Skip to main navigation menu Skip to main content Skip to site footer

Commentary

Vol. 20 No. 2 (2022): New Horizons: Innovation in Medicine

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

DOI
https://doi.org/10.26443/mjm.v20i2.901
Submitted
May 25, 2021
Published
2022-04-19

Abstract

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.

References

  1. Rosenberg PS. Epidemic Curve. In: Wiley StatsRef: Statistics Reference Online. Hoboken, NJ: John Wiley & Sons; 2015. Available from: https://doi.org/10.1002/9781118445112.stat05266.pub2
  2. Kermack WO, McKendrick AG, Walker GT. A contribution to the mathematical theory of epidemics. Proceedings of the Royal Society of London Series A, Containing Papers of a Mathematical and Physical Character. 1927 Aug 1;115(772):700–21. Available from: https://doi.org/10.1098/rspa.1927.0118
  3. Farr W. Report on the mortality of cholera in England, 1848-49. London: Her Majesty’s Stationary Office; 1852.
  4. Fraser DW, Tsai TR, Orenstein W, Parkin WE, Beecham HJ, Sharrar RG, et al. Legionnaires’ Disease: Description of an Epidemic of Pneumonia. N Engl J Med. 1977 Dec 1 [cited 2020 Oct 23];297(22):1189–97. Available from: https://doi.org/10.1056/NEJM197712012972201
  5. Jones DS, Helmreich S. The Shape of Epidemics. Boston Review. 2020 Jun 26 [cited 2020 Sep 21]. Available from: https://bostonreview.net/science-nature/david-s-jones-stefan-helmreich-shape-epidemics
  6. Public Health Agency of Canada. COVID-19 daily epidemiology update. 2021 [cited 2021 Sep 19]. Available from: https://health-infobase.canada.ca/covid-19/epidemiological-summary-covid-19-cases.html
  7. Government of the United Kingdom. Coronavirus (COVID-19) in the UK: Cases. 2020 [cited 2020 Sep 21]. Available from: https://coronavirus.data.gov.uk/cases
  8. Dong E, Du H, Gardner L. An interactive web-based dashboard to track COVID-19 in real time. The Lancet Infectious Diseases. 2021 May [cited 2020 Apr 3];20(5):533–4. Available from: https://doi.org/10.1016/S1473-3099(20)30120-1
  9. State of Michigan. Coronavirus - Michigan Data. 2021 [cited 2021 Jan 16]. Available from: https://www.michigan.gov/coronavirus/0,9753,7-406-98163_98173---,00.html
  10. CTV News. Tracking every case of COVID-19 in Canada. CTV News. 2021 Jan 16 [cited 2021 Jan 16]. Available from: https://www.ctvnews.ca/health/coronavirus/tracking-every-case-of-covid-19-in-canada-1.4852102
  11. The COVID Tracking Project. The COVID Tracking Project. 2020 [cited 2020 Sep 21]. Available from: https://covidtracking.com/
  12. Berry I, Soucy J-PR, Tuite A, Fisman D. Open access epidemiologic data and an interactive dashboard to monitor the COVID-19 outbreak in Canada. CMAJ. 2020 Apr 14 [cited 2020 Apr 13];192(15):E420. Available from: https://doi.org/10.1503/cmaj.75262
  13. Ontario Agency for Health Protection and Promotion (Public Health Ontario). COVID-19 regional incidence and time to case notification in Ontario. Toronto, Canada: Queen’s Printer for Ontario; 2020 [cited 2020 Sep 21]. Available from: https://www.publichealthontario.ca/-/media/documents/ncov/epi/covid-19-regional-epi-summary-report.pdf?la=en
  14. Ontario Agency for Health Protection and Promotion (Public Health Ontario). iPHIS User Guide: Enteric and Zoonotic Diseases. Toronto, Canada: Queen’s Printer for Ontario; 2019 [cited 2020 Sep 21]. Available from: https://www.publichealthontario.ca/-/media/documents/i/2019/iphis-user-guide-enteric-zoonotic.pdf?la=en
