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Sometimes it seems like the world is at constant risk of being overrun by disease. Zika, Ebola, bird flu, swine flu, and SARS were all threats that rocketed from obscurity to the front of every magazine and the top of every newscast. When it comes to epidemics and pandemics, there are often two vocal camps: the handwringers and the eye-rollers. These groups, however, share the common desire to be right. The handwringers don’t want to be overreacting, and the eye-rollers don’t want to be unduly dismissing a lethal threat. 

To help thread the needle, we spoke with Jeffrey Shaman, associate professor in the department of environmental health sciences at Columbia University’s Mailman School of Public Health. Here’s how to responsibly assess the next public health crisis:

1. Understand What Pandemic and Epidemic Mean

An epidemic is an outbreak of a disease, condition, or even behavior that is beyond normal. Just as we have an epidemic of obesity, so do we have epidemics of influenza. A pandemic, in comparison, is a geographic designator — it means the issue is more global. For example, Ebola was considered an epidemic because it was largely confined to West Africa. We feared it would become a pandemic but it did not. Shaman cautions that even officials and experts use these words interchangeably at times. It’s also possible for a health issue to move from one category to another.

2. Pay Attention to Pandemic Influenza

The flu doesn’t seem like something worth any special concern, but it spreads from person-to-person rather easily and, while epidemic flu isn’t so bad, pandemic flu can be a much more dangerous virus. The difference is in how they are generated.

Epidemic influenza arises from little mutations in the flu strain’s code as it copies. These build up over time and, because the changes are small, much of the population remains immune to the flu for a few years at a time.

Pandemic flu is the result of multiple viruses combining. This kind of change can be extremely hazardous because it’s so drastic. “If that virus is functional (which is one big if) and if it’s capable of infecting humans, then what you have is a virus that is so brand-spanking-new that no one’s immune system has encountered it before,” says Shaman. In this scenario, which happened with swine flu (H1N1), over 80 percent of the population may be susceptible to the hybrid virus. Shaman says that means about 50 percent of the world would be infected within one to two years. It was lucky for us, then, that H1N1 wasn’t an especially deadly form of flu.

3. Find Out Who’s at Risk

Zika is an obvious example for why this piece of information matters. From what we know so far, women who are pregnant or could become pregnant soon are the ones who are at the greatest risk from Zika because it is associated with the birth defect microcephaly. Men with female partners in these categories should also be wary, because Zika can be spread through sex. If you don't fall into these categories, you have less reason to be alarmed. Zika has been connected to cases of Guillain-Barré Syndrome (GBS), but the connection is rare and similar to that of GBS with other infections, including influenza and AIDS.

4. Know Where The Outbreak Is

If a person is trying to learn about an epidemic, location plays a big role. People in Sweden don’t really have to be concerned about the epidemic of obesity in the United States. The location of pandemics is also important but not as informative because they can travel far, quickly in our interconnected world. While knowing the location of an epidemic can help put a person at ease, there are few assurances about the eventual reach of pandemics. Checking travel warnings from governments and health organizations can be an especially clear way to identify the places that are at risk.

5. Pay Attention to How You Get the Disease

To judge the seriousness of a disease, learn how it infects people. Know whether it’s transmitted through blood, sexual fluids, spit, or other bodily secretions. Would a person have to come in contact with the infected? Does the disease survive on surfaces? Does it travel through the air? These details are why Ebola was so scary. Ebola can spread from person-to-person through various bodily fluids, and a symptom of the disease is bleeding, which increases chances of exposing others. That’s a dangerous scenario. It’s worth noting, however, that Ebola is much more difficult to catch from someone than the common cold, which can be passed along in the air. (Of course, the common cold is far less deadly.)

6. Know What the Disease Does

Having a clear picture of what a disease does to people is crucial. The swine flu in 2009 was a pandemic but not as bad as many feared. It spread widely but it wasn’t especially deadly. If it had been a more aggressive influenza strain, such as the one that caused the 1918 flu epidemic, it could have been far more catastrophic. 

7. Figure Out How To Defend Yourself

Even if someone is staring down a formidable disease that he could catch in his area, he can arm himself with knowledge about how best to stay healthy. With the common cold, people should wash their hands and not touch their faces too often. When it comes to HIV, always use protection during sex. During the Ebola epidemic, people had to change their burial practices to keep themselves from coming into contact with infected remains. Even with the best precautions, some diseases will be hard to avoid, so knowing early symptoms and seeking appropriate medical care is important too.

8. Think About Indirect Exposure and How It May Influence Your Risk

Along with what diseases can do to individuals, they can have devastating effects on populations and society. Shaman says the Ebola epidemic required grand, immediate action because it decimated the health infrastructures of Liberia, Sierra Leone, and Guinea. Health care workers were more likely than other people to become infected, and that meant people weren’t getting help with births, vaccines, or malaria treatments. In the case of Zika, Shaman says the virus is most likely to affect poorer populations, who tend to spend more time outside, unprotected from mosquitoes. It is common for diseases to spread in poorer communities first, which can leave people outside these communities unaware of the extent of the impacts.

9. Find Credible Sources

No one can guarantee perfect information, particularly with epidemics and pandemics. The reason these diseases become outbreaks is usually because they are acting in a new way and, in some cases, that means our knowledge about them is extremely limited. For example, we found out that Zika and Ebola can be transmitted sexually due to their respective outbreaks even though these aren’t new diseases. Although explanations may be incomplete, Shaman says the best resource for epidemic and pandemic information is the Centers for Disease Control and Prevention (CDC). He also recommends the World Health Organization (WHO), the Pan American Health Organization (PAHO), and health experts at local universities. He advises against relying on chat rooms. News and media sources can also be of questionable quality.

10. Listen to the Experts

When someone whose job it is to study the trajectory of diseases is speaking about diseases spreading, listen up. Alarmists are often made fun of, especially once there is the hindsight to say a disease didn’t end the world. In the case of Ebola, Shaman says the people who were losing sleep were on the right track. He was steeped in the efforts to address Ebola, meeting with health and government officials, and says that even he called colleagues in a panic during the outbreak. “I actually thought the level of coverage was insufficient and that the level of information out there, which was making people a little jittery, was almost necessary,’ he says. “It’s very strange for me to say that because I wouldn’t encourage panic on anything, but we really needed to motivate an enormous response to the tunes of billions of dollars. It had to be done.”