.”

Test Sensitivity

The NAATs also have the advantage of higher sensitivity compared with traditional tests, observes Dr. Hook. “For chlamydia the old tests would detect only about 60% of infections, while these newer tests have a sensitivity approaching 95%. That means we diagnose 50% more chlamydial infections and that’s a tremendous advance.”

Male Testing

Dr. Hook feels the availability of a less invasive test may also be the solution to increasing the rate of screening among men, who have traditionally been less engaged in regular reproductive health care checkups than women. Male screening is important, he notes, not just to avoid complications, but to reduce the risk of asymptomatic men unknowingly spreading infection to their sexual partners. “This issue of asymptomatic infection carried from one person to another, not out of malice but unknowingly, represents a major public health problem. The average American woman has 4 sexual partners before she’s 20 years of age, and the average male has slightly more. So these are daunting figures.”

Syphilis Testing

While testing for chlamydia and gonorrhea test for the organism, the testing for syphilis entails a serologic test to identify antibodies. The traditional test used for diagnosis of syphilis was either a rapid plasma reagin (RPR) test or a venereal disease research laboratory (VDRL) test but more recently there has been a shift to treponemal enzyme immunoassays (EIAs). “The EIAs are quite convenient for laboratories,” notes Dr. Hook, “and they do a good job. But clinicians need to be aware that patients may remain positive for years after the disease has been successfully treated, since a low level of antibody may remain in the blood” For this reason, the change in titer must be observed in subsequent serological tests. In addition, while the problem of occasional falsely positive RPR or VDRL tests is widely appreciated by clinicians, many are not aware that the EIAs also have occasional false positive tests as well.


Once an infection has been diagnosed effective treatments are available. “They’re easy to take, highly effective, well tolerated and relatively inexpensive,” says Dr. Hook. “Once we’ve made the diagnosis we’ve really overcome the major barrier to improving healthcare for our patients.”

One issue of growing concern regarding treatment and therapeutic options is that the gonorrhea bacteria is becoming increasing resistant to the antibiotics recommended for therapy. “In the last few years we’ve seen treatment for gonorrhea, with drugs like the quinolone antibiotics – ciprofloxacin and levofloxacin - become ineffective because of the development of resistance. Unfortunately, it appears that gonorrhea is now becoming resistant to the only class of drug that is currently recommended for treatment – cephalosporin antiobiotics, like ceftriaxone or cefixime. So this is a topic our healthcare providers will be hearing more about in the not too distant future because it’s a matter of great concern to public health officials.”

A New Approach to Sexual Health

Looking ahead, Dr. Hook supports the need for a new approach to encourage greater awareness of sexual health. “We’re moving away from the approach we’ve had for the last 100 years - scaring people by focusing on all the bad things that can happen to them. This hasn’t worked. So the CDC is taking a new approach, which emphasizes to all patients, men and women, that they have a right to good health, including sexual health. And the way you stay healthy in terms of sexual health is by getting repeated screening.”

“This approach also has important implications for healthcare professionals,” he continues. “With the old model, doctors were concerned that they couldn’t answer all the questions patients had about how long they had been infected or who had given them the infection. The new approach allows for an honest admission that we may not know all the answers. But we do have great therapies. Combined with convenient, sensitive testing, these enable us to achieve our goal for all patients: to keep them healthy and make them healthier.”


  1. Sexually Transmitted Disease Surveillance 2010. U.S. Department Of Health And Human Services. Centers for Disease Control and Prevention. Division of STD Prevention. November 2011
  2. Sexually Transmitted Diseases Treatment Guidelines, 2010. MMWR. 2010. 59 [12]
  3. Laboratory Diagnostic Testing for Chlamydia trachomatis and Neisseria gonorrhoeae.  Expert Consultation Meeting Summary Report. January 13-15, 2009 Atlanta, GA. Association of Public Health Laboratories/Centers for Disease Control and Prevention.

Released on Tuesday, June 26, 2012