Centor / McIsaac Criteria (streptococcal pharyngitis)
Probability of group A streptococcal pharyngitis to guide testing and antibiotic decisions.
About this calculator
The Centor / McIsaac score estimates the probability of streptococcal pharyngitis caused by Streptococcus pyogenes (group A β-hemolytic streptococcus). Developed by Centor (1981), modified by McIsaac (CMAJ, 1998) with age adjustment. Goal: reduce antibiotic overuse for viral pharyngitis. Criteria (1 point each). Temperature >38°C. Absence of cough. Tender anterior cervical lymphadenopathy. Tonsillar exudate or swelling. McIsaac age adjustment: 3-14 years +1, 15-44 years 0, >=45 years -1. IDSA 2012 interpretation. 0-1 – strep probability 1-10%, no antibiotics or testing. 2 – probability 11-17%, rapid antigen test or culture. 3 – probability 28-35%, rapid test with empiric therapy if positive. 4-5 – probability 51-53%, empiric antibiotics may be started without testing in primary care, or test by choice. Clinical use. Differentiates bacterial from viral pharyngitis in primary care and ED. First-line for confirmed strep – amoxicillin 1 g once daily for 10 days or penicillin V. With penicillin allergy – cephalexin 500 mg twice daily or azithromycin 500 mg once daily for 5 days. Limitations. Not used in children under 3 (rheumatic fever risk minimal; fever usually viral). Does not distinguish carriage from active infection – 15-20% of school-age children are chronic carriers needing no treatment. Not validated for atypical pathogens (Mycoplasma, Chlamydia, Arcanobacterium).
Source
Formula version: centor-1981-mcisaac-1998-idsa-2012-v1