establishing inspection and maintenance programs for water sources under the operation’s
control; establishing cleaning and sanitation procedures for harvesting equipment, field tools,
containers and packing lines; and proper composting procedures for raw animal-based soil
amendments or purchasing from suppliers that use validated or verified antimicrobial
treatments.
Each of these may be of greater or lesser importance depending on the commodity or region of
production. Food safety guidances from FDA or industry for specific commodities can be of
value in determining relative levels of risk, including for romaine lettuce (e.g., FDA Guidance for
Industry: Guide to Minimize Microbial Food Safety Hazards of Leafy Greens (ref); and California
and Arizona Leafy Greens Marketing Agreement guidance documents (ref)). Each operation
should establish a documented food safety plan, identifying the hazards and their sources
reasonably likely to occur at their specific operation and the controls or mitigations that will be
used to minimize or monitor their occurrence. Plans should include procedures that will be used
to verify implementation and effectiveness of the controls, potentially through observation,
recordkeeping, self-audits or testing. Third-party audits like USDA (ref) and GLOBALG.A.P.
(ref), both of which use the industry-developed Harmonized Standards (ref), can be another
means of verification and can provide checklists useful for self-audits. Before testing is ever
used, it is important to understand what sampling protocols will be used and what the results will
mean; this is true whether testing produce or any of the inputs described above.
2.3. Limitations because of product shelf-life
2.3.1. Inability to resample/retest
Field testing is preferred to post-harvest testing for several reasons: a) should the testing
demonstrate that the crop is contaminated with a pathogen, it is preferable to know that before
making further investments into harvesting and post-harvest handling; b) once harvested, the
saleable life of Romaine lettuce is only a few days, and preharvest testing allows for an
assessment without impacting that shelf-life.
However, should the testing yield a positive result for a pathogen, resampling and retesting are
rarely practical. When field testing is performed, it is usually done as close to the expected
harvest date as possible; e.g., scheduled to obtain the test results the day before harvest so that
a no-harvest decision can still be made. Testing earlier is not recommended because of the
potential for a contamination event to be missed. Consequently, should testing yield a positive
result, the time needed to resample and retest would put the field beyond its saleable quality.
Even if shelf life weren’t an issue, retesting is probably inappropriate. As noted in the
Microbiological Testing of Fresh Produce
white paper, even if the subsequent test does not
confirm the initial positive results, a negative result doesn’t negate a positive result. Simply
retesting the field would not provide data that would allow harvest.
2.3.2. Need for rapid test method
The desire to harvest as close to harvest as possible (so as to minimize the risk of not detecting
a pre-harvest contamination event) and the short post-harvest shelf-life of Romaine lettuce
