On Tuesday, China’s National Health Commission (NHC) reported the first human case of H10N3 bird flu in the city of Zhejiang, China, according to Live Science.

The NHC website says the H10N3 strain of avian influenza causes mild disease in birds, and until now, there were no human cases of the viral infection.

However, on April 23, a 41-year-old man in the city of Zhenjiang developed a fever that progressed over the following days, and on April 28, he went to a local hospital for treatment, per Live Science.

Bird flu or avian flu is a common illness in wild aquatic birds and can infect domestic poultry and other bird and animal species, according to the U.S. Centers for Disease Control and Prevention (CDC). However, the virus does not normally infect humans, but these crossover infections do happen.

The agency says infected birds shed avian flu in their saliva, mucus, and poop, and humans can get infected when the virus gets in the eyes, nose, or mouth, or is inhaled from infected droplets or dust.

The NHC statement said on May 38, the Chinese Center for Disease Control and Prevention (CCDC) performed a genetic analysis on specimens from the infected man and determined he was infected with H10N3.

The Chinese health agency then monitored the surrounding province of Jiangsu for additional cases of bird flu and specifically sought out the man’s close contacts. However, no additional cases were discovered.

According to the statement, the infected man is now in stable condition and ready for discharge from the hospital.

Filip Claes, Regional Laboratory Coordinator, Food and Agriculture Organization of the United Nations, told Reuters, “Scientists will need to thoroughly examine the genetic material of the strain that infected the man to see how it differs from H10N3 samples collected in the past.”

He explained that H10N3 generally doesn’t crop up very often in its natural hosts, birds.

“From the late 1970s to 2018, scientists isolated about 160 samples of the viral strain from infected animals, mostly from wild birds and waterfowl, and the strain hadn’t been detected in chickens, Claes noted.

The CCDC did not specify how or when the infected man may have picked up the virus from a bird, according to Reuters. But the agency noted that there is little risk of the virus spreading on a large scale.

The U.S. CDC says, “When avian influenza viruses make the leap from birds to humans, they usually don’t spread between humans, and when they do, their transmission is typically ‘limited, inefficient and not sustained.’”

It is important to monitor new cases of the infection in humans because although rare, avian flu could spark major outbreaks among people.

The last bird flu outbreak in humans was associated with the H7N9 virus, which killed more than 300 people from 2016 to 2017, according to Science magazine.

The H7N9 virus strain has a fatality rate of about 40%, according to CDC’s Morbidity and Mortality Weekly Report.

Live Science previously reported that earlier this year, Russian health officials reported the first human cases of an avian influenza virus called H5N8, which passed from poultry to humans.

Experts have expressed their concern over the first case of the H10N3 virus.

Infectious disease specialists Dr. Amesh Adalja of Johns Hopkins Center for Health Security said, “It’s a critical barrier for an avian virus to cross. Only a small subset of avian flu viruses can do this,” according to prevention.com.

Another infectious disease expert Dr. William Schaffner of Vanderbilt University School of Medicine said, “The big concern is whether a particular strain of bird flu that’s in humans has the capacity to readily be transmitted from person to person. If it had that capacity, it would be the setting for a pandemic of influenza.”