Chapter 30-4: Group A Beta-Hemolytic Streptococci (GABHS) pharyngitis

TEXTBOOK PRESENTATION

The presenting symptoms and signs of GABHS pharyngitis include rapid onset of severe throat pain, moderate fever (39–40.5°C), malaise, and headaches. Examination of the throat reveals edema and erythema of the posterior pharynx and tonsils are often covered with gray-white exudates. The anterior cervical lymph nodes are tender. Gastrointestinal symptoms of nausea, vomiting, and abdominal pain may also be present, especially in children.

DISEASE HIGHLIGHTS

1. GABHS is generally suspected when fever and throat pain are present and cough, coryza, and rhinorrhea are absent.

2. Untreated GABHS typically lasts 8–10 days. Patients are infectious during the acute illness and for up to 1 week afterward.

3. GABHS infection is associated with 2 important postinfectious syndromes.

   1. Acute rheumatic fever

      1. Presents 1–5 weeks after throat infection

      2. Clinical diagnosis based on Jones criteria (2 major or 1 major and 2 minor)

         1. Major: Carditis, arthritis, chorea, subcutaneous nodules, erythema marginatum

         2. Minor: Fever, arthralgia, elevated acute phase reactants, prolonged PR interval on ECG

      3. Due to aggressive treatment of GABHS, acute rheumatic fever is uncommon in the developed world (but still common in developing nations). Annual incidence in the United States is 1/1,000,000 population.

   2. Acute post-streptococcal glomerulonephritis

      1. Presents 1–2 weeks after GABHS pharyngitis

      2. Important findings are edema, hematuria, proteinuria, and hypertension

EVIDENCE-BASED DIAGNOSIS

1. Clinical diagnosis of GABHS pharyngitis

   1. Pretest probability

      1. The pretest probability of a patient having GABHS pharyngitis is based primarily on the patient’s age, clinical setting, and season.

      2. The pretest probability of strep throat in the adult clinic–based population is 5–10%.

      3. Because strep throat is more common in autumn and winter, it may be appropriate to adjust this estimate upward or downward according to season.

   2. Clinical findings and clinical decision rules

      1. The modified Centor score, one of the best validated clinical decision rules, assigns 1 point for each of the following findings: tonsillar exudates, swollen tender anterior cervical nodes, absence of cough, history of fever, and age < 15 years. One point is subtracted for age over 45 and older.

      2. The likelihood ratios and posttest probabilities given a pretest probability of 10% are given in Table 30-3.

2. Laboratory diagnosis

   1. Throat culture

      1. A single swab throat culture has a sensitivity of approximately 90–95% and specificity of 95–99%.

      2. The major disadvantage of throat cultures is the 24- to 72-hour delay in obtaining results.

   2. Rapid antigen detection test (RADT)

      1. Results from RADTs are available within a few minutes

      2. Sensitivity ranges from 70% to 90% when compared with throat culture with sensitivities in actual practice being toward the lower end of this range.

      3. Specificity for RADTs ranges from 90% to 100%.

3. Integrated use of clinical decision rules and laboratory methods

   1. Generally, clinicians use the results of a clinical decision rules to determine which patients require further testing.

   2. Patients at the lowest risk (modified Centor score 0–1, low pretest probability) receive no testing.

   3. Patients at higher risk (modified Centor score 2–3, posttest probability 5–50%) should ...