The Centers for Disease Control and Prevention (CDC) assembled a panel of national health experts, including physicians with expertise in internal, family, emergency and infectious disease medicine, to develop evidence-based guidelines for evaluating and treating adults with acute respiratory disease. The goal of the guidelines, which were compiled by the CDC and other members of the panel, is to provide physicians with practical strategies for limiting antibiotic use to patients who are most likely to benefit. The complete treatment guidelines were published in the March 20, 2001 issue of Annals of Internal Medicine, and they can be viewed online athttp://www.annals.org/issues/v134n6/full/200103200-00013.html.
The following information taken from the guidelines focuses on appropriate antibiotic use in acute pharyngitis. Acute pharyngitis accounts for 1 to 2 percent of all visits to outpatient clinics, physician offices and emergency departments. Approximately 5 to 15 percent of adult cases are caused by group A beta-hemolytic streptococcus. Antibiotics are prescribed to approximately 75 percent of adult patients with acute pharyngitis even though, in an otherwise healthy adult, the illness is self-limited and rarely produces significant sequelae.
Physicians report that they prescribe unwarranted antibiotics because they believe that patients expect them, that patients will reconsult if antibiotics are not prescribed, that patients will be unsatisfied without a prescription and that it is quicker to write a prescription than to explain why antibiotics are not needed. Physicians are not good at predicting which patients expect antibiotics, and patient satisfaction depends less on whether an antibiotic is prescribed, or even whether patient expectations are met, than on whether the physician shows concern and provides reassurance.
Diagnosing streptococcal pharyngitis remains controversial because the best criterion standard has not been definitively established. Testing for a significant increase in antistreptolysin titers and use of throat swab cultures cannot provide real-time results—results that are available when a decision about antibiotic use must be made. The delayed decision to use antibiotics eliminates the primary benefit (i.e., symptom relief) of antimicrobial therapy in adults. Throat cultures also have low test–retest agreement; do not always correlate with antistreptolysin titers; produce varied results depending on technique, sample site, culture medium, incubation conditions and whether the results were checked at 24 or 48 hours; and fail to distinguish acute infection from the carrier state.
In clinical screening, the most reliable predictors are the Centor criteria. These include tonsillar exudates, tender anterior cervical lymphadenopathy, absence of cough and history of fever. The presence of three or four of these criteria has a positive predictive value of 40 to 60 percent, and the absence of three or four criteria has a negative predictive value of approximately 80 percent.
Rapid antigen tests can be done at the bedside, and treatment decisions can be made in real time. The potential advantage of this test compared with clinical models is that it has approximately the same sensitivity and greater specificity than a throat culture.
Reasons to consider prescribing antimicrobials to treat streptococcal pharyngitis include a desire to prevent rheumatic fever, acute glomerulonephritis and suppurative complications, decrease contagion and ameliorate symptoms.
Because of repeatedly low and unchanging reported rates of acute rheumatic fever, the CDC dropped this disease from active national surveillance in 1994.
Acute glomerulonephritis does occur, but it is rare even in the absence of antibiotic treatment. There is no evidence that antimicrobial therapy decreases the incidence of this complication.
The incidence of suppurative complications is low, regardless of antibiotic treatment. The risk of peritonsillar abscess is not reduced because many patients do not seek treatment until after the complication has developed.
Streptococcal infection often occurs in epidemics, and contagion is a problem in areas of overcrowding or close contacts, such as schools, day care facilities and health care institutions. This is difficult to combat because there is an incubation period of two to five days, during which the infection unknowingly can be transmitted to others. For clinical decision making, it is reasonable to consider whether an adult is living in close quarters with others, especially small children.
Antimicrobial agents instituted within two to three days of symptom onset hasten improvement among patients with a positive throat culture or in patients with a high clinical likelihood of pharyngitis, but not in those with a negative culture.
Antibiotic therapy should be limited to patients with a high likelihood of pharyngitis who are likely to benefit from treatment, taking into consideration the patient's epidemiologic circumstances. If antimicrobial treatment is instituted, physicians should choose an agent with the narrowest possible spectrum of action. Penicillin is the first choice, and erythromycin should be used in patients who are allergic to penicillin.
The panel recommends the following strategies to select patients for antibiotic therapy. Use of the strategies should achieve the goal of treating a substantial portion of true-positive patients while limiting unnecessary antibiotic use.
Physicians should limit antimicrobial prescriptions to patients who are most likely to have streptococcal pharyngitis. All adult patients with pharyngitis should be clinically screened for the presence of the Centor criteria. Patients with none or one of these criteria should not be tested or treated. For patients with two or more criteria, physicians should use one of the following options: (1) test patients with two, three or four criteria using a rapid antigen test, and limit antibiotic therapy to patients with positive test results; (2) test patients with two or three criteria using a rapid antigen test, and limit antibiotic therapy to patients with a positive test result or patients with four criteria; or (3) do not use any diagnostic tests, and limit antibiotic therapy to patients with three or four criteria.
Throat cultures should not be performed for the routine primary evaluation of adults with pharyngitis or for confirmation of negative rapid antigen tests when the test sensitivity exceeds 80 percent.
All patients with pharyngitis should be offered appropriate doses of analgesics, antipyretics and other supportive care.
The preferred antimicrobial agent for treatment of acute pharyngitis is penicillin, or erythromycin for penicillin-allergic patients. There is no evidence of group A beta-hemolytic streptococcus resistance to or tolerance of penicillin, and erythromycin resistance rates are low in the United States.
These guidelines do not apply to patients with a history of rheumatic fever, valvular heart disease, immunosuppression, recurrent or chronic pharyngitis, or to patients with sore throats not caused by acute pharyngitis. Also, the guidelines should not be used during a known epidemic of acute rheumatic fever or streptococcal pharyngitis or in nonindustrialized countries in which the endemic rate of acute rheumatic fever is much higher than in the United States.