We must change the way we do testing and case definition


I had the opportunity to talk with Dr. David Fisman, epidemiologist at the University of Toronto. He believes we need to change the way we are doing COVID-19 testing in Ontario.

The current narrow scope of testing is puzzling. Despite claims that there is no test backlog there still does seem to be a backlog of 1000 cases (a great improvement). However, test submissions have fallen probably because testing criteria seem so restrictive. Current guidance around testing appears to still emphasize travel and case contact. That needs to end immediately (and indeed should have ended in early March).

The province must increase its testing capabilities. Any accredited diagnostic lab in Ontario with the ability to do COVID-19 PCR should now be enlisted to test for COVID-19 PCR.

We need to use increased test capacity in four ways:

1. Clinical care--we are already doing this.

2. Infection control—we need to protect our hospitals, long term care facilities, shelters and correctional facilities as they are dry tinder for COVID-19 transmission. We cannot protect them from something we cannot see, so we need abundant regular testing of staff, as well as admission screening of patients to be admitted to hospitals, no matter what their primary complaint (heart attack, car accident, labour and delivery… all need to be tested). 

Part of protecting long-term care facilities is also making sure that PSW and regulated staff (RNs and RPNs) work only in one facility (as directed by Dr. Sheela Basrur during SARS) . Work at multiple facilities has created a network that ensures that a COVID-19 outbreak at one facility will spread rapidly to others. In British Columbia this is already happening and government augmented compensation to enable workers to sustain themselves. 

3. Case-based control (isolation of cases and quarantine of contacts). We are meant to be doing this already. This is probably less of a priority for disease control than is physical distancing, but case-based control might be enhanced with institution of probable (clinical) case definitions as below.

4. Surveillance.  We are currently looking for COVID-19 only where we expect to find it (in hospitalized individuals and ill healthcare workers). In order to see and understand this epidemic we need to do surveillance. In a pandemic disease, all in the population should be equally vulnerable to infection. Testing in Ontario has overwhelmingly identified COVID-19 in older individuals (because they tend to be sick). We need a large-scale effort to sample the Ontario population to evaluate prevalence of COVID-19. The fact that clinics are now closed makes it difficult to do sentinel site surveillance so other approaches will have to be devised.

Testing will only get us so far. We want to identify not only COVID-19 that is diagnosed through lab testing but also to use clinical case definitions in order to manage cases and to do proper surveillance. The delays in testing in Hubei, China in February resulted in similar expansion of case definitions. 

Dr. Fisman’s suggestion is to define case categories as follows:  

  • Suspect case: fever and new cough in an individual in Ontario.
  • Probable case: suspect case + radiographic evidence of interstitial pneumonia +/- leukopenia.

Quebec has recently changed surveillance to include probable cases. Note that the SARS outbreak was controlled entirely based on clinical case definitions as the pathogen was only recognized towards the end of the outbreak.