Infectious diseases are no longer the major killers in the U.S. that they once were, but they still surprise us.

According to a report published Tuesday in JAMA, the journal of the American Medical Association, deaths from infectious disease accounted for 5.4 percent of deaths from 1980 to 2014.

That's a big change from 1900, when infectious diseases like pneumonia, tuberculosis and diarrhea accounted for almost half of all deaths. The historical decline represents great progress in sanitation, antibiotic discovery and vaccination programs, says Heidi Brown, an assistant professor of public health at the University of Arizona and an author of the research letter. "We've done phenomenal and amazing things with respect to infectious diseases," she says.

But if you dig into the data a bit, she says, you can see where new diseases make an appearance, sometimes a deadly and dramatic one. For example, between 1980 and 1995, the number of deaths per 100,000 people from HIV/AIDS rose by an average of more than 85 percent per year. Then when new antiretroviral drugs became available, that rate fell by an average of more than 10 percent annually from 1995 to 2014.

"We went from not understanding [the disease] to being able to do something about it in a relatively short period of time," says Brown. (To be sure, even with the gains we've made, the epidemic is not over.)

West Nile virus also shows how new diseases can pop up. The disease, which is transmitted by mosquitoes, arrived in the U.S. in 1999 and "very quickly became endemic," says Brown. In 2014 it killed about 3 people for every 10 million in the population. (This chart, from the Centers for Disease Control and Prevention, shows the impact of the disease through 2015.)

Now public health officials are warning about the threat from other vector-borne viruses like Zika and chikungunya. Just last week, the World Health Organization said Zika was no longer a public health emergency, but that it has become is a chronic problem, here to stay.

The emergence of new public health threats shows the need for vigilance, despite the reassuring statistics, says Brown. "Infectious diseases still not conquered," she says. "There's still that vulnerability."

Katherine Hobson is a freelance health and science writer based in Brooklyn, N.Y. She's on Twitter:@katherinehobson.

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