Timely, accurate diagnosis of group A streptococci (GAS) pharyngitis prevents acute rheumatic fever and limits antibiotic overuse. The illumigene group A Streptococcus assay (Meridian Bioscience, Cincinnati, OH) is a molecular test for GAS pharyngitis with high sensitivity and specificity. We sought to determine whether the illumigene test is more likely than throat culture to be positive in patients without pharyngeal symptoms and explore the limits of detection of the test.
Patients 3–17 years of age were eligible if they had no history of pharyngitis or use of antibiotics within the previous 2 weeks; there were no upper respiratory infection symptoms, sore throat or fever and no signs of infection. Culture and illumigene were performed on duplicate throat swabs. Excess lysate from a subset of illumigene tests was evaluated by real-time polymerase chain reaction. Institutional Review Board approval was obtained.
We enrolled 385 patients from February 2016 to October 2017; mean age was 10 yr; 51% were male. Most visits were for health supervision (69%). Significantly more illumigene tests (78/385, 20.3%) than throat cultures (48/385, 12.5%) were positive (χ2; P =0.0035). Illumigene was “indeterminate” for 3 patients, leaving 382 pairs of swabs for analysis. Results were discordant for 32 of 382 pairs (8.4%); 31 of 32 (97%) were illumigene-positive/culture-negative (McNemar test; P < 0.000001). Real-time polymerase chain reaction was negative in 4 of 13 (31%) tested illumigene-positive lysates; the paired culture had been negative in all four. The limit of detection for the illumigene test was 55 colony forming units/mL.
The illumigene test is significantly more likely than throat culture to yield positive results in patients without GAS pharyngitis. Failure to appropriately select patients for testing may negatively impact antimicrobial stewardship efforts without benefit to patients.
From the *Division of Academic General Pediatrics, Ann & Robert H. Lurie Children’s Hospital of Chicago
†Northwestern University Feinberg School of Medicine
‡Pediatric Residency Training Program
§Special Infectious Diseases Laboratory, Department of Pathology and Laboratory Medicine
¶Division of Infectious Diseases, Ann & Robert H. Lurie Children’s Hospital of Chicago, Chicago, Illinois.
Accepted for publication January 21, 2019.
This work was supported by funds within the Division of Academic General Pediatrics and the Division of Infectious Diseases, Ann & Robert H. Lurie Children’s Hospital of Chicago, Chicago, Illinois.
R.R.T. and S.T.S. received support from Meridian Bioscience Corporation (Cincinnati, OH), the developer of the illumigene test, for a study unrelated to this article. Meridian Bioscience Corporation provided 100 illumigene tests for this study. No one involved in this project received payment to produce it. The other authors have no conflicts of interest to disclose.
R.R.T. designed this study, enrolled patients, supervised all aspects of the study, performed the data analysis and drafted and revised the article. E.J.R. designed this study, enrolled patients and contributed to the article. J.L.R. directed the Special Infectious Diseases Laboratory, performed laboratory studies, managed the data and contributed to the article. R.L.D. enrolled patients, collected throat swabs and reviewed the article. C.L.O. enrolled patients, collected throat swabs and reviewed the article. C.L.L. performed laboratory studies, managed the data and reviewed the article. S.T.S. contributed to study design, data interpretation and article preparation.
Dr. Ranniger is currently at the Crawford County Memorial Hospital, Denison, Iowa.
Presented in part at the 2018 Pediatric Academic Societies’ Annual Meeting; May 7, 2018; Toronto, Ontario, Canada.
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Address for correspondence: Robert R. Tanz, MD, Division of Academic General Pediatrics, Department of Pediatrics, Ann & Robert H. Lurie Children’s Hospital of Chicago, 225 E. Chicago Ave., Box 16, Chicago, IL 60611. E-mail: firstname.lastname@example.org.