Pseudoepidemic of streptococcal pharyngitis in a hospital pharmacy

Context: Streptococcus pyogenes has recently re-emerged as a significant pa thogen causing disease ranging from pharyngitis to lethal systemic infectio n. Six hospital pharmacy employees were diagnosed as having streptococcal p haryngitis during I week, and antibiotic prophylaxis was requested to halt the outbreak. Objective: Outbreak investigation. Design: Review of initial cases and prospective evaluation of the remaining pharmacy employees and the antigen detection test being used. Setting: Pharmacy and occupational health department of a university hospit al. Population: Sixteen employees of the hospital pharmacy and 19 other employe es of the hospital. Results: The 6 pharmacy employees who had positive streptococcal antigen de tection tests did not have symptoms suggesting streptococcal pharyngitis. O f the 10 remaining pharmacy employees, none had a positive throat culture f or S pyogenes. Specificity of the antigen detection test being used was 53% (95% CI, 30%-75%) in prospective evaluation. Conclusions: This was believed to represent a pseudoepidemic because none o f the 6 cases had signs or symptoms typical of streptococcal pharyngitis, n one of the remaining 10 pharmacy employees had positive throat cultures, an d prospective evaluation found low specificity of the antigen detection tes t. Whereas use of an accurate test in such a low prevalence setting could h ave resulted in a higher percentage of results being false-positive, the lo w specificity of the antigen detection test being used also contributed to the pseudoepidemic.