Syndemic
The worst of the 20th century influenza pandemics was the 1918 pandemic, where between 20-40 percent of the world’s population became ill between 40-100 million people died. More people died of the so-called Spanish flu (caused by the H1N1 viral strain) pandemic in the single year of 1918 than during all four-years of the Black Death. The pandemic had devastating effects as disease spread along trade and shipping routes and other corridors of human movement until it had circled the globe. InIndia, the mortality rate reached 50 per 1,000 population. Arriving during the closing phase of the World War I, the pandemic impacted mobilized national armies. Half of U.S. soldiers who died in the "Great War," for example, were victims of influenza. It is estimated that almost ¾ of a million Americans died during the pandemic. In part, the death toll during the pandemic was caused by viral pneumonia characterized by extensive bleeding in the lungs resulting in suffocation. Many victims died within 48 hours of the appearance of the first symptom. It was not uncommon for people who appeared to be quite healthy in the morning to have died by sunset. Among those who survived the first several days, however, many died of secondary bacterial pneumonia. It has been argued that countless numbers of those who expired quickly from the disease were co-infected with tuberculosis, which would explain the notable plummet in TB cases after 1918.
Middle Eastern theatre of World War I
The significance of disease on this front can be best illustrated by comparing British the number of hospitalizations from disease/injury (frostbite, trench foot, etc.) in this theater to the Western Front. In France and Flanders, 2,690,054 British Empire troops were killed, wounded, died of wounds, missing, or captured, while there were 3,528,486 hospitalizations due to "non-battle casualties", a rate of 1.3 NBCs for every 1 battle casualty. In Mesopotamia there were 82,207 troops killed, wounded, died of wounds, missing, or captured, and 820,418 hospitalizations for sickness or injury, while in the Sinai and Palestine Campaign 51,451 men became battle casualties (not counting Indians) and 503,377 were hospitalized as non-battle casualties. In both cases, the rate is approximately 10 NBCs for every 1 battle casualty. Additionally, while by the listed numbers the Mesopotamia and Sinai-Palestine campaigns had only had 5% the battle casualties of the Western Front (136,658 v 2,690,054), they had over 70% of the disease deaths (22,693+ v 32,098).