A janitor sprays disinfectant over empty chicken cages at a market in New Taipei City, Taiwan, on Monday, April 29. Asian countries have stepped up vigilance against the spread of H7N9 bird flu after a case of the deadly strain showed up in Taiwan, the first outside mainland China.
Bird flu scare spreads —
A janitor sprays disinfectant over empty chicken cages at a market in New Taipei City, Taiwan, on Monday, April 29. Asian countries have stepped up vigilance against the spread of H7N9 bird flu after a case of the deadly strain showed up in Taiwan, the first outside mainland China.
Mandy Cheng/AFP/Getty Images
A New Taipei City Department of Environmental Protection truck sprays a virus disinfectant in a park on April 29.
Bird flu scare spreads —
A New Taipei City Department of Environmental Protection truck sprays a virus disinfectant in a park on April 29.
PICHI CHUANG/Reuters /Landov
Doctors hold a consultation on the treatment for a patient surnamed Luo, the province's first human case of H7N9 avian influenza, at the No. 2 Hospital in Longyan City, in southeast China's Fujian Province, on April 27. Luo, 65, a local resident, showed symptoms of repeated coughing, low fever and a tight chest on April 18. Luo tested positive for the H7N9 virus on Friday by the Chinese Center for Disease Control and Prevention. Thirty-seven people who have been in close contact with Luo have not shown any abnormal symptoms so far.
Bird flu scare spreads —
Doctors hold a consultation on the treatment for a patient surnamed Luo, the province's first human case of H7N9 avian influenza, at the No. 2 Hospital in Longyan City, in southeast China's Fujian Province, on April 27. Luo, 65, a local resident, showed symptoms of repeated coughing, low fever and a tight chest on April 18. Luo tested positive for the H7N9 virus on Friday by the Chinese Center for Disease Control and Prevention. Thirty-seven people who have been in close contact with Luo have not shown any abnormal symptoms so far.
WEI PEIQUAN/Xinhua/Landov
A vendor stands by her chicken coop in Fuqing, southeast China's Fujian Province on April 26. At least 20 people have died from the virus which, while common in birds, hadn't been detected in humans before the first cases were reported in March.
Bird flu scare spreads —
A vendor stands by her chicken coop in Fuqing, southeast China's Fujian Province on April 26. At least 20 people have died from the virus which, while common in birds, hadn't been detected in humans before the first cases were reported in March.
ZHANG GUOJUN/Xinhua /Landov
A woman wearing a medical mask walks past vending machines that sell masks outside National Taiwan University Hospital in Taipei on April 26. A 53-year-old Taiwanese businessman has contracted the H7N9 strain of bird flu while traveling in China, Taiwan's Health Department said on April 24. It's the first reported case outside of mainland China. The man was hospitalized after becoming ill three days after returning from Suzhou on April 9.
Bird flu scare spreads —
A woman wearing a medical mask walks past vending machines that sell masks outside National Taiwan University Hospital in Taipei on April 26. A 53-year-old Taiwanese businessman has contracted the H7N9 strain of bird flu while traveling in China, Taiwan's Health Department said on April 24. It's the first reported case outside of mainland China. The man was hospitalized after becoming ill three days after returning from Suzhou on April 9.
PICHI CHUANG/Reuters /Landov
Disease control workers examine a chicken in a poultry farm in Fuqing on April 26.
Bird flu scare spreads —
Disease control workers examine a chicken in a poultry farm in Fuqing on April 26.
ZHANG GUOJUN/Xinhua /Landov
Three people wearing masks walk outside the National Taiwan University Hospital in Taipei on Thursday, April 25. China has reported 83 cases of H7N9 avian influenza.
Bird flu scare spreads —
Three people wearing masks walk outside the National Taiwan University Hospital in Taipei on Thursday, April 25. China has reported 83 cases of H7N9 avian influenza.
SAM YEH/AFP/Getty Images
An H7N9 bird flu patient walks in the corridor of a hospital after his recovery and approval for discharge in Bozhou, in central China's Anhui Province, on Friday, April 19.
Bird flu scare spreads —
An H7N9 bird flu patient walks in the corridor of a hospital after his recovery and approval for discharge in Bozhou, in central China's Anhui Province, on Friday, April 19.
STRINGER/AFP/Getty Images
Chickens line the walls at a poultry farm on Thursday, April 18, in Yuncheng, China.
Bird flu scare spreads —
Chickens line the walls at a poultry farm on Thursday, April 18, in Yuncheng, China.
ChinaFotoPress/Getty Images
