Contents

ENExposureConfiguration

The object that contains parameters for configuring exposure notification risk scoring behavior.

Declaration

class ENExposureConfiguration

Mentioned in

Overview

The ExposureNotification framework defines an Exposure Risk Value (ERV) to allow Health Authorities to define when to alert a user that they may have been exposed to someone diagnosed with COVID-19. The app uses the ERV to calculate the user’s Meaningful Exposure Minutes (MEMs) value. Health Authorities have flexibility in calculating this value by setting weights and values related to Bluetooth attenuations, infectiousness of the affected individual, and diagnosis report type. They can also determine what threshold will result in a notification.

The calculation method described in this document is available starting with iOS 14. To adopt this method of risk assessment, set the ENAPIVersion key to the integer value 2 in the app’s Info.plist file. For more information on the V1 calculation used in earlier versions of iOS, see Exposure Risk Value Calculation in ExposureNotification Version 1.

The following diagram shows how to calculate an ERV:

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The class defines three sets of weights that give priority to the components of the ERV: minutes-at-attenuation, infectiousness, and report type.

The weighted minutes-at-attenuation assigns priority to the amount of time that the user is near beacons at different Bluetooth attenuations. Assign values between 0–250 percent to weights that represent Immediate, Near, Medium, and Other distances.

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The infectiousness weight modifies the ERV based on the affected userʼs infectiousness level for the day of exposure relative to the day of symptom onset. To set the infectiousness level for when there is no symptom onset date provided, use ENDaysSinceOnsetOfSymptomsUnknown. A user’s infectiousness level can be ENInfectiousness.high, ENInfectiousness.standard, or ENInfectiousness.none. Assign both infectiousnessHighWeight and infectiousnessStandardWeight a value between 0 percent and 250 percent.

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The weighted report type assigns priority to the method of diagnosis. Assign values ranging from 0–250 percent to weights that represent a confirmed test diagnosis, clinical diagnosis, self- reported diagnoisis, and recursive diagnosis.

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In addition to setting the weights, you can perform additional filtering by setting daysSinceLastExposureThreshold to limit the number of days to consider when calculating the risk level.

Calculating an Example Exposure Risk Value

The following diagrams illustrate calculating an ERV using a real-world scenario.

The weighted minutes-at-attenuation shows 5 minutes of immediate exposure with a 150 percent weight, 10 minutes of near exposure with a 100 percent weight, 10 minutes of medium exposure with a 50 percent weight, and 5 minutes of other exposure with a 0 percent weight.

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The weighted infectiousness indicates days –14 to –6 from the current day with no infectiousness, days –5 to –3 with 100 percent of standard infectiousness, days –2 to +5 with 200 percent high infectiousness, days +6 to +10 with 100 percent standard infectiousness, and days +11 to +14 with no infectiousness.

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Here are the weighted report types for all three tests:

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The result of the calculation shows an ERV of 45 minutes:

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Topics

Configuring Duration

Configuring Infectiousness

Configuring Report Types

Determining Exposure Risk Level in Version 1

See Also

Exposures