Incidence & epidemic curve

Methods for the two-week cumulative incidence map and the epidemic curve map are based on guidance from the CDC. National-level maps can be accessed here

Two-Week Cumulative Incidence Rate

The two-week cumulative incidence rate summarizes new cases reported in the past two weeks per 100,000 people. It looks at recent incidence to capture the potential burden of currently ill people who may be infectious and/or currently accessing healthcare. 

The sum of each region’s number of reported cases in the past two weeks (in other words, the difference between the total number of cases from two weeks ago from the current total number of cases) is divided by that region’s population. The resulting rate is multiplied by 100,000 to get a two-week cumulative incidence rate per 100,000 people.

  • Low: There have been 10 or fewer new cases per 100,000 people in the past two weeks.
  • Moderate: There have been between 10 and 50 new cases per 100,000 people in the past two weeks.
  • Moderately high: There have been between 50 and 100 new cases per 100,000 people in the past two weeks.
  • High: There have been more than 100 new cases per 100,000 people in the past two weeks.

Current Epidemic Curve

The current epidemic curve categorizes counties into phases of the epidemic curve based on two-week incidence and recent slope. It provides a more detailed view into the burden of illness and the trajectory of new illnesses. 

Counties are categorized based on (1) the number of new cases per 100,000 in the past two weeks, and (2) the trajectory of the three-day moving average daily incidence per 100,000. By hovering over each region, you can see a figure detailing how three-day moving averages of daily incidence and the corresponding phase of the epidemic curve have changed over the past month. 

The ‘Two-Week Cumulative Incidence Rate’ section above details how the number of new cases per 100,000 in the past two weeks is calculated for each region.

Three-day moving average daily incidence rates per 100,000 are calculated for each region by first totalling the number of new cases by date reported to the state. The total number of cases reported on each day is divided by each region’s population, and multiplied by 100,000 to get a daily incidence rate per 100,000 people. The three-day moving average is the mean of daily incidence rates per 100,000 for the current and past two days. 

  • Low incidence growth: There have been ten or fewer new cases per 100,000 in the past two weeks. Incidence is low, but increasing.
  • Elevated incidence growth: There have been more than ten new cases per 100,000 in the past two weeks. Incidence is high and increasing.
  • Elevated incidence plateau: There have been more than ten new cases per 100,000 in the past two weeks. Incidence is high and remaining stable.
  • Sustained decline: Incidence is consistently decreasing. 
  • Low incidence plateau: There have been ten or fewer new cases per 100,000 in the past two weeks. Incidence is low and remaining stable.

Region-Specific Incidence

For regions with >5 cases in the past two weeks, a smoothing trend line was fit to three-day moving average incidence by date reported to the state. 

The magnitude and direction of change of the smoothing trend line is shown below incidence. This line describes the changes that are occurring in the above smoothing trend line.

 

Access the incidence data files 

 

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