A worker cleans empty cages, which were used to transport chickens, after morning trading at a wholesale poultry market in Hong Kong April 8, 2013. China is confident it can control an outbreak of a new strain of bird flu, a senior Chinese health official said on Sunday as the World Health Organization (WHO) said there had now been 21 human cases of the H7N9 flu with six deaths. REUTERS/Bobby Yip (CHINA - Tags: HEALTH ENVIRONMENT)