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What is microbial contamination?

Exposure to microbial contamination presents a global threat to human health. According to the World Health Organisation (WHO) 1 in every 10 people becomes ill from eating contaminated food.

Foodborne diseases contribute significantly to deaths around the world and are a particular threat in the developing world, places of extreme hardship or poverty or in countries where large numbers of the population have restricted access to healthcare. If everybody, everywhere, had access to sufficient amounts of clean water, then the number of deaths attributed to diarrhoeal diseases, would be cut by a third (Tropical Medicine and International Health 2014).

In the UK, we are privileged to have access to clean, running water and a health service that is free at the point of use. However, a five-year-long study conducted by the Food standards Agency (FSA) aimed at estimating the societal burden of foodborne illness, predicted the total burden of foodborne illness in the UK was an eyewatering £9 billion (based on 2.4 million cases per year).

Norovirus and campylobacter were responsible for the greatest economic and societal burdens, costing an estimated £1.8 billion and £0.71 billion, respectively, to the country.

Advocating good hygiene practices is one of the most cost-effective health interventions possible, and as food and water are necessary for survival, providing cleaner water and safer food for all, could ultimately save many lives.

A parasite contaminating food

What is microbial contamination

Microbial contamination is the unintentional introduction of microbial agents such as bacteria, viruses, chemicals or parasites. Humans are often exposed to these contaminants after they somehow enter the food chain and are inadvertently consumed.

Microbial contaminants can also enter the body in other ways, such as during surgical procedures at a hospital or dentist.

The effects of microbial contamination on the human body can range from slight or moderate, to severe or even fatal.

How does microbial contamination affect the body?

Bacteria, viruses and parasites that enter the human body either through consuming contaminated food and water or by other means, can have a negative impact on health.

Eating contaminated food can make people ill, with varying degrees of severity, depending on:

  • The type of contaminant.
  • How much of the contaminated food was consumed.
  • The age of the affected person.
  • The overall health of the infected person.
  • Whether there is access to adequate medicine and healthcare.

The very young, the elderly, those with low immune systems and pregnant women can suffer significantly more severe effects than other people if they eat or drink contaminated items.

Some common symptoms people suffer after microbial contamination include:

  • Diarrhoea/diarrhoeal illnesses.
  • Sickness/nausea.
  • Fever.
  • Pain.
  • Malnutrition (this can lead to stunted growth in children).
  • Dehydration.
  • Disease.

Sometimes the effect of microbiological contamination is almost immediate, for example, if food that contains the common virus called norovirus is consumed, signs of sickness will usually be seen within 24 hours.

For other biological contaminants, such as arsenic (As) that is found in rice, the ill effects on the body are caused by a build-up of the poison over time. Some studies suggest that consuming trace levels of arsenic over long periods could be associated with developing cancer, cardiovascular disease and diabetes.

Rice absorbs these contaminants from the soil where it is grown and through a cultivation process known as ‘flooding irrigation’ which often involves the usage of groundwater that is sometimes contaminated with As. Rice is able to absorb many times more of this group 1 carcinogen than other crops, such as maize.

Man ill from microbial contamination

How do microbial contaminants enter food?

Microbial contaminants including bacteria, viruses, fungi and chemicals can act as contaminants to food sources. They can enter the food chain at any point including during the process of growing and cultivating food, keeping and slaughtering of livestock, during transportation or storage and whilst food is being prepared, cooked or stored after cooking.

Examples of how microbial contaminants might enter food:

  • Food is grown in soil that is exposed to sewerage or contaminated animal waste.
  • Livestock are kept in unhygienic conditions.
  • Problems during production or storage of food. Food is made or kept in an unhygienic way.
  • Lack of hygiene during preparation (food handlers are unwell, have poor hygiene or work in an unclean environment).
  • Undercooking food or not following guidelines.
  • Food-prep tools or equipment are not sterile.
  • Unclean or untreated water is used or drank.

Bacteria is a common contaminant. It is often spread through having unclean hands. Given optimum conditions bacteria will spread rapidly and some strains can make people very ill.

