Shanghai health authorities denied Wednesday that they had covered up cases of the new strain of avian influenza virus, H7N9, or delayed informing the public of findings of the virus.

Lu Hongzhou, deputy director of the Shanghai Public Health Clinical Center and one of the researchers studying the new virus, told the Global Times that Shanghai authorities did not stifle news of the virus after it was first detected in early March.

The denial came in response to a report by the Guangzhou-based Nandu Daily, which claimed it took almost one month for local authorities to report the new virus to the central government.

The newspaper said health officials in Shanghai found out about the new strain on March 4, when it had already killed one patient infected in mid-February, but waited 18 days to submit the virus sample to the Chinese Center of Disease Control and Prevention, which informed the public nine days later on March 31.

Lu said they had only come up with preliminary results on March 17, not March 4, when only one lab had confirmed the finding of the new strain.

 "It was only when the second infected case, a 27-year-old patient surnamed Wu, died on March 10, that we realized the virus was not SARS, H1N1 or any other virus that had appeared before," Lu said.

After two infected patients died of unknown causes in Shanghai, a Sina Weibo post asking for an explanation was quickly transmitted, but was soon deleted, Nandu Daily reported, even when authorities had already confirmed that the first death was not the result of any known bird flu virus.

"That post was ridiculous for me then so I paid no attention. But we should have replied to the Web user in a timely manner," Lu said.

Health authorities then sought to clarify the situation on March 8, saying the two deaths were caused by a normal flu virus and the respiratory infections had occurred due to seasonal changes.

The news report triggered several discussions amid fears over daily increases in infections.

Five more cases of infection, including three from Jiangsu and neighboring Zhejiang provinces and two from Shanghai, were confirmed Wednesday.

By late Wednesday, the country had reported 33 H7N9 infections, including nine deaths, or 11 if the two fatal cases before March 31 are included.

"The emergency system should be further improved," an anonymous doctor from Peking Union Medical College Hospital told the Global Times. "If officials had started to develop vaccines or alerted people to stay away from live poultry, maybe we would have fewer cases."

The Chinese Academy of Sciences' Key Laboratory of Pathogenic Microbiology and Immunology said on Wednesday that no genes from the H7N9 virus were traceable to pigs, thus excluding them as intermediate hosts for the deadly new strain of bird flu.