Legionella testing in Arizona detects the presence of Legionella pneumophila and related species in building water systems, cooling towers, and other engineered water sources where the bacterium thrives between 77 and 113 degrees Fahrenheit. Despite Arizona’s arid desert environment, the state’s hot climate actually creates ideal growth conditions inside building plumbing systems, making Legionella a significant and often underestimated public health risk for facilities across Tucson, Phoenix, and statewide.

The Desert Misconception: Why Hot and Dry Does Not Mean Safe

There is a persistent and dangerous misconception that Legionella is primarily a problem in humid, temperate climates with older infrastructure. Facility managers and building owners in Arizona frequently assume that the desert environment provides natural protection against waterborne pathogens. This assumption is wrong, and it leads to preventable illness and death every year.

How Arizona’s Climate Creates Legionella Risk

Legionella pneumophila, the bacterium responsible for Legionnaires’ disease, thrives in water temperatures between 77 and 113 degrees Fahrenheit (25 to 45 degrees Celsius), with optimal growth occurring around 95 degrees Fahrenheit. Consider how Arizona’s climate interacts with building water systems:

• Incoming water temperature: During summer months, municipal water delivered through underground pipes in the Phoenix and Tucson metropolitan areas can arrive at building connections at 85 to 95 degrees Fahrenheit, already within the prime Legionella growth range. In many other states, incoming water is well below the growth threshold and must be heated before risk begins.
• Exposed piping and rooftop equipment: Water sitting in pipes exposed to Arizona’s 110-plus degree ambient temperatures during summer effectively becomes an incubator. Rooftop water storage tanks, solar water heating systems, and exposed distribution piping can reach temperatures that actively promote Legionella proliferation.
• Hot water heater stratification: Many buildings set water heaters to 120 degrees Fahrenheit to prevent scalding. However, if the incoming water is already at 90 degrees and the heater is not well-mixed, large volumes of water within the tank sit in the ideal growth zone. Stratification, where cooler water settles at the bottom and sides of the tank, creates persistent niches for Legionella colonization.
• Cooling tower operation: Arizona’s extreme heat means cooling towers operate at high capacity for 6 to 8 months of the year. These towers are the single highest-risk source for community Legionella outbreaks because they generate aerosols that can carry the bacterium miles downwind. Extended operation seasons mean extended exposure periods.

Arizona Legionella Data: The Numbers Tell the Story

According to the Arizona Department of Health Services (ADHS), reported cases of Legionnaires’ disease in Arizona have increased steadily over the past decade. Between 2015 and 2024, Arizona reported over 1,200 confirmed and probable cases of Legionnaires’ disease, with annual case counts rising from approximately 70 per year to over 170 per year. The case fatality rate nationally is approximately 10%, meaning that Legionella infections in Arizona result in an estimated 10 to 17 deaths annually.

These numbers almost certainly undercount the true burden. Legionnaires’ disease is frequently misdiagnosed as community-acquired pneumonia, and the CDC estimates that only a fraction of cases are correctly identified and reported. Many mild cases caused by Legionella, known as Pontiac fever, resolve without medical attention and are never reported at all.

Maricopa County and Pima County consistently report the highest case counts, reflecting both population density and the concentration of large building water systems, cooling towers, and healthcare facilities in the Phoenix and Tucson metropolitan areas.

Where Legionella Grows: High-Risk Sources in Arizona Buildings

Legionella does not grow in natural desert water sources. It grows in engineered water systems where conditions of warm temperature, stagnation, biofilm, and nutrient availability converge. Understanding these high-risk sources is the first step toward effective water management.

Cooling Towers

Cooling towers are the highest-risk source for large-scale Legionella outbreaks. These systems work by evaporating water to remove heat from building HVAC systems, and in the process they generate fine aerosol droplets that can carry Legionella bacteria into the surrounding air. A single contaminated cooling tower can cause illness in people hundreds of meters or even miles downwind.

In Arizona, cooling towers run almost continuously from April through October, with peak operation during June through September when outdoor temperatures routinely exceed 100 degrees Fahrenheit. This extended operation season, combined with the warm water temperatures that promote Legionella growth, makes Arizona cooling towers particularly high-risk.

