What Could Be Lurking in Your Sandwich?

Find out what could be lurking in your sandwich and how to properly handle sandwich fillings to ensure they're safe to eat.
What Could Be Lurking in Your Sandwich?
August 6, 2019

We tend to think of sandwiches as low-risk foods. In reality, because sandwiches typically aren't cooked after being assembled, they’re as high-risk as any other food. In other words, the bread surrounding your high-risk fillings doesn’t protect you from food-borne illness.

Let’s take a look at the five most common sandwich fillings in Canada:

  1. lettuce
  2. tomatoes
  3. mayonnaise
  4. deli meat (turkey, chicken, ham, bacon)
  5. cheese

Each of these ingredients have been linked to food-borne illness outbreaks. Even seemingly harmless lettuce can harbour E. coli O157:H7, the pathogenic strain of E. coli which can cause bloody diarrhea or even kidney failure.

So what could be lurking in your favourite sandwich and how can you ensure your sandwich is safe to eat? Read on to find out.

Lettuce & tomatoes

Lettuce and tomatoes are grown close to the ground and can easily become contaminated with bacteria like Salmonella and E. coli. In the field, Salmonella and/or E. coli can be transferred onto raw fruits and vegetables from the soil, from contaminated water, or from animals or manure.

After harvesting, fruits and vegetables can become contaminated by improper food handling or storage at the grocery store or in your refrigerator; or from counters and cutting boards through cross-contamination or inadequate cleaning and sanitizing. Roughly 25% of food-borne illness outbreaks in Canada are linked to raw fruits and vegetables.


Commercial mayonnaise, which is typically too acidic to cause food-borne illness on its own, can become dangerous under certain conditions.

For example, if you add low-acid foods to commercial mayonnaise (e.g. hard-boiled eggs, chicken), you alter the pH balance, which can allow for bacterial growth. Combine that with poor personal hygiene (e.g. touching your face, particularly around the eyes or nose) and temperature abuse (not keeping the food out of the Temperature Danger Zone*), and you have a recipe for food poisoning.

If you make your own mayonnaise, the risk is even greater because many homemade mayo recipes do not incorporate acid and the raw egg could introduce Salmonella bacteria.

*In the province of Manitoba, the Temperature Danger Zone is considered to be between 5°C and 60°C. Everywhere else in Canada, it is between 4°C and 60°C.

Deli meat

Deli meats like ham, turkey, chicken and others have been implicated in a number of food-borne illness outbreaks, including one of the worst outbreaks of listeriosis in Canadian history. Listeriosis, a food-borne infection caused by the bacterium Listeria, is the food-borne infection that is most frequently associated with processed meats, but salmonellosis and Campylobacter infection have also been known to occur.

Listeriosis results in more deaths than any other food-borne infection in Canada and can have serious consequences for pregnant women and people with impaired immune systems (which is why they are advised to avoid eating deli meat altogether), but even healthy people can get seriously ill from Listeria.


Dairy products (which includes cheese) can harbour pathogenic bacteria, which can multiply to unsafe levels and cause food poisoning if handled or stored improperly.

Soft cheeses made from raw or unpasteurized milk, such as feta, queso fresco or brie, pose a much higher risk of infection with Salmonella, E. coli or Listeria than pasteurized or hard cheeses because they haven’t been treated to eliminate bacteria.

Vulnerable groups, including pregnant women, young children, the elderly and immunocompromised people, should avoid eating unpasteurized soft cheeses.

How to prepare a safe sandwich

The good news is that sandwiches are just the same as any other high-risk food, which means you simply follow the same food safety rules.

This includes:

  • keeping food out of the Temperature Danger Zone
  • storing food properly (e.g. ready-to-eat foods on shelves above raw foods)
  • rinsing any raw vegetables or fruit in cool, running water (don’t soak them in a sink full of water)
  • throwing away any ingredients with signs of spoilage (e.g. bad smells, slimy skin)
  • washing your hands and practicing good personal hygiene
  • preparing raw fruits and vegetables separately from raw meat, poultry or seafood
  • using only clean and sanitized equipment and utensils
  • not handling food if you’re sick

Of course, this is not an exhaustive list of everything that needs to be done to ensure food safety; it’s important to remember that what passes for safe food handling at home generally doesn’t cut it in a commercial food business.

Food businesses are responsible for training all employees who handle food in the business on food safety best practices and procedures, as well as the food safety risks that can occur if something goes wrong (or if they cut corners). Find out why food safety training is important.

A few things to consider if you’re preparing sandwich fillings in bulk, or pre-assembling sandwiches for sale in a food business:

  • Only take as much from the fridge as you can prepare in a short amount of time. Preparing food in small batches ensures that food doesn’t sit out at room temperature for too long.
  • Store ready-to-eat foods (e.g. pre-cut tomato slices, shredded lettuce, cheese slices) on shelves above raw foods in your refrigerator.
  • Wear gloves and a hair net when preparing ready-to-eat foods like sandwiches to prevent contaminating it with bacteria from your hands or body.
  • After assembling ready-to-eat sandwiches, refrigerate them ASAP.

Once sandwiches are prepared, store them in a chilled display case or in a refrigerator until purchase.