[Use of the rapid antigen technique in the diagnosis of Streptococcus pyogenes pharyngotonsillitis]

Abstract

Introduction: Streptococcus pyogenes is the most frequent bacterial cause of acute tonsillopharyngitis. The validity of the rapid antigen test was analysed for its diagnosis in a Paediatric Primary Care setting. The clinical profile with better diagnostic yield was also identified. The unnecessary use of antibiotics was quantified when the rapid antigen test or only the clinical diagnosis was used. The sensitivity of the assay to penicillin, erythromycin and clindamycin was also determined.

Patients and methods: Cross-sectional study was conducted on children between 2 to 14 years with acute tonsillitis and/or pharyngitis seen in five Primary Care Centres, from January 2008 to May 2010. After a clinical diagnosis, two swabs were taken for pharyngotonsillar smears: the first was used for a rapid antigen test, and the second one for a culture and a study of antibiotic sensitivity, with its analysis being blind to the rapid test result. A total sample of 546 consecutive was envisaged and with consecutive sampling.

Results: A total 192 patients were included. The prevalence of Streptococcus pyogenes was 38.7% (95% CI: 31.4-45.7). Odynophagia and scarlatiniform rash were most likely with positive cultures, the Streptococcus pyogenes was sensitive to penicillin in 100%, to erythromycin in 97.3% and to clindamycin in 86.3%. The specificity of the rapid antigen test was 91.5% and with a Negative Predictive Value of 91.5%. About half (49.2%) of those who would have receive antibiotics for clinical suspicion would have been treated unnecessarily, with this decreasing to at least in 29.5% when using the rapid antigen test.

Conclusions: The rapid antigen test can lead to a better use of antibiotics. Its use in Paediatric Primary Health Care could be useful when, as when the result is negative, there would be no need to confirm by a culture, in those Health Centres with difficult access to laboratory.