The United Nations is warning of a serious threat to human health posed by the bird flu pandemic recurring in Asia. The U.N. Food and Agriculture Organization (FAO) called for greater surveillance of people exposed to infected birds, especially those working in the poultry industry and urged heightened surveillance and quarantine measures. The strain of bird flu that killed 24 people in Southeast Asia early this year has erupted again in Thailand and China. The two countries said outbreaks of the H5N1 strain in farms were under control. China culled more than 20,000 chickens in central Anhui province to isolate the new outbreak of bird flu. Health officials have also conducted health checkups on 37 people who have been in contact with the slaughtered birds and have found no human-infections of the avian influenza as of yet.