Food is happiness for many of us. Nonetheless, as we eat to our heart’s content, we must be mindful of germs that may be present in our food and drinks. These germs, when ingested, will give us an unenjoyable episode of food poisoning instead.
You would most probably have experienced food poisoning sometime in your life. It could have caused a mild stomach discomfort which dissipated after a short while, or severe diarrhoea and vomiting that incurred a stay in the hospital. Knowing more about the pathology of food- and water-borne germs and how food safety can prevent an infection will help us to prepare and enjoy our next meal safely.
What is Food Poisoning?
Food poisoning, medically known as bacterial gastroenteritis, is an illness experienced when disease-causing bacteria or parasites in food and drinks infect our gut and release toxins that cause injury to our body and induce hurtful symptoms. Most of these symptoms, such as abdominal cramps and diarrhoea, are localized along our lower digestive tract. Although the majority of cases of food poisoning are mild and can recover within a few days without the need for medical treatment, severe cases can result in life-threatening complications and will require urgent medical care.
The common culprits of food poisoning include Escherichia coli (E. coli), Salmonella sp. and Staphylococcus aureus, which are usually found in contaminated raw meat, vegetables, and water. Rarer but more deadly instances of food poisoning can be caused by Clostridium botulinum bacteria, Entamoeba histolytica parasites, and other germs.
A stomach flu is also a food-borne illness that is similar to and often mistakenly referred to as food poisoning. However, the topic of stomach flu should be discussed separately as, despite many similarities, it is a different illness with different pathologies and treatment methods.
Stomach Flu vs Food Poisoning
It is often difficult to differentiate stomach flu from food poisoning as both exhibit similar symptoms. However, their pathology and disease management strategies differ greatly and it is important to identify the illness correctly in order to treat and prevent the spread of infection.
Unlike food poisoning, stomach flu (acute gastroenteritis) is usually caused by a virus, such as Hepatovirus A, rotaviruses, and noroviruses. The SARS-CoV-2 virus, which is causing the current COVID-19 pandemic, can also cause stomach flu. Viruses generally spread much more easily than bacteria and parasites, meaning that a stomach flu will generally be more contagious than food poisoning. Someone with stomach flu can easily spread the virus to others if they handle shared food or come into close contact with another person, through kissing for example. Hence, it is even more crucial for a person with stomach flu to take extra care in washing their hands regularly and avoiding contact with shared food and others, compared to someone suffering from food poisoning.
The symptoms of stomach flu and food poisoning are similar. These common symptoms include abdominal pain, diarrhoea, and vomiting. However, there are still some differences that can differentiate the two.
Since the stomach flu is caused by a viral infection, there is generally a longer incubation period before the infection takes hold and it may take many days for symptoms to appear after exposure to an infected food item or person. Contrarily, food poisoning is often caused by our body’s immediate reaction towards bacteria, parasites, and their toxins, usually producing symptoms within a couple days, or even a few hours, after the ingestion of contaminated food.
Additionally, the viral infection causing stomach flu often causes body aches and upper respiratory symptoms, such as a sore throat, on top of symptoms of the digestive tract. These symptoms are not observed in cases of food poisoning.
Another key difference is the treatment for viral versus bacterial and parasitic infections. Medical intervention can be used to relieve symptoms and treat complications such as dehydration in both cases. However, the viral stomach flu can only be ended by allowing our immune system to run its course in eradicating the virus in our body. Meanwhile, antibiotics can be used to kill disease-causing bacteria and parasites to relieve food poisoning promptly. Antitoxins may also be required to counter deadly toxins from bacteria such as botulinum neurotoxins from Clostridium botulinum.
Food Poisoning Symptoms
As the infection proceeds through your digestive system, most immediate symptoms involve the stomach and intestines. These include:
- Abdominal cramps & pain
- Watery or bloody diarrhoea
Other symptoms, such as a fever, may develop as your body fights the infection. However, an infection with neurotoxin-producing bacteria or a worsening infection that has spread to the bloodstream and other organs can cause dangerous complications. Seek medical attention immediately if you are experiencing the following symptoms:
- Muscle weakness or paralysis
- Slurred speech or dysphagia
- Blurry vision
- Dizziness or lightheadedness
- Frequent vomiting or diarrhoea that persists for more than three days
- Dry mouth, extreme thirst, and little to no urination (symptoms of dehydration)
- Extreme abdominal pain
- Persistent fever above 38°C
For some pathogens such as Cryptosporidium sp., mild infections in otherwise healthy individuals may not give rise to any symptoms.
