VICTORIA - British Columbia's top doctor says old-fashioned contact tracing, not an app, is the primary tool that's been helping public health officials find people who could be infected with COVID-19.

Dr. Bonnie Henry said officials are accustomed to tracking people who could have come into contact with carriers of other diseases and COVID-19 is no different, except that 600 people have been focused on the task.

An app would be more useful for when people may have spread or contracted the illness in a large crowd of people, Henry said.

Prime Minister Justin Trudeau has promoted a voluntary app called COVID Alert, which will be tested in Ontario before being rolled out across the country.

Henry said keeping the number of contacts low as well as physical distancing and hand washing have prevented a surge in cases in B.C.

The province reported 13 more cases Tuesday, for a total of 2,835, as well as one death, bringing the number of fatalities to 170 since the start of the pandemic.

Henry said contact rates are at about 65 of normal in B.C., up from 30 per cent, but it's all the more important to continue limiting gatherings to 50 people to allow for quick contact tracing if the illness spreads.

Up to 97 per cent of contacts have been found within a few days after a case is identified, she said.

Going to an 80 per cent rate of normal contacts would result in a dramatic increase in cases before a vaccine is available, she said.

"What I see is us maintaining this balance as we do more things in our communities," Henry said, adding a slow, gradual transition out of the former stay-at-home measures is working.

Henry said the BC Centre for Disease Control has been working on developing a way to assess the genetic material of the virus in waste water samples, similar to what other countries have done.

"Recently, Italy has reported out on some of the sampling that they did retrospectively," she said.

The samples were taken in December and January, she said, indicating there was likely circulation of the virus in parts of Italy before it was recognized.

Five weeks of testing in the Vancouver area has shown no positive results and that reflects the low level of transmission, she said.

Testing is likely to be rolled out in smaller communities, Henry said.

This report by The Canadian Press was first published June 23, 2020.

News from © The Canadian Press, 2020