LEGIONELLA GLOSSARY

Technical terms used in Legionella surveillance, environmental sampling and water-system disinfection. Definitions follow ECDC, WHO and Italian national guidance.

34 entries

A–Z of Legionella terminology

Curated for international researchers, journalists and water-safety professionals.

Legionella: Genus of Gram-negative bacteria, ubiquitous in fresh water and engineered water systems. Includes more than 60 species; Legionella pneumophila accounts for the majority of human disease.
Legionnaires' disease: Severe pneumonia caused by Legionella spp., usually L. pneumophila serogroup 1. Notifiable in Italy through the SEIEVA surveillance system.
Pontiac fever: Self-limiting flu-like illness caused by Legionella spp., without pneumonia. Considered the milder clinical form of legionellosis.
Serogroup 1 (sg1): Serogroup of L. pneumophila responsible for ~80% of community-acquired Legionnaires' disease cases worldwide.
CFU/L: Colony-forming units per litre — the unit used to express Legionella concentration in water samples after culture on BCYE selective agar.
UNI EN ISO 11731:2017: International standard for the enumeration of Legionella in water samples via the culture method. Reference method for Italian and EU sampling protocols.
BCYE agar: Buffered charcoal yeast extract agar — selective medium used to grow Legionella from environmental samples (7–10 days at 36 °C).
Biofilm: Microbial community embedded in a self-produced extracellular matrix attached to a surface. Biofilms harbour Legionella and protect it from disinfectants.
Dead-leg: Section of pipework with little or no water flow. A common reservoir for Legionella growth; mitigation requires hydraulic removal or scheduled flushing.
Distal point: End-use outlet of a water distribution system (taps, showers). Standard sampling location for risk assessment.
DHW / DCW: Domestic hot water / domestic cold water — the two main subsystems of a building water network monitored for Legionella.
Thermal shock: Disinfection technique raising water temperature above 70 °C at all distal points for at least 30 minutes. Effective short-term remediation.
Hyperchlorination: Shock chlorination at elevated free-chlorine concentration (typically 20–50 mg/L for several hours) to disinfect water distribution systems.
Copper-silver ionization: Continuous disinfection technology releasing Cu²⁺ and Ag⁺ ions into the water stream. Effective against planktonic Legionella and biofilm.
Chlorine dioxide (ClO₂): Continuous disinfection agent, effective against biofilm at low residual concentrations. Common in Italian healthcare facilities.
Monochloramine: Slow-release chlorine-based disinfectant with strong biofilm penetration. Used as secondary disinfection in DHW systems.
UV disinfection: Point-of-entry disinfection using ultraviolet radiation. Effective at the point of treatment but provides no residual downstream.
Water Safety Plan (WSP): WHO framework for the systematic risk management of drinking-water supplies, from catchment to consumer.
Risk assessment (Legionella): Documented, systematic evaluation of all water systems to identify and control Legionella risk. Mandatory in Italy under the State-Regions Agreement of 7 May 2015.
State-Regions Agreement 7 May 2015: Italian national guidelines ("Linee guida per la prevenzione e il controllo della legionellosi"). Reference document for risk assessment, sampling and corrective actions.
ECDC ELDSNet: European Legionnaires' Disease Surveillance Network coordinated by the ECDC. Italy contributes through ISS.
ISS: Istituto Superiore di Sanità — Italian National Institute of Health, responsible for the national Legionella surveillance system (SEIEVA / SIMI).
SEIEVA: Sistema Epidemiologico Integrato dell'Epatite Virale Acuta — Italian integrated surveillance system that also covers legionellosis notifications.
Cooling tower: Evaporative heat-rejection device. A known vehicle for Legionella aerosol transmission; subject to mandatory monitoring in Italy.
Aerosol: Suspension of solid or liquid particles in air. Legionella infection occurs by inhalation of aerosols generated by water systems.
Whirlpool / spa pool: Heated agitated water installation — high-risk environment for Legionella amplification and aerosol dispersion.
Sampling plan: Documented strategy specifying sampling points, frequency, methodology and acceptance criteria for Legionella monitoring.
Chain of custody: Documented chronological control of the sample from collection to laboratory analysis. Required for accredited results.
ISO/IEC 17025: International standard for the competence of testing and calibration laboratories. Required for accredited Legionella analyses.
ACCREDIA: Italian National Accreditation Body, signatory of EA, IAF and ILAC mutual recognition arrangements.
Set-point temperature: Operating temperature of a DHW circuit. National guidance requires storage ≥60 °C and ≥55 °C at any point of the recirculation loop.
Action level: Concentration threshold (in CFU/L) triggering corrective actions according to ISS guidance: <100, 100–1,000, 1,000–10,000, >10,000.
Outbreak: Two or more linked cases of Legionnaires' disease. Triggers epidemiological investigation by the local health authority.
Travel-associated case: Case of Legionnaires' disease in a person who stayed in commercial accommodation in the 2–10 days before symptom onset. Reported through ECDC ELDSNet.