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When you think about the technology that helps us prevent outbreaks, what do you think of? Vaccines? Lab tests? Medications? What about toilets? That's right! Toilets are an important piece of technology that can help us prevent outbreaks! Toilets are a part of infrastructure, the important system that we'll be talking about in this episode of Crash Course Outbreak Science. We'll look at how from physical infrastructure, from toilets, to sewers, to roads, and more, creates healthier environments for us and helps us prevent and deal with outbreaks.

This episode of Crash Course Outbreak Science was produced by Complexly in partnership with Operation Outbreak and the Sabeti Lab at the Broad Institute of MIT and Harvard—with generous support from the Gordon and Betty Moore Foundation.

Episode Sources:,down%20sinks%20instead%20of%20binned.

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There’s all kinds of cutting edge technology that helps tackle infectious disease outbreaks, from genetically engineered insects to mRNA vaccines to drugs discovered by artificial intelligence. But there’s a two hundred year old piece of technology that’s just as important for tackling outbreaks, all over the world: the humble toilet! Toilets, like sewer drains, windows and even roads, are all part of infrastructure, a system that plays a huge role in maintaining our health by keeping our surroundings free of germs. When infrastructure fails, or when we lack it entirely, it can create new risks of outbreaks too. In this episode, we’re going to dive deeper into how physical infrastructure creates healthier environments for us to live in and how it helps us prevent and tackle outbreaks.

I’m Pardis Sabeti, and this is Crash Course Outbreak Science!

 [Theme Music]


 Infrastructure is what we call all the physical structures and facilities that help provide the basic services we use everyday. That means things like roads, buildings, the water supply, and communication networks, to name a few. In the case of outbreaks, infrastructure plays a big part in both preventing them and responding to them. We can learn a lot about that part by taking a closer look at something we all have probably used at one time or another: the toilet. While you’ve probably flushed a toilet many thousands of times over the course of your life, it’s worth appreciating the incredible work they do for us. First and foremost, they carry away the waste produced by our bodies that harbors pathogens! And, since science demands clarity, I mean your pee and poop.

Human waste can carry a whole host of pathogens, the tiny germs that make us ill, such as the kind responsible for cholera or hepatitis. The modern toilet’s waste-whisking power is in large part thanks to Scottish inventor, Alexander Cummings. In 1775, he patented a toilet with what we call an “S”-bend, a curved piece of piping that traps a pool of water in the bottom of the bend. That water creates a seal which stops waste and noxious gases coming back up through your toilet. When you flush a toilet, it fills the bowl with water and forces it through the bend. Once the water is finished draining, it seals the bend in the pipe up with water again. Nowadays, most toilets use what we called a “U” bend, and it works pretty much the same way. The flush mechanisms on toilets and the plumbing network they feed into make sure the waste, and the pathogens they carry, are quickly and efficiently taken away from contact with people and the resources we use like our food and water.

But even though that waste is carried out of our homes and other buildings, it might still end up some place where it can infect us unless we deal with it. So, ideally, wastewater feeds into a water treatment facility. There, it goes through a series of steps to filter or kill as many pathogens as possible. There are physical processes, like screens that block bigger solids such as debris, rags, and coins. People flush some weird things down the toilet. There are also biological and chemical processes, like the activated sludge process--no, really. We use bacteria to eat organic compounds in the water. After that, we add chemical disinfectants to it, like chlorine, which kill off the pathogens that remain, before discharging the much, much cleaner water into a water source like a stream or river, where it will no longer harm us, or the environment! In fact, a similar process is used to clean the water we use to drink. When we get drinking water from, say, a local reservoir, that water first passes through a series of filters to remove dirt and even some large pathogens before adding chlorine, to, once again, kill off the pathogens, while still being totally safe for us to drink.


 We know having clean drinking water is important-- as we’ve seen in previous episodes, if that water is contaminated by pathogens, it’s an easy way for people to become infected by them. And because many people might rely on the same water source, like a nearby lake, contaminated water sources can become a reservoir for an outbreak. Water is also something we use to keep our environments clean, which we call sanitation, and our bodies clean, which we call hygiene. Because of this, flush toilets, plumbing, and water treatment facilities have a big impact on preventing outbreaks of diseases like cholera, dysentery, hepatitis A, typhoid and polio, just to name a few!


Toilets and plumbing are just one example of sanitation, but there are others, like sewer pipes and trash disposal. When it comes to hygiene, as you probably know, to keep our bodies free of dirt and the pathogens that might be lurking in it, we need clean water and soap. An important part of this is washing our hands, especially after using the bathroom! Water, sanitation and hygiene are collectively referred to as W-A-S-H or, “WASH”, and lie at the heart of many global public health campaigns. We’re only scratching the surface here, but it’s clear that WASH infrastructure, like sinks, pipes, and yes, toilets, is critical for preventing outbreaks. In fact, one of the places we most often use a toilet is an important kind of infrastructure of its own: housing.

 Of course, a house with sturdy walls and the right fixtures, plumbing, and materials to support piping and water supplies is a great home for a toilet-- and us--but it’s more than that. Housing also plays an important role in our relationship to infectious diseases. In tropical countries, homes constructed with solid materials, like brick walls and tiled roofs, can keep out vectors of disease, like mosquitoes. That reduces the chances of being infected with malaria or other diseases from a bite. But when homes aren’t built up to par, they can also increase risk of infection too. For example, if there’s a problem with your plumbing, instead of whisking waste away, your toilet could end up spilling it everywhere instead. And you definitely wouldn’t want that happening close to where your food is stored, since it could end up contaminating it. Then there’s what happens when we flush the toilet. As water rushes into the bowl, it also sends out tiny droplets of water, which might be contaminated, into the air. And evidence suggests, those droplets could be responsible for spreading diseases like Legionnaires’ disease. So homes also need proper ventilation, like windows that allow air flow in and out of rooms, to stop pathogens lingering in the air, and decreasing the odds that we breathe them in and become infected by them. Even when everything is fine with our toilet and the infrastructure around it, there’s another element of housing that could increase the risk of outbreaks: overcrowding.

