Confirmed US cases of COVID-19 have surpassed 50,000. How many are really out there?

Here’s everything you need to know.

Follow all of PopSci’s COVID-19 coverage here, including travel advice, pregnancy concerns, and the latest findings on the virus itself. For global updates, see here.

This post has been updated.

The novel coronavirus first identified in Wuhan, China in December 2019 is now spreading extensively throughout communities in the United States and has reached global pandemic status. We’ve collected some of the latest news and findings on COVID-19 to inform your decisions during this time.

What is COVID-19?

COVID-19 is the disease caused by the novel coronavirus. You can read more about the virus and what we know about its origins here. Common symptoms of COVID-19 include fever, shortness of breath, and a dry cough. Symptoms are mild in the vast majority of cases, and the virus may spread even with no noticeable symptoms present. But for some patients—especially those over the age of 60 and/or with underlying health problems—the virus can lead to deadly pneumonia.

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Check here for more info on how to distinguish COVID-19 from a cold or flu.

Should I be staying at home to avoid catching or spreading COVID-19?

The short answer is yes: Everyone who is able to do so should be practicing “social distancing” to limit the spread of COVID-19 and “flatten the curve.” Ideally, one should stay at least six feet away from all other people, but maintaining contact with your family members is okay as long as you’re all doing your best to avoid getting close to people outside the household. Even if you don’t have symptoms at all, spending as much time as possible in isolation means you’re lowering the risk that you will spread COVID-19 to someone vulnerable.

Implementing preventative, social-distancing measures will reduce the number of people who are sick at one time. Without measures, many people get sick all at once, leading to a tall, narrow curve. With these social-distancing measures, you can flatten the curve—just as many people may get sick overall, but they’ll be spread out over time. For a healthcare system, especially an overwhelmed one, it’s far better to have a million people sick over the course of a year than have that same million sick in the span of three months.

The Washington Post has an excellent interactive graphic to demonstrate the importance of social distancing, if you don’t understand why it’s important.

How serious is COVID-19 in the United States?

On Tuesday afternoon, NBC reported 50,206 COVID-19 cases across the United States. There have been at least 637 deaths. Every state has confirmed cases as well as Washington, DC. The US territories Guam, the US Virgin Islands, and Puerto Rico have reported positive results as well.

It is important to note, however, that testing rates in the US remain too low for health officials to confidently estimate the true number of cases. The United States has been far slower to implement widespread testing than other affected countries, and the country’s per capita testing rates fall far below those in the United Arab Emirates, Australia, Germany, Austria, the UK, and Iran.

While social distancing will help slow the spread of disease, the World Health Organization argued last week that keeping tabs on accurate case counts is a crucial component to such a strategy.

“We have a simple message for all countries: test, test, test,” WHO Director General Tedros Adhanom Ghebreyesus said in a press briefing on March 16. “You cannot fight a fire blindfolded. And we cannot stop this pandemic if we don’t know who is infected.”

On Monday, Surgeon General Jerome Adams warned that this week would be a particularly bad one for the US.

“Right now, there are not enough people out there who are taking this seriously,” he told the TODAY show. “Everyone needs to act as if they have the virus right now. So, test or no test, we need you to understand you could be spreading it to someone else. Or you could be getting it from someone else. Stay at home.”

President Donald Trump said on Tuesday that he wanted the country “opened up” by Easter (April 12). Public health officials have warned that lifting restrictions on public outings and businesses too soon will enable COVID-19 to spread rapidly.

How serious is COVID-19 globally?

COVID-19 has infected around 400,000 people worldwide since December and killed roughly 18,000. While cases have slowed down dramatically in China, Italy remains on complete lockdown and is facing serious hospital shortages, with a staggering 69,000 cases that continue to rise. Deaths in Italy are now close to 7,000—more than double those seen in mainland China. Spain has more than 39,000 cases and Germany has more than 27,000. There is evidence of sustained community spread of COVID-19 on every continent except for Antarctica.

How can we prevent the spread of COVID-19?

Proper hand washing (instructions here) is still the best defense we have against a disease like COVID-19. While hand sanitizer is less effective, it’s a good substitute in a pinch—here’s a DIY recipe if your local stores are sold out.

It is also important to practice social distancing if you are able, even if your area is not yet considered to be in the midst of an active outbreak, and to be diligent about washing your hands if you have to go out and interact with people. Do not go out to bars or restaurants; ordering takeout (or, even better, delivery left at your front door) is the best way to get food from your favorite local business. Trips outside the home should be limited to isolated exercise (jogging by yourself in an area without crowds, for example) and getting medicine and groceries, while maintaining six feet of distance from other people. You should wash your hands frequently and avoid touching your face while out conducting essential errands.

A version of this article was originally published on March 17. It has been updated.

Rachel Feltman

Rachel Feltmanis the Executive Editor of Popular Science and the host of the podcast The Weirdest Thing I Learned This Week. She's an alum of Simon's Rock and NYU's Science, Health, and Environmental Reporting program. Rachel previously worked at Quartz and The Washington Post. Contact the author here.