Cooling towers are essential to modern HVAC and industrial operations, but they can also be one of the most overlooked sources of dangerous pathogens. Among the most serious is Legionella pneumophila, the bacteria responsible for Legionnaires disease, a severe, potentially fatal form of pneumonia. Outbreaks of legionnaires disease, as well as pontiac fever, have been repeatedly linked to contaminated cooling systems, especially those with poor water management, biological growth, or infrequent maintenance.

Legionella treatment is not just about reacting to a positive test result. It is a comprehensive strategy aimed at preventing bacterial growth before it reaches infectious levels. As more facilities face regulatory scrutiny and rising health and safety expectations, water treatment professionals are being asked to deliver solutions that control biological risk without compromising operational uptime.

For industries ranging from healthcare and hospitality to manufacturing and data centers, the consequences of overlooking Legionella risk can be severe. In this article, we will break down how Legionella spreads through cooling towers, the health dangers it presents, and the most effective water treatment strategies to control it.

How Legionella Spreads in Cooling Towers

Cooling towers provide an ideal environment for Legionella growth due to their warm temperatures, abundant moisture, and recirculating water flow. When these systems are not properly treated or maintained, biofilms and sediment can form on surfaces, allowing Legionella bacteria to multiply rapidly.

As water circulates through the tower and evaporates to provide cooling, it releases fine droplets or mist into the air. If Legionella is present, these aerosolized particles can carry the bacteria into the surrounding environment. Inhalation of contaminated mist is the primary route of exposure that leads to infection, and the onset of legionnaires disease, particularly for individuals with weakened immune systems or chronic lung conditions.

Several risk factors can increase the likelihood of Legionella colonization in a water treatment system. These include inconsistent biocide dosing, stagnant water in low-flow areas, scale buildup, and poorly maintained fill media. Even the design of a system can influence risk. For example, towers with complex piping or “dead legs” can allow water to stagnate, giving Legionella time to grow.

Because cooling towers are often located on rooftops or near building air intakes, there is also the danger of Legionella-contaminated air being drawn into indoor ventilation systems. This presents serious concerns for facilities adjacent to hospitals, senior care centers, or any building that houses high-risk populations.

Health Risks: The Real Cost of Infection

Legionnaires’ disease is not a minor illness. It is a serious lung infection that can lead to severe pneumonia, respiratory failure, septic shock, and even fatality especially in people with chronic lung disease, weakened immune systems, or other underlying conditions. The disease is caused by inhaling aerosolized water droplets contaminated with Legionella bacteria, and cooling towers are a well-documented source of exposure.

Symptoms of Legionnaires’ disease typically begin within two to ten days after exposure and may include fever, cough, shortness of breath, muscle aches, and headaches. In more severe cases of Legionnaires disease, patients can develop gastrointestinal issues, confusion, and neurologic symptoms. While some may mistake these for other respiratory infections, Legionnaires’ disease can quickly escalate without proper diagnosis and treatment.

Pontiac fever, a milder illness also caused by Legionella, presents flu-like symptoms but does not lead to pneumonia. Still, its occurrence signals the presence of Legionella in the environment and highlights the need for intervention.

Healthcare-associated Legionnaires’ disease, including nosocomial pneumonia acquired during hospital stays, is of particular concern. Immunocompromised patients, transplant recipients, and individuals in intensive care units face an increased risk of severe disease. Cases of hospital-acquired pneumonia linked to cooling towers or potable water systems have led to major outbreaks, litigation, and lasting reputational harm.

Diagnosis and Clinical Management of Legionnaires’ Disease

Timely diagnosis of Legionnaires’ disease is essential to avoid severe complications, particularly in vulnerable populations. Because the early symptoms of legionnaires disease often resemble other forms of pneumonia, accurate identification depends on specific diagnostic testing methods.

The most widely used tool is the Legionella urinary antigen test, which detects Legionella pneumophila serogroup 1 or the most common cause of Legionnaires’ disease. This test can yield rapid results and is especially valuable in severe community-acquired pneumonia or when healthcare-associated legionella infection is suspected. In addition to urine testing, respiratory samples such as sputum or bronchoalveolar lavage fluid may be cultured to confirm the presence of other Legionella species.

Supportive laboratory tests, including blood tests and chest imaging, help evaluate the extent of lung infection and monitor the progression of mild disease. In more complex cases, lung tissue samples may be examined to rule out other pathogens or determine the precise cause of infection.

Most patients require antibiotic therapy, often involving macrolides or fluoroquinolones, to effectively treat Legionella pneumonia. For patients with severe pneumonia, combination therapy or extended treatment durations may be necessary to ensure a full recovery. Early intervention is critical for improving clinical outcomes, especially in immunocompromised patients or those developing acute kidney injury or respiratory failure.

