Five of Ottawa's 21 confirmed cases of COVID-19 appear to have resulted from community transmission, the city's medical officer of health said Sunday.

Vera Etches confirmed they're the first confirmed cases that can't be directly linked to travel or other known cases.

"We have people in our community who became ill and it's been determined it's coronavirus, COVID-19, and they had no contact with another case that we can find," Etches said during an afternoon briefing.

What's more, Etches said computer modelling suggests as many as 4,000 people could be infected across the city.

Etches also confirmed a health-care worker at the Ottawa Hospital has tested positive for the respiratory illness, and said health officials are trying to trace that person's interactions, both inside and outside the health-care system.

Ottawa Public Health and The Ottawa Hospital will be reaching out to anyone who came into contact with the unidentified worker, who is in their 30s. The worker lives in the United Counties of Prescott and Russell, according to a release from the Eastern Ontario Health Unit.

Priority testing still in effect

Etches noted that testing for COVID-19 will continue to prioritize front-line workers, patients with symptoms who have been hospitalized and people who are in facilities where they are considered more vulnerable, such as long-term care homes and retirement homes.

Ottawa Public Health is asking residents to maintain social distancing and is looking at additional steps to ensure people are only leaving their house for essential purposes.

"It is worth preparing, psychologically and practically, to imagine that we need to maintain the social distancing for a much longer period of time," said Etches.

How long people could be asked to practise social distancing is still unknown.

She advised people to develop new daily routines and to prepare for an unprecedented challenge to avoid having an influx of patients flood the health care system.