Strep Pharyngitis Centor Score

The scoring method explained

Pharyngitis (sore throat) is a common presentation that can be caused by several factors, including a streptococcal agent, this cause being most common in young children.

The Centor score facilitates the first stage of diagnosis and can offer guidance to clinicians as to whether further diagnosis (strep culture) should be pursued.

The five criteria included in the score are:

■ Patient age: with three age groups, reflects the low probability of GAS in children younger than 3 and in the elderly;

■ Exudate or swelling on tonsils;

■ Tender/Swollen anterior cervical lymph nodes;

■ Fever more than 38C, 100.4F;

■ Cough present.

The presence of three or more of the above clinical signs should trigger further diagnosis for Group A beta-haemolytic streptococcus (GABHS). If positive, the patient is 40-60% likely to require antibiotic therapy.

New IDSA guidelines recommend the pursuit of testing or throat culture before any antibiotic treatment is prescribed.

The National Institute for Health and Clinical Excellence (NICE) recommends initiation of antibiotic therapy in all cases with Centor scores greater than 3 and positive cultures.

Although not 100% certain, the absence of all the clinical signs presented above indicates an 80% chance of negative diagnosis, thus no need for antibiotic therapy.

The main limitation of the score resides in the fact that it may provide false negative results in cases where the symptoms are mild.

Result interpretation

Each of the five criteria is given a different weight in the final score. There are three age categories:

■ 3 to 14 (1 point);

■ 15 to 44 (0 points);

■ 45 and above (-1 point).

Because streptococcal pharyingitis is a condition with predisposition to affect children and maximum young adults, patients over 45 are considered highly unlikely to develop it, thus the (-1) weight.

The other 4 criteria are risk factors for positive diagnosis thus are awarded 1 point if present.

The Centor score varies from -1 to 5. The probability of positive GABHS diagnosis is described in the table below:

About the original studies

In 1981, Centor et al. published criteria for the initial evaluation of patients presenting to ER with sore throat.

A model was constructed based on logistic regression analysis on patient data. It was found that likelihood of positive culture was linked to the number of clinical criteria found in the examination:

The main limitation found was that the model might encourage an over-reliance on physical exam and less use of patient history.

In 1998, McIsaac et al. intended to validate the score in patients with group A Streptococcus (GAS) that presented to ER with sore throat.

A single throat swab was used as the gold standard for diagnosing GAS infection and clinical information was recorded from a cohort of 521 patients. Score criteria were identified by means of logistic regression modelling.

The sensitivity, specificity and likelihood ratios of the score was compared to those of throat culture. The score was then validated in a smaller cohort of patients.

It was found that the proportion of patients being initiated on antibiotic would have been reduced by 48% if the score was applied. No increase in throat culture use was observed.

The modified version of the Centor score is an age-appropriate model for identification of group A Streptococcus infection.

Streptococcal pharyngitis guidelines

Streptococcal pharyngitis is a type of upper respiratory tract infection commonly diagnosed after throat culture.

However, there are costs and time wasting before results are provided and this means that both unnecessary determination may take place and necessary antibiotic therapy may be delayed.

Throat culture determinations have a generally high rate of false positives, which further on leads to unnecessary antibiotic treatment.

In the US and UK, antibiotic recommendations are addressed to patients with group A β-haemolytic streptococcal (GABHS) pharyngitis. Culture-confirmed Streptococcal infections, occurring in 5 to 17% of cases, require antibiotics.

Timely initiation of antibiotic therapy stops the spread of the disease, relieves the symptoms and reduces the risk of complications such as peritonsillar abscess, bacteraemia, acute glomerulonephritis or rheumatic fever.

Because most pharyngitis cases have a viral rather than bacterial origin, they do not respond to antibiotic treatment and their symptom management should be done with steroids (e.g. dexamethasone) and nonsteroidal anti-inflammatory drugs (NSAIDS)

Original sources

1. Centor RM, Witherspoon JM, Dalton HP, Brody CE, Link K. The diagnosis of strep throat in adults in the emergency room. Med Decis Making. 1981; 1(3):239-46.

2. McIsaac WJ, White D, Tannenbaum D, Low DE. A clinical score to reduce unnecessary antibiotic use in patients with sore throat. CMAJ. 1998; 158(1):75-83.

Validation

Fine AM, Nizet V, Mandl KD. Large-Scale Validation of the Centor and McIsaac Scores to Predict Group A Streptococcal Pharyngitis. Arch Intern Med. 2012; 172(11): 847–852.

Other references

1. McIsaac WJ, Kellner JD, Aufricht P, Vanjaka A, Low DE. Empirical validation of guidelines for the management of pharyngitis in children and adults. JAMA. 2004; 291(13):1587-95.

2. Shulman ST, Bisno AL, Clegg HW, Gerber MA, Kaplan EL, Lee G, Martin JM, Van Beneden C. Clinical practice guideline for the diagnosis and management of group A streptococcal pharyngitis: 2012 update by the Infectious Diseases Society of America. Clin Infect Dis. 2012; 55(10):1279-82.

3. Aalbers J, O’Brien K, et al. Predicting streptococcal pharyngitis in adults in primary care: a systematic review of the diagnostic accuracy of symptoms and signs and validation of the Centor score. BMC Medicine. 2011; (9):67.