Pharyngitis (Strep Throat)

Acute pharyngitis is a very common illness that can be caused by different viruses and bacteria. When caused by Streptococcus pyogenes, which are also called group A Streptococcus or group A strep, acute pharyngitis is also known as strep throat. The etiology, clinical features, diagnosis and treatment options, prognosis and complications, and prevention are described below.

Etiology

Group A strep pharyngitis is an infection of the oropharynx caused by S. pyogenes. S. pyogenes are gram-positive cocci that grow in chains (see figure 1). They exhibit β-hemolysis (complete hemolysis) when grown on blood agar plates. They belong to group A in the Lancefield classification system for β-hemolytic Streptococcus, and thus are also called group A streptococci.

Clinical Features

Group A strep pharyngitis is an acute pharyngitis that commonly presents with

• Sudden-onset of sore throat
• Odynophagia
• Fever

These symptoms may be accompanied by headache, abdominal pain, nausea, and vomiting — especially among children. Cough, rhinorrhea, hoarseness, oral ulcers, and conjunctivitis are not typically seen in patients with group A strep pharyngitis and are therefore strongly suggestive of a viral etiology.

On clinical examination, patients with group A strep pharyngitis usually have

• Pharyngeal and tonsillar erythema
• Tonsillar hypertrophy with or without exudates
• Palatal petechiae
• Anterior cervical lymphadenopathy

Patients with group A strep pharyngitis may also present with a scarlatiniform rash; the resulting syndrome is called scarlet fever or scarlatina.

Respiratory disease caused by group A strep infection in children younger than 3 years of age rarely manifests as acute pharyngitis, but rather as mucopurulent rhinitis followed by fever, irritability, and anorexia (called “streptococcal fever” or “streptococcosis”). In contrast to typical acute group A strep pharyngitis, this presentation in young children is subacute and high fever is rare.

Transmission

Group A strep pharyngitis is most commonly spread through direct person-to-person transmission, typically through saliva or nasal secretions from an infected person. People with group A strep pharyngitis are much more likely to transmit the bacteria to others than asymptomatic pharyngeal carriers. Crowded conditions — such as those in schools, daycare centers, or military training facilities — facilitate transmission. Although rare, spread of group A strep infections may also occur via food. Foodborne outbreaks of pharyngitis have occurred due to improper food handling. Fomites, such as household items like plates or toys, are very unlikely to spread these bacteria.

Humans are the primary reservoir for group A strep. There is no evidence to indicate that pets can transmit the bacteria to humans.

Treating a person with group A strep pharyngitis with an appropriate antibiotic for 24 hours or longer generally eliminates their ability to transmit the bacteria. People with group A strep pharyngitis or scarlet fever should stay home from work, school, or daycare until they are afebrile and until 24 hours after starting appropriate antibiotic therapy.

Incubation Period

The incubation period of group A strep pharyngitis is approximately 2 to 5 days.

Risk Factors

Group A strep pharyngitis can occur in people of all ages, but it is most common among children 5 through 15 years of age. It is rare in children younger than 3 years of age.

The most common risk factor is close contact with another person with group A strep pharyngitis. Parents of school-aged children and adults who are often in contact with children will have a higher risk for group A strep pharyngitis than adults who do not frequently interact with children.

Crowding, such as found in schools, military barracks, and daycare centers, increases the risk of disease spread.

Diagnosis and Testing

The differential diagnosis of acute pharyngitis includes multiple viral and bacterial pathogens. Viruses are the most common cause of pharyngitis in all age groups. Group A strep, the most common bacterial cause, is estimated to cause 20% to 30% of pharyngitis episodes in children and approximately 5% to 15% of pharyngitis infections in adults.

History and clinical examination can be used to diagnosis viral pharyngitis when clear viral symptoms (e.g., cough, rhinorrhea, hoarseness, oral ulcers, conjunctivitis) are present; these patients do not need testing for group A strep. However, clinical examination cannot be used to differentiate viral and group A strep pharyngitis in the absence of viral symptoms, even for experienced clinicians.

The diagnosis of group A strep pharyngitis is confirmed by either a rapid antigen detection test (RADT) or a throat culture. RADTs have high specificity for group A strep but varying sensitivities when compared to throat culture. Throat culture is the gold standard diagnostic test.

See the resources section for specific diagnosis guidelines for adult and pediatric patients^1,2,3.

Special Considerations

Group A strep pharyngitis should be confirmed in children older than 3 years of age in order to appropriately guide treatment decisions; antibiotics should be given to children with confirmed group A strep pharyngitis to reduce risk of developing sequela (acute rheumatic fever). Testing for group A strep pharyngitis is not routinely indicated for children younger than 3 years of age or adults since acute rheumatic fever is very rare in those age groups.

A positive RADT can be used as confirmation of group A strep pharyngitis in children. However, a negative RADT in a child with symptoms of pharyngitis should be followed up by a throat culture. Clinicians should have a mechanism in place to contact the family and initiate antibiotics if the back-up throat culture is positive.

Treatment

When left untreated, the symptoms of group A strep pharyngitis are usually self-limited; however, acute rheumatic fever and suppurative complications (e.g., peritonsillar abscess, mastoiditis) are more likely to occur when it is left untreated. Antibiotic treatment is indicated for patients, regardless of age, who have a positive RADT or throat culture. Viral pharyngitis should not be treated with antibiotics.

The use of a recommended antibiotic regimen to treat group A strep pharyngitis also shortens the duration of symptoms and, through eradication of the organism from the upper respiratory tract, reduces the likelihood of transmission to family members, classmates, and other close contacts.

