Controlling the Chain of Infection

by Water Hygiene Centre, on 06-03-2019
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chain of infection chart

If we’re to control the ‘chain of infection’ we must first understand what it entails so that we can identify what is within our control.  In doing so, this may enable us to devise and implement an effective ‘preventative management strategy’ in order to mitigate the risk of infection and subsequent disease.

The chain of infection can be defined as the list of events and factors leading to an infection and subsequent disease which can be underpinned by two key considerations: 

  • Environmental considerations;
  • Clinical considerations.

Environmental Considerations

Microorganisms are all around, moreover bacteria are ubiquitous in the environment!   Therefore, whilst there’s little that may be done about these environmental considerations, our focus should be centred on ensuring that we adequately manage ‘risk systems’ such as water systems [and associated components] so that they don’t become colonised and a reservoir for contamination.


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If then we accept that our water systems [and associated components] frequently contain a variety of different waterborne bacteria and that eliminating bacteria from our water systems is not reasonable or practicable (as our water is not a sterile product…) then the effectiveness of our preventative management strategy will depend upon how well we control the bacterial load within these water systems [and associated components] in order to mitigate colonisation. 

We can distil this even further by basing our preventative management strategy around the understanding of biofilm formation and the associated challenges of managing biofilm bacteria as opposed to free-floating or planktonic bacterial cells.  Bacteria will only colonise water systems [and associated components] if conditions are conducive to this, such as; nutrient-rich, slow moving or stagnant water within a temperature range of 20-45˚C. 


Within such conditions planktonic bacteria will move towards the inner surface of pipework and adhere to these surfaces using protein structures known as bacterial pili (fimbriae).  These hair-like structures on the outside of the bacterial cell wall will ‘cement’ the bacteria to the attached surface and certain (primary-infecting) bacteria like Pseudomonas will very quickly start producing biofilm for other bacteria of the same and different species and genus to live within.  This is a disconcerting phenomenon which often allows bacteria to share resistance characteristics with each other as the bacterial pili have also demonstrated to facilitate the transfer of resistance genes as well as attachment to surfaces – evidenced by the phenotypic differences between planktonic and biofilm bacteria.


Once a ‘mature biofilm’ has formed within a water system, the microorganisms that live within are often well protected by the ‘architecture’ of the biofilm – often making it very difficult for remediation methods to demonstrate long-term effectiveness which may eventually lead to the affected system being replaced which can be; time consuming, disruptive and expensive.  Moreover, the impact of biofilms on the pathogenicity of microorganisms that live within are a major public health consideration, when you consider the possibility of individuals/patients becoming infected with multidrug resistant strains of bacteria.


Clinical Considerations

The clinical consideration needs to start with the ‘transmission pathways’ (how a pathogen may cause infection and subsequent disease) and then consider the clinical outcome which may be determined by pathogenicity and the immune status of those affected by a pathogen, as the probability of a poor prognosis is higher when immunocompromised or neutropenic individuals are infected by pathogenic microorganisms. 

Three routes of transmission/transmission pathways exist when individuals become infected by a microorganism: 

  • Direct contact
  • Inhalation/aspiration
  • Ingestion 

The route of transmission may vary dependent upon the microorganism for example, ‘opportunistic’ pathogens (so called because they await a breach in the host defences) such as Pseudomonas aeruginosa may be spread through direct contact with the pathogen, whereas pathogens such as Legionella pneumophila may only be acquired following the inhalation or aspiration of aerosolised water droplets containing the pathogen and ingestion may define the route of transmission for enteric illness caused by pathogens such as Escherichia coli.  Following the adequate processing  of water by the water undertaker – ensuring that ‘wholesome’ water is delivered to the point of entry of buildings connected to a mains supply, contamination with enteric pathogens is seldom a concern within the UK, but the adequate management of Pseudomonas and Legionella bacteria remain a Duty Holder responsibility.


As such, the ACoP L8, HSG 274 (Parts 1, 2, 3) and for healthcare organisations there is HTM 04-01 (Parts A, B, C) detail a prescriptive set of guidance notes which can be used to safely manage water distribution systems.  These guidance documents are the backbone of effective water safety plans/written schemes of control and compliance in this regard is also considered the ‘minimum requirement’. 


In closing, detailed knowledge of your; water systems, their design, operation and components [environmental considerations] coupled with knowledge about those who may be exposed to these systems i.e. the end user be it a member of staff or someone who is immunocompromised, will help those responsible for the water system [responsible person / authorised person] with what actions are necessary to break the chain of infection.


If you enjoyed this blog and would like to hear more from Water Hygiene Centre add a comment below or follow us on LinkedInTwitter or Facebook.

Editors Note: The information provided in this blog is correct at date of original publication - March 2019. 

© Water Hygiene Centre 2019


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About the author

Water Hygiene Centre

The Water Hygiene Centre was established in 2009 to address the lack of independent water hygiene consultancy within the industry. From our humble beginnings, we have established ourselves as a market leader, helping clients identify and minimise the risk of waterborne contamination and disease, whilst improving compliance performance.

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