How often should legionella control measures be reviewed?

There is no single review interval that applies to every premises. Legionella control measures should be checked continuously through routine monitoring and subjected to a formal review at intervals justified by the risk assessment. A formal review should also take place whenever the system, its operation, occupancy, management arrangements or evidence from monitoring changes in a way that could affect legionella risk.

The review should assess whether the existing control scheme remains suitable and is being applied as intended. It should consider:

• temperature monitoring results, including evidence of persistent low temperatures or inadequate hot-water recovery;
• disinfection, cleaning, flushing and other preventive tasks, including whether they were completed at the required frequency;
• water quality test results and trends rather than isolated results alone;
• maintenance records, defects, alarms, plant failures and periods when equipment was out of service;
• changes in water demand, occupancy, vulnerable occupants or how parts of the building are used;
• staff competence, supervision and whether responsibilities remain clearly allocated; and
• the effectiveness of corrective actions raised during earlier inspections or audits.

A formal review is commonly scheduled at least annually because this gives the responsible person a defined opportunity to examine performance, update records and confirm that the control scheme still reflects the premises. The appropriate interval may be shorter where the system is complex, the consequences of exposure are significant, monitoring is unstable or previous deficiencies have been identified. The review frequency should be stated in the written scheme rather than left to individual judgement each time.

Routine control activity must not be confused with the formal review. For example, temperature checks, sentinel outlet monitoring, flushing, inspection and sampling may be required at intervals set by the risk assessment and the characteristics of the system. Completing those tasks does not remove the need to evaluate whether the overall programme is working. A series of completed checks may still reveal that the chosen control limits, sampling locations or remedial arrangements are inadequate.

Additional review is appropriate after events such as:

• alterations to pipework, storage tanks, calorifiers, outlets or water treatment equipment;
• changes to building use, occupancy or operating patterns;
• extended shutdowns, low-use periods or recommissioning;
• changes in the responsible person, contractor or maintenance arrangements;
• an outbreak, suspected case or other incident involving possible exposure;
• unsatisfactory sample results or repeated failures to meet control parameters; and
• new information indicating that the original assessment no longer represents the system accurately.

Following a significant change, the review should be completed before the altered system is treated as adequately controlled, where practicable. The assessment may need to be revised, control limits or monitoring points changed, and additional measures introduced. Temporary arrangements should also be documented rather than relying on informal instructions.

Each review should leave an auditable record. This normally includes the date, scope, people involved, information considered, findings, decisions, assigned actions, completion dates and any changes to the written control scheme. It should also record why the existing measures were retained if no changes were considered necessary. A review that simply carries forward an old document without examining current records is unlikely to demonstrate effective management.

The responsible person should use the findings to keep the legionella risk assessment, written control scheme, monitoring schedules and training arrangements aligned. Where specialist sampling, technical interpretation or remedial work is needed, competent advice can help establish whether a recurring result reflects a local fault or a wider weakness in system control.