NEW DELHI — Every year, as winter approaches and an acrid haze fills the sky, Jharna Sarkar fears for her health. This time, she's terrified.

The 66-year-old retiree suffers from asthma that is aggravated by the severe pollution in India’s capital. Now a virus that makes people struggle to breathe is stalking her family.

Sarkar’s son and older brother were both infected with the novel coronavirus. Although her son recovered, her brother died in October. This year is “particularly frightening,” she said.

Delhi is battling both toxic air and a record surge in coronavirus cases. Doctors and scientists say the combination will have deadly consequences, as exposure to pollution increases the risk of severe respiratory illnesses. Air pollution also makes people more prone to infections, they say.

India has recorded more than 8.7 million coronavirus cases, second only to the United States. While fresh cases nationwide have fallen sharply since September, Delhi is an exception to the trend.

The city is adding more than 7,000 cases a day, and that figure is expected to rise. More than 100 covid-19 deaths were reported in Delhi on Thursday, a record. Meanwhile, the number of open hospital beds equipped with ventilators is dwindling.

The fresh wave of cases comes as Delhiites have thronged markets and malls during India’s festival season. This past weekend marked the advent of Diwali, a major Hindu holiday, and public heath experts fear that celebratory gatherings could spread the virus.

Arvind Kejriwal, Delhi’s chief minister, appealed to city residents to observe the festival at home and banned the use of firecrackers, a traditional way of marking the holiday that also causes a spike in pollution.

The air quality in greater Delhi, home to 30 million people, has already deteriorated dramatically. Each autumn, when temperatures fall and wind speeds drop, a polluted smog settles over the city. Vehicle exhaust, construction dust, industrial emissions and crop burning in neighboring states all contribute to the mix.

Delhi just experienced five straight days of “hazardous” air quality, according to standards set by the U.S. Environmental Protection Agency. On Nov. 10, the level of particulate matter considered most harmful to human health briefly spiked to 30 times the safe limit prescribed by the World Health Organization. Such particles can lodge deep inside the lungs and have been linked to high blood pressure, heart disease, respiratory infections and cancer.

Researchers also believe that such pollutants contribute to a higher risk of death from covid-19. A recent study by scientists in Europe estimated that 15 percent of covid deaths worldwide could have been avoided if pollution levels were lower.

Air pollution leads to “greater vulnerability and less resilience to covid-19,” Thomas Münzel, a cardiologist and co-author of the paper, said in a statement.

The study also hypothesized that air pollution could play a role in spreading infections: It “seems likely that fine particulates prolong the atmospheric lifetime of infectious viruses, thus favoring transmission,” the researchers wrote.

Doctors in Delhi say the confluence of the pandemic and the bad air is daunting. “It will be a very difficult winter,” said Davinder Kundra, a pulmonologist at a private hospital in the city. The situation is “life-threatening.”

Dirty air inflames the linings of the windpipe and lungs, rendering people more susceptible to infections of all kinds, said Arvind Kumar, chairman of the Center for Chest Surgery at Sir Ganga Ram Hospital in Delhi. A community heavily affected by pollution will have “a higher chance of contracting covid and a higher chance of dying of covid.”

The bad air is also a challenge for those recovering from coronavirus infections. Ajeet Jain, a doctor at Rajiv Gandhi Super Specialty Hospital, a major covid treatment center, said the percentage of patients reporting post-infection respiratory problems has risen together with the pollution.

“My advice to them is, ‘Go to a place where the air quality is better,’ ” Jain said. “That is the first and foremost treatment. Leave this place, at least for a while.”

Some Delhiites who have contracted the coronavirus say they can feel the pollution making it worse. Nidhi Sabarwal Arora, 34, is a housewife whose entire family tested positive for the virus. She was asymptomatic until a day of particularly bad pollution last week. Then she became feverish.

“I definitely feel pollution is a culprit,” Arora said. She smelled smoke in her house, which is close to a major highway, and it seemed as if the air she was breathing was heavy.

For people like Sarkar, the retiree, every day of bad air quality is a struggle. She is coughing badly despite the medication she takes for her asthma. Wearing a mask is necessary but difficult, and she says the smell of sanitizer can trigger her condition.

She would like to be somewhere with cleaner air but doesn’t want to leave family behind and worries that many Indian cities now grapple with pollution.

“I often feel like we cannot live here,” Sarkar said, adding: “I do not know where I can go.”