How Will We Know When the COVID-19 Pandemic is Getting Better?

Kenny Lin, MD
Mar 27, 2020 · 10 min read
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https://www.nytimes.com/interactive/2020/world/coronavirus-maps.html

A guide to interpreting COVID-19 data

With the endless stream of headline-grabbing numbers and figures being reported about the COVID-19 pandemic, it is easy to lose sight of what we might learn from the data. As a physician, I believe decisions must be guided by science and data, and for that we must understand data in context. Ultimately, we are all desperately hoping to see signs that the COVID-19 pandemic might be improving.

  1. How do limitations on testing affect the data?
  2. How can we tell if social distancing is working?
  3. What is not being reported?
  4. What kind of data should we be asking for?
  5. What are the signs that an outbreak has been contained?

Principles for interpreting COVID-19 data

1. Look for trends and patterns
Drawing conclusions from a single data point is one of the easiest mistakes to make. Because day-to-day variations in testing or reporting remains unpredictable — for example, testing capacity is often reduced over the weekend — we must be prudent to verify a trend over several days. I suggest using at least a 3-day running average on daily data to smooth out the variance. In the figure below showing daily cases in Italy, you may have preemptively concluded that the epidemic peaked after seeing declines on Mar. 10 or Mar. 13. While we cannot predict the future, using a 3-day running average makes trends easier to identify.

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Data as of 3/26/20 from https://www.worldometers.info/coronavirus/country/italy/
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Data as of 3/25/20 from https://www.worldometers.info/coronavirus/country/italy/
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Data as of 3/25/20 from https://www.worldometers.info/coronavirus/country/italy/
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Data as of 3/25/20 from https://www.worldometers.info/coronavirus/country/italy/
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Data as of 3/25/20 from Politico
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Source: Robert Williams @isfBob, updated March 26
  1. The denominator (cases) depends on the number of diagnosed cases, which is limited by testing. As testing is prioritized for the sickest patients, current mortality rates will likely be an over-estimate.
  2. Keep in mind that deaths trail diagnosis by a period of 5–7 days. In other words, a patient who dies today was likely diagnosed 5–7 days ago — so the mortality rate based on current data does not factor in those who were recently diagnosed and are still being treated. This effect causes the reported mortality rate to be an under-estimate. The figure below shows this 5 day delay between case and deaths in Italy.
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Data as of 3/24/20 from https://www.worldometers.info/coronavirus/country/italy/

What are the signs that an outbreak has been contained?

1. Decrease in rate of growth of daily cases (flattening of the logarithmic curve).
This will be the earliest sign that the spread of COVID-19 is slowing. We hope to see this approximately 2–3 weeks after social distancing measures are enacted. We are starting to see this sign in Italy’s logarithmic curve but not yet in the United States.

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Kenny Lin, MD

Written by

Otolaryngologist; former resident at New York Presbyterian Hospital. All views my own.

The Startup

Medium's largest active publication, followed by +773K people. Follow to join our community.

Kenny Lin, MD

Written by

Otolaryngologist; former resident at New York Presbyterian Hospital. All views my own.

The Startup

Medium's largest active publication, followed by +773K people. Follow to join our community.

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