Covid-19 is being "weaponised" by offenders, according to one police force which has seen spitting and coughing assaults on officers double.
North Wales Police saw twice as many such assaults between March and June compared with the same period in 2019.
Almost one-third of assault charges on South Wales Police officers were related to spitting or coughing between March and May, BBC research shows.
Maximum sentences for assaults on emergency workers are being doubled.
"It's just absolutely appalling to weaponise a virus or disease against police officers and emergency service workers" said North Wales Police Federation general secretary Mark Jones.
"It's unlike anything we've ever seen before, to be threatened with what is an unseen and silent killer is really terrible."
PC David Roberts-Ablett was coughed at by a man who claimed he had coronavirus symptoms after he was arrested for being violent towards staff at a Tesco supermarket in Cardiff.
Darrell Glen Humphries had been taken to the city's University Hospital of Wales so an injury could be treated when the 53-year-old coughed in PC Roberts-Ablett's face.
"In these times of Covid, there's a concern. It was a very worrying moment," said the constable of nearly 20 years.
"He had been quite aggressive so I asked him to calm down. It was a very deliberate motion by him, he turned his head, his eyes, fixated on me.
"It was almost like he was targeting me, and he picked my face, and then deliberately looked straight at me and coughed at me. Fortunately I was wearing my glasses and a mask at the time so I was protected."
Humphries, of Canton in Cardiff, was sentenced to 26 weeks in prison by the city's magistrates in May for the attack.
"It was a very worrying moment, thinking 'have I now got Covid?'," the officer said.
"I thought what do I do? Where do I go?
"There is being a police officer and dealing with the criminal aspect of things, but there's a more humane side to it as well, where there's a lot of implications on me and my family, my colleagues and the people I am serving in Cardiff.
"It does play on your mind because for a while you just don't know."
Police forces across the UK saw a 21% increase in assaults on their officers in the first three months of lockdown.
In the North Wales force area, 30 of the 157 crimes recorded against police officers were coughing and spitting, up from 14 the previous year.
Of those, 23 people were charged, up from 10 in 2019, according to a freedom of information request by the BBC.
"The amount of deliberate coughing and spitting at police officers has risen quite sharply," Mr Jones said.
"To see that form of assault and attack on a police officer is quite worrying."
In the South Wales force area, the largest in Wales, of the 167 charges of police officer assaults, 55 were "weaponising" Covid-19 as threat and related to PCs being spat or coughed on.
"What we have seen is a number of people effectively making a weapon out of spitting and then presenting that they've got or believe they might have Covid-19," said Chief Constable Matt Jukes.
"A colleague who'd been involved in an incident said 'in some ways I'd rather be shoved, or punched, than get bitten or spat out, because of that long-term worry about the impact on health'.
"What the spitting and biting does is leaves officers with real uncertainty, until they can get test results.
"It's not always Covid-19, sometimes it's other infectious diseases. Sometimes they have to wait for reassurance or knowledge that there may be another issue they need to deal with."
Assaults against police officers have also risen in the Gwent force area from 54 to 57 year-on-year, but they decreased in Dyfed-Powys from 111 to 96.
Maximum sentences for those convicted of assaulting emergency workers in England and Wales are to be doubled, the home secretary said in September.
"Every day they risk their lives to protect ours - they should never face being punched, kicked or spat at," said Justice Secretary Robert Buckland.
"Anyone looking to harm prison officers, police, fire personnel or health workers should be under no illusion - your disgraceful behaviour is unacceptable and you will feel the full force of the law."