In our last climate change episode, we took a look at how climate change affects the spread of infectious disease. Fortunately, that isn't the end of our discussion of disease on a warming planet.

Waterborne diseases are already a serious public health threat. As climate change continues and increases in intense rainfall, periods of drought and temperatures, our struggle with waterborne diseases are gonna increase too. That's the topic of this week's Healthcare Triage.

Water. It's about as important as it gets. We need it, and we need it clean.

That's a big problem in some places on our planet, with more than 2 billion people currently living in water-stressed countries. And it's projected to become a bigger problem as the climate changes. According to the Intergovernmental Panel on Climate Change, the United Nations' body for assessing science related to climate change, there's a very high confidence that the risk of water-borne diseases will increase if something isn't done about the warming on our planet.

How big of a concern are water-borne diseases? To answer that, we should start with what actually those are. A water-borne disease includes any infection transmitted via water consumption, and it can include a bunch of different pathogens that cause a variety of symptoms.

Some of the diseases caused by these pathogens include cholera, dysentery, hepatitis A, and typhoid. The various symptoms of these diseases can include fever, liver damage, and lots of other stuff that's pretty much terrible -- like excessive diarrhea.  But what do we mean by terrible? Like, a long night of severe abdominal discomfort?

Unfortunately, we're worried about things on a much larger scale. Persistent and prolonged bouts of diarrhea can introduce severe issues of malnutrition and dehydration. Globally, diarrheal diseases are the second leading cause of death in children aged five and under.

While it's hard to make precise predictions because of the number of factors involved, some models project huge increases in diarrheal diseases under various climate change scenarios. For example, one projection looking at climate scenarios in Bangladesh estimates 2.2 million additional cases of E. Coli-associated diarrhea by the end of the century.

Increases in temperature are one contributing factor, with evidence supporting a relationship between temperature and diarrhea caused by bacterial pathogens, likely due to increased survival and strength of the pathogens. In Zanzibar, an increase in temperature of 1 degree Celsius translated to a 2-fold increase in cholera cases. Both heavy precipitation and periods of drought brought on by climate change can also increase diarrheal diseases.

For example, in Fiji, areas where flooding of a stream or river have occurred are more likely to see cases of typhoid. While heavy precipitation can move and distribute pathogens by overflowing various water sources, drought is thought to affect the concentration of pathogens in different ways. One example of this is cattle grazing patterns during drought.  Cattle can carry pathogens, such as E. coli, and during a drought, they're more likely to graze closer to the scarce sources of water.

Then they defecate, sometimes end up dying, near or in those sources of water, thereby contaminating them. If humans then drink from those sources, or if a later increase in precipitation moves this water ot other sources utilized by humans, the potential for human contamination seriously increases. And I'm not just making up this scenario.

This whole drought-cattle grazing-heavy rain situation appears to be responsible for a major E. coli outbreak in southern Africa in 1992. Rainfall also increases the risk of contamination by wastewater. In many major cities in both developed and underdeveloped countries, systems of sewer and storm water are combined.

That means a single pipe is collecting storm water, sewage, and industrial waste. That, in turn, means that this one pipe gets quite a bit busier when it rains. And finally, that means that a particularly intense rainstorm could overwhelm it, and when that happens, we get overflow of sewage and industrial waste along with the rainwater.

That's a big contamination problem for humans, because that overflow sometimes ends up in water sources that we use for drinking or recreational activities like swimming. And these types of systems are pretty common. Just in the United States, we have these combined systems in over 30 states, including major cities like Boston and New York City.

And in many places, water systems are not formally or centrally managed at all, making them even more vulnerable to contamination during climate change events. For example, in Lagos, Nigeria, there is no central sewage system, and even the treatment plants from other areas that serve a very small percent of the city's population are in pretty bad shape. These conditions mean water-borne diseases are already an issue, and intense weather arising from climate change will only exacerbate the situation.

Importantly, this is an issue even in areas where overall rainfall is decreased by climate change, because the expectation is that rainstorms, however rare, are becoming more intense and more able to overwhelm water management systems in a short period of time. And don't forget about those ever-rising sea levels. Those rising sea levels increase the waste water management systems already being overwhelmed and/or damaged, leaving drinking water at risk of contamination by the fallout.  At this point, it might sound like this episode is a warning of what's to come.

But we think it's really important to be clear that we are already experiencing these issues across the globe as the climate heats up, including in developed countries. A 2001 study reported a significant association between rainfall and disease in the United States. Outbreaks of pathogens have been seen in England and Wales when rivers were at maximum flow, in Canada following groundwater contamination with cattle manure after rare, intense rainfall, and in US states following excess rainfall and flooding.  So what, we're just all destined to encounter a potentially deadly pathogen in our water in years to come?

I mean, maybe. But only if we don't do something. We've got a decent idea of the issues, which gives us a leg up in adapting our infrastructure to deal with them.

And some places are already doing that. For example, New York City initiated a Climate Change Adaptation Task Force way back in 2008 to start examining how the city's critical infrastructure would be affected by climate-related events. Beyond changing the infrastructure itself, we'll need to make changes to how we operate these systems, how much demand we put on them, the policies we create around their management and use, ensuring we take our environmental impacts into account, and what our plans and backup plans are when emergencies arise.

We CAN do all those things. We're already doing some of those things in some places. We just need to do more in more places.

Our health truly depends on it.  Hey did you enjoy this episode? You might enjoy this previous episode on climate change and infectious disease. We'd appreciate it if you'd like this video, subscribe to the channel down below, consider going to patreon.com/HealthcareTriage, where you can help support the show, make it bigger and better.

We'd especially like to thank our research associates, Joe Sevits and Edward Liljeholm, and of course our surgeon admiral Sam.