Clinical research has found that nearly 60 percent of the more than 100 people infected with the H7N9 virus are aged 60 or older.

Meanwhile, the number of infected male patients is double that of females, said Zhong Nanshan, head of Guangdong province's expert committee on the prevention and control of H7N9 bird flu.

Seniors, and those with chronic conditions such as hypertension, diabetes, cerebrovascular, chronic obstructive pulmonary and coronary diseases are most easily infected. The gender difference, however, is not statistically significant, according to Zhong in a phone interview on Friday.