positive rapid strep tests do not
necessitate a back-up culture
because they are highly specific.
1. The routine use of back-up throat
cultures for those with a negative rapid
strep test is not generally recommended
for adults, because of the low incidence
of GAS pharyngitis, and because the
risk of subsequent acute rheumatic
fever is exceptionally low. Physicians
who wish to ensure they are achieving
maximal sensitivity in diagnosis may (of
course) continue to use conventional
throat culture or back up negative rapid
strep tests with a culture.
2. Anti-streptococcal antibody titers are
not recommended in the routine
diagnosis of acute pharyngitis as they
reflect past but not current events.
Who Should Undergo
Testing for GAS Pharyngitis?
1. Testing for GAS pharyngitis usually is
not recommended for children or adults
with acute pharyngitis with clinical and
epidemiological features that strongly
suggest a viral basis (e.g, cough, runny
nose, hoarseness, and oral ulceration).
2. Diagnostic studies for GAS pharyngitis
are not indicated for children under
three years old because acute rheumatic
fever is rare in children under three
years old, and the incidence of
streptococcal pharyngitis and the classic
presentation of streptococcal
pharyngitis are uncommon in this age
group. Selected children under three
years old who have other risk factors,
such as an older sibling with GAS
infection, may be considered for testing
3. Follow-up post treatment throat
cultures or rapid strep testing are not
recommended routinely but may be
considered in special circumstances
4. Diagnostic testing or empiric
treatment of asymptomatic
household contacts of patients with
acute streptococcal pharyngitis is not
routinely recommended
If the results of the rapid strep test are
positive, further testing is not necessary, and
treatment can be started immediately.
Testing Guidelines
l. The Rapid Strep Test (RST)
Description
A major disadvantage of throat cultures is
the delay (overnight or longer) in obtaining
“ Physicians who wish
to ensure they are
achieving maximal
sensitivity in diagnosis
may (of course)
continue to use
conventional throat
culture or back up
negative rapid strep
tests with a culture.”
Irwin Z. Rothenberg, COLA Resources, Inc.
results. RSTs have been developed for the
identification of GAS pharyngitis directly
from throat swabs, with shorter turnaround
time. Rapid ide ntification and treatment of
patients with GAS pharyngitis can reduce
the risk of spread, allowing the patient to
return to school or work sooner, and can
reduce the acute associated morbidity. The
use of RSTs for certain populations (e.g,
patients in emergency departments) was
reported to significantly increase the
number of patients appropriately treated
for streptococcal pharyngitis, compared
with traditional throat cultures.
RSTs currently available are highly
specific (approximately 95%) when
compared with blood agar plate cultures.
False-positive test results are highly
unusual, and therefore therapeutic
decisions can be made with confidence
on the basis of a positive test result.
Unfortunately, the sensitivity of most of
these tests is 70%–90%, compared with
blood agar plate culture.
The first RSTs used latex agglutination
methods, were relatively insensitive, and
had unclear end points. Newer tests based
on enzyme immunoassay techniques offer
increased sensitivity and a more sharply
defined end point.
The practitioner should be aware that
some of these rapid strep tests are not
waived, and therefore, require proper
certification or accreditation of the
physician's laboratory. Neither conventional
throat culture nor RSTs accurately
differentiate acutely infected persons from
asymptomatic streptococcal carriers with
viral pharyngitis. Nevertheless, they allow
physicians to withhold antibiotics from the
great majority of patients with sore throats
for whom results of culture or RST are
negative. This is of extreme importance,
because nationally up to 70% of patients
with sore throats seen in primary care
settings receive prescriptions for
antimicrobials, while only 20%–30% are
likely to have GAS pharyngitis.
Since the sensitivities of the various
RSTs are <90% in most studied
populations of children and adolescents,
and because the proportion of acute
pharyngitis due to GAS in children and
adolescents is sufficiently high (20%–30%),
a negative RADT should be accompanied
by a follow-up or back-up throat culture in
children and adolescents, while this is not
necessary in adults under usual
circumstances, as noted above.
Procedure
Obtaining a specimen is the same
whether your doctor will do a throat
culture or rapid test for strep. A cotton
swab (similar to a Q-tip) is quickly
rubbed over both tonsils as well as the
back wall of the mouth (the posterior
pharynx). It is important to avoid contact
with other structures inside the mouth
such as the tongue or cheeks. The swab is
then placed in a specialized container
and the rapid test performed. Many
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