Legionella Control in Cooling Systems

Preventing Legionella growth in cooling towers requires more than just occasional testing or chemical dosing. It demands a proactive, documented, and professionally managed legionella treatment plan. That is exactly what EAI delivers.

With over 30 years of experience in cooling system safety and disease control, EAI offers end-to-end services designed to reduce legionella growth, meet evolving regulations, and protect both health and operations. Our approach integrates best practices from the Cooling Technology Institute (CTI), ASHRAE 188, OSHA, and other leading regulatory and advisory bodies.

Water Safety Plan Development

Every effective legionella treatment program begins with a detailed Water Safety Plan. This includes system assessment, identification of biological risk factors, and the definition of control measures before any testing or disinfection takes place. EAI’s certified team members, including ASSE-certified experts, partner with facility managers to document and implement this foundational plan.

Tower Cleaning & Disinfection

Regular cleaning is not optional, it is critical. EAI performs scheduled and corrective cleanings according to CTI protocols, including:

• Pre- and post-disinfection with oxidizing biocides
• Manual removal of debris, scale, and biofilm
• Physical cleaning of internal components such as drift eliminators and fill media
• Complete project validation reports to document compliance and demonstrate proactive maintenance

Many facilities, especially those in healthcare or adjacent to vulnerable populations, now perform biannual cleanings to meet regulatory expectations and minimize liability. Even for non-healthcare sites, routine disinfections support more consistent biocide performance.

On-Line Disinfection and Emergency Response

When offline cleaning is impractical, EAI can execute on-line disinfection using existing chemical feed systems. This method allows disinfection while the system remains in service, minimizing operational disruptions. If a positive Legionella test occurs, EAI can deploy emergency disinfection resources on demand (onsite or remotely supported) using pre-stocked materials to mitigate exposure risk without delay.

Microbial Testing and Advanced Surveillance

EAI provides both rapid on-site testing and third-party laboratory sampling for Legionella spp and other atypical pathogens. We work closely with clients to determine optimal testing frequency, ensuring compliance without unnecessary cost. Surveillance includes heterotrophic dip slides, ATP meters, and full pathogen swab testing.

Tower Inspection and Risk Assessment

Cooling tower inspections are a vital component of long-term legionella treatment. EAI inspects:

• Pump performance, belts, bearings, and drift eliminators
• Fill media and baffle condition
• Tower basin cleanliness and dead leg risk zones
• Chemical feed systems and flow consistency

Findings are incorporated into your Water Management Program documentation, supporting audit readiness and public health compliance.

Health & Safety Operator Support

EAI equips your team with the training and operational knowledge required to prevent Legionnaires’ disease outbreaks. From chemical handling and water testing to recognizing symptoms of legionella infection, our operator support services reduce human error and increase program accountability.

Learn more about EAI’s Legionella control in cooling towers and our water treatment services in healthcare industry.

Regulatory Requirements and Guidelines

In response to repeated outbreaks of Legionnaires’ disease, regulatory agencies and public health authorities have tightened expectations for cooling tower oversight. Today, legionella treatment is already considered as a legal and professional responsibility for many facilities.

Guidance from ASHRAE Standard 188 sets a national benchmark for minimizing the risk of Legionella in building water systems. It requires facility managers to implement a water management program that identifies hazardous conditions, outlines control measures, and documents testing procedures. Many states and local health departments have adopted or adapted these requirements into enforceable regulations, especially for high-risk buildings like hospitals, senior care facilities, and schools.

The Centers for Medicare & Medicaid Services (CMS) mandates that healthcare providers receiving federal funding maintain Legionella control programs in building water systems. Facilities without these protocols risk inspection citations, loss of accreditation, or legal action following a confirmed case of hospital-acquired legionnaires disease.

Other important standards come from OSHA, the Cooling Technology Institute (CTI), and local building codes that require routine tower inspections, microbial testing, and action thresholds for Legionella presence. These requirements often extend to any facility using potable water systems or cooling towers near occupied areas.

Strengthen Your Legionella Treatment Plan Today

Controlling Legionella in cooling towers is an ongoing effort that requires technical knowledge, field experience, and regulatory insight. EAI brings all three.

With decades of experience managing water systems across healthcare, higher education, commercial, and industrial facilities, EAI understands the diverse challenges facilities face when implementing a legionella treatment program. We go beyond standard chemical applications to offer fully integrated support: planning, testing, disinfection, documentation, and training.

Cooling towers are critical to your facility’s operations, but they also carry one of the highest risks for legionella bacteria transmission. Whether you manage a hospital, university, or commercial building, having a documented, proactive legionella treatment program in place is essential.

EAI can help you implement or improve a compliant and effective water safety plan. From microbial testing and system inspections to emergency disinfection and staff training, our team is here to reduce your risk and protect your people.

Don’t wait for a positive test to take action.
Contact EAI today to take the next step in cooling tower safety.