This post is in direct response to a question that was asked recently. There is a surprising amount of dogma around the subject of strep testing, but one major piece is that children under three years of age should not be tested for strep because of its reported rarity. However, there have been multiple studies that disagree with this claim, and we took a mini deep-dive on the subject.
First off, why does it matter? Group A Streptococcus (GAS) is an easily testable infection that can help us modify our management. In the patient with URI symptoms where GAS is a suspected cause versus potentially a viral infection, a positive test can lend us to appropriate treatment. The debate about if strep throat needs to be treated is an entirely separate issue. However, if you are interested in that debate check out sources like REBEL EM.
It is confusing and difficult to find primary literature on the subject of testing children under three years of age because guidelines either do not cite the primary source directly or defer to previous guidelines. This is where we start to get concerned for the development of dogma. As a reminder, dogma is defined as "a principle or set of principles laid down by an authority as incontrovertibly true."
The IDSA published guidelines in 2012 regarding the diagnosis and management of GAS. In those guidelines they state, "Diagnostic studies for GAS pharyngitis are not indicated for children <3 years old because acute rheumatic fever is rare in children <3 years old and the incidence of streptococcal pharyngitis and the classic presentation of streptococcal pharyngitis are uncommon in this age group."
Sounds simple enough, right? The Infectious Diseases Society of America (IDSA) has an educated and exhaustive search. However, in further discussion, they start to contradict themselves. In the same publication they report that GAS pharyngitis is 37% in school-aged children, 24% in <5 years, and 10-14% in children <3 years of age. Although lower in these younger age groups, it is still clinically significant. They further discuss that these numbers drop more when a corresponding rise in ASO is required with it ranging as low as 0-6%. Both the 1994 and the 1999 studies cited have smaller populations but even in those studies they acknowledge that strep can happen within the first year of life! Remember, the dogma here is that GAS is rare if not non-existent in those under three years of age and we should not test them.
Furthermore, the IDSA publication even mentions in its own work that testing should be considered in those with known risk factors such as an older sibling with GAS or being in a setting such as daycare where there are known GAS cases. However, they also acknowledge the presentation can be different in these young patients with symptoms such as fever, mucopurulent rhinitis, excoriated nares, and diffuse adenopathy. The exudative pharyngitis is actually rare in this age group but is more common and looked for in the older age groups.
How young should we be testing? That part is difficult, but one case report demonstrated a 62 day old infant with GAS. A two month old is admittedly rare, but it acts as an important reminder that GAS still occurs and should at least be considered in the differential.
A meta-analysis of 29 articles was published in 2010 that also supported that children under five years of age did have GAS, but it was at lower rates versus those over five years of age. Even though disease prevalence was less, it was still there. In one accessible article from a single emergency department, GAS caused 30% of pharyngitis in children between 2-3 years of age alone!
Some may want to turn to Centor Criteria to argue that strep testing should not be done in those children under three years of age. Although it is true that the criteria started at 3 years of age, remember that young children present differently. More importantly though, even the authors admit that the criteria was originally designed for adults and not pediatric patients. In Dr. Centor's comments on MDCalc, "We studied adults, and thus have always been wary of applying it to children. More recently, we have published a review that shows that pre-adolescent pharyngitis has many differences from adolescent/young adult pharyngitis. McIsaac has developed an adjustment for age which might be appropriate for pre-adolescents." The key word there is "might" and like Ken Milne on The SGEM reminds us it we should also substitute it for "might not" when we see that word.
Finally, the argument could be made about its importance to diagnose in this age. This in some ways goes back to the argument about needing to treat GAS at all. Although rare, acute rheumatic fever among others is a serious complication. Of the 541 new cases of acute rheumatic fever reported from Salt Lake City, only 5% involved individuals under 5 years of age. The youngest case though was less than 2 years of age. Again, this is not a never event and goes against the dogma. With the global burden of GAS and its complications, if the argument alone to not test is because of age, we should reconsider.
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