More Heat Means More Diarrhea

A look at recent trends suggests developing countries will be burdened with millions more cases of diarrhea as the planet heats up

New climate research just plain stinks. As temperatures rise so, too, do cases of diarrhea in many countries.

The findings are serious, potty humor aside: The types of bacteria scientists expect to incite this surge already cause half a million deaths a year, mostly in developing countries that lack access to clean water.

Maybe investing in water and sanitation improvement should be considered a form of climate adaptation. 

- Karen Levy,
Emory University

Globally there are about 1.7 billion cases of diarrhea disease every year, according to the World Health Organization. These diseases, caused by bacteria like E. coli and Shigella, cause extreme dehydration, starving the body of necessary water and salts. With all causes taken into account—viral infections, bacteria, parasites, food allergies—around 760,000 children aged 5-years-old or younger die from diarrhea each year.

The study, published this week by Emory University scientists in the  Journal of Infectious Diseases , highlights the interconnected nature of climate change, infectious disease and children's health. Efforts to treat current diarrhea diseases risk being overwhelmed as temperatures rise and spur more illness.

800,000 more cases of diarrhea by 2035

In Bangladesh alone the Emory University researchers estimate an additional 800,000 cases of E. coli-driven diarrhea by 2035. Temperatures are projected to increase .8 degrees Celsius by then. By the end of the century, when temperatures are expected to be 2.1ºC higher than today, the researchers estimated an additional 2.2 million cases.

"That's just for one type of E. coli in one country," said senior author Karen Levy, an assistant professor of environmental health at the university's Rollins School of Public Health.

"When you multiply a large number [of diarrhea cases] like you have in Bangladesh by even a very small number, you get a large number of additional cases," she said.

There are many different causes of diarrhea: viruses, bacteria and parasites. Levy and colleagues looked at disease rates associated with one common pathogen, E. coli, and how temperature and precipitation influence its incidence.

Summertime peak for diseases

For the most part, diarrhea caused by E. coli peaks in the summer, most commonly by ingesting food or water tainted by feces. Across 15 countries highlighted in 18 studies, Levy and colleagues found an 8 percent increase in E. coli-caused diarrhea for every 1ºC temperature increase.

It's not entirely clear why warmer weather means more E. coli-driven diarrhea, but there are a few possibilities, said Erin Lipp, a professor at University of Georgia's College of Public Health who was not involved in the study. People behave differently when it's warmer, eating more meals outside, for instance. Seasonal changes in animals that harbor the pathogens could also figure somehow, she said.

Poverty-stricken countries are most vulnerable. The illness is almost always—90 percent of time, according to estimates—caused by unsafe water, poor sanitation or insufficient hygiene.

An underreported disease

In recent years scientists have been sounding the alarms over climate change and diarrhea.

Norway researchers reported that temperature increases of up to 4ºC in the tropics would increase diarrhea risk by about 8 percent. Even the most "conservative estimates," they warned, indicate "substantial impacts from climate change on the incidence of diarrhea."

But the disease remains underreported, Lipp said, which makes it difficult for researchers to project what climate change will or will not mean for diarrhea illness.

One place with a lot of data? Bangladesh, Levy said, which is why they zeroed in on the country.

The projected diarrhea risk increase there is troublesome: It's a country with a booming population, glaring gaps in proper sanitation, acute poverty. Over the past 35 years the country's population has increased 77 percent. Almost a quarter of Bangladesh's 160 million people lives in poverty. Equally troubling, about two thirds of the country sits less than 16 feet above sea level, leaving it at high risk of flooding.

Link to flooding and downpours

Flooding and heavy rains, expected to become more frequent under climate change scenarios, have been linked to increases in diarrhea. But the relationship is less clear, said Elizabeth Carlton, an assistant professor at the University of Colorado, Anschutz Medical Campus.

Carlton and colleagues found that in Ecuador from 2004 to 2007 following dry periods, heavy rains were associated with a 39 percent increase in diarrhea cases.

Levy examined increased precipitation as well, but didn't see the strong link as they did for temperature. She said, while too much or too little rain can impact diarrhea illnesses, it's much more tied to a country's sanitation and flood-control efforts.

Carlton said there are solutions to the global diarrhea problem—and they're what some researchers refer to as "no fail."

"Clean water for drinking and abundant water for washing and hygiene … and sanitation, not just toilets, but sewer systems that prevent people from coming into contact with human waste," Carlton said. "Investing in water and sanitation, one way or another, will help improve public health."

Clean water as climate adaptation?

Levy hopes the study is taken into account as developing nations plot how to deal with climate change.

"When we think of adapting to climate change we think of building houses on stilts, moving to higher ground," Levy said.

"If we believe these estimates of increasing amount of diarrhea under warming temperatures, then maybe investing in water and sanitation improvement should be considered a form of climate adaptation."

Source: The Daily Climate

Taxonomy

• Environment
• Climate Change