A 7-year-old girl, who was the first confirmed bird flu case in Beijing, is discharged from Beijing Ditan Hospital on Wednesday, April 17.
Bird flu scare spreads —
A 7-year-old girl, who was the first confirmed bird flu case in Beijing, is discharged from Beijing Ditan Hospital on Wednesday, April 17.
Lintao Zhang/Getty Images
Health workers collect blood samples from chickens at a poultry farm in Taizhou, China, on April 17.
Bird flu scare spreads —
Health workers collect blood samples from chickens at a poultry farm in Taizhou, China, on April 17.
ChinaFotoPress/Getty Images)
Chickens roost at a poultry farm in Taizhou, China, on Wednesday, April 17.
Bird flu scare spreads —
Chickens roost at a poultry farm in Taizhou, China, on Wednesday, April 17.
ChinaFotoPress/Getty Images
Pedestrians in Shanghai wear face masks to protect themselves from the H7N9 bird flu virus on Tuesday, April 16.
Bird flu scare spreads —
Pedestrians in Shanghai wear face masks to protect themselves from the H7N9 bird flu virus on Tuesday, April 16.
MARK RALSTON/AFP/Getty Images
A man throws ducklings into a stove at a duck farm in Zhangzhou in China's Fujian province on Sunday, April 14. The farm has had to kill more than 400,000 newborn ducks every week after the H7N9 bird flu affected the domestic poultry market.
Bird flu scare spreads —
A man throws ducklings into a stove at a duck farm in Zhangzhou in China's Fujian province on Sunday, April 14. The farm has had to kill more than 400,000 newborn ducks every week after the H7N9 bird flu affected the domestic poultry market.
STRINGER/AFP/Getty Images
A woman uses a lamp to illuminate a batch of eggs in the hatchery of a duck farm in Zhangzhou on April 14.
Bird flu scare spreads —
A woman uses a lamp to illuminate a batch of eggs in the hatchery of a duck farm in Zhangzhou on April 14.
STRINGER/AFP/Getty Images
Cheng Jun, vice president of Beijing's Ditan hospital, shows a video of the first bird flu victim in intensive care during a press conference on Saturday, April 13.
Bird flu scare spreads —
Cheng Jun, vice president of Beijing's Ditan hospital, shows a video of the first bird flu victim in intensive care during a press conference on Saturday, April 13.
STRINGER/AFP/Getty Images
Officials in Hong Kong test poultry at the border with mainland China on April 11 as authorities step up measures against the spread of the deadly H7N9 bird flu.
Bird flu scare spreads —
Officials in Hong Kong test poultry at the border with mainland China on April 11 as authorities step up measures against the spread of the deadly H7N9 bird flu.
PHILIPPE LOPEZ/AFP/Getty Images
Empty cages are seen at a closed bird market on April 10 in Shanghai.
Bird flu scare spreads —
Empty cages are seen at a closed bird market on April 10 in Shanghai.
ChinaFotoPress/Getty Images
A technician conducts tests for the H7N9 bird flu virus at the Kunming Center for Disease Control on April 10 in Kunming, China.
Bird flu scare spreads —
A technician conducts tests for the H7N9 bird flu virus at the Kunming Center for Disease Control on April 10 in Kunming, China.
ChinaFotoPress/Getty Images
Medical workers take part in a drill that simulates human infection of the H7N9 bird flu virus on April 9 in Hefei, China.
Bird flu scare spreads —
Medical workers take part in a drill that simulates human infection of the H7N9 bird flu virus on April 9 in Hefei, China.
ChinaFotoPress/Getty Images
People wear masks to protect themselves from the H7N9 virus, or bird flu, while riding the underground in Shanghai on Tuesday, April 9.
Bird flu scare spreads —
People wear masks to protect themselves from the H7N9 virus, or bird flu, while riding the underground in Shanghai on Tuesday, April 9.
PETER PARKS/AFP/Getty Images
Employees work on the production line of Shufeng Jiedu Capsule, an herbal medicine for treating avian influenza patients, at a workshop of Anhui Jiren Pharmaceutical Co., Ltd on Monday, April 8 in Bozhou, China.
Bird flu scare spreads —
Employees work on the production line of Shufeng Jiedu Capsule, an herbal medicine for treating avian influenza patients, at a workshop of Anhui Jiren Pharmaceutical Co., Ltd on Monday, April 8 in Bozhou, China.
ChinaFotoPress via Getty Images
A public park staff carries a cage to catch pigeons at a public area in People's Square, downtown Shanghai on Saturday, April 6. Shanghai municipal government has ordered workers to remove pigeons from public area to prevent the spread of H7N9 bird flu to humans, local media reported.
Bird flu scare spreads —
A public park staff carries a cage to catch pigeons at a public area in People's Square, downtown Shanghai on Saturday, April 6. Shanghai municipal government has ordered workers to remove pigeons from public area to prevent the spread of H7N9 bird flu to humans, local media reported.
