The Infectious Diseases Society of America (IDSA) recently updated a 1997 guideline for the diagnosis and management of group A streptococcal pharyngitis. The revised guideline was published in the July 15, 2002 issue of Clinical Infectious Diseases.

The IDSA defined group A streptococcal pharyngitis as an acute infection of the oropharynx or nasopharynx that is caused by Streptococcus pyogenes. Accurate diagnosis and optimal treatment of this infection are important to:

• Prevent acute rheumatic fever.

• Prevent suppurative complications (e.g., mastoiditis, peritonsillar abscess, cervical lymphadenitis).

• Improve clinical signs and symptoms.

• Reduce transmission to close contacts of patients.

• Minimize potential adverse effects of inappropriate antibiotic therapy.

Diagnosis

Viruses are responsible for most cases of acute pharyngitis. Group A beta-hemolytic streptococcus is the most common bacterial cause, accounting for 15 to 30 percent of cases in children and 5 to 10 percent of cases in adults. It is the only common cause for which antimicrobial therapy is clearly indicated. Thus, the physician needs to determine whether acute pharyngitis is caused by group A streptococcal infection.

EPIDEMIOLOGIC AND CLINICAL FEATURES

Acute group A streptococcal pharyngitis occurs mainly in children five to 15 years of age. In temperate climates, this illness occurs more often in the winter and early spring. Common presenting features include sudden onset of sore throat and fever; patients may also have headache, nausea, vomiting, and abdominal pain. Physical findings include inflammation of the pharynx and tonsils (with or without exudate) and lymphadenitis (cervical nodes); patients may also have a red, swollen uvula, palatal petechiae, excoriated nares, or a scarlatiniform rash. A viral etiology is strongly suggested by the absence of fever or the presence of conjunctivitis, coryza, cough, or diarrhea.

A history of close contact with a well-documented case of group A streptococcal pharyngitis can be significant. High prevalence of the illness in the community also can be helpful in patient assessment. While clinical and epidemiologic findings can be useful in determining the probability of group A streptococcal pharyngitis, they cannot definitively predict its presence.

MICROBIOLOGIC TESTING

The IDSA recommends that, if acute group A streptococcal pharyngitis is suspected, laboratory testing should be performed to support the diagnosis. Throat culture or a rapid antigen detection test (RADT) may be used.

Culture of a throat swab specimen remains the standard for identifying group A beta-hemolytic streptococci (sensitivity: 90 to 95 percent) and confirming the clinical diagnosis. However, culture results are not available for a day or longer. RADTs identify group A streptococcal carbohydrate on a throat swab. Compared with blood agar plate culture, most currently available RADTs have excellent specificity (greater than 90 percent) but lower sensitivity (80 to 90 percent or less). For some RADTs, the Clinical Laboratory Improvement Act has not waived the need for laboratory certification.

The IDSA notes that a positive result on a throat culture or RADT adequately confirms the diagnosis. Unless the physician has determined that the RADT used is comparable to throat culture, negative RADT results in children and adolescents should be confirmed with a throat culture. In adults, RADTs are an acceptable alternative to throat culture for the diagnosis of group A streptococcal pharyngitis. Because of the low incidence of streptococcal infection in adults and the extremely low risk of rheumatic fever, negative RADT results do not have to be confirmed by culture in adult patients.

Except in patients with a history of rheumatic fever, follow-up culture is not routinely indicated if a course of appropriate antibiotic therapy has been completed and symptoms are absent. Follow-up culture should be considered during outbreaks of acute rheumatic fever or poststreptococcal acute glomerulonephritis, during outbreaks of group A streptococcal pharyngitis in closed or partially closed communities, or when “ping-pong” spread has been occurring within a family.

Therapy

Antibiotic therapy can be initiated before laboratory results are available. Treatment should be discontinued if test results are negative. The IDSA notes that rheumatic fever can be prevented even if treatment is postponed for up to nine days after symptom onset.

Antibiotics with demonstrated efficacy against group A beta-hemolytic streptococci include penicillin and congeners (e.g., ampicillin, amoxicillin, semisynthetic penicillins), a number of cephalosporins and macrolides, and clindamycin. Dosage and duration of therapy should be sufficient to eradicate group A beta-hemolytic streptococci from the pharynx (Table 1).

Because of proven safety and efficacy, narrow spectrum, and low cost, penicillin remains the treatment of choice for patients who are not allergic to the drug. Once-daily amoxicillin therapy could become an alternative regimen if the results of preliminary investigations confirm efficacy. In young children, amoxicillin is often used in place of oral penicillin V.

Intramuscularly administered penicillin G benzathine is preferred in patients who are unlikely to complete a full oral course. Patients who are allergic to penicillin can be treated with erythromycin or first-generation cephalosporins (if there is no immediate-type hypersensitivity to betalactam antibiotics).

Management of Household Contacts

Household contacts may harbor group A streptococci in their upper respiratory tract but have no symptoms. It is usually not necessary to test these asymptomatic contacts or to treat them if test results are positive. When post-treatment testing of a patient is necessary (see microbiologic test discussion), the IDSA recommends cultures for asymptomatic family contacts, with treatment given to those who have positive results. The management of close contacts of patients with invasive group A streptococcal infections (e.g., necrotizing fasciitis, toxic shock syndrome) is beyond the scope of this guideline.

Management of Recurrent Acute Pharyngitis

Patients with a single recurrence of group A streptococcal pharyngitis shortly after treatment may be treated using the regimens given in Table 1. If oral therapy was used for the first course, consideration can be given to using intramuscularly administered penicillin G benzathine for the second course.

When multiple episodes of group A streptococcal pharyngitis occur over months or years, differentiating viral pharyngitis in a Streptococcus carrier from true group A beta-hemolytic streptococcal infection may be difficult. Suggested treatments for recurrent episodes are described in Table 2.