Rapid antigen tests may provide faster bacterial pharyngitis screening

Rapid antigen detection testing (RADT) may improve diagnosis of acute bacterial pharyngitis in the community by providing quicker yet comparably sensitive results as throat culture, according to a local study.

In a paper recently published in the Universiti Kebangsaan Malaysia (UKM) in-house journal Sains Malaysiana, a team of UKM and Queen Elizabeth Hospital researchers reported on an investigation which evaluated RADT in screening for Group A Streptococcal (GAS) pharyngitis among children at a primary care clinic. [2021;50(11):3345–3354]

The study included 110 children aged 3–15 years who presented with sore throat, inflamed pharynx, or enlarged tonsils at a primary care clinic over a 1-year period. Both throat cultures and RADT were used to assess for GAS.

Among the group, RADT identified eight (7.3 percent) cases of GAS, while throat culture identified six. Using throat culture results as the gold standard, RADT provided a sensitivity and specificity of 100 percent (95 percent confidence interval [CI], 54–100 percent) and 98 percent (95 percent CI, 93.2–99.8 percent) respectively. Both RADT and throat culture results were in strong agreement, as determined by Cohen’s kappa analysis (κ=0.848; 95 percent CI, 0.640–1.055; p<0.001).

“Theoretically, RADT is easy to perform in clinical settings, particularly in primary care clinics. The ability to provide results during the same clinic session, [versus] the traditional culture method which requires 42–72 hours, can help reduce the time-to-result for the clinician to decide on giving appropriate antibiotics,” said the researchers.

While acute pharyngitis may be due to a variety of viral or bacterial agents, GAS is known to account for 15–30 percent of cases among children aged below 15 years, based on a US study. [Infect Dis Clin North Am 2007;21:449–469]

“The non-specific nature of clinical signs and symptoms for bacterial pharyngitis require additional tools to assist diagnosis. RADT showed a good sensitivity and specificity when evaluated against throat cultures as a laboratory reference method,” they added.

The same study also evaluated the McIsaac score, a standardized clinician’s tool for classifying the risk of bacterial pharyngitis based on symptoms and age range. [JAMA 2004;291:1587–1595]

“[We found that the] combination of RADT and McIsaac score proved useful as a screening tool for bacterial pharyngitis. This could reduce the over-prescription of antibiotics and help to prevent antimicrobial resistance in the community,” concluded the team.

Patients excluded from the study were those who refused throat swabs, had received antibiotic therapy in the 2 weeks before presentation at the time of the study, or who could not provide informed parental consent.

The researchers acknowledged that the 7.3 percent prevalence of GAS among the study group might not reflect the wider national prevalence, as participants were drawn from a single-centre urban setting. Other limitations included the use of only a single commercially available RADT kit rather than a variety.