CLEVELAND, Ohio — The Ohio Department of Health confirmed Friday that 13 people tested positive for the novel coronavirus, which causes COVID-19.

That is more than double the number confirmed Thursday.

Ohio Health Department Director Dr. Amy Acton said nine of the cases are males, and the other four are females, ranging in age from 34 to 66 and located in six counties in the state. Four have been hospitalized.

Those who tested positive for coronavirus are in Belmont, Butler, Cuyahoga, Stark, Summit and Trumbull counties. The three positive cases in Cuyahoga County are in home-quarantine.

Cleveland Mayor Frank Jackson said the city is closely monitoring the situation.

“We know there are no boundaries” for the virus, Jackson said during a news conference Friday.

The city will halt water and electricity shutoffs to help residents during the pandemic, Jackson said.

Health officials have identified 56 people who were in close contact with the three initial patients who came down with the novel coronavirus, Terry Allan, Cuyahoga County Board of Health commissioner, said during a news briefing Friday.

All of the 56 individuals are in self-quarantine at home and are reporting their temperatures and symptoms to health officials twice a day, Allan said. The quarantine period is 14 days.

Allan said he did not have details about where or when the 56 individuals came into contact with the three initial COVID-19 patients.

In total, 159 people in the state are under investigation by the state as of Friday afternoon, meaning they have symptoms of COVID-19 or were possibly exposed to the virus.

ODH began testing for COVID-19 on Saturday and continues to ramp up testing as more test kits arrive. Other private companies, including LabCorp and Quest, also will be offering tests. Before that, only a handful of people had been tested, and those tests were shipped to the Centers for Disease Control and Prevention.

The number of Ohioans under public health supervision climbed to 333. This figure reflects travelers referred to ODH for monitoring; the number includes travelers who have finished their self-monitoring home quarantine, health officials said.

The number of Ohioans who have tested negative for COVID-19 is 50, according to Friday’s update.

Because of community-level spread, it is likely the number of Ohioans with the virus is much higher, Gov. Mike DeWine said Thursday during a news conference.

Acton estimated that as many as 1% of Ohioans, or more than 100,000, could have the virus.

“It’s going to feel a lot like whack-a-mole. It’s going to be all over every county,” Acton said Friday.

DeWine on Monday declared a state of emergency, and, on Wednesday, Cuyahoga County Executive Armond Budish did the same. Cleveland Mayor Frank Jackson on Wednesday also issued a proclamation of civil emergency. And the World Health Organization on Wednesday declared the coronavirus a pandemic, meaning the virus is spreading quickly in many geographic areas around the world. On Friday, the Trump administration declared the pandemic a national emergency.

The community-level spread of the coronavirus also prompted DeWine to roll out a series of orders this week promoting social distancing, including banning large gatherings and shutting down K-12 schools temporarily.

DeWine’s measures to close schools and cancel large events are part of public health efforts to slow the spread of the novel coronavirus, Allan said.

“We are trying to blunt the curve,” Allan said, referring to epidemiology graphs of epidemics that typically show a sharp rise in cases at the beginning of an outbreak. Slowing the outbreak will help ensure that local health systems aren’t overloaded, Allan said.

People need to take COVID-19 seriously because its ability to infect people is higher than influenza, he said. While 80% of those who become ill will have mild symptoms, the rest could have serious complications or even die.

A state call center to answer questions regarding COVID-19 is open seven days a week from 9 a.m. to 8 p.m. at 1-833-4-ASK-ODH (1-833-427-5634).

Summit County Public Health also has set up a call center to answer questions about the illness from 8 a.m. to 3:30 p.m. Monday through Friday. Call 330-926-5795.

The MetroHealth System also has launched a hotline to address the community’s questions and concerns about COVID-19. Call 440-592-6843 (440-59-COVID).

COVID-19 is a respiratory illness with symptoms similar to those of the flu — fever, cough and shortness of breath — that has sickened thousands and killed 4,600 globally, according to WHO. There is not yet a vaccine for COVID-19, nor are there any medications approved to treat it, according to the CDC.

Latest COVID-19 statistics, as of 2 p.m. Friday:

Countries, territories and areas with confirmed cases: 118

U.S. states reporting cases: 46 and Washington, D.C.

Total cases in U.S.: 1,629

Total deaths in U.S.: 41

Worldwide information is from the WHO, and U.S. numbers are from the CDC.

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