Nonpolio Enterovirus Activity during the COVID-19 Pandemic, Taiwan, 2020

In Taiwan, lower nonpolio enterovirus activity during the coronavirus disease pandemic in 2020 compared with 2014–2019 might be attributable to adherence to nonpharmaceutical interventions. The preventable fraction among unexposed persons indicated that 90% of nonpolio enterovirus activity might have been prevented during 2014–2019 by adopting the same measures enforced in 2020.

analyze data from outpatient department and ER visits for non-polio enterovirus (NPEV) infections. We assigned the whole population of outpatient department and ER visits during the 2019-2020 season to the "exposed" group. In this case, the "exposed" condition means that the population adhered to infection control measures after the first imported COVID-19 case ( Figure   1). The populations of outpatient department and ER visits during the past 5 seasons were assigned to five "unexposed" groups. Since the National Health Insurance of Taiwan includes >99% of Taiwan residents, the risk of NPEV is calculated as the ratio of total weekly number of outpatient department and ER visits that yielded an NPEV diagnosis to the total weekly number of outpatient department and ER visits for all diseases.
The basic equation for the model is where is the expected mean value for subject i at week j; Exposure is a binary indicator that the subject is exposed to the infection control measures; Week denotes the specific week; and ε is the error term for the outcome measure of subject i at week j.
This model has an equivalent representation as follows.
where is the weekly total number of outpatient department and ER visits for all diseases in year i and week j. log� � acts as an offset in the model, which is used to account for the variation in the total number of outpatient department and ER visits for all diseases in different weeks and different years. The parameter 0 is the intercept; 1 to 19 are unknown parameters to be estimated. With the log link function, is expressed as a linear function of the explanatory variables. All of the statistical analyses were performed using SAS software, Version 9.4 (SAS Institute Inc., Cary, NC, USA). All p values are two-sided and p < 0.05 was considered to be statistically significant.

Preventable Fraction among the unexposed
Preventable fraction among the unexposed ( ) is the proportion of incidents in the unexposed group that could have been prevented by exposure to infection control measures. It is calculated as where RR is the relative risk. Risk for NPEV infections among the exposed is defined as the number of weekly outpatient department and ER visits for NPEV out of all individuals seeking health care in the 2019-2020 season. Risk for NPEV infections among the unexposed is Page 5 of 12 defined as the average number of weekly outpatient department and ER visits for NPEV out of the average number of individuals seeking health care in the 2014-2019 seasons. RR is the ratio of the risk in the exposed group to the risk in the unexposed group. The adjusted RR is a relative risk adjusted for the total number of outpatient department and ER visits for non-polio enteroviruses and for all diseases, respectively, at week 1. Poisson regression model was used to estimate the adjusted RR and the 95% confidence interval. Consequently, adjusted is obtained.
We also calculate the relative risk and preventable fraction among the unexposed in four age groups (0-2, 3-4, 5-9, and 10-14   Normalized by the total number of outpatient department and emergency room visits for non-polio enteroviruses and for all diseases, respectively, at week 1.
b All values were statistically significant except those underlined.
Page 11 of 12 Appendix All values were statistically significant.