Infectious disease outbreaks, such as the COVID-19 pandemic, have a special distinction in their spread between cases and infections. While “case” indicates individuals with a confirmed case of COVID-19, “infections” additionally include those individuals who had the disease but were not confirmed because they either had mild symptoyou can stay up to date with her teams work and get a more in depth overview of the methodology and data from her working group’s website.ms or were asymptomatic. Either metric can be used to calculate mortality rates, case fatality rate (CFR) or infection fatality rate (IFR), depending on the question of concern as they both offer different looks into the dynamics of the virus.
While interesting metrics in their own right, a research group from the University of Washington led by Martina Morris has been using these metrics to estimate by “back-calculation” the total number of cases and infections in King County. By distinguishing between cases and infections the team is able to estimate not only the population that has a perceptible, symptomatic, form of COVID-19 but also how well testing in the county has been able to detect the case affected population. As of writing the groups model estimate that over 80% of cases remain undetected in the county. This low detection rate can likely be attributed to the lack of testing availability, however, new efforts to increase testing may put a dent in this percentage as time passes and data is further updated. Dr. Morris’s work is still under development but you can stay up to date with her teams work and get a more in depth overview of the methodology and data from her working group’s website.