DIAGN MICROBIOL INFECT DIS 1991;14:281-285
281
Evaluation of the Modified Visuwell Strep-A Enzyme Immunoassay for Detection of Group-A Streptococcus from Throat Swabs Murray Drulak, William Bartholomew, Leonard LaScolea, Daniel Amsterdam, Nils Gunnersen, Juanita Yong, Colette Fijalkowski, and Scott Winston
The modified VisuwelI Strep-A enzyme immunoassay (EIA) was compared with culture for detection of group-A Streptococcus from throat swabs. Throat swabs in modified Stuarts medium obtained after culture at two institutions were tested in Visuwell. Cumulative results were n = 417, sensitivity 87.8%, specificity 89.9% predictive value positive (PVP) 67.9%, predictive value negative (PVN) 96.8%, and accuracy 89.5%. At another site, swabs were delivered to the laboratory without transport medium, cultured, and subsequently tested by. Visuwell (n = 202, sensitivity 79.6%, specificity 84.5%,
PVP 65.2%, PVN 91.9%, accuracy 83.2%). When 1 + culture-positive specimens were considered negative, the sensitivity and PVN increased from 79.6% to 90.2% and 91.9% to 97.1% respectively. Overall performance of the modified Visuwell was comparable with that of the initial assay for throat swabs transported with or without modified Stuarts medium. Cross reaction with organisms other than group-A Streptococcus normally found in the oropharynx was negligible in Visuwell and the limit of detection of group-A Streptococcus was 5 x l(P colony-forming units.
INTRODUCTION
the patient is both s y m p t o m a t i c and infectious, thereby resulting in reduction of the risk of further transmission (LaScolea, 1989). Latex agglutination tests have been used for the rapid detection of groupA Streptococcus in throat swabs (Chang and Mohla, 1985; C a m p o s and Charilaou, 1985; Miceika et al., 1985). This m e t h o d o l o g y was followed by the dev e l o p m e n t and s u b s e q u e n t evaluation of e n z y m e i m m u n o a s s a y s (EIA) (Schwabe et al., 1987; Kellogg et al., 1987a; Clegg et al., 1987; Manasse, 1989). A sandwich EIA that utilizes microwells coated with anti-group-A streptococcal a n t i b o d y and a ureaseconjugated detector antibody t e r m e d Visuwell was evaluated versus culture (Drulak et al., 1988). Visuwell Strep A was recently modified by reformulating the substrate, reducing the substrate incubation time, and reconforming the kit. In this study, Visuwell Strep-A E1A was c o m p a r e d with culture for throat swab specimens with and w i t h o u t transport m e d i u m .
Rapid diagnosis of group-A Streptococcus as the cause of pharyngitis could initiate early selective antimicrobial treatment. This may shorten the time period From the Department of Clinical Microbiology,BuffaloChildren's t tospital (L.L.S.), Department of Clinical Microbiology, Erie County, Medical Center and State University of NY at Buffalo (W.B., D.A., N.G.), Buffalo,New York, USA;and ADI Diagnostics Inc. (M.D., J.Y., C.F., S.W.), Rexdale, Ontario, Canada. This paper was presented previously by M. Drulak et al. (1989) in the Abstracts of the Annual Meeting of the American Society of Microbiology. Dr. LaScolea's present address: Department of Microbiology State University of New York, Buffalo, NY 14214, USA. Dr. Bartholomew's present address: Microbiology Section, Veterans Administration Medical Center, Kansas City, MO 641282295, USA. Address reprint requests to Dr. M. Drulak, ADI Diagnostics, 30 Meridian Road, Rexdale, Ontario, Canada M9W 4Z7. Received 17 July 1990; revised and accepted 1 October 1990. © 1991 Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010 0732-8893/91/$3.50
282
M. Drulak et al.
TABLE 1 Organisms Tested in Visuwell Streptococcus agalactiae Group-C Streptococcus Streptococcus faecalis Group-G Streptococcus Group-F Streptococcus Staphylococcus aureus Serratia marcescens Klebsiella pneumoniae Pseudomonas aeruginosa Neisseria meningitidis~ ftaemophilus influenzad' Candida albicand' Streptococcus pneumoniad' Enterobacter cloacad'
ATCC 13813 ATCC 12388 ATCC 19433 ATCC 12394 ATCC 12392 ATCC 12598 ATCC 8100 ATCC 13883 ATCC 27853 Strain 614-W135
';Obtained from the Laboratorx, Center for Disease Control, Ottawa, Ontario, Canada. ;'Clinical isolates obtained from MDS Laboratories, Rexdale, Ontario, Canada.
