Strategic COVID-19 Pandemic Committee

How should we interpret daily data updates to understand the threat of COVID-19?

COVID-19 Questions & Myths

People naturally tend to focus on the number of new cases; however, other pieces of information add understanding.

Current hospitalizations and deaths show how many are severely affected and indicate if the system is overwhelmed today. Currently, in Alberta 3-4% of COVID19 cases from the original variant of the virus are hospitalized and 1% die, but 20-25% of the elderly require hospitalization and greater than 10% die.  While the average age of mortality from COVID-19 in Alberta is 82 (Range 20 to 107 years), the average age of hospitalization with an ICU stay is 59 (Range 0-89 years). We have yet to see what the UK and Brazil variants will be as they spread more easily and cause more severe disease.

Public health restrictions are needed until the hospital system is able to resume full normal care for COVID-19 and non COVID-19 patients. Our capacity has expanded for COVID-19 patients by delaying other less urgent care and increasing the patient care beds and workload of available health care workers.

Looking at the daily new cases trend reported by Alberta Health over 1-2 weeks informs us if hospitalization and deaths will increase or decrease. Patients entering hospital today typically first had symptoms 7-10 days ago, and likely tested positive 2-3 days into symptoms.

Next, we look at percent positivity. The percent positive is the percentage of all COVID-19 tests done that day that are actually positive (Johns Hopkins Bloomberg School of Public Health). This indicates how widespread infection is, and whether the total number of tests is sufficient. A high percent positive means that many community cases are being missed, and more testing should be done. For example, in some places one out of every five tests is positive (20% positivity) which suggests that there are many undetected cases.  The World Health Organization recommends that governments should not consider reopening until there has been under 5% positivity for two weeks.

The R value also describes disease transmission trends. Also called the reproduction number, it describes whether community transmission is increasing, decreasing or staying the same. It tells us the average number of people that someone with COVID-19 will infect. If the R value is one this means on average one infected person will infect one other person and the outbreak will continue. If the R is greater than 1 the outbreak is growing. We look for a trend of the R value to be 0.8 or less before easing public health restrictions. BioMed Central published an article showing the R value of the original COVID-19 variant without restrictions in place early in the pandemic was usually in the range of 2 to 3, and that of seasonal influenza about 1.3.

References:
i. COVID-19 Testing: Understanding the “Percent Positive”, Johns Hopkins Bloomberg School of Public Health
ii. Cases in Alberta, Alberta Health
iii. Estimates of the reproduction number for seasonal, pandemic, and zoonotic influenza: a systematic review of the literature, Biggerstaff, & et al., BioMed Central