If there is one important piece of advice that Lt. Gov. Josh Green can tell Hawaii residents to help prevent the spread of the coronavirus, Dr. Anthony Fauci, the nation’s top infectious disease expert, said it would be to “wear a mask.”

“I’m serious. That’s it,” said Fauci toward the end of a 30-minute conversation with Green livestreamed on ‘Olelo Community Media early Wednesday morning. “There’s no doubt that that works. Wear a mask and try to avoid congregate settings — a whole bunch of people together, some of whom don’t have masks, crowded, indoors, is really bad news.”

Fauci, director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health and a member of the White House Coronavirus Task Force, also said Hawaii can revive its tourism- dependent economy if done prudently and carefully.

Other simple public health measures, he said, include keeping a distance and following the 6-foot rule, avoiding crowds and opting for activities outdoors rather than indoors, and washing your hands frequently.

“If we do those five things,” Fauci said, “we know from a number of studies, you will prevent surges and you will be able to get in a situation where you don’t have a large amount of community spread. We know that. It’s been proven.”

Fauci said the United States seemed well prepared prior to the onset of the coronavirus pandemic, but that “as it played out, we got hit worse than any other country in the world,” with more than 210,000 deaths and more than 7 million cases.

“If you look at where we are right now we’re stuck at 40,000 new infections each day,” he said. “That is what I call a baseline level that we need to get much, much lower than that. The reason I say that is, that in and of itself inherently is too high. We need to get down way below 10,000. Because when you’re that high there’s so much community spread that the standard ways of identification, isolation and contact tracing don’t work very well.”

Fauci said one of his concerns is that — with the exception of Hawaii — as fall and winter arrive, more people will be driven indoors, causing a respiratory disease such as COVID-19 to get worse.

An estimated 40% to 45% of people who are infected with the new coronavirus do not have symptoms, according to Fauci, and that causes a big problem in identifying who is spreading the infection in a community.

As for Hawaii’s new pre-travel testing program, which begins next week, he said he had no definitive answer on what to do.

Starting Oct. 15, visitors who get an approved negative test for COVID-19 within 72 hours of their departure to Hawaii will be able to bypass a mandatory, 14-day quarantine, according to Gov. David Ige, who greenlighted the program last month after numerous delays.

On Wednesday afternoon, Ige said the program would proceed, and include random testing of 10% of travelers four days after arrival to help determine its effectiveness. Mayors from neighbor isles, however, favor a follow-up test for travelers after their arrival to Hawaii, and can opt out of the program.

“The reality is no matter what you do, there are going to be infected people who slip through the cracks,” said Fauci. “It’s inevitable.”

Surveillance testing for travelers after they arrive in Hawaii is a possibility, he said, with special attention to those at greater risk, including college students coming back from hot spots. But Hawaii should be prepared, and take measures to prevent infection rates from surging up again.

Green said he favored strategic surveillance testing on high-risk travelers.

During the conversation, Green shared that he himself had just recovered from COVID-19 about a week ago.

Green said that he and a colleague, previously disclosed as a member of his security detail, were both masked while sharing a car. His colleague had no major symptoms other than a mild cough. But they took their masks off while sipping coffee, which Green said is how he caught it.

Fortunately, Green, 50, said he improved after two bad days of symptoms, but added that he has seen “terrible suffering from the disease” in the hospital.

Fauci clarified that the new coronavirus can be spread through aerosolized droplets, which can linger in the air for several minutes, particularly indoors, and possibly farther than 6 feet. There have been cases of people sitting on different ends of a restaurant who got infected, he said.

His advice is to wear a mask, conduct activities outdoors rather than indoors and, if indoors, to keep windows open.

People in Hawaii should be able to enjoy going to the beach, he said, with some precautions, such as staying in separate pods and wearing a mask when out of the water or when congregating.

“It’s much less of a risk,” he said, “but it is a risk if you’re congregating in a way where for prolonged periods of time, you’re really close together.”

On Wednesday, the state Health Department reported three additional coronavirus-related deaths, and 110 new infections statewide, bringing the totals since the start of the pandemic to 163 deaths and 13,045 cases.

Fauci said he was cautiously optimistic the U.S. will know whether it has a safe and effective vaccine for COVID-19 by November or December.