AUTHOR=Oluwole Olusegun Steven Ayodele TITLE=Seasonal Influenza Epidemics and El Niños JOURNAL=Frontiers in Public Health VOLUME=3 YEAR=2015 URL=https://www.frontiersin.org/journals/public-health/articles/10.3389/fpubh.2015.00250 DOI=10.3389/fpubh.2015.00250 ISSN=2296-2565 ABSTRACT=
Seasonal influenza epidemics occur annually during the winter in the northern and southern hemispheres, but timing of peaks and severity vary seasonally. Low humidity, which enhances survival and transmission of influenza virus, is the major risk factor. Both El Niño and La Niña phases of El Niño-southern oscillation (ENSO), which determine inter-annual variation of precipitation, are putative risk factors. This study was done to determine if seasonality, timing of peak, and severity of influenza epidemics are coupled to phases of ENSO. Monthly time series of positive specimens for influenza viruses and of multivariate El Niño-Southern Oscillation Index from January 2000 to August 2015 were analyzed. Seasonality, wavelet spectra, and cross-wavelet spectra analyses were performed. Of 31 countries in the dataset, 21 were in the northern hemisphere and 10 in the southern hemisphere. The highest number of influenza cases occurred in January in the northern hemisphere, but in July in the southern hemisphere,