A study from UHN, Canada’s largest research hospital, reveals the percentage of symptomatic and asymptomatic healthcare workers infected with the novel coronavirus.

“A key question that we wanted to answer was ‘how many asymptomatic healthcare workers are unknowingly infectious or have been exposed to the virus,’” says Dr. Deepali Kumar, senior author and a clinician investigator at the Toronto General Hospital Research Institute (TGHRI).

To answer this question, two tests were used: swab tests, to see if the virus was present and able to spread; and blood antibody tests, to see if past exposure to the virus had occurred.

The results revealed that, of symptom-free staff, around 0.5 per cent had positive swab tests. This means that around one out of every 200 staff were potentially infectious. When staff had symptoms, that number jumped to 3.4 per cent, or around seven out of every 200 individuals.

Using blood antibody tests, the research team found that between 1.4 per cent to 3.4 per cent of symptom-free staff tested positive, depending on which antibody test was used.

“This means that somewhere between three and seven staff out of every 200 had been infected with the virus without ever reporting symptoms,” says Dr. Victor Ferreira, the first author of the study and a scientific associate at TGHRI, where he works with Senior Scientist and co-author Dr. Atul Humar.

Symptoms that were considered were fever, headache, new or worsening cough, shortness of breath, sore throat, runny nose, pink eye, diarrhea, loss of sense of smell or muscle aches.

“Our findings reaffirm the importance of remaining vigilant in the screening of health care and other front line workers regardless of whether they experience COVID-19-like symptoms,” says Dr. Ferreira.

These results come from the first phase of the study called Research Platform to Screen and Protect Healthcare Workers study—or RESPECT for short, which enrolled front-line health care workers at UHN between March and June 2020. Given the success of the first phase, RESPECT 2.0 has since been initiated and expanded to include broader clinical personnel, research personnel and other workers, such as those in the food industry.

“This observational study has important implications for infection control, as well as staff and patient safety. And it could not have been possible without the multidisciplinary team of physicians, researchers, nurses and other allied health professionals that contributed. Thank you to everyone at TeamUHN that made this possible,” says Dr. Brad Wouters, UHN’s EVP of Science and Research.

The study was funded by the Mount Sinai Hospital and University Health Network Academic Medical Organization, the Ontario Institute for Cancer Research, the Government of Ontario, and the Toronto General & Western Hospital Foundation. T Pugh is a Tier 2 Canada Research Chair (CRC); M Cybulsky and B Wouters are Tier 1 CRCs.