MATERIALS AND METHODS Cross-Reactivity and the Limit of Detection of Group-A Streptococcal Antigen McFarland no. 1 suspensions of organisms other than group-A Streptococcus commonly found in the oropharynx (Table 1) were prepared in 0.85% NaCI solution, and 10 ~1 of each suspension was extracted and tested in Visuwell. Dilutions of a suspension of group-A Streptococcus [American Type Culture Collection (ATCC) 19615] were extracted and tested in duplicate with Visuwell according to methods previously described (Drulak et al., 1988).
Source and Storage of Throat Swab Specimens A total of 417 throat specimens were transported to the laboratory in modified Stuarts medium. Table 2 summarizes where throat specimens were obtained, cultured, and tested in Visuwell. Of the specimens from Erie County Medical Center (ECMC), 140 were
TABLE 2 Source of Throat Swabs Tested in Visuwell Throat Swabs Location ECMC BGH ADI BCH
Obtained and Cultured
VisuwellTested
140 277 0 202
228'~ 0 189;' 202
"The additional 88 throat specimens were from BGH. ;'[hroat swabs from BGH.
collected from children and adults with pharyngitis using a double-rayon swab and transported in modified Stuarts medium using the Culturette transport system (Marion Laboratories, Kansas Ci~, MO). Both swabs were cultured and stored at 4°C for a maximum of 72 hr prior to the testing of one swab in Visuwell. The 277 throat specimens from Buffalo General Hospital (BGH) were collected using a single-rayon swab and transported in Culturette. The swab specimen was cultured prior to being tested in Visuwell. Of these specimens, 88 were stored for a maximum time period of 72 hr at 4°C prior to being tested in Visuwell at ECMC. The other 189 swabs were stored at -70°C for
281
Evaluation of the Modified Visuwell Strep-A Enzyme Immunoassay for Detection of Group-A Streptococcus from Throat Swabs Murray Drulak, William Bartholomew, Leonard LaScolea, Daniel Amsterdam, Nils Gunnersen, Juanita Yong, Colette Fijalkowski, and Scott Winston
The modified VisuwelI Strep-A enzyme immunoassay (EIA) was compared with culture for detection of group-A Streptococcus from throat swabs. Throat swabs in modified Stuarts medium obtained after culture at two institutions were tested in Visuwell. Cumulative results were n = 417, sensitivity 87.8%, specificity 89.9% predictive value positive (PVP) 67.9%, predictive value negative (PVN) 96.8%, and accuracy 89.5%. At another site, swabs were delivered to the laboratory without transport medium, cultured, and subsequently tested by. Visuwell (n = 202, sensitivity 79.6%, specificity 84.5%,
PVP 65.2%, PVN 91.9%, accuracy 83.2%). When 1 + culture-positive specimens were considered negative, the sensitivity and PVN increased from 79.6% to 90.2% and 91.9% to 97.1% respectively. Overall performance of the modified Visuwell was comparable with that of the initial assay for throat swabs transported with or without modified Stuarts medium. Cross reaction with organisms other than group-A Streptococcus normally found in the oropharynx was negligible in Visuwell and the limit of detection of group-A Streptococcus was 5 x l(P colony-forming units.
INTRODUCTION
the patient is both s y m p t o m a t i c and infectious, thereby resulting in reduction of the risk of further transmission (LaScolea, 1989). Latex agglutination tests have been used for the rapid detection of groupA Streptococcus in throat swabs (Chang and Mohla, 1985; C a m p o s and Charilaou, 1985; Miceika et al., 1985). This m e t h o d o l o g y was followed by the dev e l o p m e n t and s u b s e q u e n t evaluation of e n z y m e i m m u n o a s s a y s (EIA) (Schwabe et al., 1987; Kellogg et al., 1987a; Clegg et al., 1987; Manasse, 1989). A sandwich EIA that utilizes microwells coated with anti-group-A streptococcal a n t i b o d y and a ureaseconjugated detector antibody t e r m e d Visuwell was evaluated versus culture (Drulak et al., 1988). Visuwell Strep A was recently modified by reformulating the substrate, reducing the substrate incubation time, and reconforming the kit. In this study, Visuwell Strep-A E1A was c o m p a r e d with culture for throat swab specimens with and w i t h o u t transport m e d i u m .
