Tests have found probable avian flu outbreaks at five new commercial poultry sites in Iowa, affecting more than 6 million birds and even more eggs, according to the state's agriculture department and the U.S. Department of Agriculture.

Additional tests are being performed to confirm the highly pathogenic H5N2 that has been spreading rapidly.  Positive results would push the national outbreak tally to more than 15.1 million birds from flocks in 13 states. To compare, the avian flu outbreak of 1983 to 1984 in the northeast, which is currently the largest in U.S. history, resulted in about 17 million birds being culled.

"This is a big deal," Iowa Secretary of Agriculture Bill Northey said during a conference call on Monday. "Going forward, the question is are we done? Or does this mean more birds as we go forward."

State officials in Iowa have quarantined the five sites.  Positive test results would mean that more than 9.5 million birds in Iowa have been affected by the virus.  On average, Iowa farms house an estimated 60 million egg-laying hens.

At the same time, the U.S. Department of Agriculture confirmed that a Wisconsin turkey farm with more than 1 million birds has also tested positive for the virus.  Currently, more than 1.9 million chickens and turkeys in Wisconsin have been affected by H5N2, state and federal officials said.

Two strains of bird flu have been discovered in the United States this year.  The H5N2 strain has been discovered in Arkansas, Idaho, Iowa, Kansas, Minnesota, Missouri, Montana, North Dakota, Oregon, South Dakota, Washington and Wisconsin.  The same strain has also been found on farms in Ontario, Canada.  The H5N8 strain has been found in California and also in Idaho.

The virus has not been reported in the country's leading chicken meat producing states in the South, which include Georgia, Arkansas, Alabama, Mississippi and North Carolina.

So far the number of birds affected by the outbreak of this bird flu virus represents only a fraction of the total flock in the United States.  Chicken dominates poultry production in the United States.  In 2014, poultry processors slaughtered nearly 8.7 billion chickens and about 237 million turkeys, according to the Agriculture Department data.

The virus itself can kill an entire flock within 48 hours.  Millions of turkeys and chickens are now in quarantine waiting to be culled and many large stocks have already been destroyed.  Officials believe that the virus is being spread by wild birds but they do not know how it is entering barns.