Influence of weather and climate on disease in the Australian Imperial Force during the First World War

The death rate in the Australian Imperial Force (AIF) during the First World War (WW1) was 18.5%, higher than rates for the UK and Canada. Around 9% of reported AIF deaths resulted from diseases and were predominantly climate sensitive. AIF hospital admissions for non-battle conditions exceeded the total number of AIF enlistments. To our knowledge, the climatic influences on these high morbidity and mortality rates have not previously been quantified. Analysing these influences provides a case study that highlights the importance in accounting for climate in determining the future health, capacity and ultimate efficacy of armed forces, particularly in a time of increasing climatic extremes. To analyse the climate-health outcomes relationship, we re-examined data available in Australia's WW1 official war histories (OWH) by C. E. W. Bean and A. G. Butler, the Australian War Memorial Roll of Honour (ROH) and the National Archives WW1 personnel files (NAA). We then reviewed meteorological data and identified that the European 1917 winter was the coldest winter for 26 yr. We have calculated the AIF UK official morbidity figure of 77743 could be under-reported by up to 2.7-fold. European winter disease deaths exceeded summer disease deaths by a factor of 3. Over 61% of AIF disease deaths in Europe occurred during the extreme 1917 winter and the Spanish flu outbreak during the 1919 winter, whereby 69% were respiratory infections. Climate-related diseases also severely affected the AIF at Gallipoli (Turkey) and the Light Horse regiments in the Jordan Valley between September and December 1918.