Autopsy No. 98 - Mucosal Inflammation and Hemorrhage in Influenza
Drawing of a section through a trachea showing necrotizing hemorrhagic inflammatory process of the mucosa. Patient otherwise healthy young male. Contracted influenza December 1919.
One of the more interesting points of the 1918 flu pandemic (otherwise known as the Spanish Flu) is the cytokine storm process that killed so many of the healthy young adults who contracted it. Their immune system was strong and reactive, and would respond to invading pathogens by launching a massive attack. Normally, this would have been good, but the H1N1 flu strain was (and is) known to induce a much larger reaction than was necessary. The immune system, instead of just killing invaders, would end up overwhelming the patient, and symptoms resulting from that over-reaction (such as hemorrhage and edema in the lungs) were the top killers of healthy adults who contracted the disease.
One of the primary symptoms of the 1918 H1N1 virus was that the cytokine storms combined with the infecting pathogen ended up as a uniquely hemorrhagic influenza. There were even large numbers of reports of people hemorrhaging from petechiae on the skin, in addition to the intestinal, tracheal, and mucous membrane hemorrhages that were widespread. Hemorrhaging from the pleurae of the lungs was particularly fatal.
Pathology of Influenza. Charles Winternitz, Isabel Watson, and Frank McNamara, 1920.