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Food Poisoning Complications
Many complications can arise from food poisoning due to prolonged deleterious symptoms or the pathology of more harmful types of germs. Some prevalent complications are described below.
The most common complication from food poisoning is dehydration due to excessive water and salt loss from frequent vomiting and diarrhoea. Severe dehydration, generally defined as fluid loss greater than 15% of total body water content, can cause organ damage, coma, and death. Dehydration can be prevented and treated by the replenishment of fluids and essential salts through drinking oral rehydration solutions, sports drinks containing electrolytes, or intravenous infusions.
Listeriosis is an infection in the blood (sepsis) and brain membrane (meningitis) by the Listeria monocytogenes bacteria that may be present on unpasteurized cheese and undercooked chicken. The adverse effects of listeriosis are especially pronounced for pregnant women, newborns, and immunocompromised individuals. Listeriosis in pregnant women can cause pregnancy complications and miscarriage, while listeriosis in newborns are commonly fatal or can cause meningoencephalitis and other permanent development defects. In immunocompromised HIV patients, the rate of mortality has been found to be 500-fold greater than a healthy individual. An intravenous antibiotic infusion is used to treat listeriosis and can be effective in preventing the transmission of the infection from a pregnant mother to her child.
Ingesting large numbers of the botulinum-producing Clostridium botulinum bacteria can result in botulism, which is a potentially lethal paralytic disease caused by botulinum, which is a neurotoxin. This neurotoxin is absorbed through the gut lining and travels to and blocks the function of nerve endings around the body. This causes various nervous and neurological effects such as double vision, slurred speech, facial paralysis. paralysis of the limbs, and respiratory dysfunction which can be fatal. Prompt infusion of the antitoxin is vital to prevent the deadly neurological effects of botulism. Hence, it is critical that one seeks medical attention immediately if experiencing food poisoning with neurological symptoms. Subsequent recovery may take several weeks to months.
Nutritional deficiencies can arise from cases of food poisoning caused by parasites such as Giardia lamblia and Entamoeba histolytica. These parasites are spread through contaminated water, which is especially prevalent in rural areas with poor sanitation. After the parasites are introduced into the digestive system, they remain in the intestines and proliferate, eventually upsetting a healthy gut flora. As a result, the absorption of nutrients and micronutrients, such as zinc and iron, is reduced and prolonged deficiencies may lead to anemia. A study in rural Bolivia has also found that around a third of children infected with these parasites experience stunted development due to malnutrition.
Food Poisoning Causes
Food poisoning is caused by the ingestion of contaminated water or food which host various species and strains of bacteria and parasites. These germs are typically present in the faeces of infected livestock and contaminate food when they come into direct or indirect contact through soil, water, and handlers. Water-borne germs in drinking sources and recreational water bodies have the potential to cause large-scale food poisoning outbreaks.
Common food items that cause food poisoning and the corresponding types of disease-causing germs that are usually found in them are listed in the table below:
|Types of Germs||Food Items|
Fruits & Vegetables
Fruits & Vegetables
Fruits & Vegetables
Exposed Cooked or Canned Food
Fruits & Vegetables
Exposed Cooked or Canned Food
|Clostridium botulinum||Exposed Cooked or Canned Food|
|Clostridium perfringens||Exposed Cooked or Canned Food|
It is important to note that cross-contamination of these germs across different types of food can easily occur through the use of common surfaces or contaminated hands and water. For example, eating raw fruits that were prepared on a chopping board that was previously used for raw meat can also introduce germs that are usually found on meat into your body.
Food Poisoning Risk Factors
The risk of contracting food poisoning and the progression of the illness depends on external factors and internal factors respectively.
