There’s more than one kind of food poisoning

DEAR DR. ROACH >> Can you tell me about food poisoning? I often hear the term, but it seems to mean different things to different people.

— V.A.

DEAR READER >> Foodborne illnesses are indeed a very large and diverse group. Although the term may refer to toxins in food, such as poisonous mushrooms or heavy metal contamination, it most often refers to illness caused by infectious pathogens, usually bacteria and viruses, but parasites as well.

The most common infectious foodborne illness is associated with what’s called a toxin-mediated diarrhea. Many bacteria, such as E. coli, can cause watery diarrhea that starts within a day or two of ingestion of a contaminated meal. Viruses, especially norovirus and similar, are very infectious and cause outbreaks in homes, institutions and cruise ships. Parasites, such as Giardia and Cryptosporidium, are often ingested through contaminated water and may cause longer-lasting symptoms. Most cases of watery diarrhea are selflimited and do not need treatment.

Some unhealthy bacteria grow in the intestine and cause diarrhea with fever and sometimes blood. There are four that may cause a fever 48-72 hours after ingestion: Salmonella, typically from undercooked eggs or poultry; Shigella, which is highly infectious and transmitted by poor hand hygiene and contaminated food; Campylobacter, also from undercooked poultry; and an especially nasty strain of E. coli called O157:H7, most associated with beef. Diarrhea with fever or blood may also go away on its own, but should still be evaluated by your medical provider since some of these causes can be quite serious.

Some foodborne illnesses cause vomiting, not diarrhea. The toxin from Staphylococcus aureus (“staph”), which often is triggered by dairy, eggs or salad that has been left at room temperature, causes vomiting about six hours after consumption of the food.

Bacillus cereus, classically from fried or other rice that has sat out, also causes acute nausea and vomiting within a few hours. Since these toxins are heat-stable, reheating the food does not prevent it from causing symptoms.

Preventing foodborne illness depends on correct kitchen technique.

Contact Dr. Roach at ToYourGoodHealth@med. cornell.edu.