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Causes and Spread of Infection


IMPORTANT: This page is in rough draft mode. We consider it to be unfinished so the detail may be less than that of a fully-completed page and it may contain errors. However, it should hopefully give you some pointers about what you need to do.

In addition, this unit was not written by us but generously donated by one of our regular visitors. Thank you.


Learning Outcome 1: Understand the causes of infection

1.1 – Identify the differences between bacteria, viruses, fungi and parasites


Bacteria are very small simple organisms, unicellular, capable of reproducing by themselves by binary fission (they grow to double size and split into two, those two into two more). They can have different shapes. Bacteria are omnipresent and some of them are very useful (bacteria in the large intestine help with digestion, or used to produce yogurt). However, some bacteria are pathogenic and can cause diseases. A bacterial infection can be treated with antibiotics, but it can become resistant to antibiotics.

Viruses are much smaller like 10 to 100 times, and more complex than bacteria. Viruses cannot multiply by themselves, they invade a host cell and take over its genetic material in order to make more virus particles. They consist of genetic materials surrounded by a protective coat of protein. Viruses do not respond to antibiotic treatment. You cannot treat an invaded cell, you have to kill that cell in order to get rid of the virus. You can control the symptoms with antiviral drugs. Viruses are the cause of many infectious diseases.


A fungus a multi-celled living organism as mushrooms and moulds or single-celled as yeast. Their cells have a nucleus and a complex internal structures, they multiply by spores. Like bacteria and viruses some types of fungi can be pathogens and cause harm. Some of them can be beneficial such as penicillin

Parasites are micro-organisms which depend on a host for their survival, they derive benefit from other’s metabolism. Virus and bacteria can be parasites.


1.2 – Identify common illnesses and infections caused by bacteria, viruses, fungi and by parasites

Common illnesses and infection caused by bacteria:

  • Chlamydia
  • Dihteria
  • Dysentery
  • Pneumonia
  • Tetanus
  • Tuberculosis
  • Whooping cough

Common illnesses and infection caused by viruses:

  • Warts and verrucas
  • AIDS
  • Bronchiolitis
  • Poliomyelitis
  • Measles
  • Hepatitis
  • Cold and flu
  • Chickenpox
  • Pneumonia

Common illnesses and infection caused by fungi and parasites:

  • Scabies
  • Athletes foot
  • Ringworm
  • Lice

1.3 – Describe what is meant by infection and colonisation


An infection is caused by the bacteria invasion. They enter and multiply in human body affecting the immune system. That can result in signs and symptoms such as fever, pus from a wound, a high white blood cell count, or pneumonia.

Colonisation occurs when micro-organisms are present in or on body but do not cause illness. Colonised pathogens have the potential to cause infection when they spread to a different area (on the same person) or to another person.


Infection means that the organism is present and is causing illnesses and need treatment. Colonisation means that the organism is present in or on body but is not causing illnesses and can clear spontaneously, continue harmlessly indefinitely or can develop into infection.

1.4 – Explain what is meant by systemic infection and localised infection


Systemic infection is when the infection caused by a pathogen spread through the body to several organs in different systems of the body, such as digestive system, respiratory system or circulatory system.

Localised infection is the infection that is confined or restricted to a specific location of the body, such as infected wound


1.5 – Identify poor practices that may lead to the spread of infection

Poor practices that may lead to a spread of infection include:

  • Lack or poor hand hygiene
  • Inadequate vaccination
  • Lack or incorrect use of PPE
  • Not storing or cooking food correctly
  • Incorrect dispose of waste
  • Airborne infection
  • Contaminated bed linen or clothing

1.6 – Identify how an understanding of poor practices, can be applied to own professional practice


There are many ways to try to reduce the risk of infection. You should wash your hands or wear gloves before and after doing individual tasks. If you do wear gloves they should be discarded after use. Many surfaces can hold germs and bacteria, so even after touching a surface hands should be washed or gloves worn where possible. Aprons should also be worn in order to stop the spread of fluids and germs that are carried on clothes.

If you cough or sneeze, this should be done into a tissue or into your arm, rather than your hand. You then need to wash your hands and discard the tissue.


Learning Outcome 2: Understand the transmission of infection

2.1 – Explain the conditions needed for the growth of micro-organisms


Temperature- the ideal temperature for bacteria to multiply is around 37 degrees C , the average human body temperature. Food-poisoning bacteria multiply at temperatures between 5 to 63 dregrees C. Freezing can make bacteria dormant but it does not kill them.

Humidity/moisture- in order to stay alive they need moisture to stay alive. Bacteria will grow and multiply on moist skin and damp areas


Nutrients – bacteria need nutrients to survive, food-poisoning bacteria prefer food that is moist and with a high level of protein, such as meat, eggs, milk, shelfish

Time – when bacteria lives in warm, moisture and nutrient will reproduce quickly


2.2 – Explain the ways an infective agent might enter the body

Usually, infective agent might enter the body through :

  • respiratory system- inhalation – breathing in airborne bacteria
  • digestive system – ingested- eating contaminated food
  • breaks in the skin direct contact with cuts and grazes, surgical wounds).
  • Other ways can be urinary and genital tract and conjunctiva.

2.3 – Identify common sources of infection


There are many common sources of infection such as:

  • contaminated equipment
  • contaminated water and food
  • contact with ill people
  • PPE or uniforms
  • body fluids
  • airborne

2.4 – Explain how infective agents can be transmitted to a person

There are different methods by which the pathogens can get from reservoir (where the micro-organism lives and reproduces) to the new host, such as:

  • Directly – actual contact with an infected person.
  • Indirectly – contact with contaminated surfaces touched by infected person or where droplets of body fluid have landed.
  • Airborne – by breathing infected particles released when an infected person cough or sneeze
  • Consumption of contaminated water or food
  • Exposure to blood

2.5 – Identify the key factors that will make it more likely that infection will occur


Key factors that can make it more likely for infection to occur are:

  • poor infection control practices
  • physical and psychological well-being
  • weak immune system
  • age – vulnerable people (elderly, babies)
  • lack of immunisation
  • poor hygiene
  • medical interventions and medical therapies, such as chemotherapy

2.6 – Discuss the role of a national public health body in communicable disease outbreaks

Public Health England – Protect and improve the nation’s health and well-being, and reduce health inequalities. It does this through advocacy, partnerships, world-class science, knowledge and intelligence, and the delivery of specialist public health services. PHE is an operationally autonomous executive agency of the Department of Health.


They protect public health by identifying the source and implementing control measures to prevent further spread or recurrence of the infection, providing specialist public health advice and operational support to NHS, local authorities and other agencies, monitoring and investigating infectious disease outbreaks and offers operational guidance for management of outbreaks of communicable diseases

Department of Health – helps people live better for longer, improving out of hospital care, creating quality healthcare services.


Health and Safety Executive – enforces COSHH (Control of Substances Hazardous to Health) and other health and safety regulations

Food Standards Agency – working with local authorities to enforce food safety in organisations, such as:


NHS trusts



nursing homes

Residential care homes

Day-care centres.

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