RIO DE JANEIRO — Two days until opening day, and the chef was sitting at a table outside the kitchen, feeling uncertain. He'd been cleared to leave the house after recovering from a coronavirus infection that almost anyone would describe as mild. But not for a chef.

When covid-19 came for Dudu Mesquita, who prepares menus for restaurants all over Brazil, it took away his sense of taste and smell. Five weeks later, they still weren’t back completely, and his doctors couldn’t say if they ever would be. He wondered what that might mean for him. For what is a chef who cannot taste?

Mesquita, 45, inspected a tomato sauce he’d made, but couldn’t quite taste. “I could do this,” he told himself. “But it would be without any satisfaction, without pleasure. Why would I do this if it’s not my passion?”

He began to cook, one more person in this disease-racked country reckoning with how the coronavirus has altered their life. The virus has exacted a devastating toll on Brazil, infecting more than 4.7 million people — more than 1 in 50. The vast majority have survived. But many are not the same. Even after the disease left them, residual damage has lingered, stripping from many their most cherished passions and pleasures.

Gabriela Montenegro, 33, who’d belted out church hymns every Sunday, now can’t sing: “Covid has changed everything.”

Roberto Godoy, a 42-year-old triathlete, doesn’t know when he’ll compete again: “Debilitating.”

But the sudden loss of taste and smell, the most distinct sign of a coronavirus infection, has proved particularly disorienting — and enduring. Studies haven’t determined how long it might last, but agree it could be a long time. Researchers in Italy found that around 20 percent of patients hadn’t recovered their smell within four weeks of the infection. A Brazilian survey suggested that 5 percent couldn’t smell or taste nearly three months later. The first reported coronavirus patient in Rio de Janeiro state still can’t taste a thing.

“It’s been gone since February 18th,” said Jeniffer Melgaço, 28. “I don’t have any hope it will come back. It’s been seven months, and I don’t have any sign it will get better.”

That uncertainty — plus the deprivation of a pleasure as basic as enjoying food — has driven thousands to Facebook support groups. Some are seeking out specialists in olfactology, until now a relatively niche field, as they try to cope with a loss few knew they could suffer.

“Other viruses have also been shown to do this,” said Fábio de Rezende Pinna, an otolaryngologist at the University of São Paulo. “But what surprises us is the high prevalence, and that people aren’t getting better.” Five percent might not seem like many, he said. But in a country approaching 5 million infections, “it’s a lot of people,” he said. “A lot.”

Scientists describe flavor as a finely harmonized duet of taste and smell. Taste is the blunter of the two, capable of discerning sweet, sour, bitter, salty and umami. But the melody, the subtleties — that all comes from smell. Aroma differentiates lime from lemon. It calls forth the robustness of coffee, the floral notes in wine.

Both senses are targets of the coronavirus, but smell is believed to be the more frequent victim. The disease lays siege to the supporting cells surrounding the olfactory bulb, causing inflammation even without congestion, and one half of the duet disappears.

“If you’re lacking the aroma, food becomes much less interesting,” said Steven D. Munger, director of the Center for Smell and Taste at the University of Florida. “People will either do one of two things. They may choose to eat less, and they lose weight. Or they go after foods that are more rewarding — heavier foods, with lots of salt, adding hot sauce to everything — to try to make food still interesting.”

For food professionals, who spend their lives exploring nuance and gradation in flavor, recourse is even more limited. Like a composer gone deaf or a painter rendered blind, they’re left to figure out how to perform a craft that’s based on a sense they no longer feel keenly — if at all.

“I don’t want to sound alarmist, but if I was a culinary professional, I would be very, very afraid,” said John Hayes, a food scientist at Penn State who has studied the palates of wine experts. “One out of five who get covid-related smell loss take longer than one month to recover their sense, and we don’t know if they will recover. If you’re a culinary professional, those are scary odds.”

Even scarier is actually losing it.

Marcos Lima, 51, a high-end sommelier in Rio de Janeiro, came down with covid-19 in May. For 20 days, he couldn’t taste or smell anything. Without any ­other income, he returned to work long before his sense of taste did. Even after he’d recovered around 70 percent of it, he found himself second-guessing everything. White wines were particularly challenging: He’d sip one and know it was more complex than he could sense. He began to wonder whether he could continue to do this work, and how he’d make his living without his sense of taste. His weekly wine tastings became nerve-racking.

“I have a very important tasting today,” he said this month. “On a day like today, nothing can go wrong.”

Nothing did. But what about the next one?

Thecla Oliosi, the lead chef at the Rio de Janeiro School of Gastronomy, couldn’t smell anything for four months — and did everything she could to hide it. Cooking became a mechanical process, muscle memory leading the way. People would taste the food, say how good something was, and she’d play along.

“I would say, ‘Oh, it is marvelous!’ ” she said. “But in reality, I couldn’t taste anything. I didn’t tell anyone. The only one who knew was my husband. If I’d told anyone, I was afraid they wouldn’t want to have my food.”

For four months, she waited. Then two weeks ago, she sat down to a breakfast she now recalls as a “miracle.” Her sense of smell had come surging back, bringing with it so many flavors she’d been worried she would never experience again.

It’s a moment that Jacilene dos Santos hopes will come soon. She has spent more than 30 years selling street food in the northeastern city of Salvador, which celebrates a flavorful cuisine influenced by Brazil’s African diaspora. But now she’s too scared to continue. Two months after contracting the coronavirus — it infected pretty much her entire family — her sense of smell is like a dulled blade. The other day, someone asked her to make the Brazilian dish moqueca, and she was ashamed.

“The smell is very strong” in the dish, she said. “But I didn’t smell anything. So I was putting more and more spices, thinking it was too weak. But the problem wasn’t the food. The problem was me.”

American chef Grant Achatz, whose Alinea restaurant in Chicago has earned three Michelin stars, lost his sense of taste after developing tongue cancer in 2007. He said it’s possible to cook without taste — he did, for a year before the sense returned — and even to become a better chef. He taught himself to use his other senses, and to rely more on other people.

“I was immature and arrogant and egocentric and wanted to do everything myself,” he said. “I had no choice but to trust the team even more, and that trusting and teamwork made the restaurant stronger.”

Some of the hardest moments, he said, were in the first discombobulating days.

That’s where Mesquita is now. In Brazil, he is known as Chef Dudu. He’s amassed nearly 100,000 followers on Instagram and appears frequently on television — an effusive tank of a man here to share not only his food but also his passion for it. Ever since he told his parents he didn’t want to become a doctor or lawyer — he wanted to be a chef — he’s thought only about cooking. Without the craft, he would have trouble recognizing himself.

“Chef,” an assistant said to him, bringing him out of his thoughts. It was time to cook. The restaurant would open soon, and they had little time to get the recipes right.

He stared down at the tomato sauce he couldn’t quite taste. He dipped in a spoon. He tilted the bin this way and that. Everything looked good.

He slathered it on a pizza dough.

“Chef,” the assistant said. “The sauce is very good.”

Mesquita smiled. All he could do was hope he was right.