context: 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. 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. 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 or intense stomach pain along with other symptoms. She 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 âfingerprintâ and which antibiotics will kill it. Microscopic exams of stool can identify parasites. Stool tests aren't always accurate, and they can take several days to come back. 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. 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. A host of other conditions can lead to many of the same symptoms of food poisoning. Most common is gastroenteritis, which is caused by a virus. Others 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. 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.