Acute Streptococcal Pharyngitis: A common Cause of Sore Throat

Pharyngitis, or inflammation of the posterior oropharynx, is a commonly encountered diagnosis both in primary care and urgent care. In the winter months, it is not uncommon for clinicians to see sore throat almost continually in the acute setting.

Given the almost 30 million visits per year for sore throat, it is important for clinicians and students alike to master the diagnosis.

Due to its’ inevitable mention by parents, specifically streptococcal pharyngitis will be discussed in this article. The focus of the article will be on the etiology, presentation, diagnosis, and treatment of “Strep throat”. 

It is important to note that the great majority of pharyngitis is viral in origin, however given the potential complications of missing the diagnosis, it is important to always consider bacterial causes of pharyngitis.


How Common is Group A Strep?

Group A Streptococcus, or Streptococcus pyogenes is the most common cause of bacterial pharyngitis, accounting for up to 30% of sore throats in the winter and early spring in children.

It causes about 10% of sore throats in adults. It is a a gram positive coccus that clusters in chains (Brown and Ho, 2016).

The disease is most common in the winter months and early spring. There can be isolated outbreaks in schools or families. Other considerations in the differential diagnosis for sore throat include numerous viral causes, Haemophilis influenza, Herpes Simplex, Moraxella Catarrhalis, peritonsillar abscess, dental abscess, esophageal reflux, and post nasal drip.


Signs and Symptoms of Strep Throat

Patients with streptococcal pharyngitis typically will complain of odynophagia, sore throat, hoarseness, and abrupt onset of headache, chills or malaise. There may be a history of interaction with a classmate or contact that was diagnosed with the disease. Of note, the symptoms of cough, coryza, and diarrhea should point the clinician in the direction of viral etiology, as these are usually not seen in strep.

One significant complication of pharyngitis in general is dehydration. Young patients may have a history of decreased oral intake or poor feeding. It is important to assess oral intake and screen for dehydration in these patients.

The physical exam in streptococcal pharyngitis is somewhat classic. Patients may appear acutely ill, but usually are non-toxic appearing.

Examination of the oropharynx will reveal tonsillitis, tonsillar or oropharyngeal exudates, erythema, and injection. The roof of the hard palate may show petechiae. Neck examination may reveal tender lymphadenopathy in the anterior cervical chain. Mucous membranes, capillary refill, and skin turgor can be assessed to test for dehydration.

Acute Streptococcal Pharyngitis


Centor Criteria for Group A Strep

The commonly used and commonly tested Modified/McIssac Centor Criteria can be used to assess the probability of Streptococcal infection based on symptoms and physical exam.

The tool is easy to use. A higher score indicates a higher probability that the cause of pharyngitis is due to Strep.

Patients who are age 3 to 14 receive one point.

Patients age 15 to 44 gain no points, while anyone greater than 45, is subtracted a point.

A point is assigned if there is visible tonsillar exudate.

A point is assigned for tender anterior cervical lymphadenopathy.

A point is assigned for a temperature > 100.4 F.

Lastly, a point is added if a cough is absent from the list of symptoms.

Scores of 3 to 4 have a high probability of strep as a cause of the sore throat, some sources suggesting up to 70 to 80%. Some sources state that patients with very high Centor Score should be given antibiotics without testing, however this decision is clinician dependent and should take into account the whole clinical picture.

Patients with 2 points have a positive predictive value of about 50%. The chance of strep in a patient scoring 1, 0 or -1 is very low, however not impossible. Some sources suggest watchful waiting.


Lab Testing

The decision to test via Rapid screening with throat swab should be individualized by patient. Rapid strep tests are performed numerous times in offices, urgent cares, and emergency departments across the country daily.

The rapid tests may have a false negative of up to 10%. Some sources suggest that up to 30% of strep can be missed via rapid antigen testing. The benefit is that this is a cheap, easy to use test with rapid results that can be achieved prior to the clinician even seeing the patient. Parents of patients may request strep testing specifically.

In patients with positive rapid antigen testing, the benefit is early treatment and fast results. Faster treatment leads to decreased length of symptoms and decreased transmissibility.

Although more expensive and more time consuming, a throat culture can provide a much higher sensitivity and specificity for the detection of bacterial causes of pharyngitis. The throat culture has 90 to 95% sensitivity for Strep. It is recommended by most institutions to order a back up throat culture if the initial rapid antigen testing in the office is negative.


Treating Tonsillopharyngitis

The treatment of pharyngitis starts with supportive care. The first line treatment for viral pharyngitis is conservative management with vigorous hydration, NSAIDs/Tylenol for pain and fever relief, salt water gargles, lozenges, and possibly viscous lidocaine for analgesia.

In patients with a confirmed cause of Streptococcal pharyngitis, the mainstay of treatment is penicillin. In children, penicillin 250 mg PO two or three times per day for 7 to 10 days is standard. Amoxicillin may also be used, the standard dose is 50 mg/kg once daily or 25 mg/kg twice daily. This may be preferred as a solution due to cost and taste preference. In patients allergic to penicillin, other alternatives include cephalexin, clindamycin, or azithromycin.

Another significant benefit to the treatment of Streptococcal pharyngitis is the prevention of acute rheumatic fever. Acute rheumatic fever can cause carditis and valvular disease which can be lifelong and progressive. Rheumatic fever is significantly rare at this point in time due to the proper use of antibiotics for the treatment of streptococcal pharyngitis. Penicillin is associated with the greatest reduction in rheumatic fever.



Brown, J.J and Ho, B. (2016). Pharyngitis. The 5 Minute Clinical Consult.

Wald, E.R. (2017). Group A Tonsillopharyngitis in Children and Adolescents: Clinical Features      and Diagnosis. UpToDate. Date of access 25 January 2018.

This article, blog, or podcast should not be used in any legal capacity whatsoever, including but not limited to establishing standard of care in a legal sense or as a basis of expert witness testimony.No guarantee is given regarding the accuracy of any statements or opinions made on the article, podcast, or blog.