[Source: PLoS Neglected Tropical Diseases, full page: (LINK). Abstract, edited.]
OPEN ACCESS / PEER-REVIEWED / RESEARCH ARTICLE
El Niño southern Oscillation, overseas arrivals and imported chikungunya cases in Australia: A time series analysis
Xiaodong Huang, Wenbiao Hu, Laith Yakob, Gregor J. Devine, Elizabeth A. McGraw, Cassie C. Jansen, Helen M. Faddy, Francesca D. Frentiu
Published: May 20, 2019 / DOI: https://doi.org/10.1371/journal.pntd.0007376 / This is an uncorrected proof.
Chikungunya virus (CHIKV) is an emerging mosquito-borne pathogen circulating in tropical and sub-tropical regions. Although autochthonous transmission has not been reported in Australia, there is a potential risk of local CHIKV outbreaks due to the presence of suitable vectors, global trade, frequent international travel and human adaptation to changes in climate.
A time series seasonal decomposition method was used to investigate the seasonality and trend of monthly imported CHIKV cases. This pattern was compared with the seasonality and trend of monthly overseas arrivals. A wavelet coherence analysis was applied to examine the transient relationships between monthly imported CHIKV cases and southern oscillation index (SOI) in time-frequency space. We found that the number and geographical distribution of countries of acquisition for CHIKV in travellers to Australia has increased in recent years. The number of monthly imported CHIKV cases displayed an unstable increased trend compared with a stable linear increased trend in monthly overseas arrivals. Both imported CHIKV cases and overseas arrivals showed substantial seasonality, with the strongest seasonal effects in each January, followed by each October and July. The wavelet coherence analysis identified four significant transient relationships between monthly imported CHIKV cases and 6-month lagged moving average SOI, in the years 2009–2010, 2012, 2014 and 2015–2016.
High seasonal peaks of imported CHIKV cases were consistent with the high seasonal peaks of overseas arrivals into Australia. Our analysis also indicates that El Niño Southern Oscillation (ENSO) variation may impact CHIKV epidemics in endemic regions, in turn influencing the pattern of imported cases.
Chikungunya virus (CHIKV) is mosquito-borne virus circulating in tropical and sub-tropical areas of the globe. Infected travellers from CHIKV-affected areas can initiate outbreaks and epidemics in countries where vector mosquitoes are present. Greater understanding of the pattern of imported cases is required to facilitate risk assessment of CHIKV outbreaks. We investigated the temporal pattern of imported CHIKV cases relative to the pattern of overseas arrivals. We also tested whether variability in El Niño Southern Oscillation (ENSO) can predict the import of CHIKV cases in Australia. We found that the number of monthly imported CHIKV cases displayed an unstable increased trend versus the stable linear increased trend observed in monthly overseas arrivals. Both the numbers of imported CHIKV cases and overseas arrivals showed substantial seasonality. High seasonal peaks of imported CHIKV cases were consistent with the high seasonal peaks of overseas arrivals into Australia. We also identified four significant transient relationships between ENSO variability and CHIKV importation. Our results suggest ENSO may impact the occurrence of CHIKV epidemics in endemic regions, in turn influencing the pattern of imported cases.
Citation: Huang X, Hu W, Yakob L, Devine GJ, McGraw EA, Jansen CC, et al. (2019) El Niño southern Oscillation, overseas arrivals and imported chikungunya cases in Australia: A time series analysis. PLoS Negl Trop Dis 13(5): e0007376. https://doi.org/10.1371/journal.pntd.0007376
Editor: Mary Hayden, National Center for Atmospheric Research, UNITED STATES
Received: January 6, 2019; Accepted: April 9, 2019; Published: May 20, 2019
Copyright: © 2019 Huang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the manuscript and its Supporting Information files.
Funding: This research was funded by the Australian National Health and Medical Research Council (APP1125317). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Keywords: Climate Change; ENSO; Chikungunya fever; Australia.