Since early January and through 13 May the outbreaks have sickened 372 people in 47 states. So far, 71 people have been hospitalized but no deaths have been reported. Just over a third (36 per cent) of the sick patients are children.

The outbreaks involve several Salmonella subtypes: Braenderup, Enteritidis, Mdbandka, and Typhimurium. The hardest-hit states, which each have more than 20 cases, are California, Kentucky, Ohio, and Tennessee.

Backyard poultry trending

During the investigations, interviews revealed that 83 per cent (190) of 228 sick people had contact with live poultry the week before they got sick. People bought live baby poultry from a variety of sources, including feed supply stores, Web sites, hatcheries, and relatives.

In background information e-mailed to journalists, the CDC said that as the trend of raising backyard poultry grows in the United States, it is seeing more Salmonella infections related to the practice.

From 1990 to 2016 the CDC logged 65 Salmonella outbreaks linked to live poultry, and the 895 illnesses recorded in 2016 was the most the CDC has ever seen.

The CDC in the e-mail said it expects outbreaks to continue for the next several months.

"Many people continue to purchase live poultry and continue to be exposed to Salmonella germs as they tend to their backyard flocks. Some of these birds can have a long life expectancy."

Officials warned that any live poultry can harbor Salmonella, even if they look healthy and clean, and that Salmonella infections can be more severe for certain groups of people, including young children, older adults, and those with chronic health conditions.

The CDC urged several safety steps for poultry owners, including washing hands after handling the birds, keeping the birds out of the house, supervising young children who touch the birds or eggs, avoiding kissing or snuggling poultry, and refraining from eating or drinking around them.