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How Do I Know If I Have Food Poisoning?

Medically Reviewed by Sabrina Felson, MD on May 03, 2021

       

If you’ve ever had food poisoning, you probably had a good idea that’s what it was even before you talked to your doctor. It’s hard to miss the main symptoms: stomach cramps, vomiting, and diarrhea. They can hit a few hours or a day or two after you eat the food that caused the problem.

Your symptoms usually pass in a few days or even in mere hours. But if your discomfort doesn’t go away, you may need to get checked and find out exactly what made you sick. You should also see a doctor if along with other symptoms you have high fever, blood in your stool, or feel dehydrated or unable to keep any food or liquid down.

Your doctor may be able to tell you what caused it after running tests. But they aren’t always necessary and don’t confirm every case.     

Do I Have Food Poisoning?

Many times, your doctor will diagnose food poisoning based simply on your symptoms.

Some 250 different bacteria, viruses, and parasites can cause food poisoning. While the main symptoms are nausea, diarrhea, vomiting, and stomach cramps, you also may have a fever, headache, muscle and joint aches, or blood in your stool. You may also be dehydrated, so your mouth and throat feel dry and you don’t pee as often as you typically do. Dehydration can make you dizzy when you stand up. Rarely, food poisoning can cause blurry or double vision, tingling, or weakness.

Tests for Food Poisoning

If your illness is severe or complicated, your doctor may run some of the following tests. 

Stool cultures are the most common lab test for food poisoning. Your doctor may order one if you have a fever, ntense stomach pain, or bloody diarrhea, or if there is an outbreak that is being tracked. They may also order one if you have symptoms that linger. A sample of your stool can help tell if your sickness is related to bacteria. It can even reveal the germ’s DNA “fingerprint” and which antibiotics will kill it. Viruses are more difficult to see in culture,  so if the specific virus needs to be identified, your doctor may order stool tests to look for the germ's DNA fingerprint.Microscopic exams of stool can identify parasites. Stool tests aren’t always accurate, and they can take several days to come back.

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Blood tests may be ordered if your doctor thinks the infection has spread into the blood. Blood tests can detect the bacteria Listeria monocytogenes and the hepatitis A virus. Specific blood tests can tell how sick you are by looking for inflammation and signs that you’re dehydrated.

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Stool or blood tests can check for toxins, such as for botulism, which can be deadly.

Imaging tests such as MRIs and CT scans aren’t often used in food poisoning cases. But they can help rule out other causes for your symptoms.     

Could It Be Something Else?

A host of other conditions can lead to many of the same symptoms of food poisoning. Most common is mon-foodborne  gastroenteritis, which is most often caused by a virus. For instance, Norovirus causes both foodborne gastroenteritis (from contaminated food or water) and viral gastroenteritis from person to person spread. Other causes include gallbladder problems, pancreatitis, and inflammatory bowel disease. So figuring out if you have food poisoning is as much about the timing as it is about the symptoms themselves.

Delayed Symptoms

In most cases, food poisoning usually shows up hours or days after you’ve eaten something that made you sick. But different organisms work at different speeds. For example, Staphylococcus aureus can give you cramps, diarrhea, and nausea in as little as 30 minutes after you eat or drink. This bacterium grows in meats, eggs, and cream that haven’t been refrigerated properly. Another, far less common, cause of foodborne illness is the hepatitis A virus. It can lie in wait as long as 50 days before making itself known. You can get the virus through foods and drinks that have been in contact with sewage water. You’re more likely to get the virus when traveling in developing countries.

WebMD Medical Reference

Sources

SOURCES:

PubMed Health: “Food Poisoning (Foodborne Illness).”

CDC: “Be Food Safe: Protect Yourself from Food Poisoning,” “Salmonella: Diagnosis and Treatment,” “Staphylococcal Food Poisoning,” “Diagnosis and Management of Foodborne Illnesses.”

UpToDate: “Patient education: Food poisoning (foodborne illness) (Beyond the Basics).”

American Family Physician: “Diagnosis and Management of Foodborne Illness,” Evaluation of Nausea and Vomitting.”

Medscape: “Food Poisoning Workup.”

FDA: “Foodborne Illnesses: What You Need to Know.”

Morbidity and Mortality Weekly Report: “Diagnosis and Management of Foodborne Illnesses.”

Clinical Microbiology Reviews: “Laboratory Diagnosis of Bacterial Gastroenteritis.”

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