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Streptococcal pharyngitis
Guidelines back the withholding
of antibiotics
an interview with Kevin R. Forward,
MD
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To treat
or not to treat?
Pharyngitis is one of the most common complaints heard by family
doctors -- approximately 1% of office visits are for sore throats.
The proportion is even higher when you consider incidents of pharyngitis
associated with other upper respiratory tract infections. While
the majority of cases are caused by a viral infection, a large percentage
of patients leave the office with an antibiotic prescription. Indeed,
there's a multitude of approaches that physicians take to the management
of pharyngitis -- a surprising observation, given that a sore throat
is seemingly one of the least complex problems seen in clinical
practice. So what's the best evidence-based approach?
Is it really
strep?
Most patients presenting with a sore throat don't have streptococcal
pharyngitis, but most get antibiotics. Streptococcus pyogenes
(group A streptococci) cause only between 15 and 30% of cases of
pharyngitis in children and even less in adults, where the rate
is approximately 5-10%.1 The incidence
changes seasonally, with an increase in winter and early spring
months. Understanding the epidemiology of streptococcal pharyngitis
is complicated by the fact that up to 10% of children may be colonized
with S. pyogenes -- without signs or symptoms. While it's
been suggested that infection and asymptomatic colonization may
be differentiated based on the number of organisms present in culture,
there's too much overlap for this information to be clinically useful.
There are a number of viruses and bacteria
other than S. pyogenes that are known to cause pharyngitis
(see
Table 1).1 In some cases,
infection is localized to the upper respiratory tract and may be
associated with other features such as rhinitis, cough and/or conjunctivitis
-- which actually makes S. pyogenes less likely. Pharyngitis
can also be a manifestation of a systemic process, e.g. infection
with the Epstein-Barr virus, Mycoplasma or Chlamydia,
as well as influenza. While Arcanobacterium haemolyticum,
group C and G streptococci, Mycoplasma pneumoniae and Chlamydophila
pneumoniae may also cause pharyngitis, the case for diagnosis
and antibiotic treatment of these isn't strong enough to justify
specific testing. When arcanobacteria and other streptococci are
reported, they often represent incidental findings in conventional
cultures.
When do we
treat with antibiotics?
Antibiotic treatment for pharyngitis typically focuses on S. pyogenes.
The duration of symptoms is shortened by only a day with these meds,
but they may prevent suppurative complications such as peritonsillar
abscesses and otitis media. While there's irrefutable evidence that
treatment of strep throat may prevent rheumatic fever, this condition
is extraordinarily rare in Canada -- and has been for the last several
decades. So the prevention of rheumatic fever can no longer be used
as justification for "empirical" antibiotic treatment of pharyngitis.
Antibiotics are also not indicated for the prevention of post-streptococcal
glomerulonephritis because they aren't effective here -- although
this isn't widely known.
What are
the telltale symptoms of strep?
Clinical features may help identify patients with a great likelihood
of streptococcal pharyngitis.2 Children and patients with fever,
cervical adenitis, pharyngeal redness and exudates are most likely
to have strep, while adults over the age of 45 and people who present
with cough are less likely. So these characteristics have been used
to develop a number of assessment tools. The most useful of these
-- the McIsaac Decision Rule -- was developed and validated in Canada
(see
Table 2).3 Table 3 relates
its assessment scores to the proportion of patients who test positive
for streptococcal pharyngitis.3
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