Chapter 031. Pharyngitis, Sinusitis, Otitis, and Other Upper Respiratory Tract Infections (Part 10)

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Diagnosis The primary goal of diagnostic testing is to separate acute streptococcal pharyngitis from pharyngitis of other etiologies (particularly viral) so that antibiotics can be prescribed more efficiently for patients to whom they may be beneficial. The most appropriate standard for the diagnosis of streptococcal pharyngitis, however, has not been definitively established. Throat swab culture is generally regarded as such. However, this method cannot distinguish between infection and colonization, and it takes 24–48 h to yield results that vary according to technique and culture conditions. Rapid antigen-detection tests offer good specificity (90%) but lower sensitivity when implemented in routine...

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Chapter 031. Pharyngitis, Sinusitis, Otitis, and Other Upper Respiratory Tract Infections (Part 10) Diagnosis The primary goal of diagnostic testing is to separate acute streptococcal pharyngitis from pharyngitis of other etiologies (particularly viral) so that antibiotics can be prescribed more efficiently for patients to whom they may be beneficial. The most appropriate standard for the diagnosis of streptococcal pharyngitis, however, has not been definitively established. Throat swab culture is generally regarded as such. However, this method cannot distinguish between infection and colonization, and it takes 24–48 h to yield results that vary according to technique and culture conditions. Rapid antigen-detection tests offer good specificity (>90%) but lower sensitivity when implemented in routine practice. The sensitivity has also been shown to vary across the clinical spectrum of disease (65–90%). Several clinical prediction systems (Table 31-3) can increase the sensitivity of rapid antigen-detection tests to >90% in controlled settings. Since the sensitivities achieved in routine clinical practice are often lower, several medical
and professional societies continue to recommend that all negative rapid antigen- detection tests in children be confirmed by a throat culture to limit transmission and complications of illness caused by group A streptococci. The Centers for Disease Control and Prevention, the Infectious Diseases Society of America, the American College of Physicians, and the American Academy of Family Physicians do not recommend backup culture when adults have negative results in a high-sensitivity, rapid antigen-detection test, however, given the lower prevalence and smaller benefit in this age group. Table 31-3 Guidelines for the Diagnosis and Treatment of Acute Pharyngitis Age Diagnostic Criteria Treatment Group Recommendationsa Adults Clinical suspicion of Penicillin V, 500 streptococcal pharyngitis (e.g., fever, mg PO tid, or tonsillar swelling, exudate, enlarged/tender anterior cervical lymph nodes, absence of cough or
coryza)b with: Amoxicillin, 500 mg PO bid, or History of rheumatic fever or Erythromycin, 250 mg PO qid, or Documented household Benzathine exposure or penicillin G, single dose of 1.2 million units IM Positive rapid strep screen Children Clinical suspicion of Amoxicillin, 45 streptococcal pharyngitis (e.g., mg/kg qd PO in divided tonsillar swelling, exudate, doses (bid or tid), or enlarged/tender anterior cervical lymph nodes, absence of coryza)
with: Penicillin VK, 50 mg/kg qd PO in divided doses (bid), or History of rheumatic fever or Cephalexin, 50 mg/kg qd PO in divided doses (qid), or Documented household Benzathine exposure or penicillin G, single dose of 25,000 units/kg IM Positive rapid strep screen or Positive throat culture (for patients with negative rapid strep screen) a Unless otherwise specified, the duration of therapy is generally 10 d, with appropriate follow-up.
b Some organizations support treating adults who have these symptoms and signs without administering a rapid streptococcal antigen test. Sources: Cooper et al, 2001; Schwartz et al, 1998. Cultures and rapid diagnostic tests for other causes of acute pharyngitis, such as influenza virus, adenovirus, HSV, EBV, CMV, and M. pneumoniae, are available in some locations and can be used when these infections are suspected. The diagnosis of acute EBV infection depends primarily on the detection of antibodies to the virus with a heterophile agglutination assay (monospot slide test) or enzyme-linked immunosorbent assay. Testing for HIV RNA or antigen (p24) should be performed when acute primary HIV infection is suspected. If other bacterial causes are suspected (particularly N. gonorrhoeae, C. diphtheriae, or Y. enterocolitica), specific cultures should be requested since these organisms may be missed on routine throat swab culture.