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Temporal Trend in % positivity of SARS-CoV-2 Testing Among HCWs

July 22, 2020 - Dr. Archer's Update on COVID-19 response from the DOM and Medicine Program

What is the evidence supporting the universal masking policy in hospitals? Here is a relevant paper, sent to me by Dr Kathie Doliszny, which summarizes the benefits of a universal masking policy at Massachusetts General Hospital/Brigham (MGB) in Boston. MGB is the largest health care system in Massachusetts, with 12 hospitals and more than 75,000 employeeIn March 2020, MGB implemented a multipronged infection reduction strategy involving systematic testing of symptomatic health care workers (HCWs) and universal masking of all HCWs and patients with surgical masks. This is similar to what we have done at KHSC.

This study assessed the association of hospital masking policies with the SARS-CoV-2 infection rate among HCWs to determine whether there was a benefit from this infection control measure, as evidenced by a fall in infection rates once the policy was implemented. I must note the infections of HCWs in our region have all been from community acquired sources; not acquired within the hospital.

In this study, by Wang et al (click here), published in JAMA on July 14th 2020, a high rate of HCW infection was noted (of 9850 tested HCWs, 1271 (12.9%) had positive tests for SARS-CoV-2, the virus that causes COVID-19). See intervention graph below:

Temporal Trend in Percentage of SARS-CoV-2 Testing among HCWs

The highest rate of test positivity amongst HCW occurred before any interventions occurred (pink zone). In the purple zone the hospital required masking of HCWs and this was associated with a flattening in rates of test positivity. The yellow zone indicates a transition period as patients were also required to universally mask. In green one sees the data from the intervention period (universal masking of both patients and HCWs). With the intervention the rate of positive tests declined. This downward slope of test positivity rate line is statistically different (post intervention) than the upward sloped line in the pink zone (no intervention). During the intervention period, the positive test rate decreased from 14.65% to 11.46%. The authors conclude the intervention (universal masking of HCW and patients) was associated with reduced rates of infections in HCWs.

Two points are worth mentioning. First, since there were many changes happening simultaneously it is hard to prove that universal masking was the main cause of the observed reduction in rates of positive tests in HCW. Second, these data are from a hospital with a very high incidence of COVID-19 (which is not the case at KHSC where few HCW were infected and virtually all were infected in the community-not at work). Indeed the rate of positive tests in Ontario is <2% (1/10 the rate in this study). Nonetheless, these findings are supportive of a universal masking policy, at least in a high COVID-19 prevalence environment. The challenge in Ontario, with its much lower disease prevalence will be deciding when to stop our universal masking policy.

Update KFL&A:

There were no new COVID-19 cases this week. The running total for the epidemic remains at 106 cases in the KFL&A region (see update from KFL&A Public Health). KFL&A now has only 1 active case and this person is recovering in the community. Our stable local epidemiology is consistent with the ongoing improvement in the epidemic we are seeing across Canada and in Ontario, with the exception of Toronto-Hamilton-Windsor, where the disease is still quite prevalent. There are no inpatients with COVID-19 in KHSC. Our test positivity rate in KFL&A continues to fall and is currently <0.4% (vs 1.99 % provincially).

Where to get a COVID-19 test?

  1. A) The public: Leon’s Centre testing facility is open for COVID-19 testing of community members (click here for details of hours). The wait time at Leon Centre is short (10 minutes).
  1. B) KHSC staff: Should KHSC staff develop symptoms consistent with COVID-19, please do not come to work! Instead, contact occupational health and safety and they will tell you how to proceed (ext 4389 at KGH site, or You will likely be tested at the Hotel Dieu testing centre. Results are usually available next day.

KHSC capacity: We continue our surgical ramp-up and resume our ambulatory care ramp up to provide better care for the 99.9% (click here for more on this). KHSC has capacity for our elective procedure ramp up; but things are busier, with the hospital inpatient census now exceeding 400 patients (see below).

KHSC COVID-19 Dashboard - Bed Management

Universal Masking Policy: Another revision of our entry mask policy is starting next Tuesday-it will allow cloth masks for entry/exit 

                                          Picture of Blue Masks    Man wearing mask

All people entering the hospital are required to wear a mask (unless an exemption has been prospectively obtained). MASKS WILL BE PROVIDED AT ALL KHSC ENTRY POINTS.

In a policy to begin tomorrow, you will be allowed to wear a cloth mask when entering the building (this includes both staff and visitors).

  1. Fabric masks cannot have an exhalation valve.
  2. Fabric masks cannot be used in patient care.

If you use a hospital provided medical mask:

  1. they should be reused for a week, storing it in a paper bag when not in use (bag provided). These are not single use masks.
  2. these masks can be used in patient care as well, with the sole exception of caring for a patient on droplet precautions, such as a patient with COVID-19. In these cases you will need to get a different mask which is available at the nursing station.

