An inside look at Canada's contact-tracing COVID-19 detectives

The phone call goes straight to voicemail. A good sign, says Julie Frederick, who is trying to reach a London, Ont., man with a positive COVID-19 test result. She expects he's on the other line and will call back there's a tight window for him to do so.

"It is something that we need to have happen the day that we get a positive result," says Frederick, a public health investigator with the Middlesex-London Health Unit, who is currently doing contact tracing for the region.

If she can't connect over the phone, her team will send someone in protective gear to knock on the door. It's rare, she says, but it happens.

On this particular weekday, Frederick's hunch that her call will be returned pans out. Standing in her workplace cubicle, headphones on, Frederick spends the next 30 minutes or so going through a precise list of questions that covers everything from symptoms, to the layout of the person's home how easily can he isolate from his family?

The man she's talking to is Mathew Mackay. He says he thinks he knows where he caught COVID-19. Someone in his small apartment complex was recently infected, and they share a laundry room.

Mackay has been self-isolating and has had no contact with anyone outside his home. His symptoms are improving. So Frederick shares some recommendations for how he and his family should continue to quarantine, makes plans to connect again, and ends the call.

It's not always that straightforward.

Working in 12-hour shifts, Frederick and her colleagues have connected with more than 460 people confirmed to have COVID-19 since the end of January. But the total number of people they've called is far greater. A crucial part of their job is to track down every person who has recently come into contact with the known cases those who haven't been tested, but who may have COVID-19 and the ability to spread it.

For each positive case, the London team wants to find any and all contacts made within a specific time frame: two days before symptoms showed up, through to 14 days after.

"We know that each case can generate, on average, about three additional cases," says Dr. Chris Mackie, Medical Officer of Health for Middlesex-London. "So, if we can bring that number [down] to two or one, it really makes a difference in terms of the outbreak spreading through our community."

Early on before people started self-isolating, case contacts could be in the dozens, and tracking them all down was incredibly difficult work. People couldn't easily recall everywhere they'd been over the two-week span during which they were potentially infectious.

The public health team has strategies for walking people back, step by step, and finding the information they need, but they were overworked, and so medical students were brought onboard to provide extra support.

The health unit now has about 60 people working from home to track cases, as well as a few core staff working in the office. Social distancing has brought people's contacts down significantly, usually to just one or two, but other parts of the job remain challenging.

Andrew Powell helps manage the team, and knows the emotional side of the business.

Since the contact tracers have to follow through with a patient until they recover, the relationship becomes personal. Powell says deaths and hospital admissions happen, and it all "takes a toll on the investigator."

The calls can be intense. Team members have had to intervene and get help for very sick patients. "They can hear the shortness of breath" over the phone, Powell says, "and they've had to respond and call 9-1-1 for the person, to get them to hospital."

Even with the countless phone calls they've made over the past few months, Powell says the investigators "remember every case."

And no two cases are alike. Some people stand out for their kindness and openness, and their willingness to cooperate. Others for their fearfulness.

Julie Frederick says that on occasion, people are afraid to share, worried they're going to get into trouble. Sometimes they haven't been entirely honest on self-assessment forms, or they have shown up at their job despite feeling ill because they need the work. When they later realize that they have the virus, they are reluctant to offer up information about their contacts over the phone.

Getting to the truth requires patience and understanding.

Frederick says, "a lot of people don't know what public health is and what public health roles and responsibilities are, and the legal responsibility that we have to follow individuals."

She says the key, in every case, is to use the right tone and approach the situation, "in a nice friendly way, but also being clear and concise."

As for Mathew Mackay, he has since told CBC News he was relieved to get that first call, happy to talk to anyone in health care about his diagnosis. And though he is still on the mend he hasn't fully shaken the cough he says he has been feeling much better.