As we’ve seen throughout this series, outbreak science is really lots of sciences. From biology to epidemiology to sociology and even economics, we’ve seen that many approaches can shed light on outbreaks and guide the actions we take in response to them. For example, during the 2004 cholera outbreak in India, we saw it took medical knowledge to detect cases of the disease, epidemiologists to trace its origins, and microbiologists to confirm which disease-causing pathogen was responsible. In other words, Outbreak Science is an interdisciplinary field, and the ability to draw on many areas of expertise at once is one of its greatest strengths when it comes to tackling outbreaks-- whether it’s a cholera outbreak in a single city or the COVID-19 pandemic that’s affected the whole world. That means everyone, including you, has a role to play. And since outbreaks haven’t gone away entirely just yet, we’ll need to keep working together to take on future ones.

 I’m Pardis Sabeti, and this is the final episode of Crash Course Outbreak Science!

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Different fields come together during and even after an outbreak. They also play a role in how we prepare for them. For example, say we’re considering ways to increase a hospital’s treatment capacity during a future outbreak with a fixed budget. A medical and clinical perspective suggests that we should stockpile equipment, like ventilators, to help cope with a high number of infected patients during an outbreak. But a psychological and social perspective emphasizes the communication between doctors and patients for making good clinical decisions and improving a patient’s sense of trust and safety.So, we might recommend investing in training additional medical interpreters to have on hand for a large influx of patients who might not speak the language used by their doctors. On a fixed budget, we’d need to balance the costs between treatments and the way our patients are treated.

Those are just two of the many considerations that would feed into our final decision, and it’s true of most parts of outbreak science. In fact, one of the most important ways we track and prevent outbreaks relies on exactly this kind of interdisciplinary mindset, involving everyone from geneticists to everyday citizens: disease surveillance. As the name implies, surveillance involves keeping tabs on where diseases are prevalent, who they affect and why. That’s done by collecting, analyzing and interpreting data on cases of disease, which is important in a couple of ways. For starters, disease surveillance helps us detect when an outbreak is happening and where, based on whether the number of cases is higher than usual. This helps us prioritize where to focus our efforts to prevent and treat a disease. Once we’ve taken steps to prevent a disease, maybe by building sanitation infrastructure, implementing public health measures or vaccinating vulnerable groups, surveillance allows us to confirm that the actions we’ve taken have really worked by checking whether the number of cases or outbreaks has declined.

As we saw previously, analyzing the data on cases to work out the prevalence and incidence of diseases is in the wheelhouse of epidemiology. But lots of other disciplines come into play in disease surveillance. One essential part of disease surveillance is recognizing new diseases from pathogens we aren’t aware of, so we can spot them and tackle them before they become a significant problem. Here, genetics plays a big role, since the genes of an unknown pathogen are a vital clue to what it is and where it came from.

To see this, let’s consider the disease surveillance program in the fictional country Hankistan and their public health agency, the Hankistani Center for Disease Control, or HCDC. In previous episodes, we saw they were vaccinating against the virus that causes the disease Hankitis. But how did they come to know about the disease in the first place? At first, things unfold much like we’ve seen before: workers at a community health center in rural Hankistan recorded a rise of cases of patients with fever, dizziness and vomiting. Some of these patients also experienced internal bleeding, organ failure, or comas, which are often lethal. As part of disease surveillance, the data about these patients is sent automatically everyday to the HCDC. The HCDC epidemiology department notices a number of patients with the same set of symptoms added to their database. So they investigate the cases, in part by looking at similar symptoms reported this time last year, and conclude, sure enough, there’s an outbreak on their hands! But from here, things start to look different from the outbreaks we’ve looked at previously.

Let’s go to the Thought Bubble.

Healthcare workers send blood and saliva samples to a microbiology lab, but all of the standard tests do not find a culprit pathogen. So, they suspect they’re dealing with a new virus, and to confirm this hypothesis, they need to enlist some geneticists, people who study the genes of people and the pathogens that infect them. The geneticists use powerful new genome sequencing tools to read out the genome, the DNA or RNA code that identifies a given organism, of everything that might be circulating in each patient’s blood and saliva. Sure enough, they find that all the patients carry a unique genome, belonging to a new virus, which they call Hankivirus.

Naturally, the disease it causes is called Hankitis. While the viral genome each patient has is definitely from Hankivirus, the geneticists notice small differences between the samples. By using the differences--mutations in the virus’s genetic code-- they create a “family tree” that they can race back to the beginning of the outbreak. That helps them identify which patients were infected first, and they realize those patients live in the same neighborhood at the edge of the town of Hanksville. While the technology they used was more advanced, the geneticists are using a similar process to the   epidemiologists who first identified Lyme disease-- identifying where most cases are located in an effort to find the potential cause of the disease.

The HCDC consults some ecologists who study the environment around Hanksville and find that a species of mouse had been driven out of their environment from deforestation, and now regularly have interactions with people living in Hanksville’s outskirts. Zoologists, who study all kinds of things about animals, like their relationship with pathogens, working alongside the ecologists, also point out that certain species of mice can spread hemorrhagic fevers-- which have the same symptoms as Hankitis--to humans.

