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The pivotal points in Mr. W’s history include his sudden onset of sore throat, fever, and headache. These symptoms suggest an infectious cause of sore throat. The differential diagnosis includes bacterial pharyngitis, most commonly GABHS. The absence of cough, rhinorrhea, and coryza make the common viral causes of pharyngitis less likely. In general, patients with viral pharyngitis have cough, coryza, rhinorrhea, and hoarseness while those with bacterial pharyngitis or mononucleosis have fever, tender anterior cervical lymphadenopathy, tonsillar erythema with or without tonsillar swelling and exudates. They do not typically have rhinorrhea, cough, or conjunctivitis.
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Influenza can cause fevers and throat pain but is usually associated with cough and myalgias. Infectious mononucleosis, which is most often caused by EBV, can also cause sore throat and fever but most often occurs in persons between the ages of 15 and 24 years and is associated with malaise and marked adenopathy. Primary HIV infection can present with nonspecific symptoms of pharyngitis, fever, adenopathy, and fatigue and should also be considered in high-risk persons. Table 30-2 lists the differential diagnosis for Mr. W.
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Mr. W is otherwise healthy. He has had no recent sick contacts and no recent travel. He is a heterosexual male, married, and monogamous with his wife. He has no history of blood transfusions or illicit drug use.
The physical exam is notable for temperature of 39.2°C, blood pressure is 130/70 mm Hg, pulse is 98 bpm, and respiratory rate is 12 breaths per minute. Sclera and conjunctiva are not injected. Oropharyngeal exam reveals bilateral tonsillar hypertrophy and exudates without ulcers. He has no cervical lymphadenopathy on exam. His abdominal is soft with normal bowel sounds. Skin exam is unremarkable.
Is the clinical information sufficient to make a diagnosis, if not what other information do you need?
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Leading Hypothesis: GABHS pharyngitis
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Textbook Presentation
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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.
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GABHS is generally suspected when fever and throat pain are present and cough, coryza, and rhinorrhea are absent.
Untreated GABHS typically lasts 8–10 days. Patients are infectious during the acute illness and for up to 1 week afterward.
GABHS infection is associated with 2 important postinfectious syndromes.
Acute rheumatic fever
Presents 1–5 weeks after throat infection
Important findings are pancarditis, rash, subcutaneous nodules, chorea, or migratory polyarthritis
Due to aggressive treatment of GABHS, this complication is uncommon in the developed world (but still common in developing nations). Annual incidence in the United States is 1/1,000,000 population.
Acute post-streptococcal glomerulonephritis
Presents 1–2 weeks after GABHS pharyngitis
Important findings are edema, hematuria, proteinuria, and hypertension
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Evidence-Based Diagnosis
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Clinical diagnosis of GABHS pharyngitis
Pretest probability
The pretest probability of a patient having GABHS pharyngitis is based primarily on the patient’s age, clinical setting, and season.
The pretest probability of strep throat in the adult clinic–based population is 5–10%.
Because strep throat is more common in autumn and winter, it may be appropriate to adjust this estimate upward or downward according to season.
Clinical findings and clinical decision rules
Because individual clinical findings (such as the presence of fever or exudates) are not very predictive of GABHS, clinical prediction rules have been developed.
These rules use the key features in the history and physical exam to predict the probability of strep throat.
The Modified Centor score (one of the best validated clinical decision rules) assigns patients 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.
The likelihood ratios and posttest probabilities given a pretest probability of 10% in given in Table 30-3.
Laboratory diagnosis
Throat culture
A single swab throat culture has a sensitivity of approximately 90–95% and specificity of 95–99%.
The major disadvantage of throat cultures is the 24- to 72-hour delay in obtaining results.
Rapid antigen detection test (RADT)
Results from RADTs are available within a few minutes
Sensitivity ranges from 70% to 90% when compared with throat culture with sensitivities in actual practice being toward the lower end of this range.
Specificity for RADTs ranges from 90% to 100%.
Integrated use of clinical decision rules and laboratory methods
Generally, clinicians use the results of a clinical decision rules to determine which patients require further testing.
Patients at the lowest risk (low pretest probability and low Modified Centor Score) receive no testing.
Patients at higher risk (posttest probability 5–50%) usually receive a RADT or throat culture.
Those at the highest risk (> 50%) are often treated empirically but may be receive a RADT or throat culture.
Given the sensitivity of RADT and the exceptionally low risk of acute rheumatic fever in adults, a throat culture is not necessary when an RADT is negative. (In children and adolescents, a negative RADT should be verified by throat culture.)
Positive RADTs do not require back up with a culture because they are highly specific.
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Patients with GABHS pharyngitis should be treated with appropriate antibiotic therapy to prevent development of acute rheumatic fever.
Penicillin and amoxicillin are the first-line antibiotics given their narrow spectrum of activity and modest cost.
For patients with an allergy to penicillin, choices include first-generation cephalosporins, clindamycin, clarithromycin, or azithromycin.
Treatment decreases severity of symptoms, reduces risk of transmission, and reduces the likelihood of suppurative complications.
There is no evidence that antibiotic treatment can prevent the development of acute glomerulonephritis.
Clinical improvement within 48 hours is expected; patients who do not improve should be re-evaluated.
Tonsillectomy is only indicated for patients with 4 or more episodes of severe pharyngitis in a year.
Any patient with documented GABHS pharyngitis who does not improve within 48 hours of treatment with an appropriate course of antibiotics should be re-evaluated.