How bacteria grows:

Temperature The danger zone for bacteria is between 5°C and 63°C. The temperature food is cooked at is crucial. Undercooked meat, in particular chicken or pork, can be especially hazardous due to the presence of bacteria such as salmonella or campylobacter. They must be cooked thoroughly and never eaten ‘pink’.

Moisture Bacteria require moisture so that they can grow. Chicken and dairy are high moisture proteins that are rich in nutrients and provide an ideal breeding ground for bacteria.

Food – Food can provide an ideal environment for bacteria to grow as it contains energy and nutrients.

Time – Under ideal conditions, bacteria can multiply to become many millions through a process called binary fission.

pH Level A highly acidic or an alkaline pH may inhibit, or slow down, bacteria growth. The ideal pH for bacteria is neutral or 7.

Man who has eaten contaminated food

What are the main sources of microbial contamination?

Foodborne microbial contamination can be caused by unsafe or unhygienic food practices in factories, farms, warehouses, stores or other places where food is grown, prepared or stored.

Non-food related microbial contamination might also occur during invasive procedures that require the skin to be penetrated.

Contamination can occur where the surroundings, instruments or equipment are not hygienic or the aftercare is poor, such as:

  • Hospitals.
  • Dental surgeries.
  • Beauticians (those offering Botox, minor cosmetic procedures or permanent make-up).
  • Tattooists (there have been instances of inks being recalled due to microbiological contamination).

The risk of microbial contamination in a hospital setting from unclean hands that can transmit microorganisms, contaminated surfaces that have not been correctly disinfected, unclean instruments used during medical procedures or lack of wound aftercare, are especially high because the host may be compromised. This is because people undergoing hospital treatment may already have a low immune system.

This is where hand hygiene and excellent standards of cleanliness and housekeeping are vital in operating theatres and wards, as well as in the hospital kitchen areas, so as patients are not exposed to any additional risks or hazards.

Food is nutrient rich and therefore can be an excellent breeding ground for unwanted microorganisms. Contamination of food can occur anywhere within the supply chain, from initial production to transportation, packing, storage, distribution and serving.

Some major sources of contamination are:

  • Water.
  • Soil.
  • Sewage.
  • Waste products.
  • Humans.
  • Livestock.
  • Wildlife/pests.
  • Refuse.
  • Pollution.
Cleaning hospital to prevent contamination

Types of microbial contamination

Bacteria – These microscopic, single-celled microbes can cause disease. A single bacterium can divide and multiply to become many millions of cells in the space of a day. Healthy human bodies are naturally covered in bacteria; some helpful, some incredibly harmful.

Parasites – These are small organisms that require a host so that they can survive. They range from microscopic, single-celled organisms to small multi-celled worms that can be seen with the naked eye.

Fungi – When some foods spoil they begin to grow mould. These moulds can produce mycotoxins that can be very harmful. Fungi that contaminate and spoil food are also known as pathogens.

Chemicals and chemical compounds – These may be naturally occurring (from deposits and sediments in soil, from rocks etc.) or from a secondary source such as a metal pipe or caused by pollution from factories and farming. It is important that chemicals in foods do not exceed safe levels. They can also enter the food chain during production, storage or cooking, such as from the tiny particles in plastics or from an accidental spillage.

Viruses – A virus is a tiny infectious agent that is only capable of reproducing inside a living organism. They can infect all living things including humans, animals, plants and microorganisms. Food is usually contaminated with pathogenic viruses by a lack of hygiene or by food coming into contact with raw sewage or animal waste.

  • Common bacteria found in food includes salmonella, E. coli, listeria and campylobacter.
  • Common viruses can include norovirus.

Other types of contaminants include:

  • Fungi such as aflatoxins (found in mouldy nuts) ochratoxins (linked to kidney problems) and patulin (found in apples that are rotting). Many are also present in soil which can affect crops.
  • Chemical contaminants such as arsenic, radium, lead and mercury.
  • Parasites such as Giardia lamblia, Toxoplasma gondii and various parasitic worms (helminths).

