PEM can serve two purposes for sanitation:

  1. For sanitation verification. Did you start out clean? Did the sanitation practices,
    policies, and procedures achieve the desired cleanliness standard? Test during post rinse or pre-operational inspections.
  2. When the facility is at its “dirtiest.” Right before sanitation (or at least 3–4 hours into
    production), test the equipment and facility to determine if any microbiological
    contaminants came in via cross-contamination during the processing period, verify
    facility sanitary design, or validate production and sanitation procedures.
    An effective program has a mix of both PEM purposes. A best practice when determining the
    timing of sample collection is to also vary the days and times of sampling locations. If staff
    know that Tuesday is swab day, there may be some bias in how the area is cleaned ahead of
    time. However, if any day could be swabbing day, then the bias can be eliminated.

Swabbing Locations

When deciding where to swab, many facilities use a zonal approach. Zone 1 starts with
product contact surfaces, and Zones 2–4 move increasingly further away from product
contact. Envision a dart board. Product contact is in the center (the bullseye); in darts, the
most points are achieved by hitting this area. Moving further away from the center moves
further away from product contact, resulting in fewer “points.”

Standard or Random Locations

An effective PEM program has a mix of standard sampling sites and randomly selected sites.
For sanitation verification or routine situations, some sampling locations will be sampled
every time after sanitation. However, some sampling locations should be random. Train and
encourage staff who are collecting samples to look around the facility. Instruct them to look
for areas they think may have a problem and sample those sites. Remind them not to look
solely at eye level. Twenty to 30 percent of swabs should be taken from above eye level, and
20–30 percent should be taken below eye level. Do not swab only what is easy to see right in
front; crouch down under equipment and use ladders to see above. Design sampling devices
so that a person can easily collect samples from different heights and locations. (Case in point:
The author once retrofitted a telescoping paint device to swab overhead air vents.) If an area
is difficult to clean (under equipment and higher than a person can reach), then it is less likely
to be cleaned. Swab the area that is the most difficult to clean to determine if microorganisms
are present. If the difficult-to-clean area is free of microbiological contaminants, then the
easy-to-clean places probably are, as well.

Results from random sampling can be very powerful data; however, random sampling
requires extra documentation. This documentation must describe some method of recording
what was sampled, and where. Never underestimate the power of pictures—they are an
excellent tool to help record the actual sample location. A picture of the sampled area with a
finger pointing to the location removes any doubt as to what/where was sampled.

If a third party lab is testing the samples, it could take up to a week before a facility knows the results.
Having good documentation of what was sampled will help an investigation if the site comes
back positive or out of specification. In addition, understanding what locations have been
sampled across the site will help in identifying trends and making decisions on what needs to
be increased or decreased as part of continuous improvement. The data needs to drive
decisions. Use trends to determine appropriate testing sites and frequencies.

Examples of some good sampling locations include:

Cracks, crevices, niches—all difficult-to-clean locations

  • Tight corners, bends, and sharp edges that may harbor biofilms
  • Locations that provide a transfer location between zones
  • Areas that show issues with sanitary design
  • Areas that are exposed due to traffic patterns (of people, trash, forklifts, etc.)
  • Areas that routinely have pooling water or collect debris
  • Sampling sites that are closest or could affect open product, packaging, or ingredients
  • Locations after the kill step (heat or pasteurization) and before final packaging (high
  • Problem areas, or areas that historically have had positive or out-of-specification

Do not think only of equipment and infrastructure; think about water quality and air quality,
too. When wet sanitation cleaning recipes are validated, it is essential that the cleaning
chemicals clean the equipment, not the water. If the water is contaminated, then all the active
compounds in the chemical will be used to clean the water, and nothing will be left over to
actually clean the equipment. Regulators and third-party audits require minimal water testing
from the main water sources. Also think about all the point-of-use areas of water, such as
hoses, sinks, mop stations, etc. Ensure that the water coming from those sources (both the
water itself and the equipment/piping) are not contaminating the product and environment.

What about air? The air touches the product and equipment; consequently, the air must not
contaminate the environment. Third-party audits require microbiological testing for product contact compressed air. In addition, the air in the processing and packaging areas should be
tested. Pour plates can be placed in the room, or a forced-air testing unit can be utilized. Also
take a sample of the filters on the HVAC system, and make sure to test only the final filter, as
the pre-filter likely will have microbiological growth since its job is to filter the air.

It is important not to forget about people. We are walking hazards to the product. Test the
hands, tools, equipment, personal protective gear, uniforms, etc., of employees to ensure
that they will not contaminate the product with microorganisms as they go about their daily