Signs and symptoms of food poisoning

Signs and symptoms of food poisoning

The signs and symptoms associated with food poisoning may last for a handful of minutes, to a few hours or several days after a contaminated substance has been ingested. Different toxic organisms interact with foodstuffs and the body differently, presenting an array of possible symptoms that can occur. At least 3 of the below signs and symptoms may occur, depending on the type of infectious organism causing contamination. 

Some food poisoning symptoms depend on which organ system in the body a contaminant affects. Pesticides or botulinum toxins can alter the neurological (nervous) system, for instance. 
Severity of symptoms ranges according to the level of contamination and the type of harmful organism ingested.

The most common signs and symptoms of food poisoning include:

  • General malaise (illness, uneasiness, discomfort): Initial signs and symptoms that the body’s immune system is reacting to a foreign organism may be fatigue, body weakness and loss of appetite, as well as aches and pains. Once the immune system detects a foreign entity or organism, chemical messengers known as cytokines are released. One of the main functions of these proteins is to help regulate the body’s immune response when signs of infection are present. Cytokines effectively ‘communicate’ where immune cells ‘need to go’ and tell them ‘how to tackle’ harmful organisms. Cytokines also send signals to the brain, which triggers symptoms like fatigue and loss of appetite. General malaise is sometimes known as ‘sickness behaviour’ – it is, in a sense, the body’s way of encouraging rest and diverting attention away from certain functions in order to prioritise fighting off an unwelcome organism. An active immune system may also result in muscle aches. Histamine, a chemical that aids in widening the body’s blood vessels, allowing for more white blood cells to travel through in order to fight off signs of infection, is released once the immune system activates as a result of inflammation. Increased blood flow means that histamine can reach various portions of the body and thus trigger pain receptors, resulting in dull aches.
  • Abdominal cramps / pain: Harmful organisms in the system produce toxins that aggravate the lining of the stomach and intestines, causing inflammation. This causes cramping (abdominal muscles contract as a means of speeding up natural bowel movements in an effort to rid the body of the unwanted organism) and pain in the trunk of the body, between the ribs and the just above the pelvic area.
  • Diarrhoea: Loose and watery stools which occur 3 or more times within a 24-hour period characterise a case of diarrhoea. Inflammation in the gastrointestinal tract causes the bowel to become less effective in reabsorbing the fluids (water) it would normally secrete during digestion. A sense of urgency to use a toilet, abdominal cramping and bloating normally accompany diarrhoea as well. Dehydration is one of the complications a person can experience when diarrhoea occurs, as the body is losing more fluid than usual. It is thus important to hydrate with fluids when experiencing diarrhoea (i.e. continuously sipping water or broths can help to prevent dehydration). One indication of dehydration may be in the colour of urine. Dark yellow normally indicates dehydration (light yellow or clear is normal).
  • Nausea: An unpleasant sensation that may or may not lead to vomiting is a common symptom associated with food poisoning. Queasiness generally occurs within 1 and up to 8 hours following ingestion of a contaminated foodstuff. For many it is one of the first indicators that “something you’ve eaten doesn’t agree with you”. A slowing down of bowel movement in the body often accompanies nausea as the body’s way of restricting the toxic organism to the stomach only, and so that it may be expelled through vomiting. 
  • Vomiting: When the diaphragm (a dome-shaped muscle which forms a critical role in the breathing / respiratory process, separating the chest / thorax from the abdomen) and abdominal muscles contract, the action forces the involuntary bringing up of the stomach contents (expelling them out through the mouth). This action is the body’s way of ridding itself of poisoning organisms that are considered harmful to normal, healthy function. In many instances, food poisoning results in several bouts of forceful, projectile vomiting, which can either subside or continue intermittently for a period of time (until the harmful organism is no longer detectable in the system). Vomiting can also lead to loss of fluids, resulting in dehydration. Intake of as much fluid (water) as possible is recommended. Where fluids cannot be tolerated (i.e. kept down), a doctor or pharmacist should be consulted.
  • Headache: Fatigue and dehydration (i.e. a lack of fluid to the brain) as a result of diarrhoea or vomiting can lead to the development of headache. 
  • Fever (mild): Pyrogens (fever inducing agents) may trigger a higher than normal body temperature (36–37°C or 97.6–99.6°F) and are either released by the immune system or an infectious bacterium. Once the body is generating more heat (losing less than normal), white blood cells increase in activity in order to naturally fend off infection. In a sense, it’s like the body’s way of attempting to make the environment (i.e. the body) too hot for the bacterium or virus and thus disrupt its ability to thrive. 
  • Body chills: Muscles in the body may also begin rapidly contracting and relaxing as a way to generate more heat. Chills can accompany a fever when pyrogens ‘trick’ the body into ‘thinking it needs to warm up’ and thus provide an environment an organism can better thrive in.

How long does a case of food poisoning last?

Symptoms of food poisoning should resolve on their own within a day or two of feeling unwell. In general, the rule of thumb for recovery depends on …

  • The particular organism, pathogen or substance that has caused the contamination
  • How much of the contaminant has been ingested (although some cases require tiny amounts to yield severe symptoms)
  • The severity of symptoms being experienced
  • Whether any complications arise

If the body is unable to naturally expel an unwanted organism and symptoms persist for longer than a day or two, a medical professional should be consulted for a thorough evaluation. Prolonged symptoms can result in more serious complications.

