Objective  To investigate the inapparent infection status of hand-foot-and-mouth disease (HFMD) in nine districts and four counties in Xi′an city of Shaanxi province.

  Methods  A total of 600 children from January 2012 to June 2018 were collected as study subjects. The anal swab/throat swab specimens were collected from the study subjects. HFMD inapparent infection status, types of enterovirus, and high incidence time of infection were evaluated among different age groups and different gender.

  Results  The HFMD inapparent infection rates were 41.00%, 20.27%, and 4.37%, respectively, in children aged 0 to 3 years, 4 to 6 years and 7 to 12 years. There was a statistically significant difference in the inapparent infection rate between children aged 0 to 3 years and 4 to 6 years (P < 0.05). The inapparent infection rate of children aged 7 to 12 years was lower than those aged 0 to 3 years and 4 to 6 years (P < 0.05). The inapparent infection rates of males at age of 0 to 3, 4 to 6 and 7 to 12 years old were higher than those of females, with the overall gender ratio of 1.67 to 1. The type of enterovirus of inapparent infection was EV71 from 2012 through 2014 (P < 0.05), and there was no significant difference in the types of enterovirus of inapparent infection between January 2015 and June 2018 (P>0.05). The inapparent infection rate was the highest in April to June, followed by in October to December, the lowest in January to March, and there was statistically significant difference in the inapparent infection rate at different time periods (P < 0.05).

  Conclusion  The inapparent infection rate of children with HFDM is relatively high in Xi′an City. It is necessary to pay attention to the prevention and control during high incidence season of infection.