strep pharyngitis

Sore throat accounts for a whopping 7.3 million outpatient pediatric visits. Group A Streptococcus (GAS) accounts for 20-30% of pharyngitis cases with the rest being primarily viral in etiology. However, clinically differentiating viral versus bacterial causes of pharyngitis is difficult and we, as providers, often don’t get it right. In addition, antimicrobial resistance is increasing.. So who do we test and when do we treat for strep throat? The 2012 Infectious Diseases Society of America (IDSA) guideline on GAS pharyngitis helps answer these questions.

Bacterial or viral pharyngitis?

Group A streptococcus (GAS) is the most common bacterial cause of pharyngitis in both children and adults. It is important to diagnosis and treat GAS pharyngitis to prevent the non-suppurative complication of acute rheumatic fever and suppurative complications such as peritonsillar abscess, retropharyngeal abscess, mastoiditis, and lymphadenitis.​1​ Additionally, it is important to rule out GAS pharyngitis so as to avoid unnecessary antibiotic use in a time of increasing antibiotic resistance patterns. 

Strep pharyngitis most commonly occurs in children ages 5-15 years old, and symptoms include sore throat, pain with swallowing, and fever. In children, headache, nausea, abdominal pain, and vomiting are also commonly present. Physical exam findings include tonsillopharyngeal erythema and exudates, cervical lymphadenopathy, uvula swelling, palatal petechiae, and a scarlatiniform rash. Viral pharyngitis may present similarly to GAS pharyngitis; however, a lack of fever and the presence of rhinorrhea, cough, conjunctivitis, stomatitis, oral ulcers, and viral exanthem suggest a more viral etiology. 

While there exist several prediction tools designed to aid in the clinical diagnosis of GAS pharyngitis, such as the Centor and McIsaac Criteria, none perform well in children.​2,3​ In some cases these scoring systems can help to identify children at low risk for GAS and therefore reduce the need for further testing; however, as many as 65% of patients who present with all of the clinical criteria in a particular tool will test negative for GAS on throat culture, indicating a viral etiology.​1​

Table 1: Classic symptoms and findings for a viral and bacterial pharyngitis
SymptomViralBacterial
Sore throat + +
Scarlatiniform rash +
Fever +/- +
Pain with swallowing + +
Headache +/- +
Nausea/vomiting/abdominal pain +
Rhinorrhea +
Cough +
Conjunctivitis +
Stomatitis/oral ulcers +
Viral exanthem +

How to test: Rapid Antigen Detection Tests and the strep culture

In patients with suspected GAS pharyngitis a Rapid Antigen Detection Test (RADT) should be used for diagnosis. RADTs allow providers to quickly test for GAS instead of relying on inadequate clinical tools or waiting for a strep culture to result. They are highly specific with a low false positive rate. Thus if positive, the patient should be treated with antibiotics and a confirmatory strep culture is not necessary. Of note, rapid strep testing will remain positive on average for 4 days after initial diagnosis, but can remain positive for up to 2 weeks depending on the individual and antibiotic compliance. Repeat testing with RADT after a course of antibiotics for GAS pharyngitis should be reserved for patients only with the recurrence of classic symptoms of strep throat.​4​

What if the rapid strep test is negative?

RADTs have a sensitivity of 70-90%, leading to some false negative results.​5,6​ Thus if the  RADT result is negative, a strep culture should be sent with a follow-up plan, should the culture become positive. Antibiotics can be initially withheld, unless the patient is at high risk (immunosuppressed, medically complex) or has high-risk contacts.

Who to test: Children younger than 3 years old don’t need to be tested

GAS pharyngitis is rare (0-14%) in children <3 years of age.​7​ Furthermore, the incidence of rheumatic fever is rare.​8​ The 2012 IDSA guidelines recommended that routine testing for GAS pharyngitis in patients <3 years of age is NOT indicated. Only in situations of a household contact with known GAS infection would it be reasonable to consider testing.​1​

How to treat GAS pharyngitis

Fortunately GAS is a relatively easy bug to kill. It is susceptible to penicillins and its sister beta-lactams, amoxicillin, and ampicillin. While penicillin is cheaper and as efficacious as amoxicillin, pediatrician tend to choose a 10-day course of amoxicillin due to its better taste and therefore higher compliance rate. 

For penicillin-allergic patients, first generation cephalosporins such as cephalexin are recommended in those without anaphylaxis to penicillins. For those with anaphylaxis to penicillins, a 10-day course of clindamycin or a 5-day course of azithromycin is recommended.​1​

Table 2: Antibiotic recommendations for Group A Streptococcal pharyngitis per 2012 IDSA guidelines, if the patient is NOT allergic to penicillin
AntibioticDosingDuration
Penicillin V *Children: 250 mg po BID/TID
*Adolescent/Adults: 250 mg po QID or 500 mg po BID
10 days
Amoxicillin * 50 mg/kg (max 1,000 mg) po daily, or 
* 25 mg/kg (max 500 mg) po BID 
10 days
Benzathine penicillin G * Weight <27 kg: 600,000 units IM
* Weight ≥27 kg: 1.2 million units IM
1 time dose
Table 3: Antibiotic recommendations for Group A Streptococcal pharyngitis per 2012 IDSA guidelines, if the patient IS allergic to penicillin (*avoid if anaphylactic to penicillin)
Antibiotic Dosing Duration
Cephalexin* 20 mg/kg/dose (max 500 mg) po BID  10 days
Cefadroxil* 30 mg/kg (max 1,000 mg) po daily  10 days
Clindamycin 7 mg/kg/dose (max 300 mg) po TID 10 days
Azithromycin 12 mg/kg (max 500 mg) po daily  5 days
Clarithromycin 7.5 mg/kg/dose (max 250 mg) po BID  10 days

What about GAS carriers? 

