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By Mayo Clinic staffContamination of food can happen at any point during its production: growing, harvesting, processing, storing, shipping or preparing. Cross-contamination — the transfer of harmful organisms from one surface to another — is often the cause. This is especially troublesome for raw, ready-to-eat foods, such as salads or other produce. Because these foods aren't cooked, harmful organisms aren't destroyed before eating and can cause food poisoning.
Many bacterial, viral or parasitic agents cause food poisoning. The following table shows some of the possible contaminants, when you might start to feel symptoms and common ways the organism is spread.
| Contaminant | Onset of symptoms | Foods affected and means of transmission |
|---|---|---|
| Campylobacter | 2 to 5 days | Meat and poultry. Contamination occurs during processing if animal feces contact meat surfaces. Other sources include unpasteurized milk and contaminated water. |
| Clostridium perfringens | 8 to 16 hours | Meats, stews and gravies. Commonly spread when serving dishes don't keep food hot enough or food is chilled too slowly. |
| Escherichia coli (E. coli) O157:H7 | 1 to 8 days | Beef contaminated during slaughter. Spread mainly by undercooked ground beef. Other sources include unpasteurized milk and apple cider, alfalfa sprouts, and contaminated water. |
| Giardia lamblia | 1 to 2 weeks | Raw, ready-to-eat produce and contaminated water. Can be spread by an infected food handler. |
| Hepatitis A | 28 days | Raw, ready-to-eat produce and shellfish from contaminated water. Can be spread by an infected food handler. |
| Listeria | 9 to 48 hours | Hot dogs, luncheon meats, unpasteurized milk and cheeses, and unwashed raw produce. Can be spread through contaminated soil and water. |
| Noroviruses (Norwalk-like viruses) | 12 to 48 hours | Raw, ready-to-eat produce and shellfish from contaminated water. Can be spread by an infected food handler. |
| Rotavirus | 1 to 3 days | Raw, ready-to-eat produce. Can be spread by an infected food handler. |
| Salmonella | 1 to 3 days | Raw or contaminated meat, poultry, milk or egg yolks. Survives inadequate cooking. Can be spread by knives, cutting surfaces or an infected food handler. |
| Shigella | 24 to 48 hours | Raw, ready-to-eat produce. Can be spread by an infected food handler. |
| Staphylococcus aureus | 1 to 6 hours | Meats and prepared salads, cream sauces and cream-filled pastries. Can be spread by hand contact, coughing and sneezing. |
| Vibrio vulnificus | 1 to 7 days | Raw oysters and raw or undercooked mussels, clams and whole scallops. Can be spread through contaminated seawater. |
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- Listeriosis. Centers for Disease Control and Prevention Division of Foodborne, Bacterial and Mycotic Diseases. http://www.cdc.gov/nczved/dfbmd/disease_listing/listeriosis_gi.html. Accessed April 20, 2009.
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