The target area for this study was Hiroshima Prefecture, one of Japan’s 47 prefectures, which has a population of about 2.8 million people [8]. The prefecture has seven public health centers that conduct weekly surveys of common infectious diseases (Fig. 2). The trends of these infectious diseases are reported to the public health centers by the four types of sentinel medical facilities (pediatric, influenza, ophthalmology, designated sentinel medical facilities; Table 1). Data on the weekly trends in common infectious diseases from January 2018 to March 2021 were provided by the Hiroshima CDC (Center for Disease Control and Prevention). As in the Hiroshima CDC Monthly Report [6], the weekly incidence of these diseases was converted to a monthly incidence by adding to results for 4–5 weeks.
Data on the number of monthly users of nurseries for children with mild illness from January 2018 to March 2021 in the 23 municipalities in Hiroshima Prefecture were obtained using a questionnaire survey. The survey form was distributed to the municipalities on April 2, 2021. The survey was resent to cities and towns that did not respond on May 6, 2021, and June 1, 2021. Collected data on the number of children using nurseries for children with mild illnesses were categorized and tabulated for each of the seven health center areas.
The Day Care Center Infectious Disease Management Guidelines (2018 Revised) [2], specify matters related to resuming daycare attendance after contracting a common infectious disease (Table 1). These guidelines indicate that most general daycare centers may not accept children with these common infectious diseases. Therefore, it is expected that there would be a strong correlation between the number of the infectious diseases listed in these guidelines and the number of users of nurseries for children with mild illness. Multiple regression analysis was performed to test the relationship between the number of users of these nurseries and the number of sentinel-reported diseases in the seven public health center areas. A dummy variable was used to represent before and during the COVID-19 pandemic.
Because of the small number of reports from designated sentinel medical facilities, this study analyzed the number of infectious diseases reported by three types of sentinel medical facilities (pediatric, influenza, and ophthalmology sentinel-reported diseases; Table 1). Pediatric sentinel medical facilities are intended for patients under age 15 years, whereas influenza and ophthalmology sentinel medical facilities are intended for adults and children. Therefore, in the multiple regression analysis with the number of users of nurseries for children with mild illness as the dependent variable, the total numbers of pediatric, influenza, and ophthalmology sentinel-reported diseases were set as separate independent variables. The pandemic dummy variable was set as 0 before March 1, 2020, and 1 thereafter, because most schools in Japan were temporarily closed to prevent COVID-19 as of March 2, 2020 [9]. Under the above conditions, the following multiple regression equation was established.
y = a1 * x1 + a2 * x2 + a3 * x3 + a4 * x4
+ (a5 * x1 * x4) + (a6 * x2 * x4) + (a7 * x3 *x4) + b
It can also be expressed as:
y = (a1 + a5 * x4) * x1 + (a2 + a6 * x4) * x2 + (a3 + a7 * x4) * x3
+ (a4 * x4 + b)
The number of monthly users of nurseries for children with mild illness was indicated by y, and the regression coefficients by a1–a7 and b. The numbers of monthly cases of pediatric, influenza, and ophthalmology sentinel-reported diseases were indicated by x1–x3, respectively, and the pandemic dummy variable (0 before March 1, 2020, and 1 thereafter) was indicated by x4.
In addition, multiple regression analysis was performed to test the relationship between the number of users of nurseries for children with mild illness and the number of each sentinel-reported disease. All statistical analyses were performed using SPSS version 23.0.0.3 (IBM Corp., Armonk), P-values less than 0.05 were considered statistically significant.