In his speech to the nation last Wednesday, Prime Minister Trudeau urged Canadians to get the Government of Canada’s Covid Alert App. I got it several months ago. A few days ago it sent me an alert. Here’s my story and the conclusions I draw.

I admit that I don’t check the app every day. I did check it last Monday night. Unlike previous occasions when it told me there was “no exposure detected” this time it told me I had been exposed to someone who had tested positive in the last fourteen days. Concerned, I checked the app to find out what “exposed” means and what I should do about it.

“Exposed” means that for more than 15 minutes I had been within 2 metres of someone who had identified him/herself as testing positive. The app told me I should get tested.

The app builds a database of contacts among people who have it on, and are carrying, their cellphones. Someone who has the app and tests positive, if acting socially responsibly, notifies the app (by getting a key). The software uses the key to go into the database to identify all contacts that person has had within the last 14 days. The contacts are then notified through the app.

The app uses Bluetooth data but not GPS, so it can’t tell you where the contact occurred.

The app could tell you the time of the contact, but it doesn’t. Unless you keep a detailed diary, it is unlikely that you will be able to reconstruct your activities with sufficient precision to remember where and who was near you at the moment the app registered your contact. The point about the imprecision of such recollections was powerfully made in the play/film Twelve Angry Men in the scene in which the smart and observant stockbroker cannot recall the title of the film he had seen four evenings before.

When I opened the app on Friday September 25 it initially displayed the “you have been exposed” message but that immediately flipped to “no exposure detected.” This implies that my exposure occurred 14 days previously on Friday September 11. I don’t have a diary entry for that day and, as expected, my recollections about what I did and whom I was in contact with are hazy.

Though I do wear a mask outside our home and I have had absolutely no symptoms of Covid, I took the app’s advice and got tested at the first opportunity, last Tuesday morning. I had to wait three hours. After four days I learned that my test for Covid – 19 was negative.

In the first month it was available, 2.2 million Canadians downloaded the ap, which is underwhelming. What would happen if Canadians heed the government’s urging, and download it in large numbers?

Approximately 150 people are testing positive in Toronto every day now. Let’s say that due to increased uptake of the app, 100 go to the app to identify themselves. And let’s say that each person who identifies is matched with another 100 app users as having made contact, a number seems reasonable for a 14-day period. This would mean that the app is generating demand for 100 X 100 = 10,000 tests every day, just in Toronto.

If all these people want tests and if tests are being done using only nasal swab technology, the system will quickly get overloaded, either at test facilities or at laboratories, or at both. This is a very sobering thought. The federal and provincial governments should be thinking hard about how to respond to the increase in demand for testing that will inexorably result from increased use of the app.

Perhaps that explains the Ontario Government’s latest diktat is that people who are asymptomatic and have had no known contact should not get tested, but that those whom the app has identified as having contact should. But it would be better if we had more capacity, say through a self-administered saliva test, than less testing.

What are the implications of my experience in terms of personal behaviour? Fifteen minutes of contact within 2 metres is not a great deal of contact. It may be impossible to avoid contact as defined by the app. For example, TTC trains and buses are now sufficiently crowded that a typical ride will register several contacts. You can avoid contact by avoiding crowds, especially indoors, as many seniors are doing. Order takeout rather than eat at the restaurant, even on the patio. Drive or take a taxi rather than public transit. If it isn’t possible to avoid contact, then it is essential to wear a mask to avoid the potentially serious health consequences of such contacts.