Historically, pertussis was a disease of early childhood, however, in recent years its resurgence in a number of countries boasting high vaccination coverage has been accompanied by shifts in the age-distribution of cases towards adolescents and adults. One leading explanation for this reemergence implicates adults as a reservoir for transmission to infants following immune waning. To identify core groups that drive pertussis transmission, we examined age-stratified incidence reports from England and Wales between 1982 and 2012, using different techniques drawn from statistics and epidemiology, including wavelets, transfer entropy and odds ratio analysis.
Results/Conclusions
The different approaches we adopted yield consistent conclusions. The data from the 1980s identify primary school children as the key age group that amplified epidemics, with incidence in this age group typically at the leading edge of the epidemic. Our transfer entropy analyses indicate that information garnered about pertussis incidence in school age children is predictive of incidence in other age groups. By focusing on relative risks prior to and following the epidemic peak, we conclude the importance of school-aged children is attributable to their higher rates of contacts. In contrast, our analyses identified no single important age group during the 2012 epidemic overall, though incidence in adults is predictive of incidence in toddlers and unvaccinated infants. We discuss the potential explanation of these results within the context of changing diagnostic and reporting practices.