Food Hygiene, Food Preservation and Food Contamination

Learning objectives

• Define food hygiene, food safety, contamination, foodborne infection, intoxication, cross-contamination and spoilage.
• Apply WHO’s Five Keys to Safer Food from purchase to serving.
• Identify biological, chemical, physical and allergen hazards and their control points.
• Explain traditional and modern food-preservation methods, their strengths and limitations.
• Recognise foodborne illness, provide initial clinical care and investigate an outbreak.

1. Definitions and public-health importance

Term	Meaning
Food hygiene	Conditions and practices that preserve food cleanliness and prevent contamination during production, handling, storage, preparation and service.
Food safety	Assurance that food will not cause harm when prepared and eaten according to its intended use.
Food contamination	Presence or introduction of biological, chemical, physical or allergenic hazards into food.
Foodborne infection	Illness caused by ingesting live pathogens that multiply or invade in the host.
Foodborne intoxication	Illness caused by a toxin already present in food or produced after ingestion.
Cross-contamination	Transfer of a hazard from one food, surface, utensil, hand, animal or container to another.
Food spoilage	Quality deterioration from microbial growth, enzymes, oxidation, pests or physical change; spoiled food may be unsafe, but dangerous food can also appear normal.
Food preservation	Processes that slow or prevent microbial growth, enzyme activity, oxidation and physical deterioration to extend safe shelf life.

Unsafe food can cause acute diarrhoea and vomiting, severe dehydration, sepsis, neurological disease, miscarriage, chronic liver disease, kidney injury, cancer from some toxins and loss of household income. Infants, pregnant people, older adults and immunocompromised patients are at highest risk of severe disease.

2. The farm-to-fork hazard pathway

1. Production: contaminated irrigation water, soil, manure, animal disease, pesticides, veterinary medicines and environmental pollutants.
2. Harvest and slaughter: dirty equipment, intestinal contents, infected animals, poor carcass handling and contaminated water.
3. Transport and market: broken cold chain, dust, flies, dirty crates, raw food dripping onto ready-to-eat foods and unsafe vendor surfaces.
4. Preparation: infected food handler, dirty hands, contaminated utensils, poor cleaning, inadequate cooking and cross-contamination.
5. Storage and serving: room-temperature holding, repeated reheating, uncovered food, dirty serving utensils and unsafe leftovers.
6. Consumer: inadequate hand hygiene, undercooking, unsafe water, poor storage and consumption of visibly damaged or expired products.

3. Types of contamination

Type	Examples	Control
Biological	Salmonella, pathogenic E. coli, Shigella, Campylobacter, Listeria, Vibrio, norovirus, hepatitis A/E, Giardia, Cryptosporidium, worms, moulds and toxins	Safe water, hygiene, separation, cooking, time-temperature control and pest control.
Chemical	Pesticides, cleaning chemicals, heavy metals, veterinary-drug residues, mycotoxins, excess additives, fuel and naturally occurring toxins	Approved suppliers, correct storage, testing, label compliance and spill prevention.
Physical	Glass, stones, metal, bones, hair, wood, insects, packaging and fragments of equipment	Inspection, protective maintenance, sieving, hygienic handling and foreign-body control.
Allergenic	Peanut, tree nut, milk, egg, fish, shellfish, wheat/gluten, soy or another individual trigger	Accurate labelling, separation, cleaning and emergency preparedness.

4. WHO Five Keys to Safer Food

Key 1: Keep clean

• Wash hands before handling food, after toilet use, after touching raw food, rubbish, animals or the face, and after coughing/sneezing.
• Clean and sanitise preparation surfaces, boards, knives, cloths and utensils; wash cloths frequently and dry them.
• Protect food from flies, rodents, pets, dust, chemicals and dirty hands.
• Food handlers with diarrhoea, vomiting, jaundice, infected wounds or fever should report illness and not prepare food until cleared according to local policy.

Key 2: Separate raw and cooked

• Keep raw meat, poultry, fish and eggs separate from cooked or ready-to-eat foods during shopping, storage and preparation.
• Use separate boards/knives or wash and sanitise between foods.
• Store raw foods below cooked foods in a refrigerator so drips cannot contaminate them.
• Use separate utensils for tasting and serving; never return a used spoon to a communal dish.

Key 3: Cook thoroughly

• Cook meat, poultry, eggs, fish and other high-risk foods until the centre is thoroughly heated; juices should run clear and the thickest part should be steaming hot.
• Stir foods such as sauces, beans and porridge so heat reaches the centre; reheat leftovers thoroughly and only once where possible.
• Use a clean food thermometer where available and follow validated time–temperature instructions for the food, altitude and equipment.
• Cooking may not destroy all heat-stable toxins or chemicals; prevent contamination and temperature abuse before cooking.

