What happens after a positive legionella result?

What happens after a positive legionella sample?

What happens after a positive Legionella result?

Receiving notification of a positive Legionella sample can understandably be concerning. However, it’s important to remember that a positive result doesn’t automatically mean people are at immediate risk or that extensive remedial works will always be required.

Instead, a positive sample is an indicator that the effectiveness of your water safety control measures should be investigated.

As every situation is different, the appropriate response will depend on factors such as the bacterial count, the type of water system, the location of the positive sample and the vulnerability of the people using the building. For this reason, a proportionate, risk-based approach is essential.

In this article, we’ll explain what typically happens following a positive Legionella sample and the steps organisations should take to investigate the result, implement appropriate control measures and reduce the likelihood of recurrence. Our approach aligns with the guidance set out in HSE Guidance HSG274.


1. Review and Communicate the Result

Once laboratory results are received, the first step is to review the findings and communicate them to the relevant people.

At this stage, we ensure our customers understand:

  • What the result means
  • How significant it is
  • Whether immediate action is required
  • The recommended next steps

By providing clear, timely communication from the outset, we help our customers understand the situation, make informed decisions and avoid unnecessary concern.


2. Assess the Immediate Risk

However, not every positive result presents the same level of risk.

To determine the most appropriate response, our team considers a number of factors, including:

  • The bacterial count
  • The species or serogroup identified (where available)
  • The location of the positive sample
  • The type of water system involved
  • Whether particularly vulnerable people use the building

For example, care homes and healthcare settings require particular consideration because residents and patients may be more susceptible to infection. By considering the wider context, we can assess the level of risk and recommend a response that is both proportionate and appropriate.


3. Review Existing Water Safety Information

Next, we review the site’s existing water safety documentation to understand what may have contributed to the result. This includes:

  • Legionella Risk Assessments
  • Written Schemes of Control
  • Previous sampling results
  • Temperature monitoring records
  • Flushing records
  • Any recent changes to the building or water system

Looking at this information as a whole, rather than in isolation, helps us identify patterns, highlight any gaps in control measures and focus our investigation on the most likely causes.


4. Identify the Underlying Cause

Once we’ve reviewed the available information, the next step is to identify what may have contributed to the positive result.

Rather than simply treating the symptom, we focus on understanding the underlying cause so that any remedial actions address the issue effectively and help reduce the likelihood of recurrence.

Common contributing factors include:

  • Hot or cold water temperatures outside recommended parameters
  • Little-used outlets or inadequate flushing
  • Water stagnation
  • Dead legs within the system
  • Scale, sediment or biofilm
  • Issues with hot water storage vessels
  • Recent plumbing alterations
  • Poor circulation or system design
  • Gaps in routine monitoring or maintenance

By identifying the root cause, we can recommend targeted remedial actions that address the source of the problem, strengthen existing control measures and support the long-term management of the water system.


5. Implement Immediate Precautions Where Necessary

Where immediate action is required, we work with our customers to implement appropriate temporary control measures while further investigations or remedial works are completed.

Depending on the level of risk, this may include:

  • Restricting access to affected outlets
  • Increasing flushing frequencies
  • Installing point-of-use filters
  • Introducing additional monitoring
  • Implementing other temporary control measures

Every recommendation is tailored to the individual site. By considering the building, its water system and the vulnerability of its occupants, we can recommend practical interim controls that help reduce risk while permanent solutions are put in place.


6. Complete Remedial Works

Once we’ve established the cause of the positive result, we agree the most appropriate remedial actions with our customer.

Depending on the investigation findings, this may include:

  • Cleaning and disinfecting outlets
  • Removing scale and sediment
  • Correcting water temperatures
  • Addressing stagnation
  • Removing redundant pipework
  • Improving circulation
  • Disinfecting part or all of the water system

Every recommendation is proportionate to the level of risk and the issues identified. By focusing on the root cause rather than simply treating the symptoms, we help our customers resolve the issue effectively and strengthen the long-term performance of their water systems.


7. Carry Out Follow-Up Sampling

After completing any remedial works, we may recommend follow-up sampling to confirm that the actions taken have resolved the issue.

These follow-up samples help us assess:

  • Whether the remedial actions have been effective
  • Whether the positive result was isolated
  • Whether further investigation or additional remedial work is required

We then review the results alongside the wider site information to determine the next steps. This ensures any decisions are based on evidence and gives our customers confidence that their control measures continue to protect the people using the building.


8. Review Ongoing Water Safety Management

Once the immediate issue has been addressed, we review the wider water safety management arrangements to help prevent similar issues from occurring in the future.

This may include reviewing and updating:

  • The Legionella Risk Assessment
  • The Written Scheme of Control
  • Monitoring frequencies
  • Flushing programmes
  • Maintenance schedules
  • Staff responsibilities

By reviewing these control measures together, we can identify opportunities to strengthen the overall water safety strategy and ensure it continues to reflect the building, its water system and how it is being used.

Ultimately, the goal isn’t just to resolve the current issue it’s to reduce the likelihood of recurrence and support the long-term management of safe, compliant water systems.


A Positive Sample Is an Opportunity to Strengthen Control Measures

While receiving a positive Legionella result can be worrying, it should be viewed as an opportunity to review and strengthen your water safety arrangements.

Rather than focusing solely on the sample itself, investigate why the result occurred and whether your existing control measures are working as intended.

Taking a structured, proportionate approach helps you identify the root cause, implement the right remedial actions and reduce the likelihood of similar issues occurring in the future.

At Nant, we guide our customers through every stage of the process—from interpreting laboratory results and assessing risk to completing remedial works, carrying out follow-up sampling and reviewing ongoing water safety management. We work in partnership with our customers to ensure they understand the findings, prioritise the right actions and maintain effective control of their water systems.

Ultimately, our role goes beyond responding to a positive sample. We help our customers strengthen their water safety arrangements, build confidence in their control measures and maintain safe, compliant water systems for the people who rely on them every day.

If you’d like to find out how Nant can support your organisation, get in touch with our team today.