False-positive rapid antigen detection test results: reduced specificity in the absence of group A streptococci in the upper respiratory tract.
Rapid antigen detection tests (ADTs) are promoted for identification of group A streptococci (GAS) in the upper respiratory tract. Although debate persists about their sensitivity, most investigators consider ADTs to be highly specific. Nevertheless, reports continue to describe false-positive ADT results (positive ADT result, negative culture result). This study examined culture results from 522 adult patients with acute pharyngitis and a positive ADT result; unexpectedly, 15% had throat culture results negative for GAS. Normal bacterial flora from 30% of these "negative" culture results produced a positive ADT result. An ADT-reactive organism belonging to the Streptococcus milleri group was isolated from 1 culture; it carried group A carbohydrate antigen. Although S. milleri previously has been associated with false-positive ADT reactions, the frequency of this phenomenon is unknown. The present, large study suggests that false-positive ADT reactions may be more common than previously reported, an observation that must be precisely explained and epidemiologically and clinically defined.
Johnson
D R
DR
Department of Pediatrics, World Health Collaborating Center for Reference and Research on Streptococci, and Department of Pediatrics, University of Minnesota Medical School, Minneapolism, MN, USA.
Kaplan
E L
EL
D000328:Adult; D000942:Antigens, Bacterial / Q000302:isolation & purification*; D005189:False Positive Reactions; D006801:Humans; D010612:Pharyngitis / Q000382:microbiology*; D011933:Reagent Kits, Diagnostic / Q000382:microbiology*; D012137:Respiratory System / Q000382:microbiology*; D012680:Sensitivity and Specificity; D013290:Streptococcal Infections / Q000175:diagnosis / Q000382:microbiology*; D013291:Streptococcus / Q000276:immunology / Q000302:isolation & purification*
D000942:Antigens, Bacterial; D011933:Reagent Kits, Diagnostic