Comparison of Gen-Probe Group A streptococcus Direct Test with culture for diagnosing streptococcal pharyngitis.
The Group A Streptococcus Direct Test (GP-ST test; Gen-Probe, Inc., San Diego, Calif.) was compared with culture for the detection of Streptococcus pyogenes from throat swabs of 767 patients with pharyngitis. Swabs were tested by the GP-ST test after inoculating a 5% sheep blood agar (SBA) plate. SBA plates were incubated at 35 degrees C in room air for 72 h. SBA plates with no evidence of beta-hemolytic colonies after 18 to 24 h of incubation were subcultured by taking a swipe across the primary inoculum from the SBA plate to an agar selective for Streptococcus spp. In a low-prevalence (11.9%) population and in comparison with the number of positive cultures detected by the 72-h single-culture method (SBA plate method), the GP-ST test had a sensitivity of 88.6%, a specificity of 97.8%, a positive predictive value of 83.9%, and a negative predictive value of 98.5%. In comparison with the growth of any colonies of S. pyogenes on the 72-h SBA plates plus a subculture onto selective blood agar, the sensitivities and specificities were as follows: 72-h SBA plate method, 96.7 and 100%, respectively; GP-ST test, 85.7 and 97.8%, respectively. The GP-ST test is an easy-to-perform, reliable test for batch screening of throat swabs for S. pyogenes.
Pokorski
S J
SJ
Department of Laboratory Medicine, Mayo Clinic, Rochester, Minnesota 55905.
Vetter
E A
EA
Wollan
P C
PC
Cockerill
F R
FR
D001431:Bacteriological Techniques; D015342:DNA Probes; D004269:DNA, Bacterial / Q000032:analysis; D004275:DNA, Ribosomal / Q000032:analysis; D006801:Humans; D007841:Latex Fixation Tests; D008163:Luminescent Measurements; D009693:Nucleic Acid Hybridization; D010612:Pharyngitis / Q000175:diagnosis* / Q000382:microbiology; D011237:Predictive Value of Tests; D011933:Reagent Kits, Diagnostic; D012680:Sensitivity and Specificity; D013297:Streptococcus pyogenes / Q000235:genetics / Q000302:isolation & purification*
D015342:DNA Probes; D004269:DNA, Bacterial; D004275:DNA, Ribosomal; D011933:Reagent Kits, Diagnostic