Key risk factors for cooling tower Legionella contamination include:

• Water temperatures consistently in the 85 to 105 degree Fahrenheit range during operation
• Biofilm accumulation on tower fill media, basins, and drift eliminators
• Inadequate biocide treatment programs
• Poor maintenance of drift eliminators, which are designed to capture aerosol droplets before they escape the tower
• Stagnation during periods of reduced operation or seasonal shutdown

Building Hot Water Systems

Domestic hot water systems in large buildings represent the second most common source of Legionella exposure. Hospitals, long-term care facilities, hotels, apartment complexes, and dormitories all maintain hot water systems with the characteristics that promote Legionella growth: warm temperatures, large volumes, complex distribution networks with dead legs, and periods of low flow or stagnation.

In Arizona, the risk is compounded by the fact that “cold” water entering buildings during summer is already warm enough to support Legionella growth. This means that even the cold water side of the plumbing system can become colonized, not just the hot water system. Facilities that rely solely on hot water temperature management to control Legionella may be overlooking half of their risk.

Decorative Fountains and Water Features

Arizona’s resorts, hotels, shopping centers, and public spaces frequently feature decorative water fountains, splash pads, and misting systems. These features create aerosols that occupants breathe, and if the water is not properly treated and maintained, they can become sources of Legionella exposure. Outdoor misting systems, which are ubiquitous at Arizona restaurants, bars, and outdoor venues during summer, use fine nozzles to create respirable water droplets and deserve particular attention.

Healthcare Facility Water Systems

Hospitals and long-term care facilities face the highest consequences from Legionella contamination because their occupants are the most vulnerable. Immunocompromised patients, the elderly, chronic disease patients, and post-surgical patients are at dramatically elevated risk of severe illness and death from Legionella exposure.

The Centers for Medicare and Medicaid Services (CMS) issued a requirement in 2017 that all healthcare facilities must develop and maintain water management programs specifically addressing Legionella risk. This requirement applies to every hospital, nursing home, and long-term care facility in Arizona and is enforced during accreditation surveys.

Regulatory Requirements for Legionella Testing in Arizona

The regulatory landscape for Legionella has evolved significantly in recent years, with new requirements at the federal, state, and industry levels creating a growing obligation for facility owners and operators to proactively manage Legionella risk.

ASHRAE Standard 188

ASHRAE Standard 188, “Legionellosis: Risk Management for Building Water Systems,” provides a framework for identifying buildings that require water management programs and implementing those programs. While ASHRAE 188 is not a law, it has become the de facto standard of care referenced by regulators, public health agencies, and courts in Legionella-related litigation.

Buildings that meet any of the following criteria should have an ASHRAE 188-compliant water management program:

• Buildings with more than 10 stories
• Buildings with centralized hot water systems
• Buildings with cooling towers, evaporative condensers, or fluid coolers
• Healthcare facilities of any size
• Buildings housing or serving immunocompromised populations

In Arizona, the combination of warm climate, large resort and hospitality properties, and significant healthcare infrastructure means that a substantial portion of commercial and institutional buildings should have water management programs in place.

CMS Requirements for Healthcare Facilities

Since June 2017, CMS has required all Medicare-certified healthcare facilities to have water management programs that reduce the risk of Legionella and other waterborne pathogens. CMS surveyors actively review these programs during accreditation surveys and can cite deficiencies that affect a facility’s certification status.

Key CMS expectations include:

• A multidisciplinary water management team
• A written water management program based on ASHRAE 188 and CDC guidance
• Identification of all water sources and high-risk areas
• Defined control measures with monitoring parameters
• Routine environmental Legionella testing as a validation measure
• Corrective action procedures when control limits are exceeded
• Documentation of all activities and decisions

Arizona State and Local Requirements

Arizona does not currently have a state-specific Legionella testing mandate for non-healthcare buildings. However, Maricopa County and Pima County environmental health departments investigate all reported cases of Legionnaires’ disease and can require environmental testing of suspected source buildings. When an outbreak is identified, public health authorities have the power to require facility shutdowns, remediation, and ongoing monitoring.