Key 4: Keep food at safe temperatures

• Keep cold food cold (refrigeration commonly below 5°C) and hot food hot (commonly above 60°C) according to local standards and equipment capability.
• Do not leave cooked or perishable food at room temperature for long periods; refrigerate promptly in shallow, covered containers.
• Do not overload refrigerators; use a thermometer and maintain the cold chain during transport.
• When in doubt about time-temperature abuse, discard rather than taste-test.

Key 5: Use safe water and raw materials

• Use water from a safe source for drinking, cooking, ice, washing produce and cleaning utensils.
• Select fresh, intact foods; avoid swollen, leaking, rusted or badly damaged cans and products past the use-by date.
• Wash produce with safe water; peeling, cooking and safe storage may be needed for high-risk foods.
• Use pasteurised milk and regulated products where possible.

5. Food-handler and kitchen hygiene

• Wear clean protective clothing, tie back hair, keep nails short and cover cuts with a waterproof dressing and glove.
• Do not cook while vomiting or having diarrhoea; seek care and follow public-health exclusion guidance.
• Keep raw and cooked zones separate; establish one-way movement from receiving to preparation to service.
• Use safe water, cleanable surfaces, adequate drainage, covered bins and pest control.
• Wash utensils with safe water and detergent, rinse and air-dry; do not dry on dirty cloths.
• Use a cleaning schedule specifying item, product, concentration, contact time, responsible person and verification.
• Store chemicals labelled and away from food; never decant them into food or drink containers.
• Maintain records for supplier, batch, temperature, cleaning, illness and corrective action.

6. Food preservation methods

Method	Principle and examples	Limitations/safety
Refrigeration	Slows microbial growth and enzyme activity; useful for milk, meat, cooked food and produce.	Does not sterilise; Listeria can grow slowly; maintain temperature, avoid overload and prevent raw-food drips.
Freezing	Stops growth while frozen and extends shelf life.	Many microbes survive; thaw in a refrigerator or safe controlled method, not on a dirty counter; refreezing can reduce quality and safety.
Drying/dehydration	Removes water needed for microbial growth; includes sun-drying, solar dryers and mechanical dehydration.	Dry thoroughly, protect from dust/insects, store airtight; some moulds can produce mycotoxins if drying is incomplete.
Salting/sugaring	Reduces available water by osmosis; used for fish, meat, fruits and jams.	Salt/sugar may not control all pathogens; use validated concentration and hygiene.
Smoking	Dries food and deposits antimicrobial compounds; used for fish and meat.	Inadequate heating may leave pathogens; excessive smoke can add harmful compounds; combine with other controls.
Fermentation	Beneficial microbes produce acid/alcohol and suppress pathogens; used for milk, cereals and vegetables.	Use a safe starter/process, control time and pH, prevent mould and contamination.
Pasteurisation	Controlled heat reduces pathogens in milk, juice and other products without full sterilisation.	Requires validated time/temperature and hygienic packaging; pasteurised food can be recontaminated.
Canning/retort processing	Heat treatment in sealed containers creates a shelf-stable product.	Low-acid foods require validated pressure processing; botulism risk occurs with faulty home canning. Discard bulging/leaking cans.
Pickling/acidification	Low pH inhibits many organisms in vegetables and other foods.	Use adequate acidity and salt; do not improvise recipes for shelf-stable low-acid foods.
Vacuum/modified atmosphere packaging	Reduces oxygen and slows oxidation and some aerobic organisms.	Does not eliminate anaerobic hazards; maintain cold chain and use-by dates.
Irradiation	Validated ionising radiation reduces pathogens, insects and spoilage organisms.	Requires regulated facilities, labelling and dose control; it does not make contaminated food a substitute for hygiene.

7. Foodborne illness: clinical patterns

Pattern	Typical onset/features	Examples/priority
Rapid toxin-mediated vomiting	Hours after a meal; nausea and prominent vomiting, sometimes little fever	Preformed staphylococcal or Bacillus toxins; supportive care and outbreak investigation.
Watery diarrhoea	Hours to days; vomiting, cramps and dehydration	Viral gastroenteritis, cholera, enterotoxigenic bacteria and some toxins.
Inflammatory/bloody diarrhoea	Fever, tenesmus, blood/mucus, severe cramps	Shigella, Campylobacter, invasive E. coli, Salmonella or amoebiasis.
Neurological syndrome	Visual disturbance, dry mouth, descending weakness or paralysis	Botulism; emergency referral and public-health notification.
Hepatitis syndrome	Fever, malaise, nausea, dark urine and jaundice	Hepatitis A/E; consider pregnancy risk with hepatitis E.
Allergic reaction	Minutes to hours; urticaria, angioedema, wheeze, vomiting or shock	Anaphylaxis; immediate emergency treatment according to protocol.

