One staff member at the Gregory Hills McDonald's restaurant, who asked to remain anonymous, said they believed there was no choice but to shut the store down as staff were "frightened" to show up for work.

But NSW Health gave the all-clear for the store to stay open as hygiene standards were being met and the 20 close contacts of the infected person were quarantined, McDonald's told the ABC.

The company felt it was best to only contact those who needed to isolate so as not to cause wider panic.

But an employee said it was a "horrible" feeling to only find out via conversations with other staff while at work.

"I left the shift shaking, I was so scared," they said.

"There's a lot of workers who are really, really angry at [McDonald's] for not telling us."

The team member said a lot of staff members had called in sick for their upcoming shifts as they were too scared to go in.

James Rickards, director of corporate relations for McDonald's, said NSW Health made all decisions about who needed to self-isolate and whether the store was safe to continue operating.

"The NSW Department of Health has confirmed the frequency and standard of the restaurant's sanitisation procedures and use of high-grade cleaning products meet their requirements and has authorised the restaurant to continue to trade," Mr Rickards said.

He said the affected individual was working with the same people for the last fortnight which left little doubt as to which other staff members could have had direct contact.

However the employee who spoke out claimed staff alternate shifts each week.

They said they did not understand how some people who had been within one to two metres of the person who tested positive were allowed to come to work.

"The person [who tested positive] was sent home last Friday and the person who came in to cover their shift used the same headset for drive-thru and they haven't been told to stay home."

The employee also said it was "impossible" to stay at a safe distance from workers and mangers were flouting the 1.5 metre ruling.

Mr Rickards said NSW Police had visited the Gregory Hills store this morning and were satisfied with control measures in place.

McDonald's also said there was no suggestion the crew member who tested positive was exposed to coronavirus in the restaurant and the 24-hour store was sanitising all day and night.