Occupational health will be reviewing requests for exemption. When there is an exemption, it will usually mean that a face shield will be worn as an alternative (i.e. some form of facial PPE will still be required). An important reminder however; face shields are not as effective as masks and personal exemptions will likely be rare.

Ontario’s COVID-19 outbreak (click here) Ontario’s prevalence rate is 255.3/100,000, much higher than in KFL&A, at 49.8 cases/100,000 population. Toronto still has a rate ~9 times higher (446.5 cases/100,000 population). The region with the highest prevalence of COVID-19 is Windsor (469.4/100,000), likely because of its border proximity with Detroit.Provincially the epidemic is in decline. There were again 203 new cases yesterday (up 0.5% from yesterday). Ontario has had a total of 37,942 total cases and 2753 deaths to date. The 0.9% rate of positive SARS-CoV-2 tests yesterday continues a trend of low positivity rates.

Prevalence Rates - Map of Ontario

The prevalence of cases in Toronto is still increasing daily due to over a dozen neighbourhoods which are COVID-19 hotspots, defined as rates over 1000 case/100,000 (click here).

Picture of Toronto Skyline with CN Tower

These neighbourhoods include: Moss Park, Newton Brook West, Yorkdale Glen-Park, Downsview Roding CFB, Maple Leaf, Rexdale-Kipling, Black Creek, Mount Olive, Beechborough, York University Heights, Mount Dennis, Glenfield Jane Heights, and Humber Heights-Westmount. Weston with 1829 cases/100,000 once again has the highest prevalence in Toronto. This rate is almost 40 times higher than in KFL&A.  The ministry has deployed public health experts, mobile testing facilities and contact tracers to deal with these “epidemics within epidemics”. While things are gradually improving in Toronto, it remains in the yellow zone due to its local outbreaks and rate of test positivity, as you can see from their dashboard (click here) and graphic below. Toronto remains in Stage 2 of recovery.

The first wave of Canada’s epidemic is resolving (some much needed good news) We have had 111,697 cases of COVID-19 in Canada and 8862 deaths (see below). Most cases are resolved. Most reassuring one can see in the past few days an increase in resolved cases, green line below, and a proportional fall in active cases (orange line below). This puts the active case load back where it was before the epidemic took off in March-Good News!!!

Canadian aggregate data

Canadian aggregate data July 22nd 2020

The epicentre for COVID-19 mortality remains our long term care facilities (LTC) (see today’s data below). Canada has ~ 7% of seniors in LTC facilities, so this is a big problem (click here).

The ~78,000 residents of Ontario’s LTC facilities account for less than 0.5% of the population but they still account for 67% of all deaths from COVID-19! There have been 1841 deaths to date. There were no news death yesterday in Ontario LTC centres. Canada had the highest rates of mortality in LTCs of any surveyed country (click here)! This is sad indictment of Canada’s LTC facilities and attests to a lack of government oversight and lack of a comprehensive plan for senior care.

Photo Diagram of Nasal Swab

Testing for SARS-CoV-2 (click here): We have tested 10.24% of all Canadians (3,917,600 people) (see below). The rate of test positivity is declining and nationally is 2.85% (vs 1.99% in Ontario). Ontario SARS-CoV-2 testing continues at a rate that exceeds the national average, with 13.19% of Ontarians having been tested. A very promising sign is that with more testing we are finding a lower rate of positive test results.

Graph - Test Performed in Canada

Ontario testing rate is 13% (similar to Alberta) and much higher than BC (<5%) and Quebec (9%)

The USA has an average rate of SARS-CoV-2 positive tests of 8.5% (click here). In some states where the governor shares the Trump government’s “hands off/ masks off” mindset, rates of COVID-19 test positivity are >20%. For example in Arizona 25% of all nasal swabs are positive! Contrast this with New Jersey (see below), and Illinois (selected because I have adult children in each of these states). Both states have run credible shelter in place program and have implemented physical distancing and masking policies. As a result, their rates of positive tests are now low, at 1.4% and 3.1%, respectively. Well done Governors Murphy and Pritzker!

Graph of cases/tests/% of positive Tests in New Jersey

The COVID-19 pandemic has grown by 3 million cases in 2 weeks! There are now 14,976,453 cases globally and 617,254 deaths. On July 6th there were “only” 11.5 million cases and now, 2 weeks later, there are 3.5 million more cases. The pandemic hot spots are in the Americas (Brazil and USA), Russia, and India (click here). These 4 countries account for over half the world’s cases. 

Cartoon picture of a sick world with thermometer in mouth

Stay Well!


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