Several Arizona municipalities are developing or considering cooling tower registration and maintenance ordinances similar to those already enacted in New York City and other jurisdictions. Proactive Legionella testing and water management programs position facilities to meet these requirements if and when they are adopted locally.

The Importance of CDC ELITE Certification for Legionella Testing

Not all laboratories that offer Legionella testing are equally qualified to perform it. The CDC’s Environmental Legionella Isolation Techniques Evaluation (ELITE) program is the only national proficiency program specifically for Legionella culture testing, and it is the standard that public health agencies, infection preventionists, and water management professionals use to evaluate laboratory competence.

What CDC ELITE Certification Means

CDC ELITE certification demonstrates that a laboratory has successfully completed a rigorous proficiency evaluation for the isolation and identification of Legionella from environmental water samples. The program evaluates the laboratory’s ability to detect Legionella at low concentrations, correctly identify Legionella species, distinguish Legionella from interfering organisms, and maintain consistent performance over multiple evaluation rounds.

Laboratories that hold CDC ELITE certification have demonstrated competence in the specialized techniques required for Legionella culture, including selective media preparation, acid and heat treatment for sample processing, and colony identification. These skills are not part of routine microbiological training and require dedicated expertise.

Why CDC ELITE Matters for Your Results

Legionella culture is technically challenging. The bacterium grows slowly (3 to 14 days for visible colonies), requires specialized media (buffered charcoal yeast extract, or BCYE), and competes with faster-growing environmental organisms that can overgrow culture plates and mask Legionella colonies. Laboratories without specific Legionella expertise may report false negatives, missing colonization that a qualified laboratory would detect.

A false negative Legionella result can have severe consequences: a facility that believes its water system is safe when it is actually colonized may fail to implement necessary controls, leading to preventable illness. For healthcare facilities in particular, the liability exposure from using a non-ELITE laboratory for Legionella testing is significant.

AATLS: CDC ELITE Certified

AATLS holds CDC ELITE certification for environmental Legionella testing, making us one of a limited number of laboratories in the southwestern United States qualified to perform this specialized analysis. Our Legionella testing program is led by experienced microbiologists with specific training in Legionella isolation and identification. We use the culture method (ISO 11731), which remains the gold standard for environmental Legionella monitoring because it detects viable, culturable organisms and provides species and serogroup identification. Review our full accreditations and certifications.

Legionella Testing: What to Expect

Understanding the practical aspects of Legionella testing helps facility managers plan effective monitoring programs and interpret results correctly.

Sample Collection

Environmental Legionella samples are collected as first-draw samples from hot and cold water outlets, cooling tower basins, and other water system components. First-draw sampling means collecting the sample immediately upon opening the tap without flushing, which captures the water and any biofilm organisms that have been sitting in the fixture and adjacent piping.

Key sampling considerations:

• Sample volume: Typically 1 liter per sample point, collected in sterile containers provided by the laboratory.
• Dechlorination: Sample containers contain sodium thiosulfate to neutralize any residual chlorine or chloramine, preventing disinfectant from killing Legionella during transport.
• Temperature measurement: Water temperature should be recorded at each sample point, as this data is critical for evaluating the effectiveness of thermal control measures.
• Location selection: Sample points should include high-risk locations such as distal outlets in patient rooms (for healthcare), low-use fixtures, hot water return loops, hot water heater outlets, and cooling tower basins.
• Number of samples: A baseline assessment typically requires 10 to 20 samples from representative locations throughout the water system. Ongoing routine monitoring may use fewer strategically selected sentinel sites.

Analytical Method and Turnaround Time

The standard method for environmental Legionella testing is culture on BCYE agar with selective supplements. Results are reported in colony-forming units per liter (CFU/L). Because Legionella is slow-growing, culture results require 10 to 14 days from sample receipt. While qPCR (molecular) methods can provide results in 1 to 3 days, culture remains the preferred method for routine monitoring because it detects only viable organisms and provides speciation data.

