Legionella spp. testing is performed to support investigations related to confirmed clinical cases of legionellosis. This section provides information for public health inspectors (PHIs) when submitting Legionella samples to the Public Health Ontario Laboratory (PHOL) for testing.
PHOL performs environmental testing for Legionella for investigations of confirmed culture clinical casesor outbreaks of legionellosis. Clinical case information must be provided to the laboratory whenenvironmental testing is requested and prior to sample collection. Sample collection requirements,sample handling, shipping conditions, test information including testing frequency, turnaround timesand reporting limits are dependent on the specific matrix.
Click on individual testing links for test directory details:
The World Health Organization (WHO) outlines Legionella infection by category; community acquired, travel associated and nosocomial infection in relation to environmental sampling sites:10
Inhalation of contaminated aerosol
Inhalation of contaminated aerosol, aspiration, wound infection
Sources of Legionella
Cooling towers; hot and cold-water systems; spa pools, thermal pools, springs; humidifiers; domestic plumbing; potting mixes and compost
Cooling towers; hot and cold-water systems; spa pools, thermal springs and pools; humidifiers
Cooling towers; hot and cold-water systems; spa pools, natural pools, thermal springs; respiratory therapy equipment; medical treatment
Industrial sites, shoppingcentres, restaurants,clubs, leisure centres,sports clubs, privateresidences
Hotels, cruise ships, camp sites, shopping centres, restaurants, clubs, leisure centres, sports clubs
Hospitals, medical equipment
The World Health Organization (WHO) also provided a list of environmental sampling sites which was adapted from Barbaree JM, et al. 1987.12 This information can be found on the table below and it can be used as a guide for selection of sampling sites, but it is not a list of mandatory sampling sites.
Potable water outside or on the boundary of the health-care facility property
Treatment plant (raw and refined water), guardhouse or other facility if water is not fed from health‑care facility, fire hydrants
General potable water system for healthcare facility
Incoming water pipe(s), water softener (pre and post), preheater (discharge side), primary heater (discharge side), circulating pumps,holding tanks (cold water, discharge side), expansion tank for hot water, back drain on sprinkler system(s), fire line where it branches off main system, water used for respiratory therapy equipment, outlets in patients’ rooms
Air compressor system
Vacuum water source
Positive pressure equipment side: Condensate from tank(s), water separator(s) directly off compressors, water source(s) near air intake(s), air samples where patients were ill with legionellosis
Potable water final distribution outlets
Haemodialysis water source, before or after demineralizer
Intensive care units
Respiratory therapy (patient’s room), cardiac, services with differentgeographical locations, ice-maker (entry water) and ice
Air handling unit serving area where disease occurredCooling towers: return from heat exchanger to water (spray/trough and gutter) distribution or pond (sump), water supply
Pool and balance tank (if fitted), jets and pipes (swab)
Decorative fountain, creeks, ponds, sites of stagnant water
The table below describes types of environmental sampling sites with typical outbreak incubation periodpattern and implicated Legionella species:10
Cooling water systems
Rapid onset over wide area, resolve within incubation period
Predominantly L. pneumophila sg 1
Hot and cold-water systems
Low numbers of cases over prolonged periods
L. pneumophila sg 1, 2, 4, 6, 12, L. micdadei, L. bozemanii, L. feeleii and others
Hot tubs, natural spa pools, thermal springs
Rapid onset confined to users and those in close proximity
L. pneumophila sg 1, L. micdadei,L. gormanii, L. anisa
Humidifiers, respiratory equipment
Low numbers over prolonged periods. Rapid onset confined to users and those in close proximity
L. pneumophila sg 1, 3, and others
Potting mixes, compost
Exclusively L. longbeachae
The following steps are recommended to organize and minimize sample collection time:
The accuracy of the test results may be affected by improper collection, handling and/or shipping. Legionella samples that do not meet the acceptance criteria may be rejected by the laboratory and a new sample may be re-submitted with a newly completed requisition. The acceptance criteria are outlined below.
Several factors must be considered when interpreting Legionella results, such as sampling points, sampling in relation to water system treatment (use of biocide or thermal shock), conditions to support microbial growth such as temperature and stagnation of water; and any delay or temperature changes in shipping conditions. Collection of water and swabs can be used to describe the colonization of the organism within the system at the time of collection only, recognizing that conditions can change over time.
The following table describes the reporting and acceptable limits for Legionella.
Detected / Not detected
Legionella is ubiquitous to the environment – water, soil and sediment; and can grow in a wide range of temperatures. If Legionella was isolated from an environmental sampling site in connection to an outbreak investigation and is a match to the clinical case, remediation is required and consultation with PHOL microbiologist is recommended. If Legionella was isolated and is not a match to the clinical case, remediation may be required and PHOL microbiologist is available for consultation.
Remedial action may be performed immediately if there is strong epidemiological information to suggest potential Legionella exposure to a susceptible population. Post remediation samples may be collected and submitted to verify if a previous laboratory confirmed positive source has been effectively treated after remedial action. Additional guidance for health care institutions can be found in the MOHLTC – Environmental Investigation of Legionella in Health Care Institutional Settings, 2016.11
Back to top ^