8. Initial clinical management

• Assess airway, breathing, circulation, mental status, temperature, hydration and urine output.
• Give ORS for patients who can drink; use IV/NG rehydration for shock, severe dehydration, altered consciousness or persistent vomiting according to current Uganda clinical guidance.
• Continue breastfeeding and suitable nutrition; avoid unnecessary fasting.
• Use antibiotics only for defined syndromes or severe/high-risk illness and according to local resistance guidance. Antidiarrhoeals may be harmful in bloody diarrhoea, high fever or certain infections.
• Consider stool, blood, electrolyte, renal, liver, pregnancy or toxicology tests based on the presentation and outbreak plan.
• Report suspected foodborne outbreaks, preserve leftover food safely if instructed, record the menu/time/food handlers and prevent further service of implicated food.

Emergency red flags

• Shock, severe dehydration, repeated vomiting, inability to drink, altered consciousness, seizures or very low urine.
• Bloody stool, severe abdominal pain/distension, high fever, sepsis or severe malnutrition.
• Jaundice with confusion/bleeding, progressive weakness or respiratory failure.
• Wheeze, facial/tongue swelling, stridor or hypotension after food exposure.
• Multiple linked cases after a meal, school, wedding, market or health-facility event.

9. Foodborne outbreak investigation

1. Define a case and establish a line list with name/identifier, age, location, onset, symptoms, foods eaten and outcome.
2. Notify district surveillance/public-health authorities and assemble a multidisciplinary team.
3. Describe time, place and person; construct an epidemic curve and identify the likely exposure window.
4. Interview cases and controls, compare foods consumed and collect clinical specimens according to protocol.
5. Inspect kitchen, water, toilets, food storage, temperatures, suppliers, food handlers and pest control.
6. Preserve leftover food and environmental samples safely when requested; document chain of custody.
7. Control the source immediately: stop unsafe food, exclude ill handlers, clean/disinfect and correct temperature or water failures.
8. Communicate findings without blaming a group; monitor new cases and verify control.

10. Food safety in schools, hospitals and emergencies

• Schools and health facilities need approved suppliers, safe water, storage thermometers, menu controls, handwashing points and trained food handlers.
• High-risk patients (neonates, older adults, transplant patients, people with HIV or chemotherapy) need stricter control of raw eggs, unpasteurised milk, undercooked meat and unwashed produce.
• During floods or displacement, use safe water, cook thoroughly, protect food from flies/dust, avoid unrefrigerated perishables and ensure communal kitchens have handwashing and waste systems.
• In power failure, record refrigerator temperatures, minimise opening, move food to a validated alternative and discard food kept in unsafe conditions rather than tasting it.

11. Uganda context and references

Food hygiene in Uganda involves households, markets, schools, health facilities, local authorities, food businesses and public-health teams. Apply the WHO Five Keys alongside Uganda Ministry of Health infection-prevention, WASH and food-safety requirements. Food handlers should be trained, medically assessed according to local policy and supported with safe water, sanitation, protective clothing and a cleanable workspace.

• WHO: Five Keys to Safer Food
• WHO: Food safety fact sheet
• Uganda National Infection Prevention and Control Guidelines
• Uganda WASH in Health-Care Facilities guidance
• WHO: Promoting safe food-handling behaviours

12. Applied cases

13. Quick self-test

1. State the WHO Five Keys to Safer Food.
2. Why can refrigeration fail to make unsafe food safe?
3. What is cross-contamination? Give two examples.
4. Which foodborne presentation requires immediate airway/anaphylaxis management?
5. List four actions during a suspected foodborne outbreak.
6. Why should bulging cans be discarded without tasting?

Answers

1. Keep clean; separate raw and cooked; cook thoroughly; keep food at safe temperatures; use safe water and raw materials.
2. It slows growth but does not kill all pathogens; some organisms grow slowly in the cold and toxins may already be present.
3. Transfer of a hazard, such as raw chicken juice onto salad or a dirty knife onto cooked food.
4. Wheeze, facial/tongue swelling, stridor or shock after food exposure indicates possible anaphylaxis.
5. Notify public health, line-list and interview cases, preserve/collect samples as instructed, inspect/control the food source and communicate prevention.
6. Bulging may indicate gas/toxin-producing organisms such as botulism; tasting can cause severe poisoning.

Key takeaways

• Food safety is a farm-to-fork responsibility; the Five Keys provide a practical framework.
• Time, temperature, water, hand hygiene and separation control most preventable food contamination.
• Food can be dangerous without looking spoiled, and preservation is not sterilisation.
• Severe dehydration, bloody diarrhoea, neurological signs, jaundice or anaphylaxis require urgent care.
• Every suspected outbreak needs rapid notification, clinical support, source control and respectful communication.

Educational note: Use current Uganda food-safety laws, district public-health instructions and clinical guidelines for temperatures, inspection, antimicrobial therapy and outbreak reporting.