Penicillin or amoxicillin is the antibiotic of choice to treat group A strep pharyngitis. There has never been a report of a clinical isolate of group A strep that is resistant to penicillin; however resistance to azithromycin and clarithromycin is common in some communities. For patients with a penicillin allergy, recommended regimens include narrow-spectrum cephalosporins (cephalexin, cefadroxil), clindamycin, azithromycin, and clarithromycin.

See the resources section for specific treatment guidelines for adult and pediatric patients^1,2,3.

Table: Antibiotic Regimens Recommended for Group A Streptococcal Pharyngitis

Drug, Route	Dose or Dosage	Duration or Quantity
For individuals without penicillin allergy
Penicillin V, oral	Children: 250 mg twice daily or 3 times daily; adolescents and adults: 250 mg 4 times daily or 500 mg twice daily	10 days
Amoxicillin, oral	50 mg/kg once daily (max = 1000 mg); alternate: 25 mg/kg (max = 500 mg) twice daily	10 days
Benzathine penicillin G, intramuscular	<27 kg: 600 000 U; ≥27 kg: 1 200 000 U	1 dose
For individuals with penicillin allergy
Cephalexin,a oral	20 mg/kg/dose twice daily (max = 500 mg/dose)	10 days
Cefadroxil,a oral	30 mg/kg once daily (max = 1 g)	10 days
Clindamycin, oral	7 mg/kg/dose 3 times daily (max = 300 mg/dose)	10 days
Azithromycin,b oral	12 mg/kg once daily (max = 500 mg)	5 days
Clarithromycinb, oral	7.5 mg/kg/dose twice daily (max = 250 mg/dose)	10 days

From: Shulman ST, Bisno AL, Clegg HW, Gerber MA, Kaplan EL, Lee G, 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):e86–e102, Table 2 (adapted).

Note: If you are interested in reusing this table, permission must first be given by the journal; request by emailing journals.permissions@oup.com.

Carriage

Asymptomatic group A strep carriers usually do not require treatment. Carriers are individuals who have positive throat cultures or are RADT positive, but who do not have clinical symptoms or an immunologic response to group A strep antigens on laboratory testing. Compared to people with symptomatic pharyngitis, carriers are much less likely to transmit group A strep to others and very unlikely to develop suppurative or nonsuppurative complications.

Some people with recurrent episodes of acute pharyngitis with evidence of group A strep by RADT or throat culture actually have recurrent episodes of viral pharyngitis with concurrent streptococcal carriage. Repeated use of antibiotics among this subset of patients is unnecessary. However, identifying carriers clinically or by laboratory methods can be very difficult. Management of these patients and determination of whether someone is a carrier is addressed in the Infectious Diseases Society of America guidelines and the Red Book.^{1, 2}

Prognosis and Complications

Rarely, complications can occur after group A strep pharyngitis. Complications are generally divided into suppurative and nonsuppurative complications. Suppurative complications result from the spread of group A strep from the pharynx to adjacent structures. They can include peritonsillar abscess, retropharyngeal abscess, cervical lymphadenitis, and mastoiditis. Other focal infections or sepsis are even less common.

Nonsuppurative sequelae of group A strep infections include acute rheumatic fever (after group A strep pharyngitis) and post-streptococcal glomerulonephritis (after group A strep pharyngitis or skin infections). These complications occur after the original infection resolves and involve sites distant to the initial site of group A strep infection. They are thought to be the result of the immune response and not of direct group A strep infection.

Prevention

The spread of all types of group A strep infection can be reduced by good hand hygiene, especially after coughing and sneezing and before preparing foods or eating, and respiratory etiquette (e.g., covering your cough or sneeze). Treating an infected person with an antibiotic for 24 hours or longer generally eliminates their ability to transmit the bacteria. Thus, people with group A strep pharyngitis should stay home from work, school, or daycare until afebrile and until at least 24 hours after starting appropriate antibiotic therapy.

Epidemiology and Surveillance

Humans are the only reservoir for group A strep. It is most common among children 5 through 15 years of age and rare in children younger than 3 years of age. In the United States, group A strep pharyngitis is most common during the winter and spring. However, CDC does not track the incidence of group A strep pharyngitis or other non-invasive group A strep infections. CDC tracks invasive group A strep infections through the Active Bacterial Core surveillance (ABCs) program. For information on the incidence of invasive group A strep infections, please visit the ABCs Surveillance Reports website.

Resources

1. Shulman ST, Bisno AL, Clegg HW, Gerber MA, Kaplan EL, Lee G, 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):1279–82.
2. Committee on Infectious Diseases. Group A streptococcal infections. In Kimberlin DW, Brady MT, Jackson MA, Long SS, editors. 30th ed. Red Book: 2015 Report of the Committee on Infectious Diseases. Elk Grove Village (IL): American Academy of Pediatrics; 2015:732–44.
3. Gerber MA, Baltimore RS, Eaton CB, Gewitz M, Rowley AH, Shulman ST, et al. Prevention of rheumatic fever and diagnosis and treatment of acute streptococcal pharyngitis: A scientific statement from the American Heart Association Rheumatic Fever, Endocarditis, and Kawasaki Disease Committee of the Council on Cardiovascular Disease in the Young, the Interdisciplinary Council on Functional Genomics and Translational Biology, and the Interdisciplinary Council on Quality of Care and Outcomes Research: Endorsed by the American Academy of Pediatrics. Circulation. 2009;119(11):1541–51.

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