No one knows whether the coronavirus will substantially threaten the U.S., where it has already been detected, but one thing is certain: American hospitals aren’t ready for the deadly virus or a future global contagion. Travelers from China’s Wuhan region are being diverted to five U.S. airports, where they can be screened. That’s sensible, but it’s no substitute for improving hospital readiness.

If the virus becomes a domestic threat, American public safety will depend on what hospitals do when someone unknowingly infected with the coronavirus shows up in the emergency room. That is the lesson of severe acute respiratory syndrome, better known as SARS, which is caused by another coronavirus.

Canada learned it the hard way in 2003, as deaths from SARS soared in the province of Ontario. Seventy-seven percent of people infected with SARS there contracted it in the hospital. They were patients, visitors and health-care workers. Another 17% got it at home, often from a health-care worker who lived with them. In short, SARS started as a travel infection but rapidly became a hospital infection because of lax infection-control standards. The same laxity is found in most U.S. hospitals today.

On March 7, 2003, two undiagnosed men with the SARS virus went to the hospital in two different Canadian cities. In Vancouver, the disease didn’t spread. But in Toronto, one infection was allowed to become a deadly outbreak, which killed 44 people in two months. For most hospitals in Ontario, “infection control was not a high priority,” according to the SARS Commission’s final report, delivered to the government of Ontario in January 2007.

In Vancouver, by contrast, “a robust worker safety and infection control culture” enabled the hospital to contain the virus, the report found. The Vancouver man with SARS felt ill after a trip to Asia and went to the hospital. Because of his symptoms, the staff whisked him out of the crowded ER within five minutes. Caregivers wore tight, moisture-proof masks and disposable gowns to protect themselves.

The same evening, the Toronto man, whose mother had come from Hong Kong two weeks earlier, went to the hospital with feverish symptoms. For 16 hours he was kept in a packed emergency department. His virus infected the man in the adjacent bed, who had come to the ER with heart problems, and another man three beds away with shortness of breath. Those two other men went home within hours but were later rushed back to the hospital, where they spread the virus to paramedics, ER staff, other ER visitors, a housekeeper working in the ER, a physician, two hospital technologists and, later, staff and patients in the critical-care units.

Poor adherence to infection-control protocols was to blame. Staff failed to wear masks and disposable gowns and didn’t wear face shields while inserting breathing tubes down patients’ airways. After the initial Toronto patient was finally admitted to a hospital room, it took five more hours for him to be isolated.

Even if this new virus peters out—the World Health Organization decided Thursday not to declare a “global health emergency”—improving infection control in U.S. emergency rooms wouldn’t be a wasted effort. It would save lives every day.

Sloppy infection control isn’t only a Canadian problem. A June 2017 literature review of shortcomings in U.S. emergency rooms found a lack of adequate distance between patients, use of contaminated equipment, failure to use shields to protect health-care workers who are intubating patients, and failure to ask coughing patients to wear masks.

During the SARS outbreak in Toronto, doctors and nurses brought the virus home to their families. That could happen here in America. Hospital workers routinely wear contaminated uniforms after work, taking them home and sometimes even into restaurants.

Have precautions improved in response to recent global health threats, such as SARS and Ebola? Yes, and the Centers for Disease Control and Prevention deserves some credit. The CDC conducted “mystery patient” drills at ERs in 49 New York City hospitals, sending in 95 patients pretending to have symptoms of measles and Middle East respiratory syndrome. In 78% of cases, the ER staff gave these patients masks and isolated them quickly. Even so, only 36% of health-care staff washed their hands. The CDC found “suboptimal adherence to key infection control practices.”

It’s a nationwide problem. More than 70,000 U.S. patients die each year from infections they contract in hospitals. The CDC warns that if you don’t have the flu and go to an emergency room, you’re at risk of getting it there. Contaminated beds, furniture and medical equipment allow bacterial infections to race through hospitals. What’s to stop the coronavirus? The CDC warns that you can pick up the virus by touching a chair or doorknob with the virus on it.

This latest coronavirus should be a red flag for American hospitals, which need to get serious about infection control. Even if luck holds, and the new virus doesn’t spread further, better infection control will still save tens of thousands of lives a year. It’s a no-brainer.

Ms. McCaughey is chairman of the Committee to Reduce Infection Deaths.

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