Apr 10, 2013 (CIDRAP News) - Five more H7N9 influenza infections have been confirmed in eastern China, all in older adults, while suspicions grow that wild birds may be the source and that the disease might be spreading to people through poultry environments.

Newly reported cases include two women from Shanghai, two men from Jiangsu province, and a man from Zhejiang province, according to separate reports today from Hong Kong's Centre for Health Protection (CHP). The illnesses boost China's number of infections with the new virus to 33, with the number of deaths holding steady at 9.

The Shanghai women are ages 76 and 81, and both are in stable condition. Of the Jiangsu men, a 70-year-old is in critical condition and a 74-year-old is in serious condition. The man from Zhejiang is 65 years old and is in stable condition.

Illness-onset dates were available for all but the Zhejiang man and range from Mar 29 to Apr 4. Most of the cases so far have been reported in middle-aged and older adults.

The World Health Organization (WHO) issued an update today on four cases that China first announced yesterday and emphasized that so far no evidence of human-to-human spread has been detected. It said Chinese officials are monitoring more than 600 close contacts and that an investigation is under way into a patient who got sick after contact with an earlier confirmed case in Jiangsu province.

In its Twitter feed today, the WHO said the behavior of the virus is more important than the exact case count. So far almost all confirmed cases have involved animal-to-human or environment-to-human transmission, such as in a farmyard or market setting.