Objective:

To establish the sensitivity and specificity of three diagnostic approaches in Group A Streptococcal pharyngitis: a rapid antigen test, a sore throat score and a combination of these two vs. culture.

Methods:

This study included 91 patients hospitalised between 15 May and 1 December 2003 in Infectious Disease Hospital from Lasi, Romania. Two pharyngeal swabs were collected from each patient, one for rapid antigen test (One Step Strep A Test Cassette – AccuBioTech – a two side sandwich immunoassay) and the other for culture. All beta haemolytic streptococci were identified as group A with a latex-agglutination kit (Slidex Strepto A – BioMerieux). The sore throat score had five criteria: age, fever, absence of cough, tender anterior cervical nodes, tonsillar swelling or exudates. The score range is -1 to 5. In this study we included only patients with no antibiotic therapy prior to examination and with no other infectious diseases.

Results:

Of the 91 patients, 30 (32.97%) had a positive result for group A streptococci (culture plus latex agglutination – considered gold standard). Rapid antigen test had two false positive and one false negative results. This test had a sensitivity of 96.67% (95%CI: 82.78–99.92%) and a specificity of 96.72% (95% CI: 88.65–99.6%). Score higher or equal to 3 had a sensitivity of 51.61% (95% CI: 33.06–69.85%) and a specificity of 60% (95%CI: 46.54–72.44%). All 10 patients with score 0 had negative results for rapid strep and culture. If we add results from rapid antigen testing to all patients with score higher or equal to 3 we will not miss any positive result (95%CI: 69.15–100%) and will have a good specificity: 93.33%(95%CI: 68.05–99.83%).

Conclusions:

The rapid antigen test we used had very good sensitivity and specificity. The patients with score 0 should be excluded from further testing. The rapid strep test performed on all patients with score higher than 0 will increase sensitivity and specificity of the score. Even if we cannot exclude culture, this diagnosis approach may give good results on a first visit of a patient for sore throat.