Risk of Infection
It is generally easier to actively mitigate external factors to reduce the risk of food poisoning. Hence, avoiding the following risk factors should be of primary consideration.
- Eating raw or undercooked food
- Poor hygiene & food safety
- Poor sanitation
- Interaction with livestock
Risk of Severe Disease
In the case where an infection has already occurred, the severity of the disease is largely dependent on the individual’s immune system and health conditions. Risk factors for severe food poisoning include:
- Young age or infancy
- Old age (above 60 years old)
- Immunodeficiency (e.g. due to HIV, cancer treatment, or immunosuppressant drugs)
- Chronic health conditions (e.g. inflammatory bowel disease (IBD), diabetes, or kidney disease)
- Type of disease-causing germ
Food Poisoning Diagnosis
If you suspect that you have ingested contaminated food or water and are experiencing an acute onset of symptoms, especially along with others that have shared the same meal, you may have a case of food poisoning.
Seek a professional diagnosis and treatment at a hospital if you are a person that is at high risk of severe disease or if your symptoms are causing severe discomfort and have not subsided after three days.
Your doctor will request for a detailed description of your diet, places where you had your meals, and potential exposure to infected environments or individuals. This will help them identify the likely sources of infection and alert the authorities if a common source, such as a particular restaurant, is observed in multiple recent cases of food poisoning as that may be an indication of a local outbreak. Subsequent tests such as blood tests and stool culture may be carried out to identify the pathogen and prescribe suitable treatments. Your doctor will also conduct a physical assessment to determine the severity of your symptoms and if you are experiencing any complications, such as dehydration.
Food Poisoning Treatment
Most cases of food poisoning are mild and will subside within a few days of rest without the need for medical treatment. Home remedies using natural antimicrobials found in plants, such as cloves, ginger, pomegranate, and thyme, can also be used to help relieve symptoms and kill some common types of pathogens that cause food poisoning. Avoid foods and drinks that may irritate your bowels or cause dehydration, such as spicy food, caffeine, and alcohol, as they could further aggravate your symptoms.
You should seek medical treatment if your symptoms are severe and persist for more than three days. People at high-risk of severe disease such as infants, young children, pregnant women, elderly, and immunocompromised individuals should also seek medical treatment if they experience symptoms of food poisoning.
If you are experiencing neurological symptoms, such as double vision and paralysis, seek treatment immediately at the emergency department of a hospital as it may be a sign of potentially lethal botulism poisoning.
Depending on the type of pathogen, treatments may include a course of antibiotics or antitoxins prescribed by a doctor. You can also obtain medication to relieve uncomfortable symptoms such as fever, nausea, diarrhoea, and pain. If you are diagnosed with dehydration, you will have to take oral rehydration solutions or receive intravenous fluids in the hospital or at home.
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Food Poisoning Prevention
Preventing an outbreak of food poisoning should be executed by national healthcare ministries and organizations. Some management strategies include:
- Strict training requirements and observation of good food safety and hygiene practices in food & beverage establishments
- Providing good sanitation systems
- Providing clean drinking water
- Public education campaigns on food safety
Nevertheless, you should be wary of food poisoning and take precautionary steps to avoid exposure to food-borne germs at home and when eating outside. The “four Cs” method is an easy way to remember key food safety practices.
The “Four C’s”
- Cleaning – Use soap and water to wash your hands and surfaces in contact with food.
- Cooking – cook or reheat food thoroughly to kill any pathogens that may be present and do not reheat food more than once as heat-tolerant toxins may have already been produced in previously warmed and exposed food.
- Chilling – food should be stored at the correct temperature to prevent the proliferation of pathogens and remain safe until its expiry date.
- (Avoiding) Cross-contamination – store and prepare raw and cooked foods separately.
Apart from ensuring food safety, maintaining a healthy immune system and gut microbiota through a healthy diet and probiotics recommended by your doctor can help you to be more resistant to food poisoning.
Preemptive antibiotic treatment is also a way to prevent food poisoning for susceptible individuals such as infants. However, antibiotics should only be used when absolutely necessary as they may adversely affect beneficial gut microbiota or give rise to antibiotic-resistant pathogens.
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