Waves of El Niño-Southern Oscillation and Influenza Pandemics

Olusegun S A Oluwole

doi:10.3389/fenvs.2016.00025

Abstract

Influenza pandemics have occurred at irregular intervals for over 500 years, unlike seasonal influenza epidemics which occur annually. Although the risk factors are known, the basis for the timing of influenza pandemic waves are unknown. Coherence of peaks of El Nino and influenza pandemic in 2009–2010, however, suggests that both waves are coupled. This study was done to determine the relation of influenza pandemics to the peaks and waveforms of El Nino southern oscillation (ENSO). ENSO cycles from 1871–2015 which had El Nino phases were windowed from Multivariate El Nino Index. Influenza pandemic peaks were mapped to ENSO monthly time series. ENSO waveforms were compared graphically, and fitted to nonstationary cosinor models. Second order polynomial regression model was fitted to the peak and duration of El Nino. Agglomerative hierarchical cluster of ENSO waveforms was performed. All influenza pandemic peaks mapped to El Nino peaks, with lags of 0–5 months. ENSO waveforms during influenza pandemics share parameters of oscillation. Nonstationary cosinor models showed that ENSO cycles are complex waves. There was second order polynomial relationship between peak and duration of El Ninos, p < 0.0001. ENSO waveforms clustered into four distinct groups. ENSO waveforms during influenza pandemics of 1889–1900, 1957–1958, and 1968–1969 linked closely. ENSO indices were significantly high from 7–16 months after onset of cycles, p < 0.0001. Surveillance for El Nino events to forecast periods of maximal transmission and survival of influenza A viruses is, therefore, crucial for public health control strategies.

Highlights

The word influenza, which attributed fever, cough, and cold to the influence of the stars, was coined in Italy in 1357 AD (Lina, 2008)
El Niño southern oscillation (ENSO) data from 1871 to 2005 were obtained from Extended Multivariate El Niño Index (MEI.ext) (National Oceanic Atmospheric Administration, 2015a), which are derived from sea level pressure and sea surface temperature (Allan and Ansell, 2006), while ENSO data from 1950 to 2015 were obtained from Multivariate El Niño Index (MEI) data (National Oceanic Atmospheric Administration, 2015c), which are derived from sea-level pressure, zonal and meridional components of the surface wind, sea surface temperature, surface air temperature, and total cloudiness fraction of the sky of the South Pacific Ocean (Wolter and Timlin, 1998)
Peaks of all influenza pandemics mapped to El Niño peaks in both MEI.ext and MEI data, Figure 1

Summary

Introduction

The word influenza, which attributed fever, cough, and cold to the influence of the stars, was coined in Italy in 1357 AD (Lina, 2008). Influenza pandemics have been documented for over 500 years, but there is consensus that influenza pandemics that occurred since 1700 were less likely to be mistaken for other febrile illnesses (Potter, 2001; Lina, 2008). The intervals between historical influenza pandemics have been estimated to vary from 10 to 50 years (Potter, 2001) and 6–149 years (Morens et al, 2010), unlike seasonal influenza epidemics, which occur annually during the winter of northern and southern hemispheres (Oluwole, 2015). Influenza pandemics peak multiple times, but the peaks are not restricted to winter seasons (Taubenberger and Morens, 2006). The basis for the timing of influenza pandemic waves are not established, it has been attributed to timing of school calendar, demography, geography, changes in virulence of influenza A viruses strains, and waning immunity (Mummert et al, 2013).

Methods

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Discussion

Conclusion