Poster Presentation Lancefield International Symposium for Streptococci and Streptococcal Diseases 2025

Serologic responses in patients with invasive group A streptococcal disease and concomitant throat findings (#232)

Ville Kailankangas 1 , Kirsi Gröndahl-Yli-Hannuksela 2 , Johanna Vilhonen 3 , Kaisu Rantakokko-Jalava 4 , Tapio Seiskari 5 , Emilia Lönnqvist 2 , Jarmo Oksi 3 , Jaana Syrjänen 1 , Jaana Vuopio 2
  1. Tampere University Hospital, Tampere, PIRKANMAA, Finland
  2. Institute of Biomedicine, University of Turku, Turku, Finland
  3. Infectious Diseases, Turku University Hospital, Turku, Southwest Finland, Finland
  4. Clinical Microbiology, Turku University Hospital, Turku, Finland
  5. Clinical Microbiology, Tampere University Hospital, Tampere, Finland

Objective

We wanted to investigate antibody kinetics across different timepoints in invasive group A Streptococcal (iGAS) infections, and the effect of presence of GAS in the throat on this. 

Materials and methods 

We recruited iGAS cases from 2018 to 2020. At timepoint A, within two days from admission, a throat swab and sera were taken. Further sera were taken five to seven days (timepoint B) and three months later (timepoint C). The sera were analyzed for streptolysin O (ASO) and deoxyribonuclease B (ADB) antibodies, and with in-house EIA for IgA and IgG antibodies. Throat swabs underwent Isothermal amplification (IAT) to detect GAS.  

Results 

Sera were obtained from 42, 35 and 26 cases at timepoints A, B and C respectively, and throat swabs from 39 cases at timepoint A. At timepoints A, B and C, 33%, 74% and 54% were ASO seropositive, and 40%, 79% and 58% ADB seropositive, respectively. IAT positive cases were more likely seropositive than IAT negatives at timepoints A (44% vs 31% for ASO, 44% vs 38% for ADB) and B (100% vs 64% for ASO, 100% vs 75% for ADB), but not statistically significantly. EIA results correlated with ASO and ADB at timepoint A for IgA and IgG, and timepoint B for IgA. 

Conclusions 

ASO and ADB mostly seroconverted around timepoint B. EIAs of IgG and IgA against GAS behaved similarly, though no seroconversion cutoffs exist. GAS throat IAT positives seemed to seroconvert more than IAT negatives, but not statistically significantly.