Summary of Awards to Date

Distribution of Salmonella in pistachios and development of effective sampling strategies.


Jan. 1, 2012 - Dec. 31, 2013

Award Number


Amount Awarded



Linda J. Harris, Ph.D.
University of California, Davis


R. Atwill



Nuts and other low-moisture foods have generally been considered low-risks for foodborne illness because they are consumed in a dry state where water activity (available moisture) is too low to support microbial growth. However, it is increasingly recognized that many foodborne pathogens can cause illness at very low concentrations, such that microbial growth is not required. In the past decade, outbreaks associated with consumption of raw almonds and in-shell hazelnuts have been documented in the U.S. In 2009 there was a recall of pistachios when Salmonella was isolated from commercial products. With the exception of almonds, very little is known about the prevalence and levels of Salmonella in tree nuts and nothing is known about overall distribution of the organism within contaminated lots. These data are important to develop robust Quantitative microbial risk assessment (QMRA) and for developing scientifically-sound product sampling schemes for verification of food safety plans. This proposal will evaluate the prevalence, levels and distribution of Salmonella in U.S. pistachios. Salmonella isolates will be characterized as a means of providing insight into potential routes of contamination. These data will be used to determine appropriate sampling schemes for the pistachio industry and will be used to update and improve a QMRA that is currently in development.