POC test for chlamydia, gonorrhea as good as lab-based assays

NEW YORK (Reuters Health) - A new 30-minute point-of-care (POC) test using self-collected vaginal swabs works as well as lab-based molecular diagnostic tests for detecting chlamydia and gonorrhea, new findings show.

The test has the potential to improve screening for and treatment of these sexually transmitted infections (STIs), which have been on the rise in the U.S. since 2013, Dr. Barbara Van Der Pol of the University of Alabama at Birmingham School of Medicine told Reuters Health by phone.

“The bottom line is that chlamydia and gonorrhea are still the most frequently reported notifiable diseases in the U.S., and it costs us in the 5-to-6-billion-dollar range to manage the consequences of untreated infections,” she said. “Unfortunately about 70% of women who are infected don’t have any symptoms, so they don’t know they need to be tested.

Centers for Disease Control and Prevention guidelines recommend annual chlamydia and gonorrhea screening for women younger than 25, men who have sex with men and people using HIV preexposure prophylaxis, Dr. Van Der Pol and her team note in JAMA Network Open. However, they add, “at least one-half of women in the eligible age range who have an encounter with the health care system are not screened per CDC guidelines.”

Patients who get tested for chlamydia or gonorrhea often must wait several days for a result, which allows for further spread of the infection and the development of pelvic inflammatory disease, the authors add. For this reason, many clinics and hospitals will treat patients based on epidemiologic prediction.

In the new study, Dr. Van Der Pol and her team analyzed swab samples from 1,523 women (53.6% with symptoms) and urine samples from 922 men (33.4% symptomatic) who presented to 11 clinics in nine cities across the U.S. They compared results from three commercial nucleic acid amplification tests (NAATs) with the binx io chlamydia/gonorrhea assay from binx health, which funded study.

Among women, there were 129 chlamydia infections (8.5%) and 45 cases of gonorrhea (3.0%). The POC test correctly identified 124 chlamydia cases (96.1%) and all 45 gonorrhea infections (100%).

The authors estimated specificity at 99.1% for chlamydia and 99.9% for gonorrhea. Positive predictive values were 90.5% for chlamydia and 95.7% for gonorrhea, and negative predictive values were 99.6% and 100%, respectively.

There were 120 chlamydia infections (13.0%) and 74 gonococcal infections (8.0%) among men. Sensitivity was 92.5% for chlamydia and 97.3% for chlamydia, while specificity was 99.3% and 100%, respectively. Positive predictive values were 94.9% for chlamydia and 100% for gonorrhea, while negative predictive values were 98.9% and 99.8%, respectively.

The sensitivity of the POC test in males was lower than for the other lab-based tests, which had sensitivities of at least 99%.

Because the test only takes 30 minutes, Dr. Van Der Pol noted, a patient could collect a swab upon arrival at her doctor’s office, with results available in time for the clinician to prescribe treatment at the same visit.

“We need to do a better job of getting testing and screening out into primary care,” she added. “We can’t rely on STD specialty services because that’s not going to help us get out of this problem.”

Dr. Emma Harding-Esch, an associate professor at the London School of Hygiene and Tropical Medicine in the UK, who studies novel diagnostic techniques for STIs, told Reuters Health by email, “This 30-minute test has the potential to transform patient care, in addition to having a wider public-health impact.”

Because it performs as well as traditional lab tests for female vaginal swabs, she added, “this means the test could replace traditional lab testing, which would be especially beneficial for patients who risk not returning for test results, or for treatment if they test positive. This could further help in the fight against antimicrobial resistance, by reducing over-prescription of antibiotics to patients who test negative for CT/NG using the POCT, but would otherwise have been treated based on symptoms.”

“While the performance of the test for female vaginal swabs is excellent, the data for male urine indicate further work is needed,” added Dr. Harding-Esch, who was not involved in the study. “In addition, test performance is not the only factor to take into account when deciding to use a new diagnostic test: other considerations include feasibility of clinical pathway adaptation, stakeholder perceptions, and of course, cost.”

Dr. Van Der Pol and several coauthors report financial ties to binx health.

SOURCE: JAMA Network Open, online May 14, 2020.