Rapid diagnosis of group-A Streptococcus as the cause of pharyngitis could initiate early selective antimicrobial treatment. This may shorten the time period From the Department of Clinical Microbiology,BuffaloChildren's t tospital (L.L.S.), Department of Clinical Microbiology, Erie County, Medical Center and State University of NY at Buffalo (W.B., D.A., N.G.), Buffalo,New York, USA;and ADI Diagnostics Inc. (M.D., J.Y., C.F., S.W.), Rexdale, Ontario, Canada. This paper was presented previously by M. Drulak et al. (1989) in the Abstracts of the Annual Meeting of the American Society of Microbiology. Dr. LaScolea's present address: Department of Microbiology State University of New York, Buffalo, NY 14214, USA. Dr. Bartholomew's present address: Microbiology Section, Veterans Administration Medical Center, Kansas City, MO 641282295, USA. Address reprint requests to Dr. M. Drulak, ADI Diagnostics, 30 Meridian Road, Rexdale, Ontario, Canada M9W 4Z7. Received 17 July 1990; revised and accepted 1 October 1990. © 1991 Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010 0732-8893/91/$3.50
282
M. Drulak et al.
TABLE 1 Organisms Tested in Visuwell Streptococcus agalactiae Group-C Streptococcus Streptococcus faecalis Group-G Streptococcus Group-F Streptococcus Staphylococcus aureus Serratia marcescens Klebsiella pneumoniae Pseudomonas aeruginosa Neisseria meningitidis~ ftaemophilus influenzad' Candida albicand' Streptococcus pneumoniad' Enterobacter cloacad'
ATCC 13813 ATCC 12388 ATCC 19433 ATCC 12394 ATCC 12392 ATCC 12598 ATCC 8100 ATCC 13883 ATCC 27853 Strain 614-W135
';Obtained from the Laboratorx, Center for Disease Control, Ottawa, Ontario, Canada. ;'Clinical isolates obtained from MDS Laboratories, Rexdale, Ontario, Canada.
MATERIALS AND METHODS Cross-Reactivity and the Limit of Detection of Group-A Streptococcal Antigen McFarland no. 1 suspensions of organisms other than group-A Streptococcus commonly found in the oropharynx (Table 1) were prepared in 0.85% NaCI solution, and 10 ~1 of each suspension was extracted and tested in Visuwell. Dilutions of a suspension of group-A Streptococcus [American Type Culture Collection (ATCC) 19615] were extracted and tested in duplicate with Visuwell according to methods previously described (Drulak et al., 1988).
Source and Storage of Throat Swab Specimens A total of 417 throat specimens were transported to the laboratory in modified Stuarts medium. Table 2 summarizes where throat specimens were obtained, cultured, and tested in Visuwell. Of the specimens from Erie County Medical Center (ECMC), 140 were
TABLE 2 Source of Throat Swabs Tested in Visuwell Throat Swabs Location ECMC BGH ADI BCH
Obtained and Cultured
VisuwellTested
140 277 0 202
228'~ 0 189;' 202
"The additional 88 throat specimens were from BGH. ;'[hroat swabs from BGH.
collected from children and adults with pharyngitis using a double-rayon swab and transported in modified Stuarts medium using the Culturette transport system (Marion Laboratories, Kansas Ci~, MO). Both swabs were cultured and stored at 4°C for a maximum of 72 hr prior to the testing of one swab in Visuwell. The 277 throat specimens from Buffalo General Hospital (BGH) were collected using a single-rayon swab and transported in Culturette. The swab specimen was cultured prior to being tested in Visuwell. Of these specimens, 88 were stored for a maximum time period of 72 hr at 4°C prior to being tested in Visuwell at ECMC. The other 189 swabs were stored at -70°C for