Signs and symptoms that may require medical assistance (although these are considered rare) include:

  • Dehydration – decreased urine output, dark coloured urine, dry mouth or throat, lack of tears (in babies and young children), excessive thirst, dizziness, low blood pressure and light headedness, and sunken eyes or fontanels (in babies)
  • Diarrhoea which lasts more than 2 days (adults) or longer than 24 hours (babies and young children)
  • Blood in stools (faeces), urine or vomit
  • Persistent vomiting (being unable to hold down any liquids or solids / rehydrate)
  • High fever (higher than 38°C / 100.4°F for adults and 37.5°C / 99.5°F for babies and young children)
  • Itching
  • Skin rash
  • Visual disturbances (blurry vision or double vision)
  • Difficulty with swallowing or speaking
  • Numbness, tingling or burning sensations in the extremities
  • Body weakness
  • Headache
  • Abdominal bloating and severe pain or cramping
  • Reactive arthritis
  • Liver or kidney function problems
  • Shock
  • Loss of consciousness
  • Seizures

Those who fall into high risk categories should also consult a doctor – pregnant women, babies and young children, seniors and those with diagnosed chronic medical conditions or who are undergoing treatments which suppress the immune system.

What kinds of complications occur with food poisoning? 

Dehydration is the most common side-effect of battling a round of food poisoning7. Persistent vomiting and diarrhoea can quickly cause a lack of sufficient fluid in the body, which can be difficult to replace while symptoms are at their worst. If a severe loss of water and electrolytes (salts and minerals) occurs, this complication can quickly become problematic enough in people of all ages to require medical assistance which involves the administering of intravenous (IV) fluids.

Depending on the pathogen or organism causing illness, certain types of complications can occur, placing certain individuals at higher risk.

Some of the most common (according to type of food poisoning organism) include:

  • Listeria: Pregnant women and their unborn baby are particularly high risk for serious complications if listeria food poisoning occurs. During early pregnancy, an expectant mother and her foetus are at an increased risk of miscarriage when listeriosis occurs. Infection during the later stages of pregnancy can result in premature birth, still birth or a potentially life-threatening infection transmitted from mother to child during childbirth. An infected baby may experience delayed development, paralysis, seizures, blindness, deafness or some degree of long-term neurological damage (mental retardation). Listeria can also cause inflammation of the brain (membranes), known as meningitis or encephalopathy.
  • E. coli: Haemolytic uremic syndrome (HUS) is one of the more serious complications (more commonly seen in children) which can arise from certain strains of E. coli. The condition results in the release of toxic substances within the digestive system which then cause damage to the tiny blood vessels (red blood cells) which line the kidneys, eventually causing kidney failure. Those with weakened immune systems are at particular risk if experiencing food poisoning from this bacterium. 
  • Shigella, campylobacter or salmonella: Food poisoning from these organisms can sometimes develop eye irritation (conjunctivitis or uveitis), joint pain and inflammation, and painful urination (or urinary tract infections / UTIs) – symptoms of reactive arthritis. This can sometimes lead to the development of chronic arthritis, which can be challenging to treat.
  • Campylobacter: This pathogen is known to trigger an immune response that prompts the body to begin ‘attacking’ its own nerves. This can result in the development of Guillain-Barré syndrome, and lead to persistent paralysis (weakness and sensory problems) lasting several weeks and requiring hospitalisation.

Other complications which can arise include:

  • Irritable bowel syndrome (IBS)
  • Lactose intolerance (secondary / ‘acquired’ lactose intolerance) due to damage caused to the bowel lining, as well as a lack of lactase (an enzyme needed for the digestion of lactose / sugar)
  • Reduced effectiveness of certain medications, especially those being taken for the treatment of diabetes, or epilepsy. Oral contraceptive medication (birth control pills) may also become less effective as the body is unable to absorb them as well during a round of food poisoning. 
  • Some pathogens are known to cause the worst complication of all – death. As many as 5 different contaminating organisms account for at least 80% of deaths caused by severe food poisoning illness. These are toxoplasma gondii, salmonella, listeria monocytogenes, campylobacter jejuni and norovirus.

Are food poisoning and stomach flu (or a stomach bug) the same thing?

Stomach flu is considered a non-specific term that essentially causes illness which occurs within a 24 to 48-hour period, otherwise known as viral gastroenteritis. 

Gastroenteritis is characterised as an infection or inflammation or the gastrointestinal tract (the stomach or intestines) as a result on infection from viral agents (food and non-food sources of contaminants). 

It is agreed that stomach flu is mostly caused by adenovirus, astrovirus, rotavirus or Norwalk virus, and is more often than not transmitted from one person to another, or through direct contact with infected vomit or stool (faeces) – making it contagious. In contrast, food poisoning occurs as a result of viral (including the aforementioned infectious agents), bacterial and parasitical contaminants.

Signs and symptoms of stomach flu include:

  • Diarrhoea and or / constipation
  • Nausea 
  • Vomiting
  • Fever
  • Abdominal (or intestinal) cramping
  • Weight loss
  • Joint stiffness / muscle aches

Symptoms of stomach flu generally resolve within a matter of days, and at its worst, within as a many as 10 days. As with food poisoning, persistent symptoms for longer than a few days should be evaluated by a medical doctor.

Which medical professionals should you see if you think you may have food poisoning?

If medical assistance is required (i.e. when symptoms have not resolved within 24 to 48 hours or have worsened), it is best to consult a family physician or general practitioner (GP) as soon as possible. Emergency medical professionals are also recommended in severe instances.


7. 6 November 2017. Food poisoning - long-term effects:  [Accessed 30.10.2017]

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