Comparison of Visuwell enzyme immunoassay to culture for detection of group A Streptococcus in throat swab specimens.
A microwell enzyme immunoassay (Visuwell) for direct detection of Group A streptococcal antigen from throat swab specimens has been developed. It incorporates urease conjugated antibody as the detector and is easily interpreted by a yellow to purple color change. Throat specimens obtained on rayon-tipped swabs were transported moist in modified Stuarts medium and cultured before being tested in Visuwell (n = 585, prevalence 17.1%, sensitivity 88%, specificity 92.4%, predictive value positive 70.4%, predictive value negative 97.4%, and accuracy 91.6%). In instances of discrepancy between culture and Visuwell, throat swab extracts were tested in a latex agglutination test. In 21 of 37 instances of Visuwell-positive, culture-negative specimens, latex agglutination was positive. Throat specimens obtained using double rayon swabs and transported to the laboratory dry had one swab cultured and the other tested in Visuwell (n = 280, prevalence 20.4%, sensitivity 75.4%, specificity 88.3%, predictive value positive 62.3%, predictive value negative 93.4%, and accuracy 85.7%). When 1+ culture positive specimens were considered negative, a sensitivity of 97.6% was obtained. In 14 of 26 instances of Visuwell-positive, culture-negative specimens, latex agglutination was positive. Cross-reaction with organisms other than Group A Streptococcus found in the oropharynx was negligible in Visuwell. Limit of detection of Group A streptococcal antigen was equivalent for Visuwell and latex agglutination.
Drulak
M
M
ADI Diagnostics, Inc., Mississauga, Ontario, Canada.
Raybould
T J
TJ
Yong
J
J
Hsiung
D
D
Smith
H
H
Winston
S
S
D000293:Adolescent; D000328:Adult; D000942:Antigens, Bacterial / Q000032:analysis; D002648:Child; D003429:Cross Reactions; D006801:Humans; D007124:Immunoenzyme Techniques; D007841:Latex Fixation Tests; D008875:Middle Aged; D010612:Pharyngitis / Q000175:diagnosis*; D010614:Pharynx / Q000382:microbiology*; D011237:Predictive Value of Tests; D013290:Streptococcal Infections / Q000175:diagnosis*; D013297:Streptococcus pyogenes / Q000276:immunology / Q000302:isolation & purification*
D000942:Antigens, Bacterial