 Thanks Thought Bubble!

Working as an interdisciplinary team, the zoologists, geneticists, and microbiologists take blood samples from the mice which show, sure enough, some of them are infected with the same virus as the human patients. Now that they’ve pinned down the root of the virus, the surveillance program can shift their resources and better track the disease. Previously, the HCDC relied on data that was sent in from all of the different healthcare facilities in the country. They received data about all diseases, regardless of symptoms. This kind of untargeted surveillance is called passive surveillance, since the HCDC wasn’t explicitly looking for cases of particular diseases, but analyzing data for other purposes. Now that they know that the mice are a risk factor, the HCDC could specifically look for cases of Hankitis in populations close to where mouse populations are high. They can also send dedicated staff to ask healthcare workers and communities for data on cases of Hankitis. Explicitly looking for cases in the healthcare system and   community is called active surveillance. And it’s not restricted to people either!

Disease surveillance also involves measuring risk factors like population size of animals that pose a risk to humans-- like the rodents that carry Hankitis-- and how prevalent diseases are in them. We call this zoonotic surveillance. As for humans, the HCDC might also find that the case numbers from active surveillance are much higher than the kind from passive surveillance. In this case, certain rural communities haven’t often been treated very well by the Hankistani healthcare system in the past, so they’ve avoided going to hospitals and clinics to seek treatments. Passive surveillance systems that relied solely on those healthcare facilities weren’t able to track those cases, or identify the susceptibility to disease that the community had. Information like this can work in a kind of feedback loop, helping public health agencies improve their approach to disease surveillance, which in turn produces better information. Ultimately, an interdisciplinary approach to outbreak science can help us find interventions we otherwise wouldn’t consider.

 For example, the HCDC might listen to ecologists and start advising people to stay away from the mice’s natural habitat, or even start replanting trees in the nearby forest to encourage the mice to stay away from us, too. And now that they’re performing active surveillance, the HCDC will be better able to tailor their interventions to the most susceptible communities. Which brings us to individuals like you and me. What can we do to prevent outbreaks and stop the ones we find ourselves in? Well, there’s something that I always like to say: Because of the exponential spread of viruses, one person can launch an outbreak. But one person also has the power to stop it.

For starters, there are the individual actions we can take to prevent becoming infected and transmitting disease. These are some of the familiar things: practicing good hygiene by regularly washing our hands with soap and water, staying at home when we or someone we live with is ill, and covering our mouths and noses when we cough and sneeze. We can also have important conversations like telling those we’ve been in contact with when we have tested positive for a disease. Depending on the kind of disease, there may be more specific guidance from a public health body, like avoiding certain animals in countries when traveling abroad, wearing a mask during a flu outbreak, and using condoms during sex. And for some diseases there’s an easy win for preventing outbreaks and stopping them: vaccines.

 If you’re eligible from your healthcare provider, getting a vaccine against diseases is an easy way to protect yourself and others from them. These might be things you’ve heard of before, but they’re worth emphasizing because collectively, actions like these save millions of lives every single year. Sometimes, we can be more deliberate in our collective action. That can look like volunteering at a community health center, vaccination clinic, or food bank, to help increase our capacity for dealing with an outbreak and its consequences. It can also involve public demonstrations and civil disobedience to change the culture of outbreak response.

For example, during the AIDS pandemic of the 1980s, a grassroots organization in the US called ACT UP organized several protests to call attention to disparities in treatments and even diagnosis of cases of AIDS. By calling public attention to the ongoing pandemic, the group was able to expand the CDC’s case definition of AIDS, allowing more people, and especially women, to benefit from an official diagnosis. Part of ACT UP’s success depended on people staying informed about both HIV/AIDS and the communities the activists lived in.

We can all do our part to stay informed today, by listening to the stories of those affected by infectious diseases or, catching up on our favorite Crash Course series about outbreaks. And yes, we can turn to medical experts and public health authorities like the WHO for guidance on how to respond to outbreaks, and they should aim to be trustworthy, transparent, and open to working with advocates like those in ACT UP. And learning about outbreak science can even be fun.

My partners and I at Operation Outbreak created a mobile app that lets you simulate a full blown outbreak in a group setting with your classmates, coworkers, or friends and test your resilience. It spreads a virtual pathogen via Bluetooth across participating phones, and it can get pretty realistic. And for those who want to take it to the next level, we have a full textbook on outbreak science coming out soon. Finally, there’s the bigger picture. Our social structures, environments, political and economic systems, and individual relationships all affect our capacity for responding to outbreaks and preventing them. Changing these things isn’t easy, but the good news is, the efforts we make to create fairer, socially equal, supportive and understanding societies have the added effect of making us less susceptible to outbreaks and more able to prevent them.

So whether you’re picking up trash on the weekend, volunteering with the elderly, campaigning for social justice or even being kind, understanding and patient with someone in your community, you’re also strengthening our collective capacity to defend against infectious disease. Because while outbreaks, as we’ve seen in this series, might be complex and span every aspect of society, when enough of us respond with persistence, determination and understanding, even our simplest actions can fight back against infectious diseases. We hope this series has been the first step on your journey to doing exactly that.

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 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 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.