Governors and other leaders scrambling to slow the spread of the new coronavirus stepped up bans on large public gatherings and a rapidly expanding list of universities moved classes online, as the U.S. government’s top infectious-disease expert today warned that the worst is yet to come.

With cases in the U.S. topping 1,000 and the number of deaths climbing to 31, lawmakers and health officials set up containment zones and sought to limit contact with those who might be infected. The outbreak has spread to more than half the states, with Arkansas and New Mexico reporting their first cases of the virus.

“Bottom line, it’s going to get worse,” Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said on Capitol Hill.

As for how much worse, Fauci said that would depend on the ability of the U.S. to curtail the influx of travelers carrying the disease and state and community efforts to contain the outbreak.

He said if mild cases of the virus are counted, the mortality rate is probably about 1 percent — “roughly 10 times more lethal than the seasonal flu.”

Kentucky Gov. Andy Beshear urged churches across the state to cancel services.

“I don’t believe that whether you go to church during this period of time is a test of faith,” he said. “I believe God gives us wisdom to protect each other and we should do that.”

In hard-hit Washington state, Gov. Jay Inslee was expected today to ban gatherings of more than 250 people in virtually the entire Seattle metro area, home to about 4 million people. The Seattle area accounts for about two-thirds of the nation’s coronavirus deaths, including at least 19 from the same suburban nursing home.

Schools and houses of worship were shuttered in the New York City suburb of New Rochelle, epicenter of the nation’s biggest known cluster of cases, with over 100. Gov. Andrew Cuomo said he intends to send the National Guard to help scrub public spaces and deliver food, though no troops appeared to be in place this morning.

UCLA, Yale and Stanford were among the universities announcing plans to send students home and hold classes remotely.

Chicago canceled its St. Patrick’s Day parade, joining Boston and Philadelphia, while the Coachella music festival that draws tens of thousands to the California desert near Palm Springs every April was postponed. Instead of hosting 100,000 at its twice-yearly conference in Salt Lake City next month, the Church of Jesus Christ of Latter-day Saints said it will hold the gathering online and on TV, with leaders delivering speeches without any attendees.

The World Health Organization declared the virus a pandemic, or a serious, global outbreak, noting that the number of cases outside China had increased 13-fold over the past two weeks. Designating the crisis a pandemic is the WHO’s way of putting countries on notice to take more aggressive action.

Meanwhile, tests by U.S. government scientists and other experts found that the virus can live in the air for several hours and on some surfaces for two to three days.

For most people, the virus causes only mild or moderate symptoms such as fever and cough. For some, especially the elderly and people with existing health problems, it can cause more severe illness, including pneumonia. Most people recover in a matter of weeks, as has happened with the majority of those infected in China, the virus’ country of origin.

“If you want to be blunt, Europe is the new China,” Robert Redfield, director of the Centers for Disease Control and Prevention, told Congress, meaning that the movement of people from Europe is the primary source of the virus in the U.S.

For those in the middle of a quarantine, it’s an anxious time waiting for the threat to pass.

Judy Aqua, who is in her 60s, is quarantining herself at home in New Rochelle after possibly being exposed to someone with the virus.

“People are really afraid to go to the supermarket. They’re afraid to go to the cleaner,” she said. When her husband made a recent run to a post office, she told him to wear gloves.

Santa Clara County in California, home to San Jose and Silicon Valley, banned all gatherings of 1,000 people or more. The ban in Washington state would apply to sporting events such as Seattle Mariners baseball, according to a person who was familiar with the decision but wasn’t authorized to discuss it publicly and spoke to The Associated Press on condition of anonymity.

It could be just the beginning of disruptions to sports: Some college games will be played without fans in Ohio and California, and the NCAA said it will make decisions in the coming days about its men’s and women’s basketball tournaments. Two conferences banned fans from their championships, and the Ivy League canceled its basketball tournaments altogether.

Massachusetts Gov. Charlie Baker declared a state of emergency as cases statewide jumped to 92. Of that number, 70 are now connected to a meeting held last month by biotech company Biogen at a hotel in downtown Boston.

A woman from suburban Houston flew home from Italy after testing positive, and now everyone on the two flights she took could be at risk. Health officials urged passengers to quarantine themselves.

Some airport workers are also dealing with the outbreak, with several Transportation Security Administration officers at the San Jose airport testing positive. All TSA employees who had contact with them over the past 14 days are being quarantined at home, the agency said.

In Oakland, California, restless passengers on a coronavirus-struck cruise ship awaited their turn to disembark. By Tuesday night, Princess Cruises said about 1,400 of the 3,500 people on board had gotten off, and efforts were underway to move them to quarantine in their home countries or at military bases in California, Texas and Georgia.

California Gov. Gavin Newsom urged the state’s nearly 40 million residents to avoid sporting events, concerts and other large gatherings and strongly warned the elderly to stay away from cruise ships.