When to Skip Cultures in Kids With Pharyngitis

William T. Basco, Jr., MD, MS


August 11, 2017

Can We Place Our Trust in 'Overt Viral Features'?

It can be difficult to differentiate between viral and bacterial pharyngitis caused by group A Streptococcus (GAS), in part because of significant overlap in the symptoms and physical findings between these two entities. Nevertheless, current guidelines suggest that clinicians should avoid the sequence of rapid antigen testing followed by throat culture for all antigen-negative tests if a patient presents with overt viral features. Rhinorrhea, cough, oral ulcers or vesicles, conjunctivitis, stomatitis, and hoarseness all qualify as overt viral features. The rationale for this recommendation is that as many as 1 in 5 children carry oropharyngeal GAS, so testing all children with viral illnesses will reveal some cases of pharyngitis with a positive culture for GAS that actually represent pharyngeal colonization.

A recent analysis from a prospective study[1] assessed a cohort of children who underwent laboratory testing for GAS pharyngitis to determine the proportion of children who had overt viral features with true GAS pharyngitis. These data were collected from children aged 3-21 years who were evaluated in a single emergency department from 2013 to 2015. All children presented with sore throat, and a rapid antigen test was conducted. Attending clinicians who saw the children documented specific symptoms and physical findings as part of the research protocol. The rapid antigen tests were performed at the point of care, and negative rapid tests were confirmed by throat culture.

Approximately 45% of the 320 total visits were made by children younger than age 18 years, and 60% were girls. About one third (35%) of the children were febrile upon admission. A rapid antigen test was obtained in 28% of the children, 6% of whom had a positive bacterial culture after a negative rapid antigen test. Overt viral features were common, with 49% of all children reporting cough and 40% experiencing rhinorrhea, but only 4% had evidence of oral ulcers or vesicles and only 2% exhibited conjunctival injection. Only 37% of the children presented with no viral features, whereas 30% had two or more features.

GAS was confirmed in 34% of the overall sample. An inverse correlation was demonstrated between overt viral features and GAS status, and there was a statistically significant trend toward decreased GAS prevalence as the number of viral features increased. The prevalence of GAS pharyngitis in patients without viral features (42%) was higher than in patients with viral features (29%; P = .01). Some viral features were present in large proportions of both GAS-positive and GAS-negative children. For example, cough was present in 51% of the GAS-negative children and 43% of the GAS-positive children. Similarly, rhinorrhea was present in 44% of the GAS-negative children and 30% of the GAS-positive children.

The study authors concluded that the number of viral features was associated with GAS status. Furthermore, they urge additional investigation with larger datasets collected in varied settings to determine whether clinicians can identify a population of patients with pharyngitis who should not undergo GAS testing.


I imagine that two opposing camps—those who believe that we overidentify and therefore overtreat GAS carriers, and those who believe that we run the risk of undertreating true GAS pharyngitis—can both find support for their arguments in these study findings. The issue I can't shake is that 23% of the children with symptoms of pharyngitis who exhibited two or more viral symptoms were indeed positive for GAS. In some populations, that percentage is identical to the carrier rate, raising the question of whether we are merely detecting carriers among those with multiple viral features. However, there's no way to connect those dots in this study. So, although the study raises intriguing questions and provides interesting data to show that the chance of identifying GAS in children exhibiting several features of viral illness is low, the number with GAS is still significant and bears consideration.


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