During Tom Frieden's seven and a half years as director of the U.S. Centers for Disease Control and Prevention, his agency was buffeted by crises that included government furloughs, H1N1 flu, laboratory safety issues, an earthquake in Haiti, and outbreaks of Ebola and Zika virus. To better manage emerging diseases—and to detect them before they spread globally—the agency is now working with dozens of countries to boost diagnostic and testing capabilities. Frieden spoke with Scientific American during his last week on the job about some of the nation's future health challenges, as well as his most memorable moments as director. An edited excerpt of that conversation follows.

Scientific American: What immediate health issues are facing the Trump administration?

Tom Frieden: Zika is not over. It is likely to spread in Latin America and the Caribbean for months and years to come, and we still don't fully understand the range of birth defects it causes. Antibiotic resistance in the U.S. is something that threatens to undermine modern medicine. The opioid epidemic is something that has quadrupled [overdose deaths] in the U.S. And we are always concerned about an influenza epidemic. We have also identified new pathogens and pathogens in new places—so we know that tick-borne pathogens are more widespread around the world than previously thought, including Crimean-Congo hemorrhagic fever.

How prepared is the CDC to deal with these problems?

It's a big problem that when there is an emerging threat, we are not able to surge or work as rapidly as we should, as a result of a lack of additional funding and legislative authority. When there is an earthquake, the Federal Emergency Management Agency doesn't have to go to Congress and say, ‘Will you give us money for this?’ But the CDC does. We have made a really good start working with 70 countries to strengthen lab systems, rapid-response and field-monitoring systems, but it is going to take a while before countries around the world are adequately prepared. A blind spot anywhere puts any of us at risk.

A technician packages a urine sample for Zika testing. Credit: Joe Raedle Getty Images

What was an experience that really stuck with you during your tenure at the CDC?

Certainly during the shutdown of the federal government, when we had to furlough [about] 8,500 staff and couldn't protect Americans as effectively because of that—that was a terrible time. During the Haiti earthquake, when Diane Caves, a 31-year-old public health employee at the CDC, died—when the hotel she was staying in in Haiti collapsed—I certainly will never forget sitting down with her husband and father to tell them that she had passed away and been killed there. But there have also been very encouraging moments: the moment we knew we had broken the back of the epidemic of Ebola in West Africa, the moment when we were able to see rigorously that our antismoking campaign had saved more than 10,000 lives, the moment when we were able to definitively say that Zika causes microcephaly and other birth defects, and the moment when the data came back on teen pregnancy showing that the programs we and others had run had driven it down. Teen pregnancy is really a perpetuation of poverty, and by reducing teen pregnancy we have been able to reduce poverty.

What do you consider unfinished business or a regret?

I hoped that we would be over the finish line on polio [eradication] by now. In Nigeria, we thought we were over the finish line—but [Islamic extremist group] Boko Haram is partly in control where polio is circulating, and that was an issue. So we have further to go.