According to a May 23rd report by the Centers for Disease Control and Prevention (CDC), 109 cases of salmonellosis associated with backyard chickens have been confirmed since May 16th. Patients ranged across 29 states with 40 percent of 82 investigated cases resulted in hospitalization. Serotypes identified include Salmonella Altona, Indiana, Infantis, Mbandaka and Typhimurium. The PulseNet system will be used to record cases in an ongoing epidemiologic investigation.
Sixty-seven percent of a group of 27 cases reported purchasing or coming into contact with chickens before onset of symptoms. Investigators in Ohio and Utah demonstrated the presence of Salmonella Altona and Mbandaka in boxes used to ship chicks from hatcheries. Whole genome sequencing confirmed commonality between the chick box isolates and those obtained from patients. Laboratory assay demonstrated that 7 out of 101 patient-derived isolates of Salmonella showed resistance to one or more of twelve antibiotics of medical importance including ciprofloxacin, tetracycline and gentamicin.
Backyard poultry are an obvious source of Salmonella infection especially for children with 43 percent of the 109 cases investigated were in patients under five years of age.
The presence of zoonotic Salmonella in day-old chicks suggests mechanical transmission from parent flocks since the serotypes isolated are not regarded as being vertically transmitted to eggs. Evidently, deficiencies in egg hygiene, chick handling and hatchery decontamination contribute to dissemination of infection.
With up to seven percent of homeowners holding backyard flocks the problem of salmonellosis will persist despite advisories on ‘safe’ handling.