What to know about the coronavirus outbreak in 17 charts and maps

The World Health Organization declared the novel coronavirus a pandemic last week; cases have been reported in more than 155 countries.

About 80% of cases are mild, according to one study, but older people with preexisting health issues are more at risk of severe complications like difficulty breathing and lung infections.

These 17 charts and graphics lay out what to know as the outbreak continues to progress.

Here's where cases have been confirmed so far — and where patients have recovered:

Several countries have declared nationwide lockdowns.

This chart shows the rate at which the coronavirus case total has shot up worldwide.

The true number of infected people is probably still higher than the official total, since some mild and asymptomatic cases are likely not tested and counted.

As the number of new cases in China has decreased, other countries have begun to experience surges in cases.

South Korea reported its first case on January 20. As of March 13, the case count had jumped to 7,979.

The spike in South Korea cases seems to have happened after a 61-year-old "super-spreader" infected 43 other members of a fringe religious group called the Shincheonji Church of Jesus. South Korea appears to be getting its outbreak under control, however — the spike in cases is leveling off.

The US has reported over 4,200 coronavirus cases.

The US has reported 73 deaths from the coronavirus as of Monday: with 42 in Washington state, 8 in New York, 6 in California, 5 in Florida, 2 in Louisiana, 2 in New Jersey, and 1 in Colorado, Georgia, Kansas, Kentucky, Nevada, Oregon, South Carolina, South Dakota, and Virginia.

Washington has confirmed 770 cases of the virus and 42 deaths. More than 50 residents of a nursing facility in King County called Life Care Center have tested positive. Nineteen of the Washington deaths are linked to the long-term care facility.

The US State Department and CDC have issued travel warnings for countries affected by the coronavirus.

Currently, China, South Korea, Iran, and much of Europe are at Level 3, meaning the CDC recommends avoiding non-essential travel to those countries.

An average coronavirus patient infects 2 to 2.5 others.

COVID-19 is more contagious than the seasonal flu, but probably less contagious than SARS. However, the R0 isn't fixed and it can decrease with strong preventive measures.

The coronavirus most seriously affects older people.

The disease's death rate is highest among more elderly groups. The study this data comes from did not report any deaths in children younger than 10, who represented less than 1% of the patients studied.

The coronavirus also poses a higher risk to people with pre-existing health conditions, such as diabetes, heart disease, and high blood pressure.

Among coronavirus patients, the preexisting condition with the highest death rate appears to be heart disease. Patients already diagnosed with heart disease had a death rate of more than 10% in the Chinese CDC study. Diabetes was the preexisting condition with the second-highest fatality rate: 7%.

Patients with the most commonly reported preexisting condition, hypertension (high blood pressure), had a death rate of 6%. Coronavirus patients with cancer had a similar death rate.

The flu and the new coronavirus have some similar symptoms, and both disproportionately affect older people. However, across the board, the coronavirus has been far deadlier.

The most crucial difference between the flu and the coronavirus is that the latter has been far deadlier. Whereas about 0.1% of people who get the flu die, the coronavirus' death rate is now hovering at about 3.4%, based on the current numbers of cases and deaths.

The fatality rate of the coronavirus is still evolving, however, as more cases are confirmed. Many health experts believe that the rate will drop as the number of cases rises.

The death rates used above are based on data from the Chinese CDC.

South Korea so far has lower overall coronavirus death rates than other countries and than the global average. But there, too, the coronavirus is still more deadly than the flu.

The coronavirus' pneumonia-like symptoms include fever and difficulty breathing.

The coronavirus primarily affects the lungs and commonly causes a fever, a dry cough, and shortness of breath. Just over 80% of coronavirus cases are "mild," according to an analysis from the Chinese Center for Disease Control and Prevention.

Some symptoms of COVID-19 overlap with those of the common cold, allergies, and the flu, which can make it tricky to diagnose without a test.

Scientists have found that the virus' average incubation period — the length of time between when a person gets infected and when they test positive for the illness — is five days.

The new research also showed that 97.5% of people who are infected develop symptoms within 11.5 days. About 1% of patients, however, show symptoms after 14 days — outside the window of the CDC's quarantine guidelines.

The total number of cases and deaths have far surpassed those of the SARS outbreak.

As the coronavirus spreads throughout the US, people have clamored for masks. Here's a breakdown of all the different types of face masks and who should — and shouldn't — be wearing them.

Social distancing and other preventative measures could keep the outbreak within the capacity of the US healthcare system. Otherwise, facilities and staff are at risk of being overrun.

Pleas to help "flatten the curve" are becoming common as the US looks for ways to curb the spread of the virus.

The idea is to reduce the number of people who are sick at the peak of the virus's spread so that the health system isn't overwhelmed and more people can get life-saving care. This is the reason for the rising number of school closures, cancellations of major events, and companies mandating employees work from home.

Here's the difference between three types of reduced social contact.

Holly Secon and Aria Bendix contributed reporting to this story.