(CNN) Local health officials in the United States are worried about another rise in anti-mask protests -- and their safety.
In cities and counties where there has been ongoing debate around mask mandates in public schools, several local health officials have reported again being intimidated by or receiving threats from anti-maskers, Lori Tremmel Freeman, chief executive officer of the National Association of County and City Health Officials (NACCHO), told CNN on Wednesday.
As a return to school gets underway, "these are heated conversations sometimes that are turning nasty and out of control," Freeman said. "We are going to see more of this in communities that have these high transmission rates and are returning to some of these mitigation efforts. We're going to have to track it closely."
Throughout the pandemic, public health officers have reported receiving death threats and harassment in response to their recommendations to wear masks and follow certain Covid-19 mitigation measures. For instance, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, has spoken openly about receiving death threats.
CNN previously reported that during a live public briefing on Facebook last year, "someone very casually suggested" Los Angeles County's public health director, Barbara Ferrer, should be shot. And in Washington state, Okanogan County community health director Lauri Jones installed a new security system and asked for police patrols around her home following repeated online threats.
Such incidents are now occurring again, according to NACCHO, and the organization is tracking reports of threats, harassment and intimidation.
"Just last week, we started seeing extremist groups come out again in opposition to their public health officers' orders in California," Freeman said. "Another example, in North Carolina, involved school board meetings where parents were picketing that there was no way they were sending their kids to school in masks. Really, this is going on in different places across the country."
Last week in Florida, about 20 anti-mask protesters gathered at the Broward County School Board headquarters in Fort Lauderdale, Florida, on Tuesday, forcing a postponement of a discussion on mask requirements for the upcoming school year, a school board member told CNN.
"Folks weren't wearing masks and refused to follow the rules -- rules that people have followed for the last year and a half," School Board Member Sarah Leonardi said of the protesters. "It made it very difficult to hold our meeting behind closed doors."
Leonardi said the group set masks on fire during their demonstration and called the protest "very disturbing."
Video of the protest from CNN affiliate WFOR showed a protester dousing a catering tray full of masks with lighter fluid before setting it on fire with a lighter.
Such protests and reports of harassment are happening as the more dangerous and highly transmissible Delta coronavirus variant circulates nationwide, leading to a surge in Covid-19 cases and hospitalizations.
In response, the US Centers for Disease Control and Prevention updated its guidance on masks last week, recommending that everyone older than age 2 wear masks in schools, whether vaccinated or not.
"We're hearing a lot of challenges on the ground, especially in states choosing not to take up the mask mandates that were recommended last week and opting to instead push decisions on masking down locally," Freeman said.
"When the state doesn't want to take a hard line, it naturally falls to community-level decisions and so we're back to local health departments being front and center of controversy around the reintroduction of masks for vaccinated people," she said.
These pressures of the pandemic seem to be taking a toll on the public health workforce.
Freeman previously told CNN in May that NACCHO has tracked more than 250 public health officials leaving the field since the beginning of the pandemic.
In Kansas alone at the time, more than 30 health officials left their posts since the beginning of the pandemic, a Kansas Department of Health and Environment spokeswoman told CNN in May. According to NACCHO, that was a loss of staff from about one-third of the state's 100 health departments.