In 2014, a disease that was no longer common in the United States resurfaced with a vengeance. People suddenly began running high fevers and developing rashes, and in some communities, people became so sick they had to be hospitalized. Throughout 2015, other outbreaks would pop up, and each time, healthcare officials would leap into action trying to identify and isolate one of the most highly contagious airborne viruses we know - measles.

In our ever-connected world, it's easy to travel to places with different approaches, opinions, and access to healthcare. For a variety of reasons, different people will be immune or unaffected by different diseases, but disease isn't always about immunity, and we can't be immune to everything. Whether it's spread person to person or because of an environmental factor or something else entirely, the presence of disease creates patterns in the landscape, and it's our job as medical geographers to spot the patterns and help with disease response. I'm Alizé Carrère, and this is Crash Course: Geography.

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In the last few episodes, we talked about how and why people move around the Earth, and in the episodes before that, we learned all about the things they take with them, from musical instruments and language to architecture and belief systems, but along with those cultural traits, people also share more deadly elements, like disease.

Disease is one of those surprisingly tricky concepts to define, because everyone's understanding of good health changes over time and with different information. Trying to describe what's broadly "normal" can not only be inaccurate, it can be hurtful to certain people or groups. So there isn't a single, universally agreed-upon definition of disease, but essentially, a disease is a social, cultural, and economic concept that describes some unexpectedly abnormal function in your body that we're trying to find the cause and effect of to maintain good health.

When measles spread in the U.S. in 2014, it first showed up as just pockets in mostly large cities where people who had traveled abroad were mixing among the population, but by the end of 2019, health agencies in the U.S. and around the world were drawing attention to a dramatic surge in cases. Now, we've studied measles for a long time, so we know measles spreads through the air and is an infectious disease, meaning a condition that can be spread from a pathogen, or organism that causes the disease like bacteria, viruses, fungi, or parasites, to a host, or the living organism that will get sick.

Diseases can also be noncommunicable, which means they're not caused by an acute infection, but instead are caused by any number of genetic, environmental, and behavioral situations rather than pathogens. Noncommunicable diseases are often chronic, because they tend to be illnesses that develop and remain for a long period of time.

For example, cases of noncommunicable disease don't have to have a direct link to each other. They might be linked to patterns of the environment, like asthma can be, or patterns of food access and consumption, like high blood pressure or diabetes. This is part of epidemiology, which studies how diseases are distributed and the factors that influence health and then applies that knowledge to control and hopefully eliminate health-related problems, including diseases.

As geographers, we can get involved by putting on our medical geographer hats and becoming detectives, utilizing those spatial skills geographers hone and combining them with an understanding of how environment and society connect to create just the right conditions for disease to manifest. We'll find medical geographers doing research, working with the public, and so much more in public health agencies, community health clinics, and global agencies, basically any agency that explores health and how to make communities healthier.

A key tool for sleuthing medical geographers is our old friend the map. In fact, in medical geography and epidemiology, British physician Dr. John Snow and his 1854 map of cholera cases in Soho, London are the stuff of legend and have influenced a lot of our modern thinking. Similarly, on this more recent map, notice that there are cases of disease starting mid-river, but none farther up the watershed, and the cases seem to follow down the river and, over time, spread out.

Hmmm. Without knowing anything about this place, it seems like the pathogen might be water-borne, or moves through water, and that it entered the water at this particular point. This is a 2010 map of the disease cholera in what's currently called Haiti. As a water-borne illness, the bacteria that causes cholera moves through water infected with the feces of someone with cholera.

But though cholera has been seen all over the world throughout history, until 2010, it hadn't appeared in Haiti for at least 100 years and possibly never at all, so something must have changed. Haitians in 2010 relied on water from the Artibonite River in part because there were few places with treated water, but also, at that time, the people of Haiti were recovering from a massive earthquake, and to help with that recovery, additional UN forces were brought in from Nepal.

Unlike pre-2010 Haiti, cholera is endemic, or common, to Nepal, meaning it's always in the background there. People from there may have immunity or strategies for living with that disease that may not be present elsewhere. Using maps after the outbreak began to help establish its origin, it became clear that those UN troops sent to help with earthquake recovery were improperly disposing of human waste. The bacteria hitched a ride to Haiti with those people, and unfortunately, it turns out that that strain of cholera that's endemic in Nepal can also thrive in Haiti.

These events led to an epidemic, or an increase of disease in a specific place for a particular period of time. This particular disease brought with it morbidity, which is another way of saying "infected with a disease," and had a specific mortality rate, or the number of deaths in a given population over a set period of time.

So in the case of the Haiti outbreak, we know that, over the course of the epidemic, an estimated 10,000 people died and over 800,000 were hospitalized, though definite numbers are hard to track because of the earthquake and already strained medical system. While it's possible not every person who died of cholera was counted, this outbreak is thought to have a mortality rate of between 19 and 34.5 people per 1,000. In comparison, Haiti's mortality rate just before the epidemic was 9 per 1,000.

