HONG KONG – Of all the mysteries surrounding the emergence of a new and deadly strain of avian influenza around Shanghai, one of the biggest is why China's hundreds of medical and veterinary labs did not spot the problem sooner – or if they did, why it was not disclosed.
Even the censored Chinese news media has begun cautiously questioning why the authorities did not say anything sooner about a disease that resulted in the first known human case in eastern China on Feb. 19, but was not announced to the public until March 31. The announcement came two weeks after the closing of the National People's Congress, a show event during which the Communist Party traditionally avoids acknowledging problems.
"People are still asking, why did it take the government so long to confirm the outbreak?" The Communist Youth Daily, the official newspaper of the Communist Youth League, said in a column several days ago. "The transparency of information from the government is still being called into question by the public and the actions the government has taken have not convinced the public."
China's Health Ministry is now finding three to five human cases a day, a brisk pace for a disease that Chinese officials and the World Health Organization assert is still transmitted from animals to people, and not from person to person. The Centers for Disease Control and Prevention in Atlanta activated its emergency operations center this week as governments around the world began making preparations in case of a flu pandemic.
Yet Chinese government officials have not yet publicly identified any farms with poultry infected with H7N9 avian influenza, the new strain of bird flu. The government has focused so far on closing wholesale markets in Shanghai and several nearby cities and has sent guards with nets to chase pigeons in Shanghai parks, to snare and later euthanize the potentially infected birds.
Chinese health officials assert that they have acted promptly upon laboratory confirmation of cases. Chinese agriculture officials have said less, but have also said that they are being transparent.
Western health officials and scientists say that they do not know whether China deliberately concealed the disease for six weeks after the first transmission to a person was confirmed. But they note that unusual properties of the virus, together with a controversial Chinese response to a previous bird flu outbreak of distributing millions of free vaccines, may have made the outbreak harder than usual to detect at first.
The virus can be detected in animals in two ways: a widely used, easily performed test for antibodies in swabs of poultry, known as a serology test, or a much more expensive and difficult experiment to isolate specific viruses from birds' blood, which can only be done in a few well-equipped labs in China.
The crucial question is whether veterinary technicians across China were doing serology tests only for H5N1 bird flu, which has been a chronic problem in China for 16 years, or whether they were testing for a broader range of avian influenza viruses and misread, ignored or decided not to publicize any detection of H7N9.
Chinese officials have been largely silent on the details of their test protocols. The agriculture ministry had no immediate response to questions submitted by fax on Wednesday.
Dr. Juan Lubroth, the chief veterinary officer of the United Nations' Food and Agriculture Organization, said that he suspected China had been testing broadly for more avian influenza viruses than just H5N1. "When you are running a serology, you usually don't run it against one, you run it against a battery of viruses that you know are circulating," he said in a telephone interview.
But while H7N9 has been spotted before in the West, it has not been documented before this spring in East Asia. Dr. Lubroth said that he did not know the details of the Chinese test protocol, and that if the Chinese were focused on H5N1 test results, these tests would not detect H7N9.
At least 31 human cases, including nine deaths, have been confirmed by the Chinese government so far. Chinese officials say that only one patient has recovered and the rest are still sick in hospitals, mostly in serious or critical condition.
Dr. Malik Peiris, the director of the Center for Influenza Research at Hong Kong University, said that another serious challenge in finding the disease was that poultry, unlike people, can be infected with H7N9 and show very few symptoms. So Chinese technicians may not have seen a need to do much testing in recent months when there was little sign of H5N1, which does kill chickens.
"Generally people don't go around testing apparently healthy poultry," he said.
The World Organization for Animal Health, a veterinary body in Paris that sets international standards for animal care, has a mandatory policy for China and other member countries. Members must report all outbreaks of highly pathogenic avian influenza in wild or domesticated birds, and outbreaks of low-pathogenic avian influenza in domesticated birds.
Dr. Alex Thiermann, the president of the organization's standard-setting Code Commission, said that H7N9 qualifies as a low-pathogenic bird flu virus, so China had an international obligation to report it to the World Organization. China did so last week.
Dr. Thiermann said that the organization's rules allowed a country to fully confirm the presence of a virus before reporting it, but he declined to say whether he thought China had been slow in reporting it.
He also expressed concern that China might have initially missed the virus because of its controversial approach to fighting H5N1 virus ever since the disease produced mass deaths of chickens in 2004 and 2005: a massive vaccination for poultry across the country.
The advantage of vaccination is that while it does not stop all infections, it greatly reduces the amount of virus that a bird sheds when infected. The disadvantage is that the poultry develops antibodies to the virus, so serology tests become unreliable.
Dr. Thiermann said that his organization recommends mass culling of birds as a more reliable way to stamp out a disease and then monitor for any resurgence. He warned that vaccination for H5N1 might have masked the emergence of H7N9.
Dr. Arnold Monto, a professor of epidemiology at the University of Michigan, said that there might have been a slight delay in disclosing the emergence of the virus in people, since the Chinese government had already calculated the entire genetic sequence of the virus before announcing it. But other scientists said that decoding a gene sequence can now be done in China in two days and was a natural step before announcing the disease.
Dr. Monto said that the difficulty in spotting the virus in seemingly healthy poultry had made the whole task more complex than usual.
"You've got to give them credit for identifying it," he said. "The thing that is worrisome is the virus itself."
Shi Da and Sue-Lin Wong contributed research.
This article originally appeared in The New York Times.