The outbreaks are added to the rising number of avian flu detections in the hardest-hit states of Minnesota and Iowa.

There have now been 174 detections of avian flu in the US since it was first found in December, and the total number of birds affected now stands at 38,946,573.

These four detections of the disease occurred on two commercial turkey farms, one commercial chicken farm and one backyard flock of mixed poultry.

The latest outbreaks were confirmed by the US Department of Agriculture's Animal and Plant Health Inspection Service.

The locations of these confirmed avian flu cases are:

• Minnesota, Kandiyohi county - 42,600 commercial turkeys;
• Minnesota, Renville county - 625,500 commercial chickens;
• Iowa, Sac county - 28,400 commercial turkeys;
• Iowa, Sioux county - backyard mixed poultry, number pending.

These cases all occurred in the Mississippi flyway.

The two latest outbreaks bring the number of detections in Iowa to 51, affecting 26,634,900 birds.

The Iowa State Department of Agriculture and Land Stewardship has announced that they are also looking into several unconfirmed outbreaks of HPAI.

The unconfirmed cases include commercial turkey and pullet farms as well as egg laying operations. They were found in Sioux, Buena Vista, Sac and Calhoun counties.

These additional detections are likely to take the tally in Iowa to 62.

The Department said they have quarantined the premises and once the presence of the disease is confirmed, all birds on the properties will be humanely euthanised to prevent the spread of the disease.

Minnesota has detected 84 outbreaks, affecting 5,116,260 birds.

The latest outbreaks were found some days before confirmation, but the Minnesota state government said that it has not received any new reports of presumed avian flu cases for five straight days, as of 20 May.

The state government also stated that the first round of backyard flock surveillance, testing and observation in all control areas is complete, with nearly 4,000 backyard flocks now tested for avian influenza or monitored for signs of the disease.

However, to date, only one backyard flock has tested positive for HPAI in Minnesota.