In a typical adult population of sore throat patients with a prevalence rate of “strep throat” infections of 5%-15%, a Centor score of 0-1 means a patient has a less than 5% likelihood of having a GABHS infection. A score of 2-3 means a 5%-30% likelihood, while a score of 4 means an approximately 30%-60% likelihood of GABHS infection.

The Centor criteria are most useful in “ruling out” the possibility of a GABHS infection if the score is 0-1.¹ Similarly, patients with “common cold” symptoms (runny or congested nose, mild cough) in addition to their sore throat symptoms have a very low likelihood of having a GABHS infection and do not require antibiotic therapy. From this estimation, we can see that a large number of patients with a Centor score of 2-3 or even 4 will receive unnecessary antibiotics.

Many societies have weighed in on this issue. There are three options recommended to help us make a diagnosis.⁸ Patients with a Centor score of 0 or 1 need no testing and should be treated symptomatically. For others:

• Do a rapid antigen test in patients with scores of 2, 3, or 4 and prescribe antibiotics only for those with positive results.
• Do a rapid antigen test for strep in patients with scores of 2 or 3. Patients with positive test results and those with a Centor score of 4 (no testing) get antibiotics.
• Do no testing and give antiobiotics to patients with Centor scores of 3 or 4.

Obviously, there are drawbacks to all of these approaches. Some patients not treated based simply on a Centor score of 2 risk undertreatment. On the other hand, children and adolescents aged 5-15 years have carriage rates as high as 25% during “strep throat season,” so treating all who have a positive rapid antigen test (or throat culture) will result in overtreatment of patients with viral pharyngitis and strep carriage. However, any approach that relies on the Centor score, rapid antigen testing, or a combination of the two is superior to, and more rational than, the approach of just giving all patients antibiotics.

Figure 1. Clinical and epidemiologic findings and diagnosis of pharyngitis due to GABHS

Features suggestive of GABHS as etiologic agent include:

• Sudden onset
• Sore throat
• Fever
• Headache
• Nausea, vomiting, and abdominal pain
• Inflammation of pharynx and tonsils
• Patchy discrete exudates
• Tender, enlarged anterior cervical nodes
• Patient aged 5-15 years
• Presentation in winter or early spring
• History of exposure

Features suggestive of viral etiology include: