Four more people in East China have been confirmed to be infected with the H7N9 bird flu virus, as a nationwide screening program has been launched for the rare but lethal strain.

The health authority in Jiangsu province said four people living in different cities are in critical condition after they developed fever, coughing and other symptoms around 20 March. They tested positive for H7N9 on Tuesday afternoon.

Two men from Shanghai, aged 27 and 87, were confirmed dead on Sunday (31 March) from H7N9 infection, with a woman from Anhui province in critical condition.

No epidemiological links have been found among the four cases announced on Tuesday, the Jiangsu health authority said.

Hundreds of people who have had close contact with the patients have not, as yet, developed fever or respiratory symptoms.

Feng Zijian, director of emergency response at the Chinese Center for Disease Prevention and Control, said the country has launched a nationwide program to screen for H7N9 among patients with pneumonia, where the cause is unknown.

The program, supported by surveillance systems at public health institutions including hospitals, is aimed at timely detection of new cases.

To determine the source of the virus, the identities, background and living conditions of existing patients will be investigated, Mr Zijian said. “It’s unclear if the virus originated in pigs or other animals,” he added.

The Jiangsu patients are three women aged 32, 45 and 48 and an 83-year-old man. They live in Nanjing, Suqian, Suzhou and Changzhou.

Only the 45-year-old woman, who works as a poultry butcher in Nanjing, has been in close contact with poultry, according to the health authority report. The others work in sheet metal processing or are unemployed.

The health department has set up a team to direct prevention and control of the virus.

Sixteen top-level hospitals in Jiangsu have been designated as treatment sites for patients confirmed to have the virus, and all levels of hospitals are required to strengthen the screening of pneumonia patients against H7N9.

Other cities, including Shanghai and Beijing, have put forward plans to deal with emergencies or large-scale outbreaks caused by the relatively unknown strain of bird flu.

Shanghai authorities on Tuesday launched a yellow warning third-level emergency in response to the new strain.

The yellow warning suggests that people are infected with the virus but that human-to-human transmission has yet to take place.

Xu Jianguang, director of the city’s health and family planning commission, said at a news briefing on Tuesday that hospitals across Shanghai will strengthen the role of fever diagnosis wards to isolate patients.

Hospitals must also take preemptive measures, such as proper disinfection and quarantine, and step up protection of medical workers.

Experts say the manufacture of a vaccine will take some time, as researchers will need a thorough understanding of the virus.

No new pneumonia cases from unidentified sources have been reported in Shanghai, said Wu Fan, chief of the city’s Municipal Center for Disease Control and Prevention.

Officials said poultry and pork for sale at local markets are safe, but people are urged not to eat wild poultry.

On Tuesday (2 April), Shanghai authorities reiterated that no bird flu virus had been found in dead pig samples from a river providing drinking water to residents.

The Shanghai Animal Disease Prevention and Control Center tested 34 samples from pig carcasses pulled from the Huangpu River and found no bird flu viruses.

Thousands of dead pigs were fished from the river last month, sparking fears over tap water safety.

Officials denied they had covered up the two bird flu deaths, which occurred on 4 and 10 March.

Wu said it is difficult and takes time to detect an unknown virus. It is still not known if the virus can be transmitted between poultry and other animals or between pigs and humans, she added.

In Beijing and Guangdong province, public health authorities said they are keeping a close eye on the H7N9 virus.

Test reagents for the virus have reached Beijing — where the deadly SARS epidemic struck a decade ago — according to the city’s health bureau.

The capital, with a population of about 20 million, has added bird flu to its monitoring system for regular flu and pneumonia, where the source is unclear.

The authority said all hospitals in Beijing have been told to brace for emergencies and ensure enough medical supplies, although no infections had been reported in the city as of Tuesday.

It is the first time the H7N9 bird flu virus has been found in humans, although three other strains in the H7 family — H7N2, H7N3 and H7N7 — have previously been found in humans, but there were no casualties.

China steps up H7N9 monitoring

Four people in east China's Jiangsu Province have been confirmed as being infected with the lesser-known H7N9 bird flu, bringing the total number of infections in the country to seven.

Statistics on pneumonia cases caused by unknown reasons will be reported daily in Shanghai where two people died from the first known human infections of the bird flu strain, the municipal government said in a press briefing Tuesday.

The city government will also set up an expert team to evaluate the severity and risk of the H7N9 bird flu, to step up research on the virus, and to closely watch the infections and people who have been in contact with them, it said.

On Monday (1 April), the Shanghai Animal Disease Prevention and Control Center tested 34 samples of pig carcasses pulled from the Huangpu River running through the city and providing it drinking water. It found no bird flu viruses.

Thousands of dead pigs were retrieved from the Huangpu River last month, sparking huge panic as well as satire among the public over tap water safety.

The health authorities in Jiangsu have designated 16 leading hospitals to accept new cases in a bid to offer better treatment and reduce the mortality rate.

The health bureau in Beijing has ordered hospitals to include the testing of H7N9 bird flu in routine monitoring and to train hospital staff on how to treat pneumonia caused by unknown factors.

Health authorities in Shandong Province have ordered morning tests of fever, cough and other respiratory symptoms at schools, nurseries and poultry farms.

The four patients, from four cities in Jiangsu Province, are in critical conditions and under emergency treatment, the Jiangsu provincial health bureau said Tuesday in a statement.

The four were confirmed as human infections with H7N9 avian influenza by an expert team summoned by the provincial health bureau, based on clinical observations, laboratory tests and epidemiological surveys Tuesday afternoon, the statement said. No mutual infections were discovered among them.

A total of 167 people who had come into contact with the four showed no symptoms of fever or respiratory illnesses, it said.

The four included a 45-year-old woman from Nanjing, a 48-year-old woman from Suqian, a 83-year-old man from Suzhou, and a 32-year-old woman from Wuxi, it said.

The woman in Jiangning district of Nanjing, surnamed Xu, fell ill with flu symptoms on March 19. She was transferred to a hospital intensive care unit in Nanjing on March 27 after her condition worsened, the statement said. She is a poultry culler.

The woman from Shuyang county of Suqian City fell ill on 19 March and was transferred to a hospital intensive care unit in Nanjing on 30 March.

Tests by the Jiangsu provincial center for disease control and prevention found the two women positive of the H7N9 strain on 30 March and further tests by the Chinese center for disease control and prevention confirmed the results on 2 April.

The man from Wujiang district of Suzhou City became ill on March 20 and was admitted to a local hospital on 29 March. He was first tested positive of H7N9 bird flu on 1 April.

The woman from Binhu district of Wuxi City fell ill on 21 March and was transferred to an intensive care unit of a hospital in Wuxi after her condition worsened on 28 March. She was first tested positive of H7N9 bird flu on 31 March.

On Sunday, three H7N9 bird flu cases were reported, two in Shanghai and one in Anhui, the first human infections of the bird flu strain. The two in Shanghai died and the one from Anhui is in critical condition and under treatment in Nanjing.

It is unclear how the three got infected, and no mutual infections were discovered among them, said the National Health and Family Planning Commission Sunday. No abnormalities were detected among 88 of their closest contacts.

The subtype of H7N9 bird flu virus has not been contracted to human beings before. The virus shows no signs of being highly contagious among humans, according to the clinical observation on the cases' close contacts.

However, as only three cases of human infection of H7N9 have been found, relatively little research has been done on it. The expert team is working to study the toxicity and human-infection capacity of the virus, the commission said Sunday.

There are no vaccines against the H7N9 bird flu virus either at home or abroad.