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Legionella: Understanding Formation, Dangers, and Thriving in Different Environments

Published on 1st June 2023

Legionella, a gram-negative bacterium, poses a significant threat to public health due to its ability to thrive in diverse environments and cause severe respiratory illnesses. In this guide, we will delve into the nature of Legionella, how it is formed, the associated dangers it presents, and its ability to thrive in different environments. We will provide insights into industries commonly affected by Legionella, including healthcare facilities, hotels and resorts, maritime environments and more.

Understanding Legionella

Legionella is the bacterium responsible for causing Legionnaires’ disease, a severe form of pneumonia, and Pontiac fever, a milder flu-like illness. It is found naturally in freshwater environments such as lakes and rivers but can colonise human-made water systems. Legionella thrives within biofilms, which are slimy layers of microorganisms that develop on surfaces in contact with water, providing an ideal environment for Legionella growth.

Formation and Growth of Legionella

Legionella bacteria can multiply rapidly under specific conditions. The formation and growth of Legionella involve several factors:

Biofilms: Legionella bacteria colonise biofilms that develop on surfaces in water systems, including plumbing networks, cooling towers, and hot water tanks. Biofilms provide a protective environment for Legionella, enabling its growth and persistence.

Protozoa as Hosts: Legionella can enter and survive within protozoa, such as amoebae, which can act as hosts. This interaction contributes to the persistence and growth of Legionella within water systems.

Associated Dangers

Exposure to Legionella occurs through inhalation or aspiration of aerosolised water droplets contaminated with the bacteria. Sources of Legionella exposure include hot tubs, cooling towers, hot water systems, decorative fountains, and other water systems. When individuals inhale the contaminated droplets, Legionella can enter the lungs, leading to infections. Legionnaires’ disease primarily affects the respiratory system and can cause severe pneumonia, while Pontiac fever manifests as a flu-like illness. The elderly, smokers, individuals with weakened immune systems, and those with underlying health conditions are particularly susceptible to severe illness caused by Legionella.

How Temperature Affects Legionella

Temperature plays a crucial role in the growth and survival of Legionella bacteria. Legionella is mesophilic, meaning it thrives in moderate temperatures, typically between 20°C and 45°C (68°F and 113°F). However, with reduced growth rates, Legionella can survive at lower and higher temperatures.

Optimal Growth: Legionella reproduces most rapidly within a temperature range of 35°C to 45°C (95°F to 113°F). This temperature range is often found in hot water systems, including water heaters and storage tanks. The warm water provides an ideal environment for Legionella growth and amplification.

Minimum Growth: Legionella can survive and slowly multiply at temperatures as low as 20°C (68°F). Although its growth rate is significantly reduced, Legionella can persist in cold water systems, such as stagnant water within plumbing networks.

Maximum Growth: Legionella growth is inhibited at temperatures above 60°C (140°F). High-temperature conditions, such as those achieved through adequate hot water system maintenance and thermal disinfection procedures, can effectively control Legionella growth.

However, it is important to note that temperature alone is not the sole determining factor for Legionella growth. Other factors, such as the presence of biofilms, nutrient availability, and the overall condition of the water system, also play significant roles in the proliferation of Legionella bacteria.

Importance of More Frequent Testing in Summer Months

Summer months provide optimal conditions for Legionella growth. During this time, the combination of warm weather and increased water usage creates an environment conducive to the proliferation of Legionella bacteria. Facilities must know this heightened risk and adjust their Legionella testing protocols accordingly. By implementing more frequent testing in summer months, facilities can proactively identify and address potential issues before they escalate into Legionnaires’ disease outbreaks.

• Summer Months Provide Optimal Conditions for Legionella Growth

The warm summer weather creates favourable conditions for the growth and multiplication of Legionella bacteria. Warmer ambient temperatures increase the temperature of water systems, particularly those exposed to direct sunlight or lacking temperature control measures. Legionella bacteria thrive in these warmer environments, multiplying faster and increasing the risk of contamination.

Additionally, increased water usage during summer, such as higher demand for cooling systems, sprinkler systems, and decorative fountains, can lead to more stagnant water and potential areas for colonising Legionella. Stagnant water and elevated temperatures provide an ideal breeding ground for Legionella bacteria.

• Planning Risk Assessments and Scheduling Tests

Considering the heightened risk of Legionella growth during summer, it is crucial for facilities to factor this into their risk assessments and Legionella testing schedules. Facilities can stay proactive in identifying and mitigating potential issues by conducting more frequent testing during these months using LegionellaMax.

