Epidemic (Epi) Curves for Coronavirus COVID-19

Updated: March 29, 2020 21:15 EDT

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COVID-19 Epidemic Curves for Selected Countries

Animated COVID-19 Epidemic Curves for Six Selected Countries: March 15–29

COVID-19 Animated Epidemic Curves for Six Selected Countries

COVID-19 Epidemic Curves for six countries (China, Iran, S. Korea, Italy, United States, and Japan) showing the period March 15–29. Note that the left axis is logarithmic rather than linear and represents the cumulative number of cases reported to WHO by each country. The availability of COVID-19 testing and speed of reporting cases to WHO influence the slope of each line, especially in the initial days of reporting. However, the overall slope of the line in the epidemic acceleration phase (compare Japan to others) and the time of graph "flattening" (compare S. Korea to others) are areas that are influenced by public health measures.

Data source: World Health Organization Situation Reports.[1] Inspired by Our World in Data.[2]

Graph by: Unbound Medicine

What is an Epidemic (Epi) Curve?

  • An epidemic curve, also known as an epi curve or epidemiological curve, is a statistical chart used to visualize the onset and progression of a disease outbreak.[3]
  • Epi curves typically display a graph of the onset of illness among cases in an outbreak. In a point-source outbreak of a known disease, for instance, an epi curve can identify the most likely time period of exposure that led to the outbreak.
  • For the COVID-19 outbreak, major agencies display cases differently:
    • World Health Organization (WHO) – show graphs based on the date of case reporting.[1]
    • US Centers for Disease Control (CDC) display cases by onset of illness. For COVID-19 the CDC has also started to report cases based on date reporting.[4]

Flattening the Epidemic Curve

Flattening the COVID-19 Epidemic Curve
Flattening the COVID-19 Epidemic Curve

See below for explanation.

Source: US Centers for Disease Control (CDC), adapted by Unbound Medicine.

  • Without speedy and coordinated public health actions such as rapid testing, isolation of cases, "social distancing" and stay-at -home policies, the number of COVID-19 cases could rise beyond the capacity of the healthcare system to handle severe cases (see red curve in relation to healthcare system capacity line in figure above). This occurred in Wuhan, China and is happening now in parts of Italy.
  • The goal is to "flatten" the curve (green curve above) – reduce the daily rate of new cases so that the number of severe cases can be handled effectively by the healthcare system.
  • Note that public health actions taken to "flatten the curve" do not guarantee the reduction in total number of cases during a pandemic. That will be determined by additional factors such the speed by which other effective prevention measures (e.g., vaccines) are developed.

Global Epidemic Curve for COVID-19

COVID-19 Global Epidemic Curve - March 29 (WHO)
Global Epi Curve for COVID-19 (WHO)

Epidemic curve of confirmed COVID-19 cases by WHO Region. Graph shows cases by date of case reporting through 29 March 2020.

Source: Coronavirus disease (COVID-2019) situation reports. World Health Organization.[1]

World Health Organization Regions
WHO Regions

WHO Member States are grouped into six regions. Each region has a regional office. The map shows the WHO regions and the location of the regional offices.

U.S. Epidemic Curve for COVID-19

COVID-19 USA Epidemic Curve - March 28 (CDC)
Coronavirus Epi Curve in the US

Epidemic (Epi) Curve for COVID-19 in the United States - through March 28, 2020. Graph shows cumulative cases based on date of reporting.

*Does not include cases among persons repatriated to the United States from Wuhan, China and Japan.

† Numbers updated Saturday and Sunday are not confirmed by state and territorial health departments. These numbers may be updated when the official numbers are provided on Monday.

Source: Coronavirus COVID-19 Cases in the United States. US Centers for Disease Control.[4]

Infographics and Tutorials

Infographic | Flattening the Epidemic Curve
Flattening the COVID-19 Epidemic Epi Curve Infographic

Slowing the spread of the virus can reduce the chance of infection among high-risk populations and reduce the acute burden on healthcare systems and workers.

Sources: Community Mitigation Guidelines to Prevent Pandemic Influenza.[5] WHO Situation Reports.[1]

Infographic: Unbound Medicine

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References

  1. Coronavirus Disease 2019 (COVID-19) Situation Reports. World Health Organization. [https://www.who.int…]
  2. Total confirmed cases of COVID-19. Our World in Data. [https://ourworldindata.org…]
  3. Interpretation of Epidemic (Epi) Curves during Ongoing Outbreak Investigations. US Centers for Disease Control and Prevention. [https://www.cdc.gov…]
  4. Coronavirus Disease 2019 (COVID-19) in the U.S. United States Centers for Disease Control and Prevention. [https://www.cdc.gov…]
  5. Qualls N, Levitt A, Kanade N, et al. Community Mitigation Guidelines to Prevent Pandemic Influenza - United States, 2017. MMWR Recomm Rep. 2017;66(1):1-34.  [PMID:28426646]
  6. Quick-Learn Lesson: Create an Epi Curve. US Centers for Disease Control and Prevention. [https://www.cdc.gov…]