Food

Microbiological Surveillance Sampling: FY14-16 Whole Fresh Avocados

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The U.S. Food and Drug Administration (FDA) set out to collect and test whole fresh avocados in 2014 as part of the agency’s new proactive and preventive approach to deploying its sampling resources with the ultimate goal of keeping contaminated food from reaching consumers.

The new approach, detailed in the Background section of this report (page 5), centers on the testing of a large number of samples of targeted foods over a relatively short period, about 18 months, to ensure that enough data are available to inform decisions. This approach may help the agency determine if there are common factors – such as origin, variety or season – associated with pathogen findings.

The FDA began the avocado assignment in May 2014 under its new sampling model. The agency collected 1,615 samples of avocados to test to determine the prevalence of Salmonella and Listeria monocytogenes in the commodity (i.e., the number of samples that tested positive for the pathogen out of the total number of samples tested). The agency collected about 70 percent of its samples from imported avocados and the rest from domestically grown avocados, approximately proportionate to their respective U.S. market shares at the outset of the assignment. The FDA designed its sampling plan such that if contamination of one percent or greater was present in the commodity, the agency would be likely to detect it. The FDA monitored the assignment closely to gather lessons learned and to make changes to its sampling procedures if needed to address trends or food safety issues.

Three months into the assignment, the FDA updated its approach to its Listeria monocytogenes testing to focus on the avocado pulp (i.e., the fruit’s edible portion), as opposed to its exterior, to better evaluate public health concerns associated with the pathogen, namely the extent to which it may be present in the part of the fruit that people eat. The agency made the change to its test method as part of its assignment monitoring and upon considering that, at the time, no outbreaks or individual illnesses had been linked to Listeria monocytogenes on the fruit’s exterior (i.e., its skin).

Based on the test results, the FDA found the overall prevalence of Salmonella on the samples collected to be 0.74 percent. Breakdowns by avocado origin, variety and season are provided in the Pathogen Findings section of this report (page 10).

Based on the test results, the FDA found the overall prevalence of Listeria monocytogenes in the avocado pulp samples to be 0.24 percent and in the avocado skin samples to be 17.73 percent. The report addresses these findings in its various sections and aggregates the discussion of them in a dedicated appendix, in addition to providing breakdowns as described above.

The FDA’s assignment was not designed to determine the concentrations of the pathogens in the samples. At low levels of exposure, Listeria monocytogenes does not cause severe illness in healthy adults. However, pregnant women, older adults and persons with weakened immune systems (such as organ transplant recipients, or those with diabetes or cancer) are susceptible to small amounts of the pathogen.

As described in the Public Health Impact section of this report (page 17), the FDA conducted whole genome sequencing (WGS) of all the avocado samples that tested positive for a pathogen under this assignment and subsequently analyzed them to determine whether any of the detected pathogens may be linked to human illness. The FDA found some of the Listeria monocytogenes strains isolated from both skin and pulp samples to be highly related to Listeria monocytogenes strains found in ill persons. However, the available epidemiological information did not indicate whether the consumption of avocados was implicated in the illnesses.

All three of the Listeria monocytogenes-positive samples of avocado pulp were detected by the FDA in imported avocados. In response to those detections, the FDA refused entries of avocados from lots associated with the positive samples and put the responsible firms and their product on Import Alert 99-23, “Detention without Physical Examination of Produce Due to Contamination with Human Pathogens.”

Listeria monocytogenes was detected by the FDA in avocado skin samples from both domestic and imported product. Of the 64 positive avocado skin samples, 33 were from domestic avocados and 31 were from imported avocados. The FDA notified the responsible firms of the test results as soon as the results were available.

Salmonella was detected by the FDA in 12 avocado skin samples from domestically grown product. No samples from imported avocados tested positive for Salmonella. In response to the detections, the FDA worked with the firms that owned or released the product to conduct voluntary recalls and followed up with facility inspections.

The findings of this assignment affirm that Salmonella may be present on avocados and that Listeria monocytogenes may be present on or in the fruit. Moreover, the findings underscore the need for avocado growers to comply with the FDA’s Produce Safety Rule[1] as applicable, and for importers of the fruit to comply with the FDA’s Foreign Supplier Verification Programs Rule[2] as applicable. Avocados require appropriate protection from environmental pathogens during growing, harvesting, packing and holding, as this study indicates.

Consumers can take steps to reduce possible microbial risks related to avocados. Foodsafety.gov recommends that consumers “wash all produce thoroughly under running water before eating, cutting or cooking.” The site also advises, “Even if you plan to cut the rind or peel off the produce before eating, it is still important to wash it first so dirt and bacteria aren’t transferred from the knife onto the fruit.” Foodsafety.gov also recommends that consumers scrub firm produce (which includes avocados) with a clean produce brush, and then dry it with a clean cloth towel or paper towel to further reduce bacteria that may be present.

Other practices associated with avocado consumption may reduce the risk to consumers as well. Consumers commonly slice avocados and extract the fruit’s pulp prior to eating it, discarding the fruit’s peel as they would a banana peel or an orange rind. Consumers also typically eat avocados shortly after slicing the fruit as its pulp tends to brown quickly once exposed to oxygen. These practices generally limit the amount of the pathogen, if present, that consumers may be exposed to.

The FDA will continue to evaluate methods to reduce microbial contamination of avocados and avocado products. Consistent with that work, the agency has published draft guidance to help industry comply with the Produce Safety Rule. The agency likewise will work with industry and other food safety experts on best practices that may be used to reduce contamination of avocado skin with Listeria monocytogenes. In addition, the agency began a related large-scale assignment in 2017 to sample processed avocados for Salmonella and Listeria monocytogenes to determine the extent to which those pathogens may be present in the processed product, the main ingredient in guacamole. The processed avocado assignment is slated to conclude in 2019.

The FDA also will continue to sample whole fresh avocados using its longstanding approach to food sampling, which centers on (but is not limited to) the following criteria:

  • A firm has a previous history of unmitigated microbial contamination in the environment (e.g., human illness, recalled or seized product, previous inspectional history, or environmental pathogens without proper corrective actions by the facility), or
  • Inspectional observations that warrant collection of samples for microbiological analyses.

Employing the approaches described above, the FDA will sample avocados as warranted and take other steps consistent with its mission to protect consumers.


[1] The Produce Safety Rule establishes, for the first time, science-based minimum standards for the safe growing, harvesting, packing, and holding of fruits and vegetables grown for human consumption.

[2] The Foreign Supplier Verification Programs Rule requires that importers perform certain risk-based activities to verify that food imported into the United States has been produced in a manner that meets applicable U.S. safety standards.

Page Last Updated: 12/07/2018
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