Washington CNN  — 

Dr. Anthony Fauci cautioned states on Friday to rethink their reopening strategies if they see increases in the number of people hospitalized with Covid-19, adding that although he hasn’t spoken to President Donald Trump about next week’s campaign rally in Oklahoma, he is urging everyone who attends to wear a mask.

“When you start seeing more hospitalizations, that’s a surefire sign that you’re in a situation where you’re going in the wrong direction,” Fauci, the director of the National Institute of Allergy and Infectious Diseases, told CNN’s Wolf Blitzer on “The Situation Room” on Friday.

Many states have loosened restrictions that began in March to stop the spread of the virus. But the lack of a vaccine, as well as more people congregating in public places and recent protests for racial justice in major cities, has troubled experts. Since Memorial Day, the number of coronavirus hospitalizations has gone up in at least a dozen states, according to data CNN aggregated from the Covid Tracking Project from May 25 to June 9.

As states reopen, “you are going to see blips of infections” but identification, isolation and contact tracing are key, Fauci said Friday. He also warned states not to skip over some of the reopening guidelines the federal government has outlined.

“If you leapfrog over different phases, you increase the risk that you’re going to have the kind of resurgences that we’re seeing in certain of the states,” he said.

Fauci, a member of the White House coronavirus task force, said he hasn’t spoken with Trump about his rally planned for Tulsa, Oklahoma, next week, where attendees must agree not to sue the campaign if they contract coronavirus. But late on Friday – after Fauci’s interview – Trump pushed the rally back a day to June 20.

Fauci had said his suggestions about the pandemic still “hold true.”

“The best thing to do is to avoid crowded areas. But if you’re not going to do that, please wear a mask,” he said.

This story has been updated to reflect that the date of Trump’s rally was moved after Fauci’s interview.