According to Iowa's agriculture department, the highly pathogenic H5 avian flu found in first tests at five more farms in Iowa. It involves commercial egg operation that houses up to 5.5 million birds.

Additional tests are in progress at a US Department of Agriculture laboratory. If the virus is confirmed at the farms in additional tests then there is a possibility that the total number of American cases might exceed 20 million birds and could also result in the biggest death toll in a bird flu outbreak in history of US.

At the egg farm in Buena Vista County employees saw an unanticipated increase in bird deaths before the flock was tested. This farm might be the largest single farm operation to be hit in the current outbreak. The outbreak has been confirmed by the egg farm's owner, Rembrandt Foods, which is the one of the top US egg producers.

"Rembrandt Foods takes biosecurity and food safety very seriously. Our focus over the past several weeks has been to diligently implement enhanced biosecurity procedures", said the company.

As per the company, it is working with state and federal regulatory authorities in order to limit the spread of the virus. According to the Iowa Department of Agriculture and Land Stewardship, avian flu was likely at four other commercial farms in Buena Vista, Sioux and Clay counties.

As per experts, if the virus will confirmed at all five farms in the coming days then the number of sites where H5 has been discovered in Iowa would increase to 17. The news came when state officials gave confirmation that an Iowa-based chicken broiler breeding farm has initially tested positive for the virus.