Performance of a predictive model for streptococcal pharyngitis in children.

CONTEXT: Group A beta-hemolytic streptococcus (GABHS) pharyngitis is a common childhood illness. The clinical diagnosis is difficult to determine and laboratory tests have limitations; hence, the condition is generally overdiagnosed and overtreated. Several clinical pediatric-specific predictive models have been published but none have been prospectively studied.

OBJECTIVE: To test the performance of a previously published predictive model for GABHS pharyngitis in children in different clinical settings and during different seasons.

DESIGN: Prospective cohort study.

SETTINGS: Pediatric emergency department and 2 pediatric outpatient clinics.

PATIENTS: Children aged between 1 and 18 years with pharyngitis on initial examination at study sites between April 1, 1999, and March 31, 2000.

INTERVENTIONS: Recording of clinical features during initial evaluation using a standardized form and recovery of GABHS from patients' throats using reference standard methods.

MAIN OUTCOME MEASURES: Posttest probability for GABHS positive throat culture associated with the model's positive predictors (moderate to severe tonsillar swelling, cervical lymphadenopathy [moderate to severe tenderness and enlargement of cervical lymph nodes], scarletiniform rash, and the absence of coryza) and the models' negative predictors (absence of the above signs and the presence of coryza).

RESULTS: Of 587 patients analyzed, 218 (37%) had a positive throat culture for GABHS. Forty-nine percent were boys. Mean +/- SD age was 6.7 +/- 3.9 years. There was no difference between the subsets within the sample. The posttest probability values for a positive throat culture associated with positive and negative predictors of the model were 79% and 12%, respectively.

CONCLUSIONS: A pediatric predictive model for GABHS pharyngitis performed better than physicians' subjective estimates for a positive throat culture and was comparable with a rapid antigen detection test. The model performed consistently well in different populations and across seasons. It can be useful if reliable microbiological testing and/or follow-up are not attainable.