Student finds tuberculosis may have been real killer in 1918 flu epidemic

By Pat McBroom, Public Affairs

08 NOVEMBER 00 | 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 Berkeley researcher in demography 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, a doctoral student in demography, a department in the College of Letters and Science. He published his findings in the 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 another mystery. Scientists who have attempted to study the gene sequence of the 1918 influenza virus have seen nothing out of the ordinary 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, the U.S. population would be safe, but it strongly suggests that we would fare much better."