Estimating the impact of school closure on social mixing behaviour and the transmission of close contact infections in eight European countries

Abstract

Background: Mathematical modelling of infectious disease is increasingly used to help guide public health policy. As directly transmitted infections, such as influenza and tuberculosis, require contact between individuals, knowledge about contact patterns is a necessary pre-requisite of accurate model predictions. Of particular interest is the potential impact of school closure as a means of controlling pandemic influenza (and potentially other pathogens).

Methods: This paper uses a population-based prospective survey of mixing patterns in eight European countries to study the relative change in the basic reproduction number (R0--the average number of secondary cases from a typical primary case in a fully susceptible population) on weekdays versus weekends and during regular versus holiday periods. The relative change in R0 during holiday periods and weekends gives an indication of the impact collective school closures (and prophylactic absenteeism) may have during a pandemic.

Results: Social contact patterns differ substantially when comparing weekdays to the weekend and regular to holiday periods mainly due to the reduction in work and/or school contacts. For most countries the basic reproduction number decreases from the week to weekends and regular to holiday periods by about 21% and 17%, respectively. However for other countries no significant decrease was observed.

Conclusion: We use a large-scale social contact survey in eight different European countries to gain insights in the relative change in the basic reproduction number on weekdays versus weekends and during regular versus holiday periods. The resulting estimates indicate that school closure can have a substantial impact on the spread of a newly emerging infectious disease that is transmitted via close (non sexual) contacts.

Figure 1

Smoothed contact matrices. Smoothed contact matrices for each country based on close contacts in the week weighted by sampling weights and corrected for reciprocity. White indicates high contact rates, yellow intermediate contact rates, and red low contact rates relative to the country-specific contact intensity.

Figure 2

Score matrices for the weekend to week comparison. Matrices of scores associated to the ratios of age-specific close-contact rates when comparing weekends to the week. The scores are based on the 95% bootstrap based confidence intervals where red indicates that the ratio is significantly lower than 1 (i.e. less contacts during the weekend), orange not-significantly different from 1 (i.e. similar numbers of contacts during the week and weekends) and yellow significantly higher than 1 (i.e. more contacts during the weekend). The matrices are shown for BE, GB, IT, LU, NL and PL for which the relative reproduction number was significantly different from 1.

Figure 3

Score matrices for the holiday to regular period comparison. Country-specific matrices of scores associated to the ratios of age-specific close-contact rates when comparing holiday to regular periods. The scores are based on the 95% bootstrap based confidence intervals where red indicates that the ratio is significantly lower than 1 (i.e. less contacts during the holiday period), orange not-significantly different from 1 (i.e. similar numbers of contacts on regular and holiday period) and yellow significantly higher than 1 (i.e. more contacts during the holiday period). The matrices are only shown for those countries for which the relative reproduction number is significantly different from 1.