Hong Kong ( CNN ) -- A third man in China has died from the H7N9 virus , a strain of avian flu not previously detected in humans , the Zhejiang provincial department of health said Wednesday , according to state-run media outlet Xinhua . The disclosure of the third death comes only days after Chinese authorities announced the first three known cases of humans infected with the H7N9 bird flu virus on Sunday . The total number of people infected with H7N9 in China has risen to nine , Xinhua reported Wednesday . The death reported Wednesday was that of a 38-year-old man who passed away on March 27 in his home province of Zhejiang in eastern China , Xinhua reported . He worked in nearby Jiangsu province , where at least four other cases of humans infected with H7N9 were reported Tuesday . Two other people who died -- men aged 27 and 87 -- lived in nearby Shanghai , according to Xinhua . The World Health Organization confirmed those deaths Monday . Chinese authorities are trying to find the source of the human infections . They have so far said there are no signs of transmission of the H7N9 virus between any of the victims or people they have come into close contact with , suggesting the virus is n't highly contagious among humans . They have also dismissed suggestions linking the infections with the discovery of thousands of pig carcasses from the Huangpu River which runs through Shanghai . The Shanghai Animal Disease Prevention and Control Center on Monday tested 34 samples of pig carcasses pulled from the river and found no bird flu viruses , Xinhua reported . On Tuesday , the Jiangsu provincial health bureau reported four cases of H7N9 in humans : a 45-year-old woman from Nanjing , a 48-year-old woman from Suqian , an 83-year-old man from Suzhou , and a 32-year-old woman from Wuxi . The Nanjing woman worked culling poultry , it said . Malik Peiris , a professor at Hong Kong University 's School of Public Health , said Monday that the H7N9 strain of avian flu , already known to exist in wild birds , had probably been transmitted to poultry , and it infected the humans . `` It 's really important to understand where this virus is coming from , '' he said . Authorities in Shanghai are gathering daily data on cases of pneumonia resulting from unknown causes and will set up a team of experts to assess the `` severity and risk '' of H7N9 , Xinhua reported Tuesday . Since the transmission of these types of viruses from animals to humans is usually `` extremely inefficient , '' there are often tens of thousands of infected birds for every human case , according to Peiris . As a result , `` it is very likely that there is a quite widespread outbreak happening '' among the animals from which it came , he said , underscoring the urgent need to track down the source . The World Health Organization said Monday it was `` in contact with the national authorities and is following the event closely . '' Because there are so few cases of H7N9 detected so far , little research has been done , according to Xinhua . There are no known vaccines against this virus , it said . But Peiris said it was likely that existing anti-flu drugs , such as Tamiflu , are likely to work against the H7N9 strain . He also noted that the WHO has identified the H7 virus family as a potential threat and earmarked possible vaccine candidates . He said other strains from the H7 family had caused previous outbreaks in poultry in countries including the Netherlands , Britain , Canada , the United States and Mexico . Human infection was documented in all of those cases except the Mexican one . The outbreak of the H7N7 strain in the Netherlands in 2003 infected 89 people , one of whom died , according to Peiris . The better known H5N1 avian flu virus has infected more than 600 people since 2003 , of which 371 have died , according to the WHO . In February , China reported two new human cases of H5N1 in the southern province of Guizhou , both of whom were in a critical condition , the WHO said . A spike in H5N1 deaths , many of them children , has been reported in Cambodia , prompting concern among health authorities . READ MORE : 2 dead in China from unusual bird flu strain . READ MORE : New killer strain of bird flu in China not previously found in humans .
NEW : first man to die lived in China in eastern China , but worked in Jiangsu province . Announcement comes Monday after the Third two other cases -- and first two deaths -- were announced . Officials are trying to find the source of the infections .