Amid the rapidly changing global health threat of coronavirus, Washington-area hospitals, schools and government agencies say they are relying on time-tested strategies for infectious disease control: Wash your hands, cover your cough, and stay home if you’re sick.

It may not sound exciting. But experts say the boring mainstays of public health and practicing good hygiene are the best defenses, for now, against the respiratory disease formally known as covid-19. They note the practices also are the best way to thwart a particularly virulent strain of the flu circulating this winter.

No cases of coronavirus have been diagnosed in the District, Maryland or Virginia. Yet elected officials and experts are following guidance from the Centers for Disease Control and Prevention to prepare for the possibility of a widespread epidemic, while working overtime to quell panic.

Maryland Gov. Larry Hogan (R) said Thursday that he will request an additional $10 million for emergency preparations. “While we are hoping for the best, we are also actively planning for the worst,” he said from the state’s emergency management headquarters in Reisterstown.

As of early March, people have tested positive for the coronavirus in about 70 countries. Officials are taking "unprecedented" actions. (The Washington Post)

Three Maryland residents are being tested for the virus, the Maryland Department of Health said Friday. In Virginia, eight residents have tested negative for coronavirus. As of Friday, the state health department had monitored 279 individuals, up from 179 on Thursday.

D.C. officials said Friday that five residents had tested negative for the virus, and Mayor Muriel E. Bowser’s office on Thursday issued a reminder that viruses do not target specific racial or ethnic groups.

“Stigma hurts everyone by creating more fear or anger towards ordinary people instead of the disease that is causing the problem,” the statement said.

Many school districts in the region have sent lengthy emails to parents saying they have canceled trips to countries where residents have fallen ill from the coronavirus and suspended exchange programs with some countries, including South Korea, Japan and Italy.

Some districts are exploring online classes, although school closures are not imminent because relatively few cases have been diagnosed in the United States.

Prince William County Public Schools posted an update online Thursday acknowledging that “recent national news regarding the COVID-19 (coronavirus) may be confusing and worrying.”

In an email to parents, Prince George’s County Public Schools gave detailed instructions on precautions, including advising people “to wash hands often with soap and water for at least 20 seconds. If soap and water are not available, use an alcohol-based hand sanitizer.”

Reports Wednesday night that California had discovered its first case of a person contracting the disease with no link to foreign travel amplified the perceived threat for many Americans and helped topple U.S. financial markets.

“We all need to remain calm and put this into perspective,” said Lisa Maragakis, senior director of infection prevention at the Johns Hopkins Health System. “While there is a fear of the unknown, one of the things that helps the most is to take concrete steps to prepare.”

She said that for all types of emergencies, there is a therapeutic benefit to having necessary medicines on hand and identifying a family meeting place.

While the flu tends to dissipate after the spring, she said, there’s no way to predict a pattern with coronavirus.

We do see seasonality for certain infections — influenza reliably comes between October and late April or May,” she said. “With a new virus, we just don’t know how it will behave.”

Experts at hospitals in the Washington region said the California report was concerning and spurred additional discussions but did not change protocols that have been in place for some time. Patients who walk into medical centers and major hospitals for any reason are asked questions to determine whether they could have the virus: Have they traveled internationally recently? Do they have symptoms of a cold?

If patients answer “yes” to both questions, they will be asked to wear a mask and placed in a private room, while providers ask detailed questions about which countries they visited, why and for how long.

The CDC on Thursday expanded its geographical area of concern, initially limited to Wuhan in China, to China, Japan, South Korea, Iran and Italy.

The local public health department then decides whether the person should be investigated for possible infection; if so, the agency arranges testing through the CDC. Currently, Maryland and Virginia labs do not have the capability to test for covid-19.

The initial procedures are not unlike protocols practiced by hospitals every flu season, said Kari Scantlebury, an emergency medicine doctor and lead physician adviser for emergency management for Inova Health System.

“This is the bread and butter of emergency medicine,” said Scantlebury, who added that she and her colleagues are closely monitoring CDC guidance. “This is what we do for a living.”

Glenn W. Wortmann, director of infectious diseases at MedStar Washington Hospital Center, said the situation is constantly in flux.

He is hoping more data will be released regarding the California case, but he said it’s inevitable that the virus will spread within the United States: “I’d like to think it won’t happen, but I think we need to be prepared for it happening.”

Wortmann said most people experience coronavirus as a bad cold, and about 15 percent require hospitalization. The elderly and those with underlying medical conditions tend to fare the worst.

“This is a new virus,” he said. “Although it’s scary, the data out of China show most people who get infected do well.”

The Virginia Department of Public Health on Thursday took the rare step of sending a letter to 150,000 doctors, nurses and other clinicians about the public health threat.

It provided an overview of the outbreak starting from Jan. 30, when the World Health Organization declared a “public health emergency of international concern,” and asked for volunteers to register with the Virginia Medical Reserve Corps.

“For the general public right now, the risk of covid-19 is very low,” Lilian Peake, director of the Virginia Office of Epidemiology, said in an interview. “But it is a time for us to be thinking about what could happen and using this time to prepare. Better to be prepared and to be wrong than to not be prepared.”

First responders are taking the same measured approach.

Montgomery County Fire and Rescue Service distributed kits — including masks for patients, masks for responders, cleansing wipes and protective face shields — to 50 transport units and stocked up on supplies in case of a future shortage.

“We treat it just like an infectious disease, so we like to think we’re prepared already,” Fire and Rescue spokesman Pete Piringer said.

Public health officials said they are applying lessons learned through treatment of the seasonal flu, but also H1N1, SARS, Ebola, Zika, West Nile and even chikungunya.

“This isn’t the first time we’re seeing it,” Scantlebury, of Inova, said. “It isn’t going to be the last time.”

Hannah Natanson and Rebecca Tan contributed to this report.