( CNN ) The latest outbreak of bird flu -- the worst in the U.S. since the 1980s -- is not a likely threat to humans , reports the Centers for Disease Control and Prevention . But as with any potential threat to human health , they are preparing for the worst just in case . The CDC and the United States Department of Agriculture held a press conference Wednesday to talk about preparations . `` The risk to humans is low , our food supply is safe , '' said Dr. John Clifford , the USDA 's Chief Veterinary Officer . `` We know how to address disease when we find it . '' Since mid-December , 16 states have seen bird flu turn up in commercial poultry , backyard chickens , and in flocks of wild and captive wild birds , according to the CDC . That number will likely grow as birds with the disease fly from one state to the next . On Monday , health leaders in Iowa said more than 5 million hens would have to be euthanized after bird flu was detected at a commercial laying facility there . In the United States , some 3.5 million birds had already been euthanized to prevent the spread of the disease , according to the USDA . Iowa has about 60 million laying hens , according to the Iowa Egg Council and is the top egg producer in the country . California and Minnesota , two of the country 's top 10 egg producing states have also seen cases . The news is bad for the birds , but not for humans . The CDC considers the likelihood of bird to human transmission of the virus `` low '' according to Dr. Alicia Fry , a medical officer with the CDC national Center for Immunization and Respiratory Disease , Influenza Division , Epidemiology and Prevention Branch . `` That said , human infections have occurred '' with another strain of the virus , found in Africa and in Asia , so the CDC can not rule out the possibility of human infection , Fry said . `` We are cautiously optimistic '' that it wo n't spread to humans , but `` we are prepared for the possibility , '' she added . They are studying the current virus and creating candidate vaccines which could be used if one were ever needed . The USDA is also working on a potential vaccine for the birds . These are typical routine public health preparedness measures . The CDC said it is also monitoring at least 100 people who have worked with sick birds . None of the workers have gotten sick themselves . Most of the people who have become infected with the other strains of the virus in Asia and Africa have had direct or prolonged contact with infected birds . The virus does not spread through people eating chickens or eggs . Birds that are sick die quickly , according to Clifford . Incubation period is three to five days generally . With turkeys , they go off their water and their feed when they are sick and become lethargic or have a condition called `` torticollis '' or `` stargazing '' he said , and they die shortly after that . Farmers also see a drop in egg production . Commercial growers have taken extra precautions to disinfect vehicle tires and any equipment that comes into contact with the birds . Workers must also disinfect their shoes and hands when they go from building to building to reduce contamination . With popular backyard birds , the USDA suggests people try and protect their animals from coming into contact with wild water fowl that may carry the virus . The CDC said , as with any evolving public health situation , they will continue to provide updated information as it becomes available . The good news is the virus does n't like warm weather or strong sunlight , according to the USDA . So the cases should go down over the summer , but they are going to monitor the situation knowing that it could come back in the Fall .
The CDC says `` the risk to humans is low , '' but , as always , they are preparing for the worst case . Comment: At least 100 people who worked with the sick birds are being monitored for any sign of sickness . So far 3.5 million birds have been euthanized .