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The Ongoing Risk of Legionnaires’ Disease

Microscopic view of Legionella bacteria responsible for Legionnaires' disease

In the summer of 1976, reports of a mysterious and terrifying outbreak dominated American news: 34 people died suddenly and 220 were hospitalized after visiting Philadelphia.

Patients suffered from severe headaches, chest pain, chills, and fever up to 107°F (41.7°C). Months later, following one of the most extensive medical investigations in history, microbiologists identified the culprit: a previously unknown bacterium named Legionella, named after the victims—military veterans attending an American Legion convention.

The Current Scope of Legionnaires’ Disease

Today, Legionella is no longer a mystery. We understand where it lurks, how it spreads, and how to prevent it. Yet, the infection remains a major public health threat:

  • Hospitalizations: Between 8,000 and 18,000 people are hospitalized with Legionnaires’ disease in the United States every year.
  • High Mortality Rates: The disease kills roughly 10% of infected individuals overall, and up to 25% of those who contract it in a healthcare facility.
  • Surging Incidence: Reported cases in the U.S. more than tripled between 2000 and 2011, making it an urgent priority for facility managers and infection control specialists.

“Legionnaires’ disease in hospitals is widespread, deadly, and preventable.”

— Anne Schuchat, M.D., Centers for Disease Control and Prevention (CDC)

How Legionella Spreads: Transmission & Environmental Sources

Legionella bacteria cause two distinct clinical conditions:

  1. Legionnaires’ Disease: A severe, potentially fatal form of pneumonia requiring targeted antibiotic treatment.
  2. Pontiac Fever: A milder, flu-like condition that resolves without medical intervention (and often goes unreported).

Neither condition is contagious from person to person. Instead, individuals become infected by inhaling airborne mist or water droplets contaminated with Legionella.

Common Breeding Grounds in Facility Infrastructure

While Legionella occurs naturally in freshwater environments in low quantities, it thrives in large, complex building water systems:

  • HVAC & Cooling Towers: Aerosolized vapor from contaminated air conditioning cooling units can travel long distances into building intakes or nearby streets.
  • Aerosolizing Fixtures: Decorative fountains, hot tubs, whirlpool baths, hotel ice machines, and commercial supermarket mist sprayers.
  • Plumbing Infrastructure: Stagnant water lines, showerheads, valves, and specialized medical aerosol devices like nebulizers and humidifiers.

Who Is Most Susceptible?

While healthy individuals can contract the disease—especially workers near high-concentration water sources like wastewater treatment plants—certain groups face a significantly higher risk:

  • Adults aged 50 and older
  • Current or former smokers
  • Patients with chronic lung disease or diabetes
  • Individuals with immunocompromised systems

Preventing Legionella Growth and Airborne Transmission

Mitigating Legionella risk requires a two-pronged strategy: strict water system management and active air disinfection.

1. Water System Temperature & Flow Control

Legionella thrives in warm water (77°F to 113°F / 25°C to 45°C). Maintaining hot water supplies at 131°F (55°C) or higher helps inhibit bacterial growth. However, facility managers must balance heat requirements against scald risk regulations and eliminate stagnant water in dead-leg pipes or unused hospital wings.

2. Airborne Pathogen Destruction

For Legionella to cause lung infection, contaminated water droplets must stay airborne and be inhaled. Studies show that airborne Legionella can:

  • Remain viable in aerosols for several hours.
  • Travel significant distances—epidemiological research shows bacterial dispersion greater than 10 kilometers from open-air sources under optimal wind and humidity conditions.

To prevent contaminated aerosols from circulating indoors, facilities should deploy continuous indoor air purification. Ultra-low energy plasma technology, such as Novaerus air disinfection systems, is lab-tested to deactivate airborne gram-negative bacteria like Legionella, rendering them harmless.

By implementing active water management controls alongside continuous air disinfection technology, healthcare and commercial facilities can effectively stop Legionella transmission before outbreaks occur.