No positive samples of the H7N9 virus have been found in pigs or farms in China so far, the World Health Organization (WHO) announced on Tuesday.
WHO spokesperson Gregory Hartl said animal samples that tested positive were from poultry markets, including live bird markets.
"So the focus at this point is on poultry markets," said Hartl. However, Hartl told reporters that for the moment, "we don't have 100 percent surety on what the source of infection is. That might not be the correct source or the only source."
He added close contacts of confirmed cases of the deadly disease had been closely monitored with none so far testing positive for H7N9.
"At this point, there is no evidence of sustained human to human transmission," he said, adding that there are some "suspected but not yet confirmed cases of perhaps very limited transmission between close family members."
"They are still being investigated," he said. Hartl told Xinhua one of the suspected family clusters was in Shanghai, with three family members having similar symptoms and one of them being confirmed of H7N9.
The confirmed case died, so has another suspected family member, according to Hartl. The other suspected family cluster, which included two family members with one of them being confirmed, was in Jiangsu Province, he said.
Hartl said that even if the infection of H7N9 is confirmed in other family member, further investigations are still needed to make sure whether that's a human to human transmission between constant and close contacts or an infection with virus from the same environmental source. He said Chinese health authorities had been working openly and closely with WHO.