Actions after an isolation

Actions after a positive isolation of L. monocytogenes from a processing environment or final product

Multidisciplinary team

Establish a multidisciplinary team to handle the implications of the isolation.  Members of the team should include senior management (to ensure any findings of an investigation are implemented), plant technical and cleaning staff, along with staff that have microbiological experience.

Review HACCP

A common initial step for an isolation of L. monocytogenes is to review HACCP schemes and HACCP-related records to determine if there was ineffective process monitoring that caused the issue.  Typically, the review takes the form of an unannounced audit.  It should be kept in mind that for some fish processes including cold smoking, there are no critical control points that can effectively control L. monocytogenes (or reduce it to an acceptable level).  Consequently, for an isolation associated with a cold smoking process, it is more usual to investigate the pre-requisite supply chain programme and secondary control points (also known as control points or operation pre-requisite programmes )

Review cleaning effectiveness

A review or audit should also include an assessment of cleaning effectiveness and review the degree of complex machine disassembly, the standard operating procedures for cleaning, cleaning frequencies and the chemicals used and at what concentrations.  The auditor should ideally be accompanied by a plant engineer to assist in the disassembly of equipment.  Poorly designed or damaged processing equipment can be a persistent source of L. monocytogenes.  A good audit will visit a plant prior to the commencement of processing and note any poorly-cleaned areas of equipment or the plant environment, especially if these are contaminated with food detritus after a clean down.  An exceptionally thorough audit will include microbiological sample collections and tests from poorly cleaned disassembled equipment. 

Scrutinise historical records

Clues to likely sources of L. monocytogenes can often be found by scrutinising the record of historical isolations in a plant.  Many auditors will plot these isolations on a plan of the plant as a way of assessing if there are geographical connections between isolations, or a role for plant infrastructures such as drains in the spread of L. monocytogenes.  Suspected geographical issues can be confirmed or excluded by extensive sample collection in the suspected problem areas.  Common strategies are to vary the sample collection surfaces from those routinely sampled by the FBO and to vary the time that samples are collected.  Plant resident L. monocytogenes can emerge from niches only after the commencement of processing and so it can be beneficial to sample during, as well as before, processing.

Examine staff movements

Assess staff and equipment movements between the Low Risk and High Care sections of the plant.  Clothes and footwear in one section of the plant should not be used in the other.  Cross contamination can occur if staff circumvent the barriers protecting the High Care Area (HCA).  The movements of plant engineering and maintenance staff and their tools should also be scrutinised.

Review wet and dry cleaning regimes

An effective strategy in dealing with L. monocytogenes is to keep the processing plant as dry as possible.  Many larger fish processors do not allow any water to be used in their HCA during routine processing.  It is a good practice to remove all non-essential hoses from the HCA and to only dry clean floors of detritus (e.g. using squeegees) during production.  A common practice for equipment that has an absolute requirement for wet cleaning during production is to remove it from the HCA and to clean it in an anteroom that is physically separated from the HCA.  Typically such rooms have elevated thresholds to contain water and equipment is cleaned on elevated mesh or slats to prevent the underside from becoming wet.  In some plants there was careful consideration of the location of cleaning anterooms, which were typically build as extensions to the main processing halls.  A number of processers had a preference for situating cleaning anterooms in close proximity to drain exits to prevent wetting the drains inside the processing halls.

Examine walls, drains and floors

Water movement through drains should be from the HCA to the Low Risk Area (LRA).  Blockages in the drains that change water movement from the LRA into the HCA can result in the transfer of L. monocytogenes into the HCA.  Drains should be checked to ensure there is no blockage after an L. monocytogenes isolation.

The plant walls, drains and floors should be repaired to prevent the establishment of plant resident L. monocytogenes in cracks and other damaged areas of the plant infrastructure.  Roofs and the drainage from them can allow the establishment of L. monocytogenes if blocked or damaged guttering results in water draining into the plant.  There is evidence in the literature that the replacement of processing equipment could result in the release of contained contamination into the plant environment.  Thus any issue may be linked to recent refurbishment.

Check positive air pressure system

Audit the effectiveness of positive air pressure systems for HCA to ensure that air movements are always inside to outside. Whilst there is currently no specific requirement for an air over-pressure in high-care areas, good practice is that the ventilation system is in balance, such that there is no large movement of air from low risk into high-care

Review hand washing, gloves and lockers

Audit employee hand washing and glove replacement frequencies.  Hand and glove swabs can be undertaken to ensure hygienic handling of product.  Gloves can become contaminated in dispensers if inappropriate cleaning is undertaken in the vicinity.  Gloves taken from a dispenser can be randomly checked for sterility. Key equipment and utensils should not be stored in personal lockers.

Where a clear trend for L. monocytogenes isolations can’t be identified, typing can be useful to discriminate if the problem is a single plant persistent strain, or lots of different isolates.  Further information on L. monocytogenes typing can be found here.