Early detection of new pandemic waves: A surveillance alternative to the 14-day cumulative incidence index. (Preprint)

BACKGROUND The current COVID-19 pandemic highlights the pressing need for constant surveillance, updating of the response plan in post-peak periods and readiness for the possibility of new waves of the pandemic. The system for monitoring and controlling the spread of the pandemic should signal an alert in the event of change in the infection process. OBJECTIVE The 14-day notification rate of reported COVID-19 cases per 100,000 population is the main indicator used for continued monitoring of the evolution of the pandemic. However, this value may neither accurately represent the current state of virus spread among the population nor provide a good approximation of the rate at which positivity changes. Thus, we propose a new way to detect changes in the virus spread. METHODS We introduce a new index, the weighted cumulative incidence index, based on the daily new cases count, which is more able to reflect both the current state of virus transmission and the current rate of change. We propose to model infection spread at two levels, inside and outside the home, to explain the overdispersion observed in the data. The seasonal component on real data, due to the detection system carried out by the public health services, is incorporated into the statistical analysis. For the first time in this context, we also provide a control chart to monitor the index, in order to detect significant variations in the virus transmission process. RESULTS Both the new index and the control chart have been implemented in a computational aid tool developed in Python, which is used daily by the Government of Navarra (Spain) in the virus propagation surveillance during post-peak periods. Automated monitoring generates a daily report showing the areas whose control charts issue an alert. CONCLUSIONS After the application of the proposed index to real data, the results confirm that our study provides a new index which is quicker at detecting significant changes in the virus spread than the commonly used 14-day cumulative index. This quickness allows to plan more efficiently the subsequent decisions in pandemic surveillance.