ALY SONG/reuters/LANDOV
A boy looks at pigeons at a public park in People's Square in Shanghaion on April 6. Health authorities in China said on Saturday that the country's 16 confirmed H7N9 bird flu cases were isolated and showed no sign that it is transmitted from human to human, Xinhua News Agency reported.
Bird flu scare spreads —
A boy looks at pigeons at a public park in People's Square in Shanghaion on April 6. Health authorities in China said on Saturday that the country's 16 confirmed H7N9 bird flu cases were isolated and showed no sign that it is transmitted from human to human, Xinhua News Agency reported.
ALY SONG/Reuters/LANDOV
A public park worker catches a dove in People's Square in downtown Shanghai on April 6.
Bird flu scare spreads —
A public park worker catches a dove in People's Square in downtown Shanghai on April 6.
ALY SONG/Reuters/LANDOV
A public park worker places a dove in a cage in Shanghai on April 6.
Bird flu scare spreads —
A public park worker places a dove in a cage in Shanghai on April 6.
ALY SONG/Reuters/LANDOV
A masked security guard stands outside Taipei Hoping Hospital on April 6, where new isolation units have been set up to treat potential new avian influenza cases.
Bird flu scare spreads —
A masked security guard stands outside Taipei Hoping Hospital on April 6, where new isolation units have been set up to treat potential new avian influenza cases.
SAM YEH/AFP/Getty Images
Taiwan's Health Minister Chiu Wen-ta checks the negative pressure system in a isolation room as he inspects preparations for the virus in Taipei City Hospital Heping Branch, on April 6.
Bird flu scare spreads —
Taiwan's Health Minister Chiu Wen-ta checks the negative pressure system in a isolation room as he inspects preparations for the virus in Taipei City Hospital Heping Branch, on April 6.
A woman wears a face mask inside a subway station in Shanghai, China, on Friday, April 5. The Chinese minister of agriculture said Thursday it had discovered the H7N9 virus in samples taken from pigeons at Huhai agricultural market, China's state-run Xinhua news agency reported.
Bird flu scare spreads —
A woman wears a face mask inside a subway station in Shanghai, China, on Friday, April 5. The Chinese minister of agriculture said Thursday it had discovered the H7N9 virus in samples taken from pigeons at Huhai agricultural market, China's state-run Xinhua news agency reported.
CARLOS BARRIA/reuters/LANDOV
Health workers gather dead chickens at the Huhai poultry wholesale market, where the H7N9 bird flu virus was detected in pigeon samples, in Shanghai on April 5.
Bird flu scare spreads —
Health workers gather dead chickens at the Huhai poultry wholesale market, where the H7N9 bird flu virus was detected in pigeon samples, in Shanghai on April 5.
STRINGER/reuters/LANDOV
Cabin attendants are seen on a thermographic imaging device after their arrival from Shanghai at the quarantine station at Haneda International Airport in Tokyo on April 5.
Bird flu scare spreads —
Cabin attendants are seen on a thermographic imaging device after their arrival from Shanghai at the quarantine station at Haneda International Airport in Tokyo on April 5.
Toru Hanai/reuters/LANDOV
Men wear face masks at a shopping mall in downtown Shanghai on April 5.
Bird flu scare spreads —
Men wear face masks at a shopping mall in downtown Shanghai on April 5.
CARLOS BARRIA/reuters/LANDOV
Chinese health workers collect bags of dead chickens at the Huhai wholesale market on April 5.
Bird flu scare spreads —
Chinese health workers collect bags of dead chickens at the Huhai wholesale market on April 5.
STRinger/AFP/Getty Images
A policeman goes after a chicken that broke loose as Chinese health workers started culling chickens at Huhai wholesale market on April 5.
Bird flu scare spreads —
A policeman goes after a chicken that broke loose as Chinese health workers started culling chickens at Huhai wholesale market on April 5.
STRinger/AFP/Getty Images
A woman cleans a birdcage at a store in Taipei, Taiwan, on Thursday, April 4.
Bird flu scare spreads —
A woman cleans a birdcage at a store in Taipei, Taiwan, on Thursday, April 4.
SAM YEH/AFP/Getty Images
Staff members from Taiwan's Center for Disease Control stand at the entrance of Sungshan Airport in Taipei.
Bird flu scare spreads —
Staff members from Taiwan's Center for Disease Control stand at the entrance of Sungshan Airport in Taipei.
SAM YEH/AFP/Getty Images
A passenger has her temperature checked by a CDC staff member at the entrance of Sungshan Airport in Taipei.
Bird flu scare spreads —
A passenger has her temperature checked by a CDC staff member at the entrance of Sungshan Airport in Taipei.
SAM YEH/AFP/Getty Images
Photos: Bird flu scare spreads

