© Carlos Garcia Rawlins/Reuters

The new coronavirus has infected more men than women.

A recent study of more than 44,000 coronavirus cases found that men were also more likely to die of the virus.

Some researchers suspect that biological factors might make men more likely to contract the virus, but others have suggested that women are just as susceptible.

Smoking, a practice more common among men than woman in China, could be a risk factor as well. But more data is needed to confirm the theory.

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The deadly coronavirus that originated in Wuhan, China, has infected more men than women, and scientists are divided about why that is.

The virus, which causes a disease known as COVID-19, has killed more than 2,700 people and infected more than 80,000, with the vast majority of cases in mainland China. (For the latest case total and death toll, see Business Insider's live updates here.)

A study of more than 44,000 confirmed coronavirus cases in China offers one of the broadest pictures of how the virus operates in humans so far. The study found that men are more likely to die of the virus, with a fatality rate of 2.8% compared to 1.7% for women. Men also represented a slight majority of cases: around 51%.

Other recent research has produced similar results. A study of nearly 140 coronavirus patients at a Wuhan University hospital found that the virus was most likely to affect older men with preexisting health problems. More than 54% of the patients in the study were men, and the median age of patients was 56.

A study of 99 coronavirus patients at Wuhan Jinyintan Hospital showed that the average patient was 55.5 years old, and men represented around 68% of the total cases. A third study of nearly 1,100 coronavirus patients (which is still awaiting peer review) identified a median age of 47, with men representing around 58% of the cases.

This data has led some researchers to suspect that certain biological factors might make men more susceptible to the virus. But Chinese men also smoke more than Chinese women, which increases the risk of respiratory problems.

In the absence of much reliable, broad data about the new coronavirus, scientists have turned to a similar outbreak - the SARS pandemic from 2002 to 2003 - for clues.

SARS was also a coronavirus that jumped from animals to people in wet markets. It shares about 80% of its genome with the novel coronavirus, and SARS also infected more men than women.

© Reuters

In 2017, researchers at the University of Iowa infected male and female mice with SARS in order to investigate that gender disparity. Mouse studies don't necessarily have definitive implications for humans, but the researchers did find that male mice were more susceptible to the virus than female mice.

The team attributed those results to genes on the X chromosome and hormones such as estrogen that may keep a virus from spreading throughout the female body.

The researchers at Wuhan Jinyintan Hospital gave a similar explanation for why more of their coronavirus patients were men, suggesting that women may have a "reduced susceptibility" to viral infections. But they also said many patients with severe cases had chronic illnesses such as cardiovascular disease or diabetes. Those illnesses tend to affect middle-aged men more than middle-aged women.

Michael Ryan, executive director of the World Heath Organization's Health Emergencies Program, said on February 14 that smoking is "an excellent hypothesis" for why the virus has affected more men. A 2010 national survey of smoking in China found that 62% of Chinese men had been smokers at some point, while only 3% of Chinese women had ever smoked.

"There is a marked difference between male and females in this outbreak in terms of severity. And there's certainly a marked difference in those habits in China," Ryan said at a press conference. "I think it should be relatively straightforward to establish the science."

But the study of 140 coronavirus patients in Wuhan found that only 1.4% of them were current smokers, so more data is needed to determine whether smoking is a factor.

© Mark Schiefelbein/AP Photo

Ryan added, however, that smoking is a risk factor many types of lower respiratory-tract infections.

"We would expect it to be no different here," he said.

Saskia Popescu, an epidemiologist at the Honor Health medical group in Arizona, told Business Insider that anyone with a history of smoking could be more vulnerable to this coronavirus.

"Since COVID-19 is a respiratory disease and often causes pneumonia, having a history of smoking could increase the risk of more severe respiratory distress or pneumonia," she said.

Aaron Milstone, an epidemiologist at Johns Hopkins University, told Business Insider that he didn't think one subset of the population was necessarily more vulnerable than another.

"When we see any new virus, the whole population is susceptible," he said.

The study from Wuhan University suggested another explanation for the higher number of male patients: The outbreak is thought to have originated at the Huanan Seafood Wholesale Market in Wuhan, which had mostly male workers. The market was shuttered in early January.

The research also showed that the share of male and female coronavirus patients in the Intensive Care Unit was about the same as the share of male and female coronavirus patients in other parts of the hospital. That suggests men's symptoms so far aren't necessarily more severe than women's overall (though many patients are still hospitalized, so their conditions could change).

Milstone said any dataset from this coronavirus outbreak is still inherently limited, though.

"There can be underreporting because of under-testing, especially because this is not a commercially available test," Milstone said. "We don't know enough yet about what's happening."

Have you been personally affected by the coronavirus epidemic? Is your city or community on the front lines of this disease? Have you or someone you know been tested or diagnosed? We want to hear your story. Please email science+coronavirus@businessinsider.com.

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