How long before we know if reopenings cause COVID-19 spikes?

FILE - In this Wednesday, May 13, 2020 file photo, Sheila Kelly, owner of Powell's Steamer Co. & Pub, center, stands behind makeshift barriers as she helps patrons at her restaurant in the El Dorado County town of Placerville, Calif. It was the first day Kelly was serving in-dining meals since the state's lockdown order to slow the spread of the coronavirus. El Dorado County was one of the first counties to win approval from the state to reopen for dining-in. (AP Photo/Rich Pedroncelli) FILE - In this Wednesday, May 13, 2020 file photo, Sheila Kelly, owner of Powell's Steamer Co. & Pub, center, stands behind makeshift barriers as she helps patrons at her restaurant in the El Dorado County town of Placerville, Calif. It was the first day Kelly was serving in-dining meals since the state's lockdown order to slow the spread of the coronavirus. El Dorado County was one of the first counties to win approval from the state to reopen for dining-in. (AP Photo/Rich Pedroncelli)

By CARLA K. JOHNSON / AP Medical Writer May 15, 2020 2 min read

U.S. states and countries worldwide are cautiously relaxing restrictions while watching for potential spikes in coronavirus infections. Getting the timing right is complicated. Disease trackers note the impossibility of seeing clearly what’s happening without widespread testing.

A look at when we might start to see any health impacts of reopening:

WHEN ARE WE GOING TO KNOW?

The virus can circulate undetected, then flare up in a nursing home or after a family gathering. So it could be several weeks to see surges in infections. What’s more, there are still new infections happening now during lockdowns. Some parts of the U.S. are seeing increasing numbers of daily new cases and some are seeing declines. Health officials will be looking at the number of new cases per day and the percentage of positive COVID-19 tests.

WHY DOES IT TAKE THAT LONG?