Download Testing for Group A Streptococcal Pharyngitis

Testing for Group A Streptococcal Pharyngitis Sore throat is one of the most common complaints seen in any primary care setting.
It is primarily a disease of school age children in the winter and spring. Most of
these sore throats are viral but of those that are bacterial, group A streptococcus is
the most common cause. [1] Strep can account for 15-30% of cases in pediatric
patients but only 5-10% of cases in adults. [2] The rate is slightly higher in adults
whose occupation brings them into frequent contact with children or those who are
parents of school aged children.
The most common complication of a strep infection is rheumatic fever. The rate of
rheumatic fever in adults is extremely low. Other complications such as
glomerulonephritis, or chorea are even rarer still. It is also clear that therapy can be
postponed for up to 9 days after onset of symptoms and still be able to prevent
sequela such as rheumatic fever. [3] Because of these facts, it is much less worrisome
to miss a strep infection in an adult on the first presentation.
The current rapid strep tests have a specificity of 95% which means the false
positive rate is only 5%. [4] So any positive test should be treated and no further
testing is needed. The sensitivity of the rapid tests ranges from 80% to 90% which
means the false negative rate ranges from 10-20%. Given the above incidence of
disease and complications and the long window of treatment opportunity in adults, it
is sufficient to routinely only do a rapid test without a backup culture on patients who
are symptomatic.
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Our lab testing process for strep throat is changing. This particular testing procedure
was looked at because sore throat is one of the most common complaints seen in all
primary care settings and therefore generates many tests. Not even experts can
distinguish a bacterial sore throat from a viral sore throat, especially in adults, based
solely on history, symptoms and exam. National data also states that approximately
70% of patients presenting with sore throat receive antibiotics which means we are
treating patients with unneeded antibiotics. [5] A laboratory confirmation of infection
provides a way of determining who really needs the antibiotics without doing an
extensive amount of testing. Proposed changes are based on national
recommendations, accuracy of the rapid test, incidence of disease in different age
groups, incidence of complications of disease in different age groups, and the cost of
care.
Our new testing protocol will be as follows: For all patients less than 21 years of age
a back up culture will routinely continue to be done on anyone that has a rapid test
done, whether ordered by a nurse or provider. There is no change in procedure for
this age group. For those 21 years of age and over 21 years of age only rapid tests
will be done unless there is a clinical reason to do a culture such as previous history
of strep complications, symptoms with a known exposure, or an
immunocompromised patient. These criteria will be clearly spelled out in the
standing order for nurses to use. However this means that when a throat culture
is indicated, it will need to be ordered separately for these patients.
There are a few other things to keep in mind. Anyone who has been treated with
antibiotics for strep within the past 2-3 weeks should only receive a throat culture
because a rapid test is not accurate in those circumstances. Also a positive test does
not distinguish those who are carriers from those who are infected. It is important to
only test those that have symptoms to avoid treating those that are carriers and not
infected. If someone has a negative rapid test and is symptomatic you may wish to
retest them if symptoms such as fever (>101) persist for more than 3 days, or
inability to swallow liquids, rash, swollen joints, or cola colored urine appear. These
precautions are also spelled out in the standing orders the nurses use and in the
patient education materials.
With the new procedure we will be able to eliminate unnecessary testing and treat
only those who have symptoms and positive tests and really need the antibiotics.
This increases patient safety, reduces the chances of developing antibiotic resistance,
and lowers the cost of care.
References:
1. Practice Guidelines for the Diagnosis and Management of Group A
Streptococcal Pharyngitis, Alan L Bisno, Michael A Gerber, Jack M.
Gwaltnery, et al. Clinical Infectious Disease (2002) 35 (2): 113-125
http://cid.oxfordjournals.org/content/35/2/113.full
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2. Linder JA, Stafford RS, Antibiotic treatment of adults with sore throat by
community primary care physicians. JAMA 2001;286:1181-6
3. Nyquist AC, Gonzales R, Steiner JF, Sane MA. Antibiotic prescribing for
children with colds, upper respiratory tract infections, and bronchitis. JAMA
1998;279:875
4. Bisno AL. Acute Pharyngitis: etiology and diagnosis. Pediatrics 1996;
97:949-54
5. Poses RM, Cebul RD, Collins M, Fager SS. The accuracy of experienced
physicians’ probability estimates for patients with sore throats: implications
for decision making. JAMA 1985:254:925-9
6. Komaroff AL, Pass TM, Aronso MD et al. The prediction of streptococcal
phyngitis in adults. J Gen Internal Medicine 1986:1:1-7
7. Bisno AL. Acute pharyngitis. New England Journal Medicine
2001;344:205-11
8. Cantazaro FJ, Stetson CA Morris AJ et al. the role of streptococcus in the
pathogenesis of rheumatic fever. Am J Med 1954;17:749-56
9. Gerber MA. Comparison of throat cultures and rapid strep tests for diagnosis
of streptococcal pharyngitis. Pediatric Infectious Disease Journal 1989;
8:820-4
Questions: Please reply to this e-mail, and your questions(s) will be directed to the
author of this Pearl, R.L. Mitchell, M.D.
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All Pearl recommendations are consistent with professional society guidelines,
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