According to a report published by the Centers for Disease Control and Prevention (CDC), there is a notable increase in Legionella cases during warmer months. The report states that Legionnaires’ disease incidence peaks in the summer and early fall, with approximately 60% of reported cases occurring between June and September. This statistic highlights the significance of more frequent testing and proactive measures during the warmer months to effectively manage Legionella risks and prevent outbreaks (Source: CDC, “Legionnaires’ Disease Surveillance Summary Report,” 2018).

Industries Commonly Affected by Legionella

Healthcare Facilities: Healthcare facilities, including hospitals and nursing homes, are particularly vulnerable to Legionella contamination. The complex water systems, such as cooling towers, hot water systems, and decorative fountains, provide ample opportunities for Legionella growth and transmission. According to the Centers for Disease Control and Prevention (CDC), healthcare-associated outbreaks account for a significant portion of reported Legionnaires’ disease cases.

Hotels and Resorts: Hotels and resorts, with their extensive plumbing networks, hot tubs, whirlpools, and decorative fountains, present favourable conditions for Legionella growth. The warm water systems and aerosol generation from spa facilities or showerheads can facilitate the transmission of Legionella bacteria to guests, posing a significant risk.

Industrial and Commercial Buildings: Large industrial and commercial buildings, including offices, factories, and shopping malls, often have complex water systems that require careful management to prevent Legionella contamination. Cooling towers, air conditioning units, and water storage tanks are common sources of Legionella in these environments.

Maritime Environments: Cruise ships, naval vessels, and offshore platforms are unique environments where Legionella can thrive. The combination of complex water systems, high occupancy rates, and prolonged periods of water stagnation during ship lay-ups increases the risk of Legionella growth and transmission. The Centers for Disease Control and Prevention (CDC) reported Legionnaires’ disease outbreaks on cruise ships, highlighting the need for effective Legionella management in these settings.

Laboratories and Research Centers: Laboratories and research centres, where water systems are used extensively for experiments, equipment cooling, and other purposes, are also susceptible to Legionella contamination. The water baths, cooling towers, and other equipment can potentially harbour Legionella bacteria if not properly managed and maintained.

Proactive measures, such as regular monitoring, water system maintenance, and comprehensive Legionella management plans, are crucial for minimising the risk of Legionella contamination in laboratories and research centres.

LegionellaMax: The Solution

LegionellaMax is a cutting-edge rapid on-site test kit specifically designed to detect Legionella bacteria in water. It offers a reliable and convenient solution for various settings, including hospitals, hotels, and other commercial buildings. With LegionellaMax, facilities can quickly and accurately identify the presence of Legionella bacteria, enabling prompt corrective measures to prevent the spread of Legionnaires’ disease.

The LegionellaMax test kit is user-friendly and delivers results within 35 minutes. It comes with all necessary materials, including a sample collection kit, a test cassette, and a control solution. Utilising the test kit is as simple as collecting a water sample from the system, adding it to the test cassette, and awaiting the results. This streamlined process ensures that facilities can swiftly assess the presence of Legionella bacteria and take appropriate actions to mitigate the risk of Legionnaires’ disease.

Benefits of LegionellaMax

Rapid Results: LegionellaMax provides rapid results within just 35 minutes, enabling prompt identification of potential problems that may lead to an outbreak. The swift detection empowers facilities to take immediate corrective actions, preventing the further spread of Legionella bacteria and safeguarding public health.

User-Friendly: The LegionellaMax test kit is designed with simplicity in mind. Operating does not require specialised training or technical expertise, making it accessible to many users. Facility staff can easily administer the test, enhancing efficiency and reducing the need for external resources.

Versatility: LegionellaMax is a versatile solution that can be applied across various settings, including hospitals, hotels, and commercial buildings. Regardless of the water system, LegionellaMax delivers reliable results, ensuring comprehensive Legionella monitoring and prevention measures can be implemented in diverse environments.

Cost-Effective: LegionellaMax offers a cost-effective approach to Legionnaires’ disease prevention. By proactively testing for Legionella bacteria in water systems, facilities can identify and address potential risks before they escalate into outbreaks. This proactive approach helps protect public health and mitigates the financial burden associated with healthcare costs, legal liabilities, and reputation damage.

For more information on Legionella and the safety options offered by Martek, please find out more below. Additionally, please contact the Martek Lifecare team today at 01709 599 222.


1. Health and Safety Executive (HSE) – Legionnaires’ Disease.

2. World Health Organization (WHO) – Legionella and the Prevention of Legionellosis. 

3. Centres for Disease Control and Prevention (CDC) – Legionella (Legionnaires’ Disease and Pontiac Fever).