After its mysterious emergence earlier this year, the influenza epidemic had appeared to abate as the summer wore on, so much so that some thought that it was effectively over. This belief was unfortunately premature. A second wave of the influenza has now erupted, emerging simultaneously in Brest, Baltimore and the West African port of Freetown, all ports playing a vital role in the Allied war effort. From these three centres it has spread rapidly across the globe, crossing the lines and affecting the malnourished Central Powers as much if not more so than the Allies.
The first wave of the influenza pandemic was more infectious than an ordinary flu but not noticeably more lethal to those who contracted it, with mortality rates remaining at around 1% of those infected. Since then however the influenza has undergone some kind of mutation and it is now killing some 2.5% of those who fall ill. The symptoms of those who die can be pretty gruesome, with haemorrhaged blood flooding lungs and the skin around the face shrinking and turning black through loss of oxygen (which may be why some refer to the disease as the Black Flu).
The influenza is also different from an ordinary flu in who it takes down. Young adults appear to be its preferred targets (with roughly half of those killed by it being between the ages of 20 and 40 years). The more usual victims of influenza (the old and children) are proportionately less affected. In the USA it is also noted that Black Americans are far less likely to be struck down than their White compatriots.
The influenza spreads quickly through the cramped conditions prevailing in army camps and troopships. Overcrowded tenements hasten its spread among the civilian populations of urban centres. Because people are infectious before they have any obvious symptoms, people now dread the sound of a neighbour coughing or sneezing, as it means that in a day or two they too will fall ill and perhaps suffer a terrible death.
Public health notice (Crozet Gazette —1918: War and Influenza, Battling on the Home Front)