They work by sharing anonymous Bluetooth beacons with nearby devices running the same software, tagging those that suggest extended and close contact associated with coronavirus spread, and saving the last 14 days of these records.
A positive test for COVID-19 in one of those states should include a code you enter into the app to upload its close-contact records to a health-authority server that then makes this anonymized data available to all these apps at their daily check-ins. If the app sees one of these reports match its saved list of close contacts, it warns of possible exposure and advises testing and quarantine.
18, 19 people had anonymously reported positive test results, but the department did not have a number for the number of exposure warnings sent to app users.
Emily Gurley, an epidemiologist with the Johns Hopkins Bloomberg School of Public Health in Baltimore, noted that these apps automatic estimates of close contacts ignore such nuances as whether a person was indoors or outdoors.
These apps also dont necessarily work across state lines, but help is coming from a nationwide server initiative launched by the Association of Public Health Laboratories, a Silver Spring, Md., group. North Dakota and Wyomings Care19 app already uses it and Virginias COVIDWISE will soon, said Jeff Stover, Virginia's Department of Health executive program advisor.
Original article