 When many people live together in a single structure, it makes it easier for outbreaks to spread from person to person. Overcrowding is also an issue in facilities that house many people, like university dorms, nursing homes, housing shelters, prisons and hospitals. Due to conditions like this, people in prisons are ten times likelier to contract tuberculosis than the general population. So when homes and buildings are designed and built with solid materials, ventilation, and space, they can give us environments that protect us against outbreaks. But even in some places where substantial infrastructure exists, unfortunately a lot of it is old and needs maintaining. Underground pipes may not hold up forever, and in areas like the United Kingdom, the plumbing infrastructure is so old that we don’t even have accurate records of where they are-- it’s hard to fix a pipe you can’t see! 


On the other hand, the reality is that much of the world still lacks the infrastructure we’ve discussed. Two billion people across the world still don’t have access to sanitation infrastructure like toilets or latrines. Hundreds of millions of people live in crowded, informally-built settlements, which often lack good quality housing and sanitation infrastructure. But that’s not to say that things are stuck that way! For example, in many countries across sub-Saharan Africa, improvements in housing over the last two decades have also decreased the number of children who died from malaria and other infectious diseases associated with poor infrastructure.

We can focus on other kinds of infrastructure to improve our responses to outbreaks as well. For example, roads are one of the most important ways for people to get to hospitals, clinics and other kinds of healthcare facilities. Only sixty percent of people worldwide could reach a healthcare facility in under an hour if they walked, but that number shoots up to over ninety percent if the roads to healthcare facilities can be accessed by vehicles, too. So roads enable more people to get to healthcare facilities when they need them. Overall, it’s clear that making improvements to infrastructure is as much about responding to outbreaks as it is about building the most impressive bridges.

One particular challenge is transporting vaccines. For example, the active ingredient in some vaccines is a weakened version of a pathogen for the body to build immunity against-- and that weakened pathogen is usually a living cell. But if the vaccine gets too hot or too cold, the cell could die and make the vaccine ineffective. So there’s a whole chain of infrastructure needed at every step of a journey to keep things cold along the way, called, a cold chain.

To see how this works, let’s consider a vaccine for the fictional disease, Hankitis. Hankistan is suffering from an epidemic of the disease but thankfully, its close ally Johnovia has developed a vaccine which it’s happy to share. The vaccine needs to be kept frozen, until a few days before it’s used and then, it can’t go above 8 degrees celsius. So how do we get it from one place to the other?

 Thought Bubble

 Let’s go to the Thought Bubble. When the vaccines are first manufactured, the production facility in Johnovia keeps them in a freezer store, a huge room designed to stay at temperatures well below freezing. From there, they need to be put onto a plane so they can be flown to Hankistan. To stay cool, the vaccines are transported from the production facility to the airport in boxes filled with dry ice, frozen carbon-dioxide that stays cooler than normal ice. The boxes are also thermally insulating so that heat struggles to get into them and melt the ice. The boxes are loaded up onto trucks to get them onto the plane. Once on the plane, they’re transferred into a special canister, this time cooled with liquid nitrogen. That keeps the vaccines frozen until they land at their destination. From there, they’re put onto trucks with freezers inside, which rely on the truck’s power to stay cold. The trucks transport the vaccines to a warehouse filled with freezers, where they can be held for a long time, until needed somewhere nearby.


 A few weeks later, a healthcare clinic asks for a batch. So the warehouse delivers them to the clinic

in the same freezer vans. At the clinic, they’re finally transferred to a refrigerator, which is warmer than any other point in the vaccine’s journey-- but not more than 8 degrees C! Once in the refrigerator, the cells in the vaccines will only have a couple of days to live, so the clinic gets to work distributing them all right away!

Thanks Thought Bubble!

 End Thought Bubble

The technology of the cold chain relies on lots of different infrastructure to work from start to finish. The vans need roads, the planes need airports, and even the freezers need to be connected to the power grid! And like other kinds of infrastructure, it relies on an abundance of different resources to work. So, as we’ve seen with housing infrastructure, and throughout this series, it’s often the case that those who are less economically and socially supported, find themselves less able to deal with outbreaks.

While it’s not often easy to hear about the scale of the challenge facing the world when it comes to problems like a lack of infrastructure, understanding the different circumstances that communities face across the world is the first step towards addressing them and providing safer environments for all. In our next episode, we’ll be taking a closer look at the different cultures and beliefs in communities, and how they influence the way that we respond to outbreaks.


We at Crash Course and our partners Operation Outbreak and the Sabeti Lab at the Broad Institute at MIT and Harvard want to acknowledge the Indigenous people native to the land we live and work on, and their traditional and ongoing relationship with this land. We encourage you to learn about the history of the place you call home through resources like and by engaging with your local Indigenous and Aboriginal nations through the websites and resources they provide.

Thanks for watching this episode of Crash Course Outbreak Science, which was produced by Complexly in partnership with Operation Outbreak and the Sabeti Lab at the Broad Institute of MIT and Harvard— with generous support from the Gordon and Betty Moore Foundation. If you want to help keep Crash Course free for everyone, forever, you can join our community on Patreon.