Risk factors for microbial contamination

The presence of certain risk factors can increase the chances of a biological contamination hazard occurring, such as:

  • Poverty.
  • Lack of training for workers.
  • Bad hygiene.
  • Poor agricultural practice.
  • Inadequate kitchen design.
  • Poor disinfection and food handling practice.
  • Poor infection control in clinical settings.
  • Failure to conduct risk assessments or understand hazards.
  • Bad housekeeping and storage procedures (especially for chemicals).

Many of these risk factors can be managed to prevent the likelihood of contamination occurring. One important way this can be done is by education and increased awareness.

Washing hands helps stop contamination

Preventing microbial contamination

For several years, during 2007–2015, the WHO spent time and money collecting data and researching the subject of foodborne disease around the world to better understand it.

Generally, the best way to prevent microbial contamination is to practise good hygiene:

  • Wash hands regularly with soap and water (especially after eating, drinking, or using the toilet).
  • In food venues, ensure staff are adequately trained and the food preparation and storage areas are clean and hygienic.
  • Business owners should check what legislation they need to comply with and perform regular risk assessments to assess and manage hazards.
  • Contamination is less likely to occur in areas that are clean, tidy, and well organised.
  • Cook food thoroughly, according to guidelines, and be careful when preparing, storing, or reheating food.
  • Avoid areas of food production when ill, especially when suffering from contagious illnesses, sickness bugs or skin conditions.

Other factors to consider in the prevention of microbial contamination:

  • Water that has been treated with chlorine gas or a chlorine solution is safer to drink. Chlorine is a disinfectant and can control microorganisms.
  • Keep chemicals in labelled bottles, stored well away from anything they could contaminate, and follow COSHH where appropriate.
  • Use only treated manure on crops.
  • Dispose of animal waste safely and hygienically.
  • Wash raw fruit and vegetables thoroughly.
  • Drink only pasteurised milk and juice.
  • When travelling abroad (especially in high-risk areas) choose bottled water and avoid having ice in drinks.
  • When farming, avoid poor agricultural practices. Do not use land for growing crops that is adjacent to animal production facilities, sewerage or waste facilities or low laying land that is subject to water run-off from above. Never keep animals is cramped, unhygienic conditions, do not harvest flooded crops and never use unsafe or unidentified water sources.

How good management can help:

  • Keep regular, accurate records – Conduct checks and note them in the Food Safety Diary.
  • Investigate and address any instances of non-compliance within health and hygiene in the business.
  • Ensure staff are trained and equipment is clean, safe and fit for purpose.
  • Workers who are ill should be sent home and in instances of sickness and diarrhoea a minimum of 48 hours is required since the last time they had symptoms before returning to a food handling role.
  • Keep on top of pest control and waste management.
  • Do not cut corners with disinfection or hygiene procedures.
  • Submit to regular checks from third parties or the local authority and action any advisories given.
  • Lead by example.
  • Keep up to date with legislation.

The implications of microbial contamination can be widespread. From the primary impact on the health and wellbeing of the person that has been exposed to the contaminant, to the secondary impacts on their family, healthcare services and wider society. There may also be consequences for the place in which the contamination occurred, especially if it is a venue that is required through legislation to maintain a certain level of hygiene.

Some of the potential implications of microbial contamination may include:

  • Health implications – Sickness/illness, pain and discomfort, malnutrition (in extreme cases death).
  • Economic impacts to affected person – Loss of wages, time off work due to illness, healthcare related costs.
  • Economic impact to venue where contamination occurred – Production may be halted due to investigation into the contamination incident, loss of productivity, potential for financial loss due to legal proceedings.
  • Impact on healthcare services – Time and money spent on consultations, treatment, investigations, hospital stays, providing medicines and care.

The economic, health and societal consequences of microbial contamination occurring can be extremely serious. Strict hygiene practices, a traceable supply chain and care during every step of food production and distribution can help to build a safer future for all.

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About the author

Vicky Miller

Vicky Miller

Vicky has a BA Hons Degree in Professional Writing. She has spent several years creating B2B content and writing informative articles and online guides for clients within the fields of sustainability, corporate social responsibility, recruitment, education and training. Outside of work she enjoys yoga, world cinema and listening to fiction podcasts.



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