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.