Early warning signals of malaria resurgence in Kericho, Kenya.

Mallory J Harris,John M Drake,Simon I Hay

doi:10.1098/rsbl.2019.0713

Abstract

Campaigns to eliminate infectious diseases could be greatly aided by methods for providing early warning signals of resurgence. Theory predicts that as a disease transmission system undergoes a transition from stability at the disease-free equilibrium to sustained transmission, it will exhibit characteristic behaviours known as critical slowing down, referring to the speed at which fluctuations in the number of cases are dampened, for instance the extinction of a local transmission chain after infection from an imported case. These phenomena include increases in several summary statistics, including lag-1 autocorrelation, variance and the first difference of variance. Here, we report the first empirical test of this prediction during the resurgence of malaria in Kericho, Kenya. For 10 summary statistics, we measured the approach to criticality in a rolling window to quantify the size of effect and directions. Nine of the statistics increased as predicted and variance, the first difference of variance, autocovariance, lag-1 autocorrelation and decay time returned early warning signals of critical slowing down based on permutation tests. These results show that time series of disease incidence collected through ordinary surveillance activities may exhibit characteristic signatures prior to an outbreak, a phenomenon that may be quite general among infectious disease systems.

Highlights

Despite modern advances in disease control, the World Health Organization reports that nearly one-third of deaths in developing countries are due to infectious diseases [1]
The test values for all indicators except for kurtosis and skewness lie in the right tails of their null distributions, consistent with the prediction that critical slowing down results in an increase in these statistics
The p-values for increases in autocovariance and variance rapidly decreased 24 months prior to the critical transition and dropped below 0.05 fifteen and four months prior to the critical transition, respectively. These results show that simple summary statistics may serve as early warning signals of disease resurgence

Summary

Introduction

Despite modern advances in disease control, the World Health Organization reports that nearly one-third of deaths in developing countries are due to infectious diseases [1]. A systematic review identified 75 resurgence events worldwide between 1930 and 2000, attributed largely to the weakening of malaria control programmes, increasing the potential for transmission and evolution of drug and insecticide resistance [2]. Those conditions are found for other diseases on the cusp of global eradication (e.g. polio [4], Dracunculiasis [5] and human Africa trypanosomiasis [6]).

Methods

Results

Conclusion