Story highlights

NEW: Nanjing becomes third city to suspend live poultry trading

Sixteen human cases of H7N9 have been reported in eastern China

No cases of human-to-human transmission have been confirmed

Poultry markets in Shanghai and Hangzhou were closed

CNN  — 

Nanjing became the third city in China to suspend live poultry trading in the wake of an unusual strain of bird flu that has so far killed six people in the country, state-run media outlet Xinhua reported Saturday

Jiangsu’s provincial capital of Nanjing joined Shanghai and Zhejiang’s provincial capital of Hangzhou in shuttering the markets, Xinhua said.

Four deaths occurred in Shanghai and two in Zhejiang, the agency said.

Chinese authorities have killed more than 20,000 birds from a live-poultry trading zone in Shanghai in an effort to deal with the issue.

Chinese health workers collect the bags of dead chickens at Huhuai wholesale agricultural market in Shanghai on April 5, 2013. Authorities in Shanghai began the mass slaughter of poultry at a market after the H7N9 bird flu virus, which has killed five people in China, was detected there, state media said. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
Chinese health workers collect the bags of dead chickens at Huhuai wholesale agricultural market in Shanghai on April 5, 2013. Authorities in Shanghai began the mass slaughter of poultry at a market after the H7N9 bird flu virus, which has killed five people in China, was detected there, state media said. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
STR/AFP/Getty Images
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Chickens are seen in a chicken farm in Zouping, east China's Shandong province on April 1, 2013. Shanghai is stepping up monitoring after a new strain of bird flu killed two people, state media said on April 1.
Chickens are seen in a chicken farm in Zouping, east China's Shandong province on April 1, 2013. Shanghai is stepping up monitoring after a new strain of bird flu killed two people, state media said on April 1.
AFP/AFP/Getty Images
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The cull at the Shanghai poultry trading zone came as researchers in the United States said they had started work on developing a vaccine for H7N9.

The H7N9 avian flu virus had been found in pigeons. The virus had not previously been found in humans until a series of cases were reported in China this week.

As of Saturday evening, China had confirmed 18 human infections of the H7N9 avian flu virus, Xinhua reported. The World Health Organization confirmed 16.

One victim, a 64-year-old man, died Thursday hours after doctors had confirmed he had been infected with the virus, Chinese officials said.

Two other men, ages 66 and 74, developed flu symptoms late last month and were diagnosed with pneumonia over the past two days, Chinese officials said. A total of 11 people who had close contacts with the two have not shown flu symptoms, officials said.

No cases of human-to-human transmission of the H7N9 virus have been confirmed.

“We don’t know yet where the humans got their virus from,” said Dr. Joseph Bresee, who heads the epidemiology and prevention branch of the U.S. Centers for Disease Control and Prevention’s influenza division.

The virus has not been shown to spread easily between humans, he said.

The CDC, based in Atlanta, is working closely with Chinese authorities trying to find the source of the human infections.