highly significantp < 0.001
By age groups, the prevalence in younger than or equal to 1 year (13.1 %, 95 % CI: 9.1–17.2; 35/266) was markedly higher than those in old than 1 year (0.9 %, 95 % CI: 0.2–1.6; 7/745), and the difference was highly significant (p < 0.001).