I just reread the most interesting book about the influenza pandemic of 1918-1919. The frontispiece says
"In the winter of 1918...history's most lethal influenza virus was born. Over the next year it flourished, killing as many as 100 million people. It killed more people in twenty-four weeks than AIDS has killed in twenty-four years, more people in a year than the Black Death of the Middle Ages killed in a century. "
You might wonder what the 1918-1919 pandemic (which most people called the “Spanish Flu Pandemic”)has to do with the current worry about bird flu (or "avian flu"). Birds are natural carriers of influenza viruses. So scientists say the influenza viruses carried by birds today are constantly mutating, and can eventually become a more deadly strain.
Right now all cases have been passed directly from birds to humans which were in close contact with birds. The virus would have to mutate to be able to be passed from human to human. All influenza viruses mutate over time to become more virulent or less virulent. The 1918-1919 version was the deadliest ever recorded.
Here are some quotes from the book: (The page numbers are from the hardbound copy.)
How many died?
p. 238 During the course of the epidemic, 47% of all deaths in the United States resulted from influenza. (The other 53% were from all other causes: heart disease, stroke, tuberculosis, accidents, suicide, murder, etc.)...Investigators believe that in the United States the 1918-1919 epidemic caused an excess death toll of about 675,000 people. The population now is bigger, so a comparable figure today would be approximately 1,750,000 deaths.
Which age groups had the highest mortality rate?
p. 239-240 Normal influenza kills high numbers of infants and elderly. The graph of deaths would look like a U. In the 1918 pandemic, the single greatest number of deaths occurred in men and women aged 25-34. So with the infants and elderly added in, the graph looks like a W. And the most likely of the most likely to die were pregnant women, their death rate ranged from 23-71 %.
Illness during the pandemic came in three different waves. What were they?
p. 370 As it passed from person to person it adapted to its new host, became increasingly efficient in its ability to infect, and changed from the virus that caused a generally mild first wave of disease in the spring of 1918 to the lethal and explosive killer of the second wave in the fall....In a city or town, the cycle from first case to the end of a local epidemic in 1918 generally ran six to eight weeks. In the army camps, with the men packed so densely, the cycle took usually three to four weeks. Individual cases continued to occur after that, but the explosion of disease ended, and it ended abruptly. ...the virus burned through available fuel. Then it quickly faded away.
p. 373 By late November 1918...the virus had made its way around the world. The second wave was over, and the world was exhausted...But the virus, even as it lost some of its virulence, was not yet finished. Only weeks after the disease seemed to have dissipated...a third wave broke over the earth. ...the virus had mutated again...and rekindled the epidemic.
Why did so many people die so quickly?
p. 249, 250-251 Viral pneumonia and Acute Respiratory Distress Syndrome (ARDS) explains why so many died in a few days after getting sick. The immune system followed the virus into the lungs and there waged war...the capillaries dilated, pouring out fluid, every kind of white blood cell, antibodies,...into the lung...even more fluid poured into the lung..The cells that line the alveoli were damaged, if they survived the virus itself....More blood flooded the lungs. The body started producing fiberlike connective tissue. Areas of the lung became enmeshed in cell debris, fibrin, collagen, and other materials. Proteins and fluid filled the space between cells. (p. 373 "water-logged lungs")
What killed the others?
p. 251, 257 Of those who did not die of ARDS, the majority died from bacterial pneumonias (normal bacteria from mouth is able to migrate down to lungs because influenza has damaged epithelial tissue in throat) .These were slower moving pneumonias caused by secondary invaders. Bacterial pneumonias developed a week, two weeks, three weeks after someone came down with influenza..Often influenza victims seemed to recover,...then suddenly collapsed again with bacterial pneumonia.
Might future pneumonia be resistant to antibiotics?
p. 252 studies found that almost half the autopsies in 1918-1919 showed ARDS (influenzal viral pneumonia). That means over half probably died of bacterial pneumonia. Since then bacterial resistance has become a major problem in medicine. Today the mortality rate for a bacterial pneumonia following influenza is still roughly 7%, and in some parts of the US, 35% of pneumococcal infections are resistant to the antibiotic of choice. When staphylococcus aureus (highly resistant to antibiotics) is the secondary invader, the death rate today rises to as high as 42%. That is higher than the general death rate from bacterial pneumonias in 1918.
How does influenza infect someone?
p. 256 Influenza is an airborne pathogen...when the virus floats in the air it can infect someone else for an hour to a day after it is exhaled (the lower the humidity, the longer it survives. The higher the humidity, the shorter it survives.) Most easily spread in crowds. Someone with influenza "sheds" the virus- can infect others- usually from the third to the sixth day after he is infected. Can catch it by inhaling it, or by hand-to-mouth-or-nose contact. The virus can remain infectious on a hard surface for up to two days.
I'll post more quotes from the book tomorrow.
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