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OPPPs – Opportunistic Premise Plumbing Pathogens

Posted by Ruth Thomas on Apr 11, 2022 11:45:00 PM

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In the past, waterborne pathogens in potable (drinking) water systems were considered to be the result of water contamination by agents of human or animal waste which then caused disease via ingestion of the water. These pathogens were contaminants but could not grow or be sustained for long periods in the water itself, they were merely transported by it (1).

Largely, these pathogens have been eradicated from causing disease by the introduction of disinfection of public drinking water systems in the early twentieth century(2) which kills the majority of free-flowing bacteria that accidentally find themselves in the water supply. Happily, this has meant outbreaks of diseases such as Shigellosis and E.coli infections are now very rare from potable water systems. However, with the creation of larger more complex municipal water systems, there is a new danger lurking in the pipes, with the emergence of pathogens that can actually thrive within these systems and hide effectively from the disinfection process.

Alongside Pseudomonas aeruginosa and Mycobacterium avium, one of the most prevalent of these so-called OPPPs (Opportunistic Premise Plumbing Pathogens) is Legionella pneumophila, the causative agent of Legionnaires’ disease. These pathogens are colonists, not contaminants and are ideally suited to grow and persist in potable water distribution and plumbing systems, particularly in multi-occupancy buildings, apartment blocks, offices and hospitals where the premise plumbing is more complex in its nature (1). The favourable conditions these bacteria enjoy result from the ideal features that these systems possess which include(4):

  • High surface to volume ratio
  • Unique pipe materials
  • Low organic carbon levels
  • Periods of stagnation (water age)
  • Dead legs
  • Warming cycles

When these features are combined with the specific traits of OPPPs including disinfection resistance, survival at high temperatures, growth in free-living amoebae and, by far the biggest contributing factor – the ability to adhere to surfaces and form biofilms (3), it is no surprise that when these pathogens get into the system they are here to stay and cause trouble!

Disinfection has proven itself to greatly reduce waterborne infections and is one of the greatest advances in the prevention of disease in the last century, however, its presence in potable water systems can also conversely encourage the growth of OPPPs. Simply reducing the number of pathogens inadvertently reduces the number of competitors for the available carbon and nutrients in the water and can give OPPPs an increased ability to proliferate(3). Bacteria such as Legionella can also protect themselves from the effects of disinfection by both hiding within the available amoebae, particularly residing in biofilms, but also have the ability to form VBNC (Viable But Non Culturable) under the stress of disinfection so that rather than be eradicated, they can survive until they can resuscitate themselves (by phagocytosis by amoebae).

Older water systems can also create problems due to ageing pipework which is difficult to replace but encourages the growth of OPPPs through corrosion and in line breaks allowing more nutrients in. On the flip side, newer initiatives to encourage more “green” water systems can also encourage the growth of OPPPs as they often utilise lower water temperatures and lower water usage thus creating more areas of “ageing water” all of which can lead to increased growth of OPPPs (4). This, in itself, demonstrates the challenging nature of the battle to control these opportunists.

Community outbreaks of Legionnaires’ disease often occur from cooling tower sources, where many people are affected due to the ability to spread aerosolised bacteria far and wide in the air for miles around the source, and these incidences of the disease usually grab attention with their media coverage and investigations. However, sporadic cases of community-acquired Legionnaires’ disease, which are most commonly attributed to the potable water system, also account for a surprisingly high number of cases (1) and should not be overlooked – the total number of these sporadic cases will vastly outnumber the high profile outbreak case numbers, but without gaining the same media attention.

Drinking infected water is not usually a source of infection for Legionellosis, though it can occur via aspiration of the water, however, drinking water is still an important source of infection. Aerosols created when using taps and showers will be an ideal mechanism by which Legionella bacteria can be breathed in and have the potential to infect.

Whilst anyone may be exposed to these OPPPs at times, it is the greater susceptibility of an ageing population and an increase in the number of immunocompromised individuals, in addition to other risk factors such as smoking which has led to an increase in infections, particularly Legionellosis, resulting from these pathogens. It is estimated that by 2025 the percentage of individuals over 60 years will be ~25%, up from 16.1% in 2000(3).

So, if both the incidence of the pathogens and those most vulnerable to them is on the increase then this begs the question of what should be done to limit their impact? The issue is a complex one. Although many options exist for remediation at various levels in the water network, complete eradication of these pathogens is unlikely due to the scale and complexity of the water systems they have inhabited.

Actions need to be taken at various levels from the water provider, building and hospital managers, and homeowners themselves in a multi-pronged approach to prevention(1). Point of use filters, increasing water temperatures, reducing water turbidity, avoiding recirculation of warm water, maintaining disinfection systems, regular cleaning and disinfection of outlets are just a few of the steps that can be undertaken at different levels to help to tackle the problem (3).

When it comes to the risk of Legionella pneumophila in the system, we at Hydrosense offer a rapid solution for testing for its presence both in the water itself, and in any biofilm build up in accessible areas. Our test will even detect the VBNC bacteria that are created under the stress of the disinfection system which a lab culture test will never detect.

We may not yet be able to fully eradicate the pathogen from these complex, often ageing, water systems, but whether you are a homeowner, building manager or water provider, Hydrosense can help to ease your concerns and prevent those most at risk from contracting an illness which can be fatal. Water safety has made huge advances in the last hundred years and with the right tools, control measures and active surveillance we can continue to ensure the safety of water for all and make turning on a tap as risk-free as it should be.

Find out how Hydrosense can help.




  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4529011/pdf/ehp.1408692.pdf
  2. https://www.cdc.gov/healthywater/drinking/history.html
  3. Opportunistic Premise Plumbing Pathogens: Increasingly Important Pathogens in Drinking Water. Pathogens 2015, 4, 373-386
  4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7766883/

Topics: Legionella, Legionella on-site testing, Legionella Risk Assessment, Legionella Rapid Test, LegionellaSeasonality, Legionnaires Disease Pools, Legionella Hot Tubs, Hydrosense, Legionella pneumophila serogroup 1, Cooling Tower Maintenance