The study, led by Yu Hongjie and fellow researchers at Fudan University's Public Health Institute in Shanghai, is based on information from all lab-confirmed human cases of H7N9 reported in the Chinese mainland as of late February.

The findings were published in Lancet Infectious Diseases this month.

A surge in human infections with the latest outbreak in China has prompted pandemic concerns. The study aimed to describe the epidemiological traits of the virus and to estimate the risks, according to Dr Yu.

In the study, virus samples collected in February from two human cases in Guangdong province were confirmed to have the mutation that made the virus capable of causing sickness and death in infected poultry as well.

China reported its first human H7N9 case in 2013, and outbreaks have occurred since then during the winter and spring.

Before the current outbreak, most infected birds did not show any symptoms, the study said. There has been no poultry vaccination against H7N9.

Notably, the number of human cases reported over the same period has more than doubled from previous epidemics, the study found, deepening concerns over mutations enabling the virus to easily jump between people - which could lead to a global spread.

Bernhard Schwartlander, China representative of the World Health Organization, told China Daily that the risk of human-to-human transmission is low, as the virus does not appear to transmit easily from person to person.

"However, experts agree that it is not a question of if, but when, the virus will adapt in ways that facilitate sustained human-to-human transmission," he warned.

It is imperative that policymakers in China identify a suite of immediate interventions, including live poultry market closures and poultry vaccination as a requirement for market access, he said.

Dr Yu agreed, aes should be permanent.

Roughly 70 per cent of infected patients reported live poultry exposure, mostly at the markets, the study found. More than 40 per cent of the patients who were hospitalized died.

Dr Schwartlander also urged Chinese authorities to remain vigilant and reinforce surveillance and control efforts to contain the virus.

Experts said well-cooked chicken is safe to eat.