Throat Culture and Anti-OF Antibodies in the Elementary School Children

Jung, Hyun Ju; Kim, Seon Ju; Kim, Yun Jeong; Maeng, Kook Young

Abstract

BACKGROUND: Anti-OF (opacity factor) antibody (Ab) is useful to study past infection or outbreak of group A streptococci (GAS) and to identify OF antigen (Ag). Throat cultures were taken from 172 elementary school children and venous blood were collected at the same time to screen the frequency of anti-OF Ab.
METHODS
The presence of OF Ag was recognized by turbidity of horse serum. OF Ag was identified with inhibition of opacity reaction by known anti-OF Ab. The sera of children were screened for the presence of anti-OF Ab with the representative OF Ag.
RESULTS
The positive rate of anti-OF Ab was very high regardless of OF production or throat culture results. Thirty two of 38 (84%) OF Ag producing GAS carriers, 25 of 35 (71%) OF Ag non-producing GAS carriers and 72 of 99 (73%) throat culture negative children harbored anti-OF Ab. While among OF Ag, non-typable and OF 22 were high in prevalence (36.8% and 29.0% respectively), anti-OF 4, anti-OF 28 and anti-OF 12 of OF Ab were identified highly (39.5%, 29.7% and 15.7% respectively). Forty-five (26.2%) among 172 children had two anti-OF Abs and 11 (6.4%) had more than three anti-OF Abs.
CONCLUSIONS
Seventy five percent of school children was proven to be previously infected with GAS through this anti-OF Ab study. The anti-OF Ab carrying rates were high, regardless of positivity of throat culture and OF Ag production. We could demonstrate that the prevalent strains of GAS changed in according to time span by proving the difference of frequency of OF Ag and anti-OF Ab and one-fourth of children had been infected with more than 2 different serotypes.