A legionella survey is a full assessment of all water systems and services within a property including everything that uses, carries or stores water such as pipework, boilers, hot and cold taps, fountains etc. In some cases cooling towers and spa pools might also be included.

The results of the legionella survey form the basis for a risk assessment that defines the action levels and frequency of monitoring for all systems. This is a key element of any WMP and the most important factor in reducing the risk of Legionnaires’ disease.

Regulations for Legionella monitoring vary between countries and states but generally rely on the AS/NZS 4766 standards, with additional requirements for healthcare facilities and evaporative cooling towers. These are supplemented by national guidelines such as the Australian guidelines and CDC recommendations.

Conducting a Legionella Survey: Steps and Recommendations

The WHO’s LRA recommendation is to monitor water systems for the presence of Legionella (Legionella spp) at least quarterly using a qPCR method. This allows for a separate identification of the seven Legionella polyvalent species known to cause human disease: L. pneumophila serogroup 1 and serogroups 2-14, and also detects L. longbeachae, L. bozemanii 1 and 2, L. dumoffii, L. germanic, and L. jordanis.

Typically, the samples are collected by suitably trained environmental consultants following standard sampling protocols and are stored in sterile containers with sodium thiosulfate to neutralize any residual biocide. These are then sent to an accredited laboratory for processing within 24 hours. If culturable levels exceed 1,000 CFU/L, then resampling and testing will be required. The resampling and follow-up actions will be determined by the site based on the results of the resampling and risk assessment.