The bird flu has struck again. Last week, the influenza virus H7N9 killed a medical worker in Shanghai.

According to the Shanghai Municipal Commission of Health and Family Planning, a 31-year-old man died on Jan. 18 from the H7N9 virus. The death is part of seven different cases of H7N9 infections this year, according to Bloomberg Businessweek.

"We need more evidence before increasing our level of concern," Ben Cowling, an associate professor of infectious disease epidemiology at the University of Hong Kong's school of public health, said about the death. "We know that there's always potential risk for health-care workers treating cases of H7N9 to be infected."

H7N9 was first found in humans in China in March. In April, reports of the illness increased, causing agriculture authorities to temporarily shut down live poultry markets. According to the World Health Organization (WHO), since the spike, there has been 199 laboratory-confirmed cases and 52 deaths.

"It's always a concern when health workers die," Gregory Hartl, a spokesman for the WHO in Geneva, said. "Hospitals and other medical facilities are a flash point for human-to-human transmission. We would be very much wanting to follow up in as much detail as possible on this case."

According to WHO, H7N9 is a subgroup of the avian influenza A H7 virus group. It is different from the infamous H1N1 in that H1N1 can be divided into viruses that typically infect people and viruses that typically infect animals. H7N9, on the other hand, is considered an animal influenza that can occasionally infect humans.

"...no human infections with H7N9 viruses have been reported until recent reports from the China," WHO says.

H7N9 has yet to cause widespread death in animals or birds as H1N1 has. TIME reports that the virus is not easily spreadable amongst humans but that it could be possible.

"Should sustained human-to-human transmission occur with an increased number of clinically severe cases, health systems are likely to be strained," WHO reports. "WHO is providing coordination and guidance regarding provisional vaccine candidates; there are currently no recommendations on the large-scale manufacture of H7N9 vaccine."

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