At AATLS, standard Legionella culture turnaround is 10 to 14 business days. We can provide preliminary results as soon as growth is observed and report final confirmed results at the end of the incubation period.

Interpreting Legionella Results

There is no EPA-regulated MCL for Legionella in building water systems. Instead, action levels are based on industry guidelines and risk management frameworks:

• Not detected: No Legionella isolated. Continue routine monitoring per your water management program.
• Low level (1 to 999 CFU/L): Legionella is present but at low concentrations. Review water management controls, increase monitoring frequency, and consider targeted remediation of positive locations.
• Moderate level (1,000 to 9,999 CFU/L): Significant colonization detected. Implement corrective actions including thermal or chemical disinfection of affected areas and review the overall water management program for deficiencies.
• High level (10,000 CFU/L or greater): Heavy colonization requiring immediate action. Emergency disinfection, restriction of water use in affected areas, and comprehensive review of the water management program are warranted.

For healthcare facilities, many infection prevention programs use a lower action threshold of 100 CFU/L or any detection of Legionella as a trigger for enhanced investigation and corrective action.

Building a Legionella Water Management Program for Arizona Facilities

Effective Legionella prevention requires a systematic water management program, not just periodic testing. Testing is a critical component, but it must be embedded in a broader framework of risk assessment, control measures, and continuous improvement.

Step 1: Assemble a Water Management Team

The team should include facility management, maintenance personnel, infection prevention (for healthcare facilities), and external expertise as needed. The team is responsible for developing, implementing, and maintaining the water management program.

Step 2: Describe the Building Water Systems

Create detailed flow diagrams and inventories of all water system components, including incoming water sources, storage tanks, water heaters, recirculation systems, cooling towers, decorative features, and all points of use. Identify dead legs, low-use areas, and locations where water temperatures may fall into the Legionella growth range.

Step 3: Identify Risk Areas and Control Measures

For each high-risk area, define specific control measures. Common controls include maintaining hot water at 140 degrees Fahrenheit or higher at the heater and above 120 degrees at distal outlets, maintaining cold water below 68 degrees Fahrenheit (a particular challenge in Arizona summers), implementing biocide treatment programs for cooling towers, flushing low-use outlets on a regular schedule, and maintaining adequate disinfectant residual throughout the distribution system.

Step 4: Implement Monitoring and Testing

Define monitoring parameters including temperature checks (weekly to monthly at sentinel locations), disinfectant residual measurements (daily to weekly), and environmental Legionella culture testing (quarterly to semi-annually as a validation measure). Testing through a CDC ELITE certified laboratory like AATLS provides the data needed to verify that control measures are working.

Step 5: Establish Corrective Actions

Define specific corrective action procedures for when monitoring results exceed control limits. This includes who is responsible, what actions to take, when to escalate, and how to verify that corrective actions were effective.

Step 6: Document Everything

Documentation is essential for demonstrating due diligence in the event of illness, regulatory inquiry, or litigation. Maintain records of all monitoring data, corrective actions, program reviews, and training activities.

Why Choose AATLS for Legionella Testing in Arizona

AATLS brings a unique combination of qualifications and local expertise to Legionella testing for Arizona facilities:

• CDC ELITE certified: We have passed the CDC’s rigorous proficiency evaluation for environmental Legionella isolation and identification, demonstrating the specialized competence required for reliable results.
• ISO/IEC 17025 accredited: Our entire quality management system meets the international standard for laboratory competence, ensuring consistent, defensible results.
• Arizona expertise: Based in Tucson, we understand the specific Legionella risk factors created by Arizona’s climate, including warm incoming water temperatures, extended cooling tower operation seasons, and the challenges of maintaining cold water temperatures during summer months.
• Comprehensive support: Beyond laboratory analysis, we can advise on sampling strategies, result interpretation, and the analytical components of water management programs.
• Veteran-owned leadership: Dr. Glenn Cherry, an Air Force veteran and scientist, leads AATLS with a commitment to protecting public health through reliable analytical testing.