For many, cheese is a beloved part of a healthy and balanced diet, providing valuable protein and calcium. However, some varieties can pose a significant health risk, primarily due to microbial contamination. While hard cheeses made from pasteurized milk are generally safe, the concern arises with soft cheeses and those crafted from raw, unpasteurized milk, which can carry dangerous pathogens like Listeria monocytogenes. Understanding these risks, and how to mitigate them, is key to making informed dietary choices.
The Primary Threat: Bacterial Contamination
Pathogenic bacteria are the main reason certain cheeses are considered high-risk. These microbes can enter the cheesemaking process at various stages, from the farm to the factory, and are particularly dangerous in cheeses that don't undergo a kill step, like pasteurization, or where contamination can occur after processing.
Listeria Monocytogenes
Listeria monocytogenes is a particularly insidious bacterium because it can grow even in refrigerated temperatures, unlike many other foodborne pathogens. This makes it a significant threat in ready-to-eat foods like deli meats and, notably, soft cheeses. Outbreaks linked to soft cheeses like queso fresco, Brie, and Camembert are regularly reported. For most healthy adults, a Listeria infection (listeriosis) may cause mild, flu-like symptoms. However, for vulnerable populations such as pregnant women, newborns, the elderly, and those with compromised immune systems, listeriosis can be severe or even fatal, leading to meningitis, septicemia, or miscarriage.
E. coli and Salmonella
Cheeses made from raw, unpasteurized milk can also be a vehicle for E. coli and Salmonella. While pasteurization, a heating process, effectively kills these pathogens, raw milk and products derived from it bypass this critical safety step. Outbreaks linked to raw milk cheeses have led to serious illnesses, including hemolytic uremic syndrome from E. coli O157:H7. In one case, an outbreak was traced back to raw-milk gouda cheese, affecting multiple states.
How Different Cheeses Carry Different Risks
The risk profile of cheese is not uniform across all types. The moisture content, acidity (pH), and salt concentration all play a role in how susceptible a cheese is to bacterial growth.
- Soft vs. Hard Cheese: The most significant distinction lies between soft and hard cheeses. Soft cheeses, like Brie, Feta, Camembert, and queso fresco, have a high moisture content and a low acidity, creating an ideal environment for bacteria like Listeria to flourish. Hard cheeses, such as Cheddar, Parmesan, and Swiss, have lower moisture and more acidic conditions, which are far less hospitable to these pathogens. For this reason, hard cheeses are a much safer option, especially for high-risk individuals.
- Pasteurized vs. Unpasteurized Milk: Regardless of the cheese's firmness, the pasteurization status of the milk is paramount. All cheeses made from unpasteurized (raw) milk carry a higher risk of contamination because the milk has not been heat-treated to kill harmful bacteria. The Food and Drug Administration (FDA) in the U.S. recommends that vulnerable individuals avoid all unpasteurized dairy products.
The Role of Processing and Handling
Even cheeses made from pasteurized milk can become contaminated if processed in unsanitary conditions. Post-pasteurization contamination can occur from environmental sources within a manufacturing facility, leading to outbreaks linked to products made with heat-treated milk. Poor hygiene during handling, like using unclean utensils or food-contact surfaces, can also introduce pathogens.
Mycotoxin Contamination
Certain fungi involved in cheesemaking, or those that contaminate the cheese during aging, can produce mycotoxins. Aflatoxin M1, a known carcinogen, is a particular concern in cheese made from milk from animals fed contaminated feed. While pasteurization can help, it doesn't eliminate all risks associated with fungal toxins. Therefore, good hygiene practices throughout the production chain are essential.
How to Reduce Risk and Make Safer Choices
For most people, cheese is safe to enjoy. However, for vulnerable populations or simply as a best practice, these guidelines can help reduce your risk of foodborne illness.
- Choose Pasteurization: Always check the label to ensure cheese is made from pasteurized milk, especially for soft varieties. This is the single most important step for safety.
- Cook Thoroughly: If you use a higher-risk cheese, such as Brie or Queso Fresco, cook it until steaming hot (to 165°F) before eating. This will kill any bacteria present.
- Practice Good Hygiene: At home, use separate cutting boards and knives for different foods to prevent cross-contamination. Always wash your hands and utensils after handling food.
- Store Properly: Keep cheese refrigerated and wrapped to prevent moisture loss and bacterial growth. Discard soft, moldy cheese entirely.
A Comparison of Cheese Safety Risks
| Feature | Soft Cheeses (e.g., Brie, Feta, Queso Fresco) | Hard Cheeses (e.g., Cheddar, Parmesan, Swiss) |
|---|---|---|
| Moisture Content | High moisture provides a hospitable environment for bacterial growth. | Low moisture and higher acidity inhibit bacterial growth. |
| Pasteurization | Must be made from pasteurized milk to be considered safe for vulnerable groups. | Generally safe even if made with raw milk, but pasteurized is still recommended for at-risk individuals. |
| Aging Process | Fresh or short-ripening periods mean less time for natural acidity or salt to inhibit pathogens. | Extended aging processes contribute to microbial safety. |
| Primary Risk | High risk of Listeria and other bacteria if unpasteurized or contaminated after processing. | Lower risk of bacterial pathogens due to inhospitable environment. |
| Risk for Vulnerable Groups | Not recommended unless cooked thoroughly and verified as pasteurized. | Considered safer options when made with pasteurized milk. |
Conclusion
While cheese offers numerous nutritional benefits, a critical distinction must be made based on its type and preparation method to ensure safety. The question of why is cheese a high risk food is not about cheese in general, but specifically about soft, unpasteurized, and improperly handled varieties that can harbor dangerous pathogens like Listeria and E. coli. For the general public, moderation and proper food hygiene are sufficient. However, for those in high-risk categories, such as pregnant women, the elderly, or immunocompromised individuals, exercising caution by avoiding soft and raw-milk cheeses is a necessary precaution. By choosing pasteurized products, practicing good handling, and understanding the risks, you can safely enjoy the wide world of cheese. For more information on food safety, visit FoodSafety.gov.
