Legionnaires’ Disease: No Longer a Mystery, Still a Threat

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

Patients developed headaches, chest pain, chills, and fevers up to 107 degrees. Autopsies of the deceased revealed lungs that resembled Brillo pads. Was it swine flu? Food poisoning? “Super” gonorrhoea? A terrorist attack? Theories abounded.

Months later, concluding the most extensive medical investigation in history, a microbiologist peered into a microscope and identified the cause: a previously unknown bacteria. Officials named it Legionella after the victims, military veterans who’d attended a convention of the American Legion.

Today, Legionnaires’ disease is no mystery. We know where it lurks and how it’s spread. We know between 8,000 and 18,000 people in the United States are hospitalized yearly with Legionnaires' disease, along with tens of thousands more around the globe. We know the bacteria kills 10 per cent of those who contract the disease —  and 25 per cent of those stricken in a healthcare facility.

And yet, Legionella continues to wreak havoc, because little is done to contain it.

“Legionnaires’ disease in hospitals is widespread, deadly, and preventable,” said a CDC official, Anne Schuchat, M.D.

The disease garners headlines after mass outbreaks — on cruise ships, at conventions, at healthcare facilities — but these outbreaks account for just 4 per cent of total cases in the United States.

Incidence of Legionnaires’ disease more than tripled in the United States between 2000 and 2011. Worldwide, cases are vastly underreported. In England and Wales, a national surveillance program detects clusters of the disease and investigates the sources of infection. Today, as researchers have noted, Legionnaires’ is considered “an increasingly important disease from a public health standpoint.”

How Legionella Spreads

The Legionella bacteria actually cause two conditions: Legionnaires’ disease, a virulent form of pneumonia that must be treated with antibiotics, and Pontiac fever, a mild, flu-like condition that resolves within a week. Since Pontiac fever resembles other conditions and doesn’t require medical attention, many cases of Legionella infection go unreported — and the source remains unidentified.

Legionnaires’ disease and Pontiac fever aren’t contagious. Patients become infected by inhaling the airborne droplets of contaminated water, typically at facilities with large water systems, such as convention centres, prisons, schools, and healthcare facilities. (Legionella is found naturally in lakes and streams, but in amounts too low to cause disease.)

Investigators eventually traced the 1976 Philadelphia outbreak to contaminated vapour that rose from air conditioning cooling units atop a hotel. The droplets fell to the street below, where they were inhaled by pedestrians and sucked into the hotel lobby by fans on the side of the building.

In the decades since, air conditioning cooling towers have been ground zero for numerous Legionnaires’ cases, including the largest recorded outbreak, at a hospital in Spain, where some 800 patients were thought to have been infected.

Other Legionella breeding grounds have been identified, too: hot tubs, fountains, showerheads, whirlpool baths, hotel ice machines, and supermarket mist sprayers. At a flower show in the Netherlands and a fair in Belgium, attendees contracted Legionnaires' disease from whirlpool spas in the exhibition halls. At a South Dakota restaurant and a hospital in Wisconsin, dozens were infected by mist sprayed from decorative fountains.

Legionella also thrives in respiratory devices such as humidifiers, vaporizers, nebulizers, and can grow in parts of building water systems that are continually wet, such as pipes, valves, and fittings.

Who’s Susceptible to Legionella Infection

Those at greatest risk of falling ill from Legionella are the medically vulnerable: people over age 50, current or former smokers, diabetes or lung disease patients, and anyone with a weakened immune system. That’s why hospital outbreaks are particularly deadly.

Still, relatively healthy people can become infected, especially if they work near contaminated water sources. For example, employees at wastewater treatment plants may be at elevated risk for infection, as sewage and aeration ponds can contain very high concentrations of Legionella.

Patients typically come down with symptoms within 2 to 10 days after exposure. Infection rates are highest in the summer when air conditioners kick into heavy use and water chemistry changes due to warmer outdoor temperatures. But Legionnaires’ disease can strike at any time of the year.

Preventing the Growth and Spread of Legionella

For facility maintenance managers, preventing Legionella infection has become a serious responsibility. After a deadly outbreak at a UK art centre, caused by a contaminated air conditioning system, the centre’s governing council and architect were charged with corporate manslaughter. Though they were acquitted after a trial, they were fined for safety breaches.

Protecting patients and patrons from Legionella infection requires vigilance on two fronts: keeping water systems clean and cleaning the surrounding air.

For years, prevention efforts at hotels, hospitals and other large venues have focused solely on the water half of the equation. Legionella bacteria are wily and hardy, easily adapting to their environment, surviving for long periods — even in chlorinated drinking water systems — and then pouncing when conditions are just right.

Water temperature plays a big role in Legionella growth. Because Legionella thrives in warm water, experts recommend hot water temperature be kept at 55 degrees Celsius (131 °F) or above. But this can be a challenge; in some countries, regulations that keep residents and hotel patrons from being scalded by showers also keep maximum temperatures too low to halt Legionella growth.

Stagnating water also allows Legionella to flourish. Facilities must take precautions during hotel renovations or off-peak seasons; hospitals must know which showers are rarely used.

Countless other water-related scenarios can promote Legionella growth. An inadequate disinfectant is introduced. Vibrations from construction cause a change in water pressure. Heating or filtering processes degrade water quality, using up extra disinfectant.

Legionella water management programs are both critical and complex, typically requiring expertise from microbiologists, industrial hygienists, or environmental health specialists.

Also critical — but much simpler — are strategies to clean the air.

In order for Legionella-contaminated vapour to be inhaled and attack the lungs, the bacteria must remain airborne. So, prevention efforts must focus on making the air less hospitable for the bacteria to survive and proliferate.

At this point, much remains unknown about how precisely Legionella is transmitted from water to air. It’s unclear, for example, what air temperature and humidity are best for the bacteria to thrive and how long Legionella can survive in the air.

What we do know: Legionella can travel long distances. In a Danish study of a Pontiac fever outbreak, bacteria were recovered 200 meters downwind of an aeration pond at a water treatment plant. And epidemiological studies have suggested Legionella can be dispersed greater than 10 kilometres from wastewater treatment plants.

What’s more, certain strains of airborne Legionella can survive for several hours, under the right conditions.

It’s therefore essential for facilities to deploy continuous and strategically placed air purification technology. Novaerus air disinfection technology has been shown in laboratory testing to reduce infectious, gram-negative bacteria like Legionella.

The year following the Philadelphia Legionella outbreak, investigators used blood samples to identify the bacteria as the culprit in other unsolved infection outbreaks, dating back to 1957. But as a documentary of the discovery noted, it is likely that Legionnaires’ disease “has been killing us for thousands of years.”

Now that we know so much more about Legionella — where it thrives, how it’s transmitted, and how to prevent its spread in the water and air — we are well equipped to stop the bacteria in its tracks. 

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