Serologic responses in patients with invasive group a streptococcal disease

OBJECTIVE: To investigate kinetics of anti-streptolysin O (ASO) and anti-deoxyribonuclease B (ADB) and an in-house enzyme immunoassay (EIA) for IgG and IgA in acute and convalescent invasive group A Streptococcal (iGAS) infection. MATERIALS AND METHODS: We recruited iGAS cases from two Finnish hospitals, between 2018 and 2020. Serum was obtained, on average 2 days, (timepoint A), 9 days (timepoint B) and 3 months (timepoint C) from admission. The sera were analyzed for ASO, ADB, and with EIA for IgA and IgG against the causative strain and the three most common emm types in Finland (emm1, emm28, emm89). RESULTS: Forty-five cases were recruited, with sera available from 42, 35 and 26 at timepoints A, B and C respectively. At timepoint A, 33% were above the upper limit of normal (ULN) for ASO, and 40% for ADB, but 52% for at least one. At timepoint B, 74% were above ULN for ASO, 79% for ADB, and 91% for at least one. EIA results did not differ between the causative and pooled strains except for IgA at timepoint A. CONCLUSIONS: ASO and ADB have utility in iGAS disease with unavailable culture confirmation. EIA results suggest emm type cross-reactivity, with possible vaccine development implications.