The Grey Bruce Health Unit has been able to identify a number of false positive results related to COVID-19 mass testing in people with no symptoms. Of the nearly 3000 tests conducted in staff and residents of long-term care homes across Grey Bruce, there have been 5 false positives; 3 residents and 2 staff. All were asymptomatic, without symptoms; there have been no false positives declared in people that have had symptoms.

As with all clinical tests, there is an expected uncertainty rate. The COVID-19 test used in Ontario is called a Nasopharyngeal Swab. A long swab goes in the nose to the back of the throat where it is held and rotated for 10-20 seconds. The swab grabs samples of any viruses that may be present.

The validity of this test was established for people with symptoms and is less reliable when testing people without symptoms. False positives become apparent when testing large numbers of people that do not have symptoms. It is worth mentioning that a negative result is extremely reliable, especially in asymptomatic. Testing asymptotic is warranted in certain situations, such as to address research questions and generate research hypotheses.

Every positive test result is evaluated in light of the laboratory, clinical, and epidemiological information. If the initial positive test result is in question, the original sample is re-tested along with two further samples. If most come back negative, a false positive is declared. This process can take from 1-10 days due to the various different labs potentially working on the test.

The impact of a false positive can be substantial when associated with long-term care and retirement homes. Upon being notified of the positive result, the facility will enter into outbreak protocols. Staff, residents, and families are notified creating a source of anxiety for all concerned. Significant equipment, resources and effort are spent for everyone’s safety and wellbeing.

Due to the significance of false positive results in these settings, more so than in individual cases, our team has been very successful in assessing these results accurately and promptly.

The initiative of mass testing of asymptomatic does not change the management of outbreaks in long-term care and retirement homes. As soon as a case is identified, all outbreak management protocols are immediately implemented regardless of the number of cases. However, this initiative successfully demonstrates both strong testing capability and capacity, when needed. This takes on significance as the public may believe that testing capacity is in question and that mass testing of asymptomatic is a panacea.

The Long-Term Care and Retirement Homes effected by the false positive tests are:

Sepoy Manor in Lucknow
Golden Dawn Long-Term Care Home in Lion’s Head
Parkview Manor in Chesley
Grey Gables in Markdale
Georgian Heights in Owen Sound

The Grey Bruce Health Unit commends the quick response and diligent efforts by all homes that have seen false positives.

source: media release, Grey Bruce Health Unit