– Pharyngitis is most commonly caused by viral infections.
– Bacterial play a much smaller; Group A Strep (GAS) is the leader of this small pack.
– GAS is primarily a disease of children (5-15yrs is the “sweet spot;” however, it does occur in younger and older.
– GAS is a self-limited disease!
So why do we care?
– GAS can lead to complications, of which, it is Acute Rheumatic Fever (ARF) that we aim to prevent with treatment of GAS.
– During epidemics, ~3% of GAS left untreated may lead to ARF. With GAS occurring in isolated sporadic events, the incidence of ARF is much lower.
– Primary ARF is generally a disease of the young (oldest case report that I have found was a 38yr old, which is young by my standards).Secondary ARF can occur at any age; once you have had it, ARF recurs easily.
– ~60% of ARF will develop Rheumatic Heart Disease (which is why we care).
– The sequela of ARF can be severe.
– Treatment of ARF is difficult, therefore prevention is better.
– Treating GAS can effectively prevent ARF; however, most pharyngitis is viral.
– How do you prevent ARF without throwing antibiotics at everyone with a sore throat?
Accurate diagnosis of GAS
– Unfortunately nothing is perfect. The physical findings overlap between GAS and Viral etiologies.
– Centor Criteria
> 1) Tonsillar Exudates, 2) Tender cerivical LAD, 3) Absence of cough, 4) Fever
> Each criteria = 1 point.
> Positive Predictive Value of 3 or 4 points = ~40% (~60% would have negative throat culture)
> Negative Predictive Value of a score of 0 = ~81%
> Works better to rule-out the condition rather than rule it in.
– Throat Culture requires “vigorous swabbing on both tonsils and posterior pharynx.”
– RADT – a negative result does not rule-out the condition, so culture is needed to confirm results.
– Because of lower incidence of GAS and even lower risk of ARF in adults, no confirmatory test is recommended.
My interpretation of what the AHA recommends
– Use Centor Criteria to determine whether your pre-test probability is low enough to avoid testing.
– If you have no access to RADT, then use clinical suspicion and high Centor scores to treat empirically. Alternatively, a throat culture can be sent and antibiotic therapy delayed (you have more than a week (~10 days) before ARF would develop).
– If you have access to RADT, use it. Treat if positive. Send culture if negative and delay antibiotic therapy until result returns (unless it is an adult, in which case do not send culture).
– I would refrain from performing a test that I did not then act upon. Ask yourself whether you are going to ignore a negative RADT prior to doing it. If you are, then don’t do it. Although, I would prefer to ensure that I get an adequate sample and believe the test. That being said, we’ve all encountered that patient who made you break into a sweat to even get past his or her lips. In that case, if I don’t believe that I got an adequate sample, I won’t send the test and will either have the kid follow-up in another day or so to re-evaluate or treat empirically, depending on the H+P (and the phase of the moon).
Bisno, A: Editorial: Diagnosing Strep Throat in the Adult Patient: Do Clinical Criteria Really Suffice? Annals of Internal Medicine. July 15, 2003: 139 (2), 150-151.
Gerber, MA et al. Prevention of Rheumatic Fever and Diagnosis and Treatment of Acute Streptococcal Pharyngitis. AHA Scientific Statement. Circulation. 2009; 119:.