UC
Berkeley demographer finds undetected tuberculosis may have
been real killer in 1918 flu epidemic
25
Oct 2000
By
Pat McBroom, Media Relations
Berkeley
- There has never been a flu epidemic like it. In one year
- 1918 - half a million Americans died from a contagion
often identified as the deadliest epidemic of the 20th century,
a flu so severe that the fear of it happening again causes
public health authorities to go on global alert.
Now a
researcher in demography at the University of California,
Berkeley, has evidence that undetected tuberculosis, or
TB, actually may have caused much of the mortality in 1918.
If so,
such a deadly flu may not occur again, at least not in the
United States which has low rates of TB infection, reports
Andrew Noymer, UC Berkeley doctoral student in demography,
a department in the College of Letters and Science. He published
his findings in the current (September) issue of Population
and Development Review, the main journal of the Population
Council.
Noymer's
evidence comes from patterns of mortality in the U.S. population
in the years after the epidemic year. Death rates from tuberculosis
fell dramatically in 1919 and 1920 and, for decades thereafter,
changed an historic gender pattern in mortality.
Apparently,
those who died from the flu already had diseased lungs.
When they got the flu, it turned into pneumonia, which in
those people with TB became especially severe. It was the
pneumonia complicated by TB that killed them, said Noymer.
Their early demise depressed the death rate from TB in the
following years.
He added
that tuberculosis creates cavities in the lungs that are
notorious breeding grounds for staphylococcus A bacteria
which causes a pneumonia that was actually the killer in
1918.
Noymer's
findings explain a peculiarity of the 1918 pandemic that
killed at least 20 million people worldwide.
Normally,
the influenza virus is not lethal to young and middle-aged
people. Most of its victims are elderly. But in 1918, the
typical victim was a man between the ages of 20 and 40,
a group that normally has a very low death rate, said Noymer.
In the
early 20th century, however, tuberculosis was a major killer
of men in that age group, apparently because of transmission
in factories where men worked in densely-packed, poorly-ventilated
conditions, Noymer said. Men were about 30 percent more
likely to die from TB than women were- a pattern closely
paralleled during the flu epidemic.
In 1918,
men were 35 percent more likely than women to die from flu.
Of the 500,000 Americans who died that year, 280,000-300,000
were men.
"This
can't be a coincidence," said Noymer. "I think TB is the
missing piece of the puzzle. It explains why younger people,
especially men, died in such great numbers. Scientists since
1918 have been searching for clues for why the 1918 epidemic
was so deadly, especially in middle age. But people did
not look at what happened to tuberculosis death rates, not
only in the epidemic year, but in the years afterwards."
His findings
explain another mystery. Scientists who have attempted to
study the gene sequence of the 1918 influenza virus have
seen nothing out of the ordinary, nothing to explain the
flu's virulence.
"Never
before or since have we seen a flu epidemic that was so
virulent," said Noymer. "The spread was extremely rapid,
as was the development of the infection. Almost everyone
who died was gone in two weeks.
"I do
believe my finding explains most of the deadliness of the
1918 epidemic. It doesn't prove that, if another strain
were to appear, that the U.S. population would be safe,
but it strongly suggests that we would fare much better."
Noymer's
analysis shows that the 500,000 people who died in 1918
were almost exactly the number who would have been in various
stages of disease from TB. Using pre-1918 death rates, Noymer
calculated that 500,000 more TB deaths would have occurred
between 1918 and 1932 had there never been a flu epidemic.
As a
result of the excess death among men in 1918, a healthier
male population was left, said Noymer. For years afterward,
the life expectancy of men, which usually lagged behind
women by six years, moved up to more closely resemble the
female pattern. It was this startling change that sparked
Noymer's research, when he saw something no demographer
had ever noticed before - a precipitous drop in 1919 in
the gender differential from six to two years.
"When
I saw that," said Noymer, " I said to myself, 'That's the
flu!' And, surprise, surprise, it leaves the same mortality
patterns on age and sex that TB does."
Co-author
on the article is Michel Garenne, senior researcher at the
French center for population and development studies, CEPED,
Centre français sur la population et le développement.
The
paper is online at: http://demog.berkeley.edu/~andrew/1918/
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