Beijing (CNN) -- The World Health Organization announced the launch of an international investigation into a new deadly strain of bird flu, as the total number of infections in China rose to 87.
"Right now it is still an animal virus that rarely infects humans," said Dr. Michael O'Leary, the head of the WHO's office in Beijing.
O'Leary said one of the goals of the mission is to determine the source of the H7N9 virus which was first discovered only three weeks ago.
Officials from the WHO, as well as experts from the U.S. and European Centers for Disease Control, are expected to investigate the virus alongside Chinese health authorities in Shanghai and Beijing in the coming days.
Five new infections of the H7N9 virus were recorded in Shanghai and nearby provinces of Jiangsu, Zhejiang and Henan.
On Thursday, the government suspended wild bird sales to try to prevent the spread of the virus, although many questions remain as to the source of infection. It follows a ban on live poultry trading in affected provinces. A large number of birds have also been slaughtered, Xinhua said.
In his statement to a room packed full of journalists, O'Leary said there was legitimate reason for concern about the new virus, but suggested it was premature to begin mass culling of poultry.
"I eat chicken every day," O'Leary said with a laugh. "Chicken is of no concern at all."
However, posts on the country's microblogging sites suggested that some users were anxious about going anywhere near poultry products.
"After H7N9, I don't even dare to eat an egg. I ate lunch box every day. I want poultry, and I want meat!!!" one wrote. Another said: "Jiaxing has H7N9 patient now, so nervous. I wasn't this nervous even during SARS."
But some were more relaxed about the potential risks: "Everyone should be careful, but I don't think it's that big deal. It's not that scary. In 2006 during another avian flu, I was in final year of high school and my parents sent me eggs every week. I ate a lot, but I'm still fine now."
Until March, the virus had only been present in birds, which is why they've become the focus of the investigation.
However, 40% of patients with H7N9 had not come into contact with poultry, according to the Chinese Center for Disease Control and Prevention.
The World Health Organization says at this stage there is "limited" evidence of human-to-human transmission.
Three clusters of infection have been identified. In each case, they involved family members living in close proximity. It was not clear whether relatives had transmitted the virus to each other, or whether they had been exposed to the same initial source of the illness.
"This becomes a different situation if the virus has human-to-human transmission," O'Leary said.
Authorities are monitoring more than 1,000 people who have come into close contact with confirmed cases.
One cluster of infection involved a family where a father and two sons fell ill.
The 87-year-old father died of the virus in March, followed soon after by his younger son. It hasn't been confirmed whether the son had the illness, according to Feng Zijian, director of the health emergency center of the Chinese Center for Disease Control and Prevention. Because he had died, further tests weren't possible, Feng added, during a press briefing on Wednesday.
The elder son was confirmed to have had the virus but has since recovered. He is one of five people who have been discharged from hospital after treatment, according to Xinhua.
So far, one boy is confirmed to have been an asymptomatic carrier of the virus, meaning he tested positive for the illness but didn't display any symptoms. The discovery of an asymptomatic carrier is worrying because it could make the spread of the infection more difficult to monitor, experts say.
The four-year old was part of a sweep of people tested for the illness because they'd come into close contact with the first reported case in Beijing.
Authorities took throat swabs from a group of people connected to 24 poultry farmers in Naidong Village, Cuigezhuang County in Beijing's Chaoyang District, according to the Beijing Municipal Health Bureau.
The WHO reported that of more than 80,000 birds tested in China, less than 40 had tested positive.
Unlike previous outbreaks of other strains of bird flu, none of the infected birds showed signs of being sick.