The Morbidity and Mortality Weekly Report (MMWR) earlier this month explored one of the ways that more than 70 Salmonella outbreaks related to backyard poultry flocks have occurred since 2000.

MMWR, published by the federal Centers for Disease Control and Prevention in Atlanta, reported on a joint study by the Michigan Department of Health and Human Services and CDC into the role of a mail-order hatchery and Salmonella risk factors.

The hatchery that is the subject of the study is located in Michigan but only referred to as “hatchery A” by the authors.

The MMWR report says environmental sampling to confirm the outbreak strain at poultry hatcheries that supply backyard flocks are conducted only infrequently during investigations, meaning the source of backyard outbreaks are rarely identified.

Last June, the Michigan Department of Health and Human Services asked for CDC to help it investigate risk factors for Salmonella infection linked to live backyard poultry originating at the Michigan hatchery.

The hatchery supplies young poultry for backyard flocks through direct sales to homeowners and through local feed stores.

“At the start of the investigation, traceback had linked 24 clinical cases of Salmonella enterica serotype Enteritidis to exposure to live poultry from hatchery A,” the MMWR said. “Whole genome sequencing analysis of the clinical isolates revealed that they were closely related (within 0-15 alleles) by whole genome multilocus sequences typing to environmental isolates sampled from shipping containers originating from hatchery A at retail outlets in several states.”

The Michigan-CDC team conducted environmental sampling at the hatchery June 19, 2018. Included items and areas were: liners used inside egg hatchers, and incubators and incubators from the inside and outside surfaces of egg hatchers and incubators, pre-shipping spaces, the resident breeding stock environment including boxes, bedding and food and water containers, and the trucks used to transport live poultry and eggs.

Best practices for biosecurity were followed by the researchers as they went about sampling. They collected samples from chick box liners and bedding and placed them in sterile whirl pack bags and sterile collection cups.

Among the 45 samples collected, Salmonella was identified in four, or 9 percent. “Three isolates collected from the same building were identified as Salmonella enterica serotype Typhimurium, and one isolate from poults in the pre-shipping area was closely related to the outbreak stain…”

Backyard poultry flocks have been linked to more than 70 outbreaks of Salmonella since 2000. The CDC says those outbreaks sickened 4,794 people, with 894 hospitalizations and seven deaths.

The most significant number ever recorded of Salmonella illnesses from backyard flocks occurred in 2017. At least two more Salmonella outbreaks in backyard blocks occurred in 2018. As many as six strains contributed to last year’s illnesses in as many as 36 states. A third of the illnesses were in children younger than 5.

The strains that were common in backyard flocks this past year were Salmonella Seftenberg, Salmonella Montevideo, Salmonella Infantis, Salmonella Enteritidis, Salmonella Indiana and Salmonella Litchfield.

Backyard poultry caused 1,120 Salmonella illness in 2017 in 48 states, sending 249 people to hospitals and causing one death. Since then CDC has stepped up educational efforts on the dangers of backyard chickens and other poultry.

Just coming into contact with live poultry or their environment can expose people to Salmonella and other pathogens. Birds carrying the bacteria can appear healthy and clean with no signs of illness.

Also, since May 2018, backyard poultry flocks in southern California have spread virulent Newcastle disease in the area, causing the destruction of both backyard and commercial poultry by the thousands.