Signs of Food Poisoning (Contaminated Food and Water)

Every year some 8 million cases of food poisoning occur in the United States and it claims approximately 9,000 lives. Most of us do not cosnider food poisoning to be serious disease. The symptoms like nausea, vomiting and diarrhea can be severe. It can last for more than just a few days but usually the disease resolves on its own with no long term complications. However, this is not always the case and food poisoning can be life threatening.

Firstly, it is important to understand what is meant by the term ‘food poisoning’. When food is contaminated with viruses, bacteria or protozoa that can causes gastroenteritis or enterocolitis in humans, then there is a risk of these illnesses arising once the contaminated food is consumed. Sometimes it is not the virus, bacterium or protozoan that causes the disease directly but instead the toxin it produces that has contaminated the food.

Food poisoning must be distinguished from chemical poisoning. The latter can arise with a host of different toxins such as pesticides or heavy metals that may have contaminated food or water sources. While these toxins can also cause disease in humans, the toxicity is not due to any infectious agent (viruses, bacteria or protozoa) or the toxins produced by these micro-organisms.

Read more on food poisoning.

Do You Have Food Poisoning?

It is not always possible to differentiate food poisoning from other infectious and non-infectious diarrheal illnesses. For exampke, viral gastroenteritis also commonly referred to as the “stomach flu”, can be spread through droplets among people. No food, beverages or other edibles may be involved. Irrespective of whether the infectious agents or toxins were transmitted through food or not, the diarrheal illness should be treated accordingly.

Symptoms that arise after consuming certain foods may not always be a reliable indicator of food poisoning. It is only in a few causes of food poisoning where the first symptoms will appear after 30 minutes to an hours after consuming the contaminated food. With the more common types, symptoms will take anywhere between a few hours to a day and sometimes two days to appear.

Although uncommon, it is possible for an infection with certain agents to cause symptoms as late as several weeks after ingesting the contaminated food or beverage. This gap from the time of consuming the contaminants to the onset of the disease is known as the incubation period. With longer incubation periods, it can sometimes be difficult to recall and identify the possible source of the infection.

How To Spot Food Poisoning

As mentioned, the onset of symptoms following the consumption of a meal is not a reliable indicator of food poisoning due to the incubation period.  Similarly not all of the causes of the symptoms below may be due to foodborne transmission of infectious agents or even due to an infection. However, if several people who consumed the same meal experience the symptoms below then food poisoning is a very likely cause.


One of the earliest symptoms that occurs in almost all cases of food poisoning is nausea. It is a feeling of wanting to vomit although actual vomiting may not occur immediately in some instances. Nausea is usually a result of irritation of the upper gut. It can continue throughout the course of the illness but may also resolve after a short period while lower gastrointestinal symptoms, like diarrhea, continue thereafter. However, nausea may sometimes not be present in some cases of food poisoning.


The next symptom that may arise is vomiting. It may start when the nausea commences or it may occur shortly after the nausea starts up. Sometimes there may be no vomiting in certain types of food poisoning despite the nausea. The vomiting can vary in severity. In the worst cases, there may be profuse vomiting to an extent that oral rehydration is not possible. Rarely, there may be bloody vomiting which is known as hematemesis.

Read more on vomiting after eating.

Abdominal Cramps and Pain

While common in most cases of food poisoning, abdominal cramps and pain may not always be present. It may start as early as the nausea or occur midway through the disease. Sometimes abdominal cramps and pain occur slightly later only once the diarrheal stage of food poisoning arises. The severity of abdominal cramps and pain can vary. It is typically worse when there is severe vomiting and diarrhea as part of the disease.


Diarrhea is considered to a be a hallmark symptom of food poisoning but this is not always the case. There are some instances of food poisoning where diarrhea may not occur. Some of the gastrointestinal infections may cause more upper gut symptoms like nausea and vomiting than diarrhea. It is also possible that the offending agents in the food and fluid are expelled with vomiting and therefore never reach the lower gut where it can cause diarrhea.

Depending on the infectious agent and several other factors, the diarrhea in food poisoning can vary. Typically the stool is watery and the number of bowel movements exceed three times in a day. There may also be undigested food and copious amounts of mucus in the stool. In conditions like cholera the diarrhea may have a milky-white appearance.  With hemorrhagic infections, the diarrheal stool may also be bloody.


Dehydration is not a symptom but a condition that arises with loss of fluid and electrolytes. It is the most common complication of food poisoning and the main reason for fatalities in iarrheal illnesses. Dehydration arises with profuse vomiting and severe diarrhea where copious amounts of water and electrolytes are lost. However, it can be minimized, prevented and quickly treated with oral rehydration where possible.

The signs and symptoms of dehydration includes:

  • Increased thirst.
  • Dry mouth, eyes and skin.
  • Little to no urine output or sweating.
  • Headaches.
  • Fatigue.


Fever can occur with many infectious diseases and some non-infectious illnesses. It is not always present in food poisoning. Therefore the lack of a fever should not be associated with a lack of an infection. When it does occur, it can be low-grade, mild or high despite the severity of the infection and illness. The fever can precede the onset of any of the other symptoms.

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