October 20, 2017
Hurricane between Florida and Cuba
Ask the Experts

Floods, Heat, and Infectious Diseases

by David Tuller, DrPH  

Arthur Reingold, MD, is a professor of epidemiology at UC Berkeley’s School of Public Health. He received his undergraduate and medical degrees at the University of Chicago and is an internationally known expert on infectious diseases. Dr. Reingold has conducted extensive research on the transmission and prevention of HIV/AIDS, tuberculosis, ebola, SARS, and many other infectious diseases. He is a member of the U.S. Advisory Committee on Immunization Practices and the National Academy of Medicine.

We recently talked with Dr. Reingold about the possible impact of hurricane flooding on infectious disease spread, as well as the future of Zika virus and other infectious-disease matters.

Hurricanes Harvey and Irma recently hit Texas, Florida, and the Caribbean, causing catastrophic flooding. How might this flooding affect the spread of disease?

A big issue is a potential increase in mosquito-borne illnessesbecauseof more standing water and breeding sites of the kinds of mosquitos that transmit Zika and dengue and other diseases. That could happen especially if vector control practices are interrupted because of all the other high-priority needs at the moment, after the hurricanes.

In addition to mosquito-borne illnesses, water-borne diseases could increase, especially if people do not have access to clean drinking water. In places like Haiti, for example, where there is already cholera, it could increase the incidence of that. Elsewhere, like in the U.S., you could get other types of diarrheal diseases from contaminated water. So making sure people have ongoing access to clean drinking water is key.

What’s currently happening with the Zika virus?

The future of Zika is really unpredictable. There seems to be very little Zika transmission in the areas we were having it before, like Brazil, Columbia, and Puerto Rico. And I think most people would agree that in some of the affected areas, a large percentage of people are already immune. They’ve been infected, mostly asymptomatically, and developed immunity. But anyone who says they can predict where Zika will become a problem this coming year will basically be guessing.

There’s obviously been limited transmission in Florida, and we also have mosquito species that can effectively transmit Zika in California, in Texas, in many other states in the southern U.S. In theory, we could get a lot of mosquito-borne Zika here. In practice, I’m not expecting that to happen. Most of the U.S. cases were acquired overseas and brought here when people returned home. In California, we have good vector control. If we do get occasional introductions, like happened in Florida, then the public health response will be fairly active in order to prevent widespread transmission.

What about the prospects for more Zika and other infectious diseases because of climate change?

A year or two ago I was on a review panel of a U.S. government-wide report on likely effects of climate change on human health, with chapters on heat stroke, heart disease, mental health, and vector-borne diseases—Lyme, food-borne illness, etc.—trying to assess what is likely to happen. The part about vector-borne diseases certainly argued that with higher temperatures there will be an expansion of new areas for various ticks and mosquitos and that may mean an expansion of vector-borne diseases—Lyme, encephalitis, possibly reintroduction of malaria. But I think at this point this is all still speculative.

Keeping track of all these risks requires regular investment in public health. Is that in danger in the current political and fiscal environment?

I think the first thing to acknowledge is that a lot of these are state-level functions, and many states independent of the federal government have been cutting funds to health departments. And then cutting some more. States have also gotten huge amounts of funding from the CDC for various programs, for example, and those federal programs are greatly endangered by the proposed cuts in the federal budget. So on top of the reductions being made by states themselves, you have the very likely possibility that federal support for the CDC will be cut significantly, and that means they will cut these crucial grants to states.

And you know as well as I do that public health suffers from its successes. When people are not getting sick, when there are not outbreaks, they cut funding for public health, for surveillance, for these boring routine infrastructure public health activities. But those are still at the heart of being prepared and picking up changes early and being able to respond quickly. You might not be able to prevent things from entering the country, for example, but if you can respond quickly with vector control and other measures you can prevent widespread dissemination.

What else do we need to be worried about? Yellow fever, which has been rampant this year in Brazil? A new flu virus?

Yellow fever is currently a big problem in Brazil. In the U.S., we certainly have effective vectors (mosquitoes) for yellow fever. We’ve had it in New York, in Philadelphia, along the entire East Coastand throughout the Southeast. So it’s possible. And of course we always worry about the next flu pandemic. There will be a pandemic at some point. We can’t predict what strain will cause it. But it should be on everyone’s agenda.

California implemented legislation in 2015 making it more difficult to obtain an exemption from vaccination for children. Have vaccination rates increased since then?

I just got e-mail from the state health department immunization branch, looking at kindergarten vaccine coverage. It has gone up quickly. People have obviously groused about the law, but it has had a demonstrated impact. In terms of the Trump administration’s position, I don’t think anybody knows—there was this discussion about Robert Kennedy, Jr., heading up a commission, and some concern he was going to start investigating so-called “corruption” at the CDC. All of that would be very distressing if it happened. Being paranoid about the possibility of this kind of investigation is not necessarily energy well-spent, but it’s good to keep it on the radar.

I do think it’s important to understand that if you give large numbers ofvaccinesto large numbers of people—infants, children, adults—bad things will happen to some of them within hours, days, and weeks, simply by chance. We do need to be able to monitor adverse events. We can’t ignore them and we can’t just write them off. Individual cases can raise hypotheses but they don’t prove a cause-and-effect relationship. I understand why parents or otherscould come to believe that a vaccine caused an illness, but whether or not that’s true or whether or not there is a risk really requires epidemiologic study. We have an obligation to see if epidemiologic studies can confirm or reject those hypotheses.

Also see How to Prevent Mosquito Bites.