Despite the increase of live poultry-related Salmonella outbreaks, environmental sampling at hatcheries is not routinely conducted leaving the outbreak source unknown.
The United States has seen 70 Salmonella outbreaks linked to contact with live poultry between 2000-2017, resulting in 4794 cases, according to reports from the US Centers for Disease Control and Prevention (CDC). The most recent surveillance reports indicate that live poultry-related outbreaks are on the rise with 9 outbreaks reported in 2016 and 10 reported in 2017.
Despite the frequency of live poultry-related outbreaks, environmental sampling is not routinely conducted during outbreak investigations. As a result, the source of the outbreak is rarely identified.
However, on June 12, 2018, the Michigan Department of Health and Human Services (MHHS) requested assistance from the CDC to investigate Salmonella risk factors at a mail-order hatchery. The findings of the investigation were published in the CDC’s Morbidity and Mortality Weekly Report.
Prior to the launch of the environmental sampling, the hatchery was identified as a potential outbreak source after traceback linked 24 clinical cases of Salmonella enterica serotype Enteritidis with exposure to live poultry from the hatchery. Whole genome sequencing found that isolates from ill individuals were closely related to isolates found in shipping containers from the hatchery that had been distributed to retail outlets in several states.
Environmental sample collectors selected 4 priority areas for the investigation, including the hatching environment, pre-shipping area, resident breeding stock environment, and trucks used for on-site and off-site transportation.
The samples were transported off-site to the MHHS and were characterized through polymerase chain reaction and pulsed-field gel electrophoresis and whole genome sequencing.
Salmonella was identified in 4 (9%) of the 45 samples collected. Three isolates collected from the same building were identified as Salmonella enterica serotype Typhimurium. The other isolate—which was taken from the pre-shipping area—was closely related to the outbreak strain (differing by 1-3 alleles).
The investigation confirmed the presence of the outbreak strain at the hatchery and the authors of the report indicated that these results promote the addition of environmental sampling at poultry hatcheries part of an outbreak response.
Current CDC guidance states that children under 5 should be under adult supervision when interacting with live poultry. All individuals should wash their hands thoroughly after contact with backyard flocks and set aside a pair of shoes to wear only when handling live poultry.
The CDC also released a guidance to mail order hatcheries in 2014 advising that hatcheries should provide health-related information to owners and potential buyers of birds, including info about preventing Salmonella. Furthermore, the US Department of Agriculture offers a voluntary certification program that certifies that mail order hatcheries are monitored for Salmonella bacteria.
The most recent outbreaks associated with live poultry were investigated by the CDC and state health departments in 2018 and were linked with several different strains of Salmonella, including Salmonella Seftenberg, Salmonella Montevideo, Salmonella Infantis, Salmonella Enteritidis, Salmonella Indiana, and Salmonella Litchfield.
In total, 334 individuals from 47 states were infected between February 15, 2018, and August 10, 2018. The outbreaks were resolved by the CDC on September 13, 2018.
As part of the epidemiological investigations for these outbreaks, health officials conducted interviews with 211 ill individuals. A total of 132 individuals (63%) reported having contact with chicks or ducklings obtained from feed supply stores, websites, hatcheries, or from relatives in the week prior to falling ill.
To view state-by-state case counts from the multistate outbreaks of Salmonella infections linked to contact with live poultry in backyard flocks in 2018, check out the Contagion® Outbreak Monitor.