Clinical rules to decide who needs rapid antigen testing for strep throat not accurate

NEW YORK - Clinical rules to decide which children with pharyngitis need rapid antigen testing for group A streptococcal infection are not accurate enough to rely on, researchers from France report.

"Our results show that existing clinical prediction rules are not sufficiently accurate to be used in children," said Dr. Jérémie F. Cohen from Paris Descartes University.

"Some rules may be sufficiently sensitive but insufficiently specific, leading to important numbers of unnecessary antibiotic prescriptions. On the other hand, some rules may be sufficiently specific but insufficiently sensitive, leading to an increased risk of missing streptococcal cases that could lead to complications," he told Reuters Health by email.

"We believe that in settings where both high sensitivity and specificity are expected, clinicians should use a diagnostic strategy based on rapid testing in all children with pharyngitis, as recommended by the European Society of Clinical Microbiology and Infectious Diseases in 2012," Dr. Cohen said.

In contrast to the European recommendations, North American guidelines advise that clinicians select patients on the basis of clinical and epidemiological guidelines.

Canada has no guideline for the management of pharyngitis, and, in fact, clinical prediction rules for pharyngitis have never been compared with each other in a single pediatric population from a high-income country, according to Dr. Cohen's team.

The researchers found eight clinical prediction rules in the literature and were able to validate six of them using a prospective multicenter cohort of French children with pharyngitis.

The most frequent predictors included tenderness of lymph nodes, fever, age, tonsillar swelling and exudate. Unfortunately, the team says, the statistical analysis used for the derivation of these rules was poor.

In their own group of 676 children (where the prevalence of group A streptococcus was 41%), rapid antigen detection test sensitivity was 93% and specificity was 88%, they report in CMAJ, online December 8.

Application of the rule-based selective testing strategies yielded sensitivities ranging from 66% to 94% and specificities ranging from 40% to 88%, with none of the strategies fitting within their prespecified target zone of accuracy (both sensitivity and specificity of more than 85%).

In fact, none of the clinical prediction rules were able to identify patients at low risk (probability of group A streptococcus of 12% or lower) or high risk (probability at least 85%), the researchers say.

"Our study focused on diagnostic accuracy, assuming that patients with streptococcal pharyngitis would benefit from receiving antibiotics," Dr. Cohen said. "However, in high-income settings such as Western Europe and North America, acute rheumatic fever and rheumatic heart disease became extremely rare. In this context, the rationale for treating streptococcal pharyngitis with antibiotics is not anymore to avoid such non-suppurative complications. The goals of antibiotic treatment are now to reduce the duration and intensity of symptoms, to avoid suppurative complications such as quinsy, and to avoid spreading the germ. However, because high-quality evidence is lacking to support the use of antibiotics to pursue these goals, some scientific and medical societies such as the Dutch ones do not recommend any longer antibiotics in children with pharyngitis, even if due to group A streptococcus."

"If physicians want to avoid unnecessary antibiotic prescriptions while ensuring adequate treatment of streptococcal cases, they should use rapid testing as much as possible and not rely on existing clinical prediction rules," he concluded.

Dr. Didier Raoult from Faculté de Médecine in Marseille, France, who was not involved in the study, said "severe pharyngitis, tonsillitis, should be treated, specifically because not only streptococcus, but also Fusobacterium necrophorum can cause it and generate abscesses."

But, he told Reuters Health by email, "there is no sense to treat pharyngitis for prevention of a disease that has vanished."

SOURCE: http://bit.ly/1Abq2ka

CMAJ 2014.

References: Reuters Health
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