Causes and Spread of Infection

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

Bacteria – Bacteria are organisms made up of just 1 cell. They are capable of multiplying by themselves, as they have the power to divide. Bacteria exist everywhere, inside and on our bodies. Most of them are completely harmless and some of them are very useful. But some bacteria can cause diseases, either because they end up in the wrong place in the body or simply because they are ‘designed’ to invade us.

Viruses – Viruses are too small to be seen by the naked eye. They can’t multiply on their own, so they have to invade a ‘host’ cell and take over its machinery in order to be able to make more virus particles. They are capable of latching onto cells and getting inside them. Fungi – Any of a group of unicellular, multicellular, or syncytial spore-producing organisms feeding on organic matter, including molds, yeast, mushrooms, and toadstools can be either moulds or yeasts. A common yeast infection is thrush, caused by Candida albicans.

Parasites – A parasite is an organism that lives in or on another organism (the host), which damages the host in some way, plus fails to compensate for this damaging by also failing to help the host to an appreciable extent. More narrowly, the term parasite is often used to describe parasitic protozoa, helminths (worms) and arthropods.

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

Viruses – Common cold – Influenza (flu) – Hepatitis – Herpes – Mumps – Measles or rubella – Warts Bacteria – Salmonella – E. Coli – Staphylococcus – Chlamydia – Tuberculosis – Impetigo. – Tonsillitis – Pneumonia Parasites – Malaria – Toxoplasmosis Fungi – Athletes foot – Ringworm – Candidiasis

3 – Describe what is meant by “infection” and “colonization”.

Infections – An infection is caused by the invasion of foreign cells, like bacteria in humans, that cause harm to the host organism. Generally, the host organism is considered “colonized” by cells that don’t belong to it. These foreign cells must be harmful to the host organism in order for the colonization to be considered an infection.

Colonization – Although people often confuse the two terms, colonization is not the same as infection. Colonization occurs when micro-organisms inhabit a specific body site (such as the skin) but don’t cause signs and symptoms of infection. Colonized pathogens have the potential to cause infection if they spread to a different site on the same patient or to another person.

Person-to-person transmission is the major route of colonization within healthcare facilities. Although a person can become infected as soon as a pathogen invades, in many cases, colonization (without signs and symptoms of infection) takes place before infection occurs.

4 – Explain what is meant by “systemic infection” and “localized infection”.

A systemic infection is one that affects the whole body, probably travelling in lymph or blood. This is in contrast to a local infection which only affects the area where the infection entered. Localized infection describes what occurs when all infected tissue is maintained within the one area. If infected tissue broke away from the original site of infection and travelled to other body parts, it would no longer be localized.

5 – Identify poor practices that may lead to the spread of infection. – Poor staff training in basic infection control – Not using the correct PPE. – Poor infection control practices and procedures – Not following policy and procedure – Not washing hands correctly – Not washing hands at all – Inadequate sanitization – Incorrect storage of waste

Outcome 2 – Understand the transmission of infection

1 – Explain the conditions needed for the growth of micro-organisms Most bacteria will grow in dark, warm, moist areas with a neutral PH balance (ph7, water, sweat, most foods) and a source of food for the bacteria, such as sugars and protein. All bacteria need to grow in conditions such as this is time. (And not very long, either. 4 hours on average). Sadly the human body is one of the most optimal places for bacterial growth. We have many nooks and crannies where sweat can gather in a dark place (such as under our clothing) and sit for long enough for bacteria to grow. This is why it’s very important to keep clean.

2 – Explain the ways an infective agent might enter the body. Infective agents will usually enter the body in one of three ways. The respiratory system, the digestive system or breaks in the skin. There are also other ways that infection can enter the body of entry, the genital tract and the conjunctiva.

3 – Identify common sources of infection It is common for us to fall ill due to infection. Be it a viral attack or some form of diseases infecting our body, all these external agents can cause to fall sick unless we do something about it. You will be amazed there are so many causes of common infection that we need to deal with in our daily lives. Hence it is important to understand about it and deal with it before it gets us down. An infection is defined to be a pathological state or a manifestation of diseases in a certain part of the body.

It is due to external invasion of pathogenic or disease causing micro-organisms. Human and animal bodies will respond adversely the moment these foreign organisms colonized and attack their bodies. There is actually a war taking place when there is infection and it is between the host organisms and the foreign invading organisms. When the host organisms lose the battle, infection happens. The invading organisms come in the form of virus or bacteria.

4 – Explain how infective agents can be transmitted to a person Infectious diseases are disorders caused by organisms – such as bacteria, viruses, fungi or parasites. Many micro-organisms colonize in and on our bodies. They’re normally harmless or even helpful, but under certain conditions may cause disease. Some infectious diseases can be passed from person to person. Some, however, are transmitted via bites from insects or animals. Others are acquired by ingesting contaminated food or water or other exposures in the environment. Signs and symptoms of infectious diseases vary, but often include fever and chills. Mild complaints may respond to home remedies, while some life threatening infections may require hospitalization and intravenous antibiotics.

Direct transmission refers to the transfer of an infectious agent from an infected host to a new host, without the need for intermediates such as air, food, water or other animals. Indirect transmission is when infectious agents are transmitted to new hosts through intermediates such as air, food, water, objects or substances in the environment, or other animals. 5 – Identify the key factors that will make it more likely that infection will occur – Age – Malnutrition – Obesity – Skin Folds – Poor personal hygiene – Skin integrity – Repeated contact with contagious agents – Diabetes.


  • Hagedorn, Monica, et al. “Infection by tubercular mycobacteria is spread by nonlytic ejection from their amoeba hosts.” Science 323.5922 (2009): 1729-1733.
  • Molesworth, Anna M., et al. “Dust clouds and spread of infection.” The Lancet 359.9300 (2002): 81-82.
  • Oliveira Melo, A. S., et al. “Zika virus intrauterine infection causes fetal brain abnormality and microcephaly: tip of the iceberg?.” Ultrasound in Obstetrics & Gynecology 47.1 (2016): 6-7.

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