The influenza pandemic of 1918 infected about a third of the world's population and killed at least 50 million people worldwide. Arizona was hit particularly hard.

A recently-published study looked into the reasons behind the devastation in the state and some of the long-term implications. 

During the late 1800s, people with tuberculosis were encouraged to move to the Southwest due to its arid climate. Epidemiologist Sushma Dahal said this was one reason she wanted to look at the pandemic's impact in Arizona.

"Arizona had a really high rate of people with TB so they were already ill," Dahal said.

Arizona was also a very poor state at the time. Phoenix had some of the worst slums in the country and Arizona had an unusually high infant mortality rate before the pandemic even hit.

The researchers analyzed thousands of death records from all 15 of Arizona's counties.

"We found northern counties had mortality rates that were even higher," Dahal said. She said Native American communities living in these counties lacked access to proper healthcare.

"Also they're probably living in isolation and maybe not exposed to the previous year's virus form," she said. 

Outside of the northern part of the state, Cochise and Yuma counties saw high death rates.

“We found that these counties had the presence of mines such as copper mines and silver mines possibly the higher concentration of people with low socioeconomic status who would be working in the mines," she said.

Both Native American and mining communities had low socioeconomic status. 100 years later, Americans in poverty are still harder hit by yearly flu outbreaks.

Dahal and her team also looked into birth records, because she said she was curious about the longer-term impact of pandemics. 

"I was surprised to see a dramatic — 43 percent — drop in births exactly 9 to 11 months after peak pandemic mortality," she said. 

Dahal said this could be attributed to a number of things. People may be attempting to conceive less during such a terrible time, or early pregnancies could have failed when the mother was exposed to the deadly flu virus.

Dahal said there are real-world policy implications to be learned from her study. She said public health officials should monitor early pregnancies during flu season and concentrate their resources on poorer areas.

EDITOR'S NOTE: This story has been updated to correct the statistics for pandemic infections and deaths.