scholarly journals How should we present the epidemic curve for COVID-19?

2021 ◽  
Vol 20 (1) ◽  
Author(s):  
Jean-Paul R. Soucy ◽  
Sarah A. Buchan ◽  
Kevin A. Brown
Keyword(s):  
Public Health ◽  
Symptom Onset ◽  
Health Authority ◽  
Public Reporting ◽  
Decision Makers ◽  
Public Health Authority ◽  
Onset Date ◽  
The Public ◽  
Epidemic Curve ◽  
Incident Cases

Epidemic curves are used by decision makers and the public to infer the trajectory of the COVID-19 pandemic and to understand the appropriateness of response measures. Symptom onset date is commonly used to date incident cases on the epidemic curve in public health reports and dashboards; however, third-party trackers date cases by the date they were publicly reported by the public health authority. These two curves create very different impressions of epidemic progression. On April 1, 2020, the epidemic curve based on public reporting date for Ontario, Canada showed an accelerating epidemic, whereas the curve based on a proxy variable for symptom onset date showed a rapidly declining epidemic. This illusory downward trend is a feature of epidemic curves anchored using date variables earlier in time than the date a case was publicly reported, such as the symptom onset date. Delays between the onset of symptoms and the detection of a case by the public health authority mean that recent days will always have incomplete case data, creating a downward bias. Public reporting date is not subject to this bias and can be used to visualize real-time epidemic curves meant to inform the public and decision makers.

scholarly journals How should we present the epidemic curve for COVID-19?

2021 ◽  
Author(s):  
Jean-Paul R. Soucy ◽  
Sarah A. Buchan ◽  
Kevin A. Brown
Keyword(s):  
Public Health ◽  
Symptom Onset ◽  
Public Reporting ◽  
Downward Trend ◽  
Public Health Authority ◽  
Onset Date ◽  
Current Response ◽  
Sample Collection ◽  
The Public ◽  
Epidemic Curve

Epidemic curves are used by decision makers and the public to infer the trajectory of the COVID-19 pandemic and to understand the appropriateness of current response measures. Symptom onset date is commonly used to date cases on the epidemic curve in public health reports and dashboards. However, third-party trackers often plot cases on the epidemic curve by the date they were publicly reported by the public health authority. These two curves create very different impressions of epidemic progression. On April 1, the epidemic curve for Ontario, Canada based on public reporting date showed an accelerating epidemic, whereas the curve based on a proxy variable for symptom onset date showed a rapidly declining epidemic. This illusory downward trend (the "ghost trend") is a feature of epidemic curves anchored using date variables earlier in time than the date a case was publicly reported, such as symptom onset date or sample collection date. This is because newly discovered cases are backdated, creating a perpetual downward trend in incidence due to incomplete data in the most recent days. Public reporting date is not subject to backdating bias and can be used to visualize real-time epidemic curves meant to inform the public and policy makers.

Considerations for Improving Reporting and Analysis of Date-Based COVID-19 Surveillance Data by Public Health Agencies

2021 ◽  
Vol 111 (12) ◽  
pp. 2127-2132
Author(s):  
Ian Hennessee ◽  
Julie A. Clennon ◽  
Lance A. Waller ◽  
Uriel Kitron ◽  
J. Michael Bryan
Keyword(s):  
Public Health ◽  
Symptom Onset ◽  
The United States ◽  
Public Reporting ◽  
National Standards ◽  
Surveillance Data ◽  
Onset Date ◽  
Public Health Agencies ◽  
Starting Point ◽  
Health Agencies

More than a year after the first domestic COVID-19 cases, the United States does not have national standards for COVID-19 surveillance data analysis and public reporting. This has led to dramatic variations in surveillance practices among public health agencies, which analyze and present newly confirmed cases by a wide variety of dates. The choice of which date to use should be guided by a balance between interpretability and epidemiological relevance. Report date is easily interpretable, generally representative of outbreak trends, and available in surveillance data sets. These features make it a preferred date for public reporting and visualization of surveillance data, although it is not appropriate for epidemiological analyses of outbreak dynamics. Symptom onset date is better suited for such analyses because of its clinical and epidemiological relevance. However, using symptom onset for public reporting of new confirmed cases can cause confusion because reporting lags result in an artificial decline in recent cases. We hope this discussion is a starting point toward a more standardized approach to date-based surveillance. Such standardization could improve public comprehension, policymaking, and outbreak response. (Am J Public Health. 2021;111(12):2127–2132. https://doi.org/10.2105/AJPH.2021.306520 )

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