Modelling infectious agent transmission using social mixing data

Abstract

Introduction The economic evaluation of new vaccines requires the modelling of infectious disease transmission within a population, which in turn requires making assumptions about specific mixing patterns in the population. In the European POLYMOD project, matrices generated from social contact studies were determined for 8 European countries. To date, no such data exist for France. The Comes-F study (Contact Matrix Estimation France) aimed to fill this gap. Methodology Contact matrices: The survey was carried out over 3 different periods (Feb-Mar, Apr, Apr-May) with 278 participants common to the first and the last periods. Participants had to list all their contacts for 2 consecutive days in a diary, with age, sex, location, frequency, type and duration of the contact, from which we estimated French contact matrices. Outbreak risk : Combining cross-sectional serological surveys from 2009 and 2013 and vaccine coverage information, we determined an optimal model for the seroprevalence of measles, mumps and rubella for the year of the data collection; age-dependent susceptibility by department was then derived for the year of interest (2016), and effective reproduction number and age-dependent relative incidence of a potential outbreak were estimated using the French contact matrices. Meteorological conditions and mixing patterns: We analysed the influence of meteorological conditions on the temporal variations in mixing patterns. The study population was split according to day and weather at the time the diary was filled in. The mean number of contacts and the potential for transmission summarized by R0 were calculated for type and location of contact under different weather conditions. Gender and mixing patterns: We conducted a systematic review on gender differences in infection, focusing on influenza, measles, mumps and rubella. Finally, we provided an exploration of the impact of gender on mixing patterns, and eventually the potential implications for modelling. Results The 2033 participants reported 38,881 contacts (median [first quartile-third quartile]: 8[5{14] per day), and 54,378 contacts with supplementary professional contacts (9[5{17]). Contrary to age, gender, household size, holidays, weekend and occupation, the period of the year as available in this study had little influence on either the number of contacts or the mixing patterns. Contact patterns were highly assortative with age, irrespective of the location of the contact, and gender, with women having 8% more contacts than men. Although most contacts occurred at home and school, the inclusion of professional contacts modified the structure of the mixing patterns. Holidays and weekends reduced the number of contacts dramatically, and as proxies for school closure, reduced R0 by 33% and 28%, respectively. The outbreak risk for mumps and rubella mainly concerned southeastern and south central France, while the risk for measles was more scattered over the country. Risk differed by gender for measles and rubella. Besides infants under 1 year of age, incidence was estimated highest for teenagers and young adults. The weather had a different effect on social mixing according to the type of day, notably weekdays and weekend. But correcting for multiple testing made some results no more significant, although the trend for a differential effect between weekdays and weekend remained. Gender differences in social mixing might explain some gender differences in infectious disease epidemiology. Using gender-specific susceptibility and gender-specific contact matrices had a significant impact on the result of the modelling. Conclusion French contact matrices shared many common aspects with and were qualitatively similar to those of other European countries, despite differences in design and conduct of the survey. Notably, school closures were likely to have a substantial impact on the spread of close contact infections in France. While the risk of a new measles outbreak persists, it predominates for mumps. The effect of weather on social mixing was mild, if not negligible. Gender differences in modelling should be emphasized.