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Chinese health officials have also identified a 4-year-old bird flu "carrier" with no symptoms of the H7N9 virus, although human-to-human spread has yet to be confirmed.
China has identified bird flu victims who had no previous exposure to poultry, although it's still unknown how these people became infected in the first place.
Further, a 4-year-old Chinese child has been identified as a symptom-free carrier of H7N9, after 24 poultry owners were screened for the virus in the Chaoyang District of Beijing.
Read more from GlobalPost: China media urge eating poultry despite bird flu
"This is one of the puzzles still (to) be solved and therefore argues for a wide investigation net," said World Health Organization spokesman Gregory Hartl said to Reuters of the unexposed bird flu victims, though he added he did not know the exact percentage.
The Beijing News newspaper reported on Tuesday that 40 percent of bird flu sufferers had not been exposed to poultry, wrote Forbes.
Bird flu cases continue to increase, wrote Xinhua, with 14 new cases of H7N9 reported on Tuesday alone. A total of 77 cases have now been reported, with 16 deaths. 30 of these cases have been reported in the city of Shanghai.
The infected 4-year-old boy, known as Zhu, is the second case of H7N9 and the first symptomless carrier, wrote CNN, which added that the boy's parents were involved in trading live poultry.
The boy is under medical observation, reports Bloomberg, which added that his case was caught as authorities investigated neighbors of a 7-year-old girl who recently came down with the virus.
It remains unknown if H7N9 is transmissible between humans, but these two recent developments are worrisome to health officials, who are concerend that more cases could be asymptomatic.
"It really depends on whether this H7N9 virus is transmissible between humans ... that key question needs to be answered," said Dr. Leo Poon Lit-man of University of Hong Kong's School of Public Health to CNN.
"If it can (transmit human to human), then it's a very different scenario -- we would not be able to detect asymptomatic carriers and that would be a huge problem," Poon added to CNN.