Chapter 209 Streptococcal Pharyngitis
Signs and symptoms of streptococcal pharyngitis (“strep throat”) resemble those of viral pharyngitis. Of children with sore throat, 15% to 36% have pharyngitis caused by group A beta-hemolytic streptococci (GABHS). Slightly lower percentages occur in adults as throat cultures yield GABHS in less than 20% of adult patients presenting clinically with a sore throat. However, it must be kept in mind that 10% to 25% of the general, asymptomatic population are carriers for group A streptococci; therefore, the true number of cases of pharyngitis due to GABHS is probably lower than reported.
Rapid “strep” screens that detect the presence of group A streptococcal antigens are a major clinical advancement. Because definitive diagnosis with a positive culture usually takes 2 days, antibiotic therapy during this period for presumed group A strep throat leads to unnecessary exposure to antibiotics and a greater likelihood of the development of antibiotic-resistant organisms. Rapid strep screens, such as the Strep A OIA test, have now shown excellent sensitivity and specificity and will soon replace throat culture as the diagnostic gold standard.1 In addition, the hope is that the use of these rapid strep screens will eliminate the unnecessary use of antibiotics. That said, these tests remain underutilized, because one analysis found that they were performed on only 53% of cases of acute pharyngitis where an antibiotic was prescribed.2 Many physicians continue to rely on antibiotics as a precaution against the sequelae of streptococcal pharyngitis even in the absence of a positive diagnosis, resulting in unnecessary prescriptions for antibiotics. Even in positive cases, antibiotics may not be necessary, because strep throat is usually a self-limited disease and most research has shown that clinical recovery is similar in cases where antibiotics are prescribed and those where they are not.3–5
The primary concern about not using antibiotics is the development of the “nonsuppurative poststreptococcal syndromes” (rheumatic fever, poststreptococcal glomerulonephritis, etc.). However, antibiotic administration does not significantly reduce the incidence of these sequelae. In developed countries, most cases of rheumatic fever and glomerulonephritis due to group A beta-hemolytic strep throat occur because the affected persons do not consult a physician.6 It is also important to point out that, although the dogma holds that acute rheumatic fever can be caused only by group A streptococcal infection of the upper respiratory tract, epidemiology indicates that streptococcal pyoderma is a major cause in the Aboriginal people of Northern Australia and perhaps other high-incidence communities. In contrast, in settings where rheumatic fever has become rare, the group A streptococcal strains causing pharyngitis are of relatively low virulence in terms of causing rheumatic fever.6
At present it appears that the use of antibiotics should be reserved those patients who are suffering from severe infection or whose sore throats are unresponsive to therapy (i.e., no response after 1 week of immune supportive therapy) and those with a prior history of rheumatic fever or glomerulonephritis. Penicillin, amoxicillin, erythromycin, and first-generation cephalosporins are the recommended antibiotics for the treatment of sore throat due to GABHS. Amoxicillin tends to be the most common prescription to children primarily for compliance reasons, whereas macrolides like erythromycin and cephalosporins have been recommended as the best first-line antibiotics, because penicillin fails to eradicate the streptococci in more than 20% of patients.7 The primary reason for this is the presence of beta-lactamase–positive organisms (Staphylococcus aureus and Bacteroides species), which shield streptococci by deactivating the penicillin. In these instances, stronger antibiotics, such as a cephalosporin, may be required.8 Nonetheless, because of the low cost and absence of resistance, penicillin is still regarded as an acceptable first choice.9
Antibiotics are often praised for their role in effectively eliminating rheumatic fever as a serious concern. However, the dramatic decrease in the incidence of rheumatic fever began before the advent of effective antibiotics.10 As for the eradication of most infectious diseases, improvements in socioeconomic, hygienic, and nutritional conditions were more important than the liberal use of penicillin. The present attack rates after a streptococcal infection are 0.4% to 2.8% for rheumatic fever and 0.2% to 20% for glomerulonephritis. Obviously such a wide range of reported sequelae makes accurate evaluation of the risk difficult.