As COVID-19 cases spiked to unprecedented levels shortly after Christmas in York Region, an analysis of per cent positive rates reveals the virus transmission has been significantly more widespread in some neighbourhoods than others in the region.
North Woodbridge had the highest positivity rate — 18.5 per cent — in the region during the first full week of January, which means almost one in five individuals who tested for COVID-19 was positive, according to data from ICES, a non-profit research institute.
It was almost three times as high as the overall per cent positivity in Ontario that week, 6.8 per cent.
Southeast Markham ranked just behind North Woodbridge during the same period, with a positive rate of 17 per cent, data shows.
The test positive rates in both neighbourhoods were much higher than the average rate of York Region, which was about 10 per cent that week.
While there isn't a "safe threshold" for per cent positivity, said Susan Rogers Van Katwyk, an epidemiologist at York University, a public health unit with 2.5 per cent positive rates or higher would be moved into the red "control" zone, according to Ontario's response framework.
"It’s a good indicator that we should probably do more testing in York Region and it’s a good indicator that there is still a real threat of coming into contact with COVID in York Region," she said.
She said the per cent positivity — together with other measures, such as case numbers — helped public health authorities understand what was going on in the community and whether stricter rules were needed.
Generally speaking, the per cent positive will be high if the number of positive tests is too high, or if the number of total tests is too low.
York Region Public Health tracks COVID-19 tests on its daily updated dashboard, which shows that 44,472 tests have been done per 100,000 population as of Jan. 20 — a significant increase from December.
A majority of hard-hit areas appeared to be in Vaughan, such as Kleinburg and Maple, where COVID-19 positive rates were well above 10 per cent.
Another hard-hit area in southern York Region was Oak Ridges, where the per cent positivity was 12 per cent, which is twice the provincial average and considerably higher than the rest of Richmond Hill.
In the north, the positive rates of most neighbourhoods were below the provincial average, but two neighbourhoods — southwest Newmarket and Holland Landing/River Drive Park — stood out.
About 11 per cent of people from southwest Newmarket, including Armitage and Stonehaven, who were tested for COVID-19 were positive the week of Jan. 3.
Close to 9 per cent of individuals from the Holland Landing area who got tested were positive as well.
Despite fluctuations in the fall, the per cent positivity has been trending upward and jumped significantly around the holiday season.
The region’s average per cent positivity was 7.5 per cent during the week of Dec. 20, soaring to 11 per cent a week later.
"I think the rules need to be a lot clearer," Van Katwyk said, noting it is still ambiguous what an essential reason to go out is.
"As long as the test positivity is still going up, we still need to have quite strong measures in place or we need to have a lot more capacity for contact tracing," Van Katwyk said.
York Region spokesperson Patrick Casey didn't directly comment on the contact-tracing capacity issue.
He noted the region uses a provincial virtual assistant tool to help identify the contacts of cases and also relies "on people being open and honest about their close contacts."