Why illness spikes when water supplies dwindle

Dr. Rocio Juarez is used to treating patients suffering from vomiting and diarrhea, but she had never seen an outbreak of intestinal disease as bad as the one that happened in February 2022 in her hometown of Monterrey, in northeast Mexico. 

“There were at least a couple of weeks in which nearly every patient I saw had diarrhea,” Juarez said of the outbreak, in which a dire water shortage coincided with a dangerous spike in intestinal disease.

But was it really just a coincidence? One young mother in the region, Mariell Gutiérrez, has her doubts. Her five-year-old daughter Rafaela nearly had to be hospitalized after her third bout of uncontrollable diarrhea in just five months. “There was a time in which we did wonder, could it have been something in the water?” Gutiérrez says.

She found the timing highly suspicious because, in February 2022, the government of Nuevo León (the state where Monterrey is the capital) issued an emergency declaration of extreme drought and threats to the water supply. About a month later, the government started shutting off water to families like Gutiérrez’s – at first, just once a week, but then for many hours every day. 

The following month, the state’s reported diarrhea cases hit a peak, reaching a rate of nearly 4.7 cases per 100,000 residents – double that of the previous year. Data from the Mexican Health Secretariat show the number of diarrhea cases in the first nine months of 2022 was almost 50% higher than in the previous year.  Water scarcity frequently triggers gastrointestinal diseases, according to Miguel Ángel López-Zavala, a water science and technology researcher at el Tecnológico de Monterrey, a private Mexican university.  

The Nuevo León water crisis is one example of what public health experts describe as a disturbing correlation: as climate change fuels hurricanes, droughts and other extreme weather events, outbreaks of intestinal diseases are also on the rise – especially in poorer communities where the water distribution infrastructure is unreliable and decaying. A 2011 study estimated climate change would increase diarrhea cases by up to 29% by the end of the century.

“When there is a lot of rain and flooding, viruses and bacteria have better conditions to develop, but when there is drought, people have less access to sanitation,” explains Cristina Bradatan, a sociologist at Texas Tech University who has studied the impact of climate change on health in Honduras. Both kinds of extreme weather can thus trigger outbreaks of intestinal disease, she says.

When water is absent or intermittent, people cannot wash their hands, clean their food or even flush the toilet, which creates perfectly suited environments for bacterial disease outbreaks. Water pollution also increases as water flow decreases, further encouraging the formation of pathogens. 

Coping with a bout of diarrhea might not seem like a big deal, but if it leads to dehydration, the consequences can be dire. Foodborne diseases, which often cause diarrhea, alone kill around 2,600 Americans each year. Digestive disorders are particularly dangerous for children. Diarrhea was the second leading cause of death in children less than five years old in 2019, killing 370,000 young kids worldwide. For older children and teenagers, there were more than 70,000 deaths. 

It’s not only a problem in developing countries like Mexico and Honduras. For most of the last summer, residents of Jackson, Mississippi, were told to boil their water before drinking it because of the risk of nausea, cramps, diarrhea and headaches. There was also a boil water notice last fall in Baltimore, Maryland, after E. Coli bacteria were detected in the water. Both cities were struck after extreme weather conditions compromised their already weak infrastructure systems and caused water flow to dwindle. 

In Monterrey, several factors conspired to raise the risk of digestive problems during the worst weeks of the water shortage last spring, according to López-Zavala.  

When people ration the water, they don’t wash their hands as frequently — an important part of overall hygiene and sanitation, López-Zavala says. Food preparation workers also may have been less attentive to good hygiene. 

“In some neighborhoods, we did not have water all day long, so I did wonder if we were cleaning food or kitchen appliances properly,” says Eduardo Santillán, another Tecnológico de Monterrey researcher who specializes in water management. “In small restaurants or [for] street food locals, I think it must have had an impact.”

Another reason for the correlation, López-Zavala explains, is that interrupting the water supply also affects water quality. When water pipes are empty, oxygen in the air enters and allows pathogens to grow. Water pipes also accumulate sediments when there’s no water flow to carry them away. 

That is why, when the water supply is re-established, the first few gallons have an unusually high concentration of sediments and are often not safe for human consumption. 

In some parts of Monterrey, the water pipes are old and rust accumulates in the water, especially when the supply is being rationed. Juárez, the physician who noticed a rise in cases, observed that the appearance of her tap water changed during the water crisis. 

“It had a layer of dirt you could notice if you let it sit for a few minutes,” she says. Juárez’s mother got diarrhea after drinking from the tap and urged the rest of the family to stop consuming it. 

As in Monterrey, the problem in Mississippi was not only extreme weather but also aging water infrastructure. Jackson’s pipes had water pressure issues after intense rain and flooding of the Pearl River. The situation was similar last summer in Baltimore, where workers had lowered the water pressure to make repairs when a heavy rain suddenly overwhelmed the system and forced further cutbacks in water flow, fostering bacteria formation, a government official told The Washington Post. 

In Nuevo León, López-Zavala says it will take many years to repair a decaying water distribution system – if it ever gets fixed at all. “It’s not something the government could do in a year or two,” he says. “It is decades of maintenance work that was not done.” State of Nuevo León health officials did not respond to Scienceline’s request for comment. 

The problem is likely to get worse as the planet warms, with the United Nations’s Intergovernmental Panel on Climate Change predicting that as both heavy storms and droughts become more frequent, so will disease outbreaks. 

Large swaths of the southwest U.S. and northern Mexico are already suffering from long-term droughts and the governments are reacting by limiting water usage or seeking alternative water sources. 

In the United States, at least, there are some reasons for hope amid the gloomy predictions of worsening conditions. The Inflation Reduction Act, which President Biden signed into law in August, includes $210 million in new spending for drought resilience projects. But in Mexico, experts think not enough has been done since the Monterrey crisis ended; although the local government announced a “Master Plan” to drill new wells and build new dams, it barely mentions spending on infrastructure repairs. 

“The rain came,” López-Zavala says, “and now we are just waiting until it happens again.”