Transmission of COVID-19 within schools was limited during the first three months of the school year, according to a new report from Ottawa Public Health (OPH).
Researchers examined the period between September and November 2020, during which an estimated 124,211 students returned to class in-person at Ottawa's four publicly-funded school boards.
The data shows COVID-19 infection rates peaked in early October and then declined, similar to trends witnessed within the broader community.
Out of 888 confirmed cases identified among students, teachers and other staff at 246 different schools during that time, 85 per cent were infected outside of the school setting, researchers found. Of the 888 people who contracted the illness, 560 attended school while infectious and around a quarter were asymptomatic.
A total of 55 outbreaks were declared at schools — which occur when two or more cases are identified with an epidemiological link and at least one could have reasonably been acquired within the school. Outbreaks ranged in size from two to 17 cases, but half were resolved with only two people testing positive, where infection spread from one person to one other person.
Half of the outbreaks stemmed from a student or staff member who was a household contact of someone who tested positive for COVID-19.
The report cautions that the actual number of people who had COVID-19 could be higher because cases could have gone undetected.
"Changes in testing guidelines and uptake might explain some of the decline in cases. Testing among Ottawa residents aged less than 20 years peaked in late September, just as testing was limited to close contacts and certain symptomatic individuals, and then declined in October," the report reads.
The report states that the percentage of tests among people under 20 that were positive increased when testing volume declined, "suggesting that more cases would have been detected had there been more testing."
The report concludes that transmission within schools was "apparently low," while cautioning that it's possible there was more spread of COVID-19 due to lower testing rates.
Data supports school reopening, Etches says
At a virtual news conference Tuesday, Ottawa's Medical Officer of Health Dr. Vera Etches said the data supports the decision to reopen schools in Ottawa.
Etches said preschool screening, mask-wearing and cohorting student groups all contribute to lower transmission rates of COVID-19 in schools than in the broader community.
"The greatest risk for transmission — where that occurs — is when there's close contact for a longer period of time, without masks and without distance," said Etches.
"So households ... is where we're most likely to have that prolonged contact without the protections, and it's the same for children. The household is where they're most likely to be exposed."
WATCH | 'Opening schools does not mean we are home free,' says Dr. Etches:
Schools in Ottawa resumed in-person learning on Monday. The city experienced a post-holiday spike of COVID-19 cases, but it's since subsided and case counts are trending downward.
As of Tuesday, OPH's COVID-19 dashboard shows only one school experiencing an active outbreak. Two staff members at Greely Elementary School have tested positive for COVID-19.
Etches warned that it's vital to reduce community spread to keep cases within schools down, so they can stay open.
"Opening schools doesn't mean we are home free or that we're ready to ease up," said Etches. "We need to continue to reduce transmission in the community."