(CNN) -- The CEO and President of South Dakota-based Sanford Health, one of the largest health systems in the U.S., says he will not be wearing a mask because he has already had Covid-19.
Hospital staff are appalled.
In an email sent Wednesday, which CNN obtained from a nurse at a Sanford Health hospital, CEO and President Kelby Krabbenhoft addressed the health system's 50,000 employees, explaining his decision.
"I contracted the virus, felt the uncertainty that accompanied the word 'positive'," he wrote.
"Experienced the lagging coughs and fatigue... but I'm back in my office," he added.
And he will be maskless.
Citing "growing evidence," that he is now immune to the virus, Krabbenhoft said "for me to wear a mask defies the efficacy and purpose of a mask and sends an untruthful message that I am susceptible to infection or could transmit it. I have no interest in using masks as a symbolic gesture."
There is not a lot of evidence yet about whether having been infected once provides immunity to reinfection from the virus, and no evidence about whether people who have recovered from one infection can transmit the virus to others. There have been multiple cases documented of people being infected a second time after recovering from one bout with the virus.
The Centers for Disease Control and Prevention is working to learn more about reinfection, and recommends people wear masks whether or not they have had Covid-19.
"It's appalling to read this from a hospital CEO," the Sanford Health nurse, who did not want be named for fear of losing her job, tells CNN. "We are supposed to be leaders in the community. How can we be taken seriously when this is our CEO?"
Sanford Health, which includes 46 hospitals and 1,400 physicians, is headquartered in Sioux Falls, South Dakota, where the City Council voted this week to approve a mask mandate. It is the first mask mandate in the state, where Covid-19 cases have skyrocketed since August.
"Kelby Krabbenhoft's email was based on his own experience with Covid-19 and his personal opinions about the virus. They do not reflect the views of our health system as a whole," Micah Aberson, Executive Vice President of Sanford Health, said in a statement to CNN.
They also took to social media to encourage mask-wearing Friday. "Our health care providers have called upon our communities to do their part by wearing masks and physically distancing to slow the spread of the virus. This is the best way to reduce stress on our health care system," a post on Sanford Health's Facebook page said.
Masks have been a divisive issue in South Dakota, where Governor Kristi Noem has refused to issue a mask mandate. "You may choose to wear a mask and be concerned about the virus. And if people are scared, I'm going to remind them, they should stay home," Noem said at a news conference Wednesday.
"Masks have been a symbolic issue that frankly frustrates me," Krabbenhoft said in the email. "The 'on-again, off-again' behavior of mask use by the general population violates every notion of serious infectious management that I was trained to adhere to, so some of this is absurd."
Krabbenhoft wrote he's "an old scrub technician from my youth" -- part of a team that would work in an OR -- and recognized the importance of masks for people who have not had Covid-19.
"For people who have not contracted the virus and may acquire it and then spread it, it is important for them to know that masks are just plain smart to use and in their best interest," he said.
"When it comes to immunity the science is evolving and we must continue to follow CDC guidelines," Sanford Health executive management said in another staff-wide email Friday, addressing Krabbenhoft's email.
"Whether you've had the virus or not, it is recommended that you wear a mask when you cannot be socially distanced," the email from executive management said.
In terms of the number of Covid-19 cases and hospitalization in the state, Krabbenhoft told South Dakota's Argus Leader Thursday that he felt it was under control. "There's not a crisis," he said.
The Sanford Health nurse called his comments "a slap in the face."
South Dakota has been among the states with the highest per capita new cases and hospitalizations in the nation over the past week, according to data from Johns Hopkins University.
CDC guidance cites a number of studies showing that masks reduce the risk of transmitting or catching the virus by more than 70% in various instances. In several scenarios, when officials told people to wear masks, infections and deaths fell significantly, the CDC pointed out.