Timely treatment of GAS pharyngitis prevents ARF. Accurate diagnosis limits antibiotic overuse. Throat culture (TC), the diagnostic standard, takes 18-48 hours. Rapid antigen tests (RTs) have inadequate sensitivity (Sens) to use alone. The Illumigene® Group A Streptococcus assay (Meridian Bioscience) uses loop-mediated isothermal amplification (LAMP) of speB to identify GAS in ≤1 hour. Both Sens and specificity (Spec) were ≥95% in 3 hospital studies.
We enrolled children (3-18 yrs) at 5 community sites: 2 intervention sites (Ofc) used LAMP: Site1- LAMP alone; Site2- LAMP for back-up of negative RTs. Duplicate throat swabs went to our lab for TC and LAMP. Sens, Spec, PPV, NPV of Ofc and lab LAMP were calculated using lab TC or lab LAMP as reference. 3 control (Ctrl) sites used RT with TC back-up. Ofc and Ctrl time to diagnosis (TTD) and time to treatment (TRx) were measured.
Site1 enrolled 366 patients, Site2 31, Ctrl sites 232. 19.4% of patients had positive LAMP or TC. Using lab TC as reference, lab LAMP had Sens .97, Spec .95, PPV .88, NPV .99; and Ofc LAMP had Sens .75, Spec .88, PPV .71, NPV .90. Using lab LAMP as reference, Ofc LAMP had Sens .68, Spec .88, PPV .73, NPV .86. TTD and TRx for Ofc LAMP were significantly shorter than for Ctrl TC (each p<.0001).
LAMP results were available and used more rapidly than TC results. Compared to lab TC and LAMP, Ofc LAMP did not perform as well as in published hospital studies.