Assessing the Food Safety Risk Posed by Birds Entering Leafy Greens Fields in the US Southwest

Abstract

In the US Southwest, it is common to observe birds in leafy green fields, though the risk they contribute to foodborne outbreaks remains unclear. In this study, we investigated and recorded the relationship between birds near leafy green fields and the risk for contaminated irrigation water or leafy green plants. We monitored the presence of birds for over two years and performed cloacal swab analysis for non-pathogenic Escherichia coli, E. coli O157:H7 and Salmonellaenterica, while also monitoring the incidence of other microbial indicators. We also assessed the risks from bird feces by performing observations in a commercial field reported with Salmonella positive samples and by analyzing the survival of foodborne pathogens in bird feces. Our results showed that most of the birds near the crop fields were resident small birds. We did not observe a correlation between the number of birds in sites and the incidence of indicator bacteria (e.g., coliforms, E. coli) in irrigation canal water, with the exception of one out of four sites where water flow was low or stagnant. Using walk-in-traps, 305 birds were captured and placed in short-term captivity to determine the presence of various bacteria. None of the birds tested positive for E. coli O157:H7 or Salmonella. However, nearly 40% of the birds captured were confirmed positive for non-pathogenic E. coli. We found no correlation between age (young, adult, unknown), gender (male, female, unknown) and the incidence of E. coli positive birds, but we observed significantly higher probability of incidence during October–December. The role of relative humidity and temperature on bacterial survival appeared to play a key role in the survival of Salmonella on the leaves of spinach plants in a commercial field. This was also confirmed in laboratory conditions where Salmonella inoculated in bird feces and exposed to 15 °C and 80% RH(Relative humidity) survived beyond 133 days, while at 26 °C and 40% RH, the organism was undetectable after 63 days. Our results suggest that local birds associated with leafy green fields likely pose a minimal impact of risk for food contamination, but also points out the need for increased analysis specifically for E. coli O157:H7. Furthermore, our study suggests the need for expanding research that addresses risks associated with large migratory birds, especially in areas where stagnated water sources would be used for overhead sprinkle irrigation.

A trait‐based framework for predicting foodborne pathogen risk from wild birds

“…Current evidence suggests that Salmonella spp. and E. coli , which were rarely found in bird feces in our study, may survive over longer time periods in bird feces (Feare et al, 1999; Fonseca et al, 2020; Kauffman & Lejeune, 2011; Moriarty et al, 2012).…”

Leafy Green Farm-to-Customer Process Model Predicts Product Testing Is Most Effective at Detecting Contamination When Conducted Early in the System before Effective Interventions

“…(iii) Small cluster contamination: 1% (1,000 lb) of the total mass was highly contaminated (100 CFU/lb). A small-cluster contamination event represented contamination due to animal intrusion or fecal contamination from wild animals, such as bird droppings directly contaminating the leaves or fecal pellets deposited in the field that could be transferred to the leaves due to irrigation or rainfall splash ( 26 , 28 , 41 ).…”

Interactions between Microbial Food Safety and Environmental Sustainability in the Fresh Produce Supply Chain

“…in avian fecal samples from crop farms (brassica plants) located in landscapes with high mammalian livestock densities, compared to farms located in landscapes with larger areas of natural habitat. Fonseca et al [ 23 ], analyzing local birds that inhabited near leafy green growing fields in the U.S. southwest, reported the absence of Salmonella spp. and E. coli O157:H7.…”