Two important examples are Giardia and Entamoeba histolytica. The latter causes amebiasis, which may lead to diarrhea, abdominal pain, and, in some cases, severe intestinal disease. Rarely, it can spread beyond the intestine and cause a liver abscess.
Contaminated water can also affect food indirectly. For example, washing vegetables with unsafe water may introduce contamination rather than remove it. Ice made from unsafe water can pose a similar risk.
How to Reduce Water-Related Risks
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Drink water from a reliable, treated source.
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When traveling, check local drinking-water advice and use sealed bottled water or appropriately treated water if the supply is uncertain.
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Avoid swallowing water from lakes, rivers, streams, or swimming areas.
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Use safe water for washing produce, making ice, brushing teeth, and preparing infant formula when local water quality is uncertain.
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Follow local public-health instructions during water-quality advisories.
Boiling is an effective method for inactivating many disease-causing organisms, including common intestinal parasites. When an official advisory recommends boiling, follow its instructions. CDC guidance commonly recommends bringing water to a rolling boil for one minute, or three minutes at elevations above 6,500 feet (about 2,000 meters), then allowing it to cool in a clean, covered container.
Some water contaminants, such as certain chemicals and heavy metals, are not removed by boiling. If chemical contamination is suspected, use an appropriate alternative water source and follow local public-health guidance.
7. Fermented, Pickled, and Lightly Processed Foods
Traditional foods such as pickled vegetables, fermented fish, cured meat, and lightly processed seafood may be prepared in many different ways. Their safety depends on the ingredients, production process, acidity, temperature, sanitation, and storage conditions.
Salt, vinegar, fermentation, and drying can inhibit some microorganisms under controlled conditions. However, these methods should not automatically be considered reliable parasite-killing treatments.
For example, marinating fish in citrus juice, as in ceviche, changes its texture and appearance but does not reliably eliminate parasites. Similarly, salting or pickling meat and fish at home may not provide the same level of protection as a validated commercial process.
If a food traditionally eaten raw or lightly processed has not been produced under appropriate safety controls, thorough cooking is generally the safer choice.
When purchasing preserved foods, choose reputable producers, check the packaging and storage instructions, and avoid products with damaged packaging, unusual swelling, leakage, or signs of spoilage.
8. Food Safety Mistakes That Can Increase Risk
Even good ingredients can become unsafe if they are handled incorrectly. Several common mistakes deserve attention.
Assuming Freshness Guarantees Safety
Freshness and contamination are not the same thing. Food may contain harmful microorganisms or parasites without visible signs of spoilage. Smell and appearance are useful for identifying some quality problems, but they cannot prove that food is safe.
Using One Cutting Board for Everything
Raw meat and seafood may contaminate ready-to-eat foods through knives, cutting boards, plates, and hands.
Use separate boards where possible, or thoroughly wash and clean equipment between tasks. Never place cooked food on a plate that previously held raw meat or seafood unless the plate has been properly washed.
Thawing Meat on the Counter
Leaving frozen meat at room temperature can allow harmful microorganisms to multiply on the outer surfaces while the center remains frozen. Thaw meat in the refrigerator, in cold water using a leakproof package, or in a microwave when it will be cooked immediately afterward.
Relying on Freezing Alone
Freezing can control certain parasites under specific conditions, but it does not reliably eliminate every parasite or every other foodborne hazard. For many foods, thorough cooking remains the simplest and most dependable option.
Neglecting Handwashing
Hands can transfer contamination from raw foods, soil, bathroom surfaces, and other sources to ready-to-eat meals.
Wash with soap and water before preparing food, after using the toilet, after changing diapers, after handling raw meat or seafood, and after gardening or touching potentially contaminated soil.
9. Who Needs to Be Especially Careful?
Although anyone can develop a foodborne infection, the consequences may be more serious for certain groups.
Pregnant people: Some infections, including toxoplasmosis, can affect the developing fetus even when the pregnant person has mild symptoms. Medical advice on safe food preparation is particularly important during pregnancy.
Young children: Children can become dehydrated more quickly than adults when they have significant diarrhea or vomiting. Caregivers should prioritize safe food and water and seek medical advice when concerning symptoms develop.
Older adults: Changes in immune function and the presence of other health conditions may increase the likelihood of complications from foodborne illness.
People with weakened immune systems: Individuals receiving chemotherapy, taking certain immune-suppressing medications, or living with conditions that weaken immunity may face greater risks from some parasitic infections.
These groups do not need to eliminate all fresh foods from their diets. Instead, they should use reliable food sources, avoid higher-risk raw foods, and follow personalized guidance from a healthcare professional when necessary.
10. Recognizing Possible Symptoms of a Parasitic Infection
Symptoms depend on the parasite, the amount ingested, and the person's immune status. Some infections cause symptoms within hours or days, while others may remain unnoticed for longer periods.
Possible symptoms include: