A Pilot Study of the Illumigene Group A Streptococcus Assay (Meridian, Cincinnati, OH) to Assist in the Rapid Diagnosis of Invasive Streptococcal Infections

Abstract

Invasive group A streptococcal infections have mortality ranging from 14% to 19%. The Meridian Illumigene group A Streptococcus assay is a loop-mediated isothermal amplification (LAMP) assay. It has been validated for the diagnosis of pharyngitis caused by group A beta-hemolytic streptococci. We hypothesized it would work with other clinical specimens. The Illumigene group A Streptococcus assay has a published sensitivity and specificity of 98.0% and 97.7%, respectively. It takes about an hour to run a single test. The swab ordinarily used for throat culture was dipped in the sample to be tested. The specimens were residual samples that would have been discarded. Samples tested were joint fluid, pleural effusion, and an abscess aspirate. The clinical diagnoses were group A streptococcal septic arthritis, lobar pneumonia, and necrotizing fasciitis. The Illumigene testing was done after culture results were available to preclude any influence on clinical management. The joint and pleural fluid samples were positive, consistent with culture results. The swab from the abscess was negative while the culture was positive. Our conclusions are five. (1) The septic arthritis and empyema patients were placed on broad-spectrum antibiotic coverage for 4 days and 36 hours, respectively. That could have been decreased had results been available earlier. (2) The septic arthritis patient had streptococcal toxic shock. An earlier diagnosis would have been useful in more rapid recognition of that diagnosis. (3) The cell counts from the pleural fluid and joint aspirate samples were: 57530 WBCs/mm3 and 9,400 WBCs/79,800 RBCs/mm3. This suggests the assay works in those environments. (4) The abscess sample was only tested once, several days after collection and additional sample was not available for further studies. (5) A larger study to evaluate the effectiveness of the Illumigene assay on samples other than oropharyngeal samples for the diagnosis of invasive group A streptococcal infections is warranted.