  15. City of Toronto. COVID-19: Status of Cases in Toronto. City of Toronto; 2020 [cited 2020 Sep 21]. Available from: https://www.toronto.ca/home/covid-19/covid-19-latest-city-of-toronto-news/covid-19-status-of-cases-in-toronto/
  16. BC Centre for Disease Control. British Columbia Weekly COVID-19 Surveillance Report: September 11–September 17, 2020. 2020 [cited 2020 Sep 21]. Available from: http://www.bccdc.ca/Health-Info-Site/Documents/BC_Surveillance_Summary_Sept_17_2020.pdf
  17. Mississippi State Department of Health. Coronavirus COVID-19. 2021 [cited 2021 Jan 7]. Available from: https://msdh.ms.gov/coronavirus
  18. Ohio Department of Health. COVID-19 Dashboard. 2021 [cited 2021 Jan 16]. Available from: https://coronavirus.ohio.gov/wps/portal/gov/covid-19/dashboards/overview
  19. Ottawa Public Health. Daily COVID-19 Dashboard. 2020 [cited 2020 Sep 21]. Available from: https://www.ottawapublichealth.ca/en/reports-research-and-statistics/daily-covid19-dashboard.aspx
  20. San Diego County. Daily COVID-19 Data Update 2021-1-6. 2021 [cited 2021 Jan 7]. Available from: https://www.sandiegocounty.gov/content/dam/sdc/hhsa/programs/phs/Epidemiology/COVID-19_Daily_Status_Update.pdf
  21. Wooten N. COVID-19 data from Georgia’s Department of Health could be ‘misleading,’ experts say. Ledger Enquirer. 2020 May 5 [cited 2020 Sep 22]. Available from: https://www.ledger-enquirer.com/news/coronavirus/article242416536.html
  22. Rodriguez B. University of Iowa researchers warn “a second wave of infections is likely” if COVID-19 prevention efforts are lifted. Des Moines Register. 2020 April 28 [cited 2020 Sep 22]. Available from: https://www.desmoinesregister.com/story/news/health/2020/04/28/university-iowa-researchers-warn-kim-reynolds-administration-second-coronavirus-wave/3040849001/
  23. Bacchetti P. Back-Calculation. In: Wiley StatsRef: Statistics Reference Online. Hoboken, NJ: John Wiley & Sons; 2014. Available from: https://doi.org/10.1002/9781118445112.stat05058
  24. Finger F, Funk S, White K, Siddiqui MR, Edmunds WJ, Kucharski AJ. Real-time analysis of the diphtheria outbreak in forcibly displaced Myanmar nationals in Bangladesh. BMC Medicine. 2019 Mar 12 [cited 2020 Jul 12];17(1):58. Available from: https://doi.org/10.1186/s12916-019-1288-7
  25. Brookmeyer R, Gail MH. Minimum Size of the Acquired Immunodeficiency Syndrome (AIDS) Epidemic in the United States. The Lancet. 1986 Dec 6 [cited 2021 Sep 20];328(8519):1320–2. Available from: https://doi.org/10.1016/s0140-6736(86)91444-3
  26. Centers for Disease Control and Prevention. Technical Notes: Provisional Death Counts for Coronavirus Disease (COVID-19). 2020 [cited 2020 Sep 21]. Available from: https://www.cdc.gov/nchs/nvss/vsrr/covid19/tech_notes.htm
  27. Walker P. Is There a Right Way to Chart COVID-19 Deaths Over Time? The COVID Tracking Project. 2020 [cited 2020 Sep 21]. Available from: https://covidtracking.com/blog/is-there-a-right-way-to-chart-covid-19-deaths-over-time
  28. Mathieu E. Why do COVID-19 deaths in Sweden always appear to decrease in the last 10 days? Our World in Data. 2020 [cited 2021 Jan 7]. Available from: https://ourworldindata.org/covid-sweden-death-reporting

Downloads

Download data is not yet available.