GAS carriers are patients with persistent GAS positive throat cultures despite treatment and without any further symptoms of GAS pharyngitis. These patients have GAS present in the pharynx but no signs of immunologic response, meaning that their antistreptolysin O (ASO) titers are negative.​9​

RADTs and strep cultures do not distinguish between active infection and carriers. Carriers do not require treatment and have a low risk of spreading infection to those in close contact. They are also at low risk for developing suppurative and non-suppurative complications.

Can we do better? 

Despite the fact that RADTs have the potential to drastically reduce the number of antibiotic prescriptions for viral pharyngitis, prescribing rates remain high. Studies cite that antibiotics are prescribed in as many as 53% of all patients with pharyngitis symptoms, which is, well above the known prevalence of GAS at 20-30%.​8​ So why are we still giving antibiotics for viral pharyngitis? The answer is probably multifactorial, including providers empirically treating sore throat without testing, testing in inappropriate cases, such as young children, and the increasing prevalence of carrier states. 

Take Away Points

  • Do not rely on the clinical diagnosis for GAS pharyngitis in children. Instead use a Rapid Antigen Detection Test (RADT) and, if negative, a throat culture for diagnosis.
  • There is no indication to test children <3 years of age for GAS pharyngitis with the RADT or strep culture unless there is a known household contact with GAS.
  • Treat with a 10 day course of amoxicillin or cephalexin in non-anaphylactic, penicillin-allergic patients. Clindamycin or azithromycin are appropriate antibiotics in anaphylactic, penicillin-allergic patients. 

References

  1. 1.
    Shulman S, Bisno A, Clegg H, et al. 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):1279-1282. https://www.ncbi.nlm.nih.gov/pubmed/23091044.
  2. 2.
    Shaikh N, Swaminathan N, Hooper E. Accuracy and precision of the signs and symptoms of streptococcal pharyngitis in children: a systematic review. J Pediatr. 2012;160(3):487-493.e3. https://www.ncbi.nlm.nih.gov/pubmed/22048053.
  3. 3.
    Fine A, Nizet V, Mandl K. Large-scale validation of the Centor and McIsaac scores to predict group A streptococcal pharyngitis. Arch Intern Med. 2012;172(11):847-852. https://www.ncbi.nlm.nih.gov/pubmed/22566485.
  4. 4.
    Homme J, Greenwood C, Cronk L, et al. Duration of Group A Streptococcus PCR positivity following antibiotic treatment of pharyngitis. Diagn Microbiol Infect Dis. 2018;90(2):105-108. https://www.ncbi.nlm.nih.gov/pubmed/29150372.
  5. 5.
    Tanz R, Gerber M, Kabat W, Rippe J, Seshadri R, Shulman S. Performance of a rapid antigen-detection test and throat culture in community pediatric offices: implications for management of pharyngitis. Pediatrics. 2009;123(2):437-444. https://www.ncbi.nlm.nih.gov/pubmed/19171607.
  6. 6.
    Gerber M, Shulman S. Rapid diagnosis of pharyngitis caused by group A streptococci. Clin Microbiol Rev. 2004;17(3):571-580, table of contents. https://www.ncbi.nlm.nih.gov/pubmed/15258094.
  7. 7.
    Nussinovitch M, Finkelstein Y, Amir J, Varsano I. Group A beta-hemolytic streptococcal pharyngitis in preschool children aged 3 months to 5 years. Clin Pediatr (Phila). 1999;38(6):357-360. https://www.ncbi.nlm.nih.gov/pubmed/10378093.
  8. 8.
    Tani L, Veasy L, Minich L, Shaddy R. Rheumatic fever in children younger than 5 years: is the presentation different? Pediatrics. 2003;112(5):1065-1068. https://www.ncbi.nlm.nih.gov/pubmed/14595047.
  9. 9.
    Johnson D, Kurlan R, Leckman J, Kaplan E. The human immune response to streptococcal extracellular antigens: clinical, diagnostic, and potential pathogenetic implications. Clin Infect Dis. 2010;50(4):481-490. https://www.ncbi.nlm.nih.gov/pubmed/20067422.
Shannon Flood, MD

Shannon Flood, MD

Pediatric Emergency Medicine Fellow
Children's Hospital Colorado
Shannon Flood, MD

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Jason Woods, MD

Jason Woods, MD

ALiEM Podcast Editor for ACEP E-QUAL Series
Assistant Professor
Department of Pediatrics, Section of Emergency Medicine
University of Colorado, School of Medicine
Jason Woods, MD

@jwoodsmd

PEM physician. Creator of @littlebigmed podcast. Views are my own and do not represent medical advice. RT≠endorsement