So we're not kidding - medical geographers really are like detectives, and part of why the work of medical geographers is important is that they can use existing patterns to describe current disease spread, but they can also help predict where disease will go so populations can change their behaviors, environments, or both to get ahead of any disease outbreaks. When there's an outbreak of cholera or any disease, we try to track its spread and predict where it will go so people can take precautions to try to protect themselves.

In practice, this can start by health officials noticing prevalence, or the proportion of people with the disease in a population. Then, as they monitor the situation, they'll watch the incidence rate, which is a measure of how often there are new cases of illness in a given time frame for a given population. Using that information, health officials can issue warnings and remind people of best behavioral changes to slow the spread of disease, like washing hands, distancing, or even boiling water, in the case of cholera. Health officials can also advocate for changing the environment, like bringing in additional water treatment or, for disease that are spread by animals or insects like malaria, changing those creatures' habitats or access to humans to reduce disease spread.

It sounds fairly straightforward, but people and disease are chaotic, and the patterns can take a careful eye to deduce. Like, here's a map of a hypothetical situation. So far, there's an increase in child mortality, or death, but only in a handful of villages. They don't seem to be connected by roads or by rivers, yet the children are all dying after having convulsions. Unlike the Haiti cholera map, there doesn't seem to be a clear connection between the outbreaks like a river or transportation route, and the disease doesn't seem to spread out from a center or hotspot.

So let's walk through how a medical geographer might tackle this mystery. First, we'd explore the area and interview the people living there, asking questions about their lives and looking for any trends. Once there, we could confirm there's no feature connecting the villages and no one has been traveling to or from the villages. They get their food and water from different sources, too, all things we might look for if this was an infectious disease outbreak.

But there are clearly distinct clusters, or groups of more disease cases than we'd expect, so after interviewing the population and exploring the environment, we'd compare answers with the other public health professionals working on the case, and we'd hopefully deduce that the common thread in this case was the vein of lead-rich gold, like the veins that run through parts of Nigeria.

When people process gold in small artisanal mines, it creates a lot of lead dust. Lead only hurts a person if it's ingested, which is why, globally, lead mostly harms children. They're more likely than adults to put their hands and other objects in their mouths. So what we have is a noncommunicable disease outbreak. Even though it wasn't spread person to person, we could still use our medical geographer training to deduce the pattern.

Nigeria isn't the only place struggling with lead. The United States also has a high rate of lead poisoning in children. Areas with homes built before lead paint was banned in 1978 can still have lead paint chips or lead dust in the home or even in the soil, which are very harmful and cause neurological damage. And using our medical geography skills to track disease can affect public health far and wide, like Dr. Richard Sadler and other medical geographers have done in the case of lead-contaminated water in Flint, Michigan, which sparked a national debate about environmental justice and the conditions and policies we need to live safe lives

Looking at disease spatially can give us all sorts of clues, but thinking spatially before people get sick is important, too. Medical geographers also study the relationship between the healthcare people need and what can be provided by looking at what's available and how people use healthcare services. For instance, we can compare countries that various metrics say have adequate healthcare, like U.S., and ones that might fall short, like India, and find cracks in both places at different scales.

Like in rural areas, which are often medically under-served for a variety of reasons. If we zoom into the U.S., more and more rural hospitals are being closed, and a lack of population is partly to blame. This, in turn, increases the cost of providing healthcare and means that patients have to travel much farther to get to a service facility.

In India, the situation is kinda the opposite. Instead of too few people, they face too many. Like, in one rural district in Bihar, there are only three hospitals for approximately four million people. Put another way, that ends up being one doctor for about every 40,000 people. So in the rural areas of both cases, people aren't able to access medical care easily.

Medical geographers study these situations and how factors like distance, transportation, and travel time affect how people seek and are able to access healthcare. Other barriers to getting healthcare can be socio-economic and cultural reasons, like poverty, gender roles, and social position, so optimizing where hospitals and clinics are located and thinking about who is able to access them is important to providing healthcare that focuses on equity.

All of this, from tracking down cholera outbreaks and clusters of lead poisoning cases to studying access to healthcare, is part of how medical geographers work to help as many people as possible achieve their highest level of health possible. Health is not the mere absence of disease. It implies well-being at the physical, emotional, mental, and psychological levels, so as geographers, we visualize disease patterns and help explain how they affect people, health, and access to healthcare for different groups of people around the world.

Many maps and borders represent modern political divisions that have often been decided without the consultation, permission, or recognition of the land's original inhabitants. Many geographical place names also don't reflect the indigenous or aboriginal people's languages. So we at Crash Course want to acknowledge these people's traditional and ongoing relationship with that land and all the physical and human geographical elements of it. We encourage you to learn about the history of the place you call home through resources like https://native-land.ca/ 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: Geography, which is filmed at the Team Sandoval Pier Studio and was made with the help of all these nice people. If you want to help keep Crash Course free for everyone forever, you can join our community on Patreon.