Bacterial cross contamination is the transfer of bacteria or other microorganisms from one substance to another.

Other types of cross-contamination include the transfer of food allergens, chemicals, or toxins though these are not the focus of this article.

Many people assume that foodborne illness is mostly caused by eating at restaurants, but there are many ways in which cross-contamination can occur, including.

primary food production from plants and animals on farms
during harvest or slaughter
secondary food production — including food processing and manufacturing
transportation of food
storage of food
distribution of food grocery stores, farmer’s markets, and more
food preparation and serving at home, restaurants, and other foodservice operations
Given that there are many points at which cross-contamination can occur, it’s important to learn about the different types and how you can prevent it.

There are three main types of cross-contamination: food-to-food, equipment-to-food, and people-to-food.

Food-to-food
Adding contaminated foods to non-contaminated foods results in food-to-food cross-contamination. This allows harmful bacteria to spread and populate.

Raw, undercooked, or improperly washed food can harbor large amounts of bacteria, such as Salmonella, Clostridium perfringens, Campylobacter, Staphylococcus aureus, E. coli, and Listeria monocytogenes all of which can harm your health if consumed.

Foods that pose the highest risk of bacterial contamination include leafy greens, bean sprouts, leftover rice, unpasteurized milk, soft cheeses, and deli meats, as well as raw eggs, poultry, meat, and seafood.

For example, adding unwashed, contaminated lettuce to a fresh salad can contaminate the other ingredients. This was the case in a 2006 E. Coli outbreak that affected 71 Taco Bell customers.

What’s more, leftovers kept in the fridge too long can result in bacterial overgrowth. Therefore, eat leftovers within 3–4 days and cook them to proper temperatures. If you plan to mix leftovers with other foods, the new meal should not be stored again as leftovers.

Equipment-to-food
Equipment-to-food is one of the most common yet unrecognized types of cross-contamination.

Bacteria can survive for long periods on surfaces like countertops, utensils, cutting boards, storage containers, and food manufacturing equipment.

When equipment is not washed properly or unknowingly contaminated with bacteria, it can transfer large volumes of harmful bacteria to food. This can happen at any point during food production both at home and in food manufacturing.

For example, a 2008 incident at a Canadian-based sliced meat company resulted in the death of 22 customers due to listeria-contaminated meat slicers.

A common example of this occurring at home is using the same cutting board and knife to cut raw meat and vegetables, which can be harmful if the vegetables are then consumed raw.

One study found that older participants were less likely to use soap and water to clean their cutting boards after working with raw meat, while younger people weren’t aware of the risks of cross-contamination. Thus, more food safety education seems to be needed across all age groups.

Finally, improper food preservation techniques can lead to cross-contamination. In 2015, home-canned potatoes used in a potato salad made 22 potluck attendees sick with botulism due to improper canning practices.

People-to-food
Humans can easily transfer bacteria from their bodies or clothes to food during many steps of food preparation.

For example, a person may cough into their hand or touch raw poultry and continue to prepare a meal without washing their hands in between.

In a 2019 study in 190 adults, only 58% of participants reported washing their hands before cooking or preparing food, while only 48% said they washed their hands after sneezing or coughing.

Other common examples include using a cellphone that’s loaded with bacteria while cooking or wiping your hands with a dirty apron or towel. These practices may contaminate your hands and spread bacteria to food or equipment.

Although this poses a concern, a 2015 meta-analysis found that food safety education both in the home and at work can significantly lower the risk of cross-contamination and unsafe food practices.

By far, the most effective way to reduce the risk of cross-contamination is to properly wash your hands with soap and water for at least 20 seconds