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Forty Years after Discovery, Legionnaires’ Disease on the Rise

​By Kay Bechtold and Ed Rutkowski
Pictured: The Bellevue-Stratford Hotel in Philadelphia, site of the 1976 American Legion Convention.

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Forty years ago this summer, an outbreak of illness at an American Legion convention in Philadelphia sickened 221 of 2,000 attendees, ultimately killing 34, and set off what has been called the largest field investigation in the history of the U.S. Centers of Disease Control. The public initially worried that the outbreak signaled the rise of a deadly new strain of flu, but eventually turned its attention elsewhere as months passed without further incidence.

In the meantime, CDC scientists worked to determine why some convention-goers had contracted the disease while others—including a few who had shared hotel rooms with the deceased—did not. More puzzling still, the victims included a teller who worked across the street from the convention site and a bus driver who had driven participants to and from the convention’s parade.

In December 1976, five months after the convention, Joseph McDade, a CDC microbiologist, discovered the cause of the outbreak: a previously identified bacterium that became known as Legionella pneumophila. He would later say that he made the key discovery following an unsettling encounter at a Christmas party, where an acquaintance expressed frank displeasure with the CDC’s inability to solve the Legionnaires’ mystery. The incident, McDade recently told the website Newsworks, prompted him to return to his lab and go over his samples one more time. Thanks to McDade’s persistence and the hard work of many CDC scientists, we now know that people become infected with Legionella by inhaling the mist from water sources where the bacteria thrive, which can include the potable water systems of homes, hospitals, and hotels. The source of the original Legionnaire’s outbreak in Philadelphia turned out to be the cooling system in the Bellevue-Stratford hotel (pictured).

Legionnaire’s Today

Today, forty years after the identification of Legionella as the cause of Legionnaires’ disease, CDC reports an alarming increase in Legionnaires’ cases in the U.S. According to the agency, during 2000–2014, the rate of reported legionellosis cases increased from 0.42 to 1.62 per 100,000 people, with four percent of cases associated with outbreaks. Last summer, 138 residents of the South Bronx were sickened and 16 were killed during an outbreak of Legionnaires’ disease. In June 2014 and May 2015, approximately 80 people were sickened and 12 died during the course of two outbreaks in Flint, Mich., and the surrounding Genesee County. The outbreak in Flint was linked to corrosive tap water, which helped create ideal growth conditions for Legionella. The rise in Legionnaires’ disease cases is not confined to the U.S.; in 2014, more than 300 people were infected during an outbreak in Portugal and 12 deaths were reported. Earlier this year, at least five people were diagnosed with the disease in Sydney, Australia.

Industrial hygienists, of course, play a critical role in preventing the spread of Legionella, responding to outbreaks and assessing building water systems. They may also evaluate preventive and corrective measures to help protect people from Legionnaires’ disease, which a 2015 Synergist article characterizes as “the most lethal building-related illness associated with waterborne bacteria.” The article introduced AIHA’s guideline Recognition, Evaluation, and Control of Legionella in Building Water Systems, which is intended to provide guidance on the recognition, evaluation, and control of Legionella colonization and amplification in common building water systems. The guideline “tightly binds sampling to validate Legionella control measures with a comprehensive water management plan based upon a risk assessment,” according to David Krause, CIH, MSPH, PhD, who co-authored the guideline.

CDC statistics help bolster the guideline authors’ contention that sampling specifically for Legionella as part of an ongoing water management program is critical to ensure that the controls in place are working properly. According to CDC, 65 percent of Legionnaires’ disease outbreaks investigated by the agency are due to process failures such as the lack of a water management program. Further, human error—such as failure to clean or replace a hot-tub filter—is a factor in 52 percent of outbreaks. Equipment  failure, such as a malfunctioning disinfection system, accounts for 35 percent of CDC-investigated outbreaks.

In June, CDC published new guidance on reducing the growth and spread of Legionella. The agency’s guidance is based on the recently revised ASHRAE standard Legionellosis: Risk Management for Building Water Systems. While CDC’s guidance does not include information related to environmental sampling for Legionella, Krause praised it as “a good starting point for discussing the need for a water management plan.”

Already, state regulations are beginning to reflect the guidance put forth by CDC and AIHA. Earlier this month, new regulations intended to protect against Legionella in cooling towers and healthcare facilities in New York State went into effect. The regulations require that New York cooling towers be registered, inspected, and tested for Legionella. All general hospitals and residential healthcare facilities will also be required to perform Legionella culture sampling and analysis of their drinking water systems.

Turning Point?

For AIHA members, the story of the discovery of Legionnaires’ disease has many familiar elements. Like McDade and other CDC scientists, industrial hygienists routinely investigate mysteries surrounding the incidence of disease in the workplace. Their interactions with the public often follow a pattern similar to McDade’s experiences: managing an initial outcry, followed by disillusionment or disappointment, and a long-delayed recognition of success—if recognition comes at all.

Will the new guidance recently issued by CDC, AIHA, and ASHRAE eventually represent a turning point in the battle against Legionnaires’ disease? What successes have you experienced in solving health-related mysteries in the workplace, and what recognition did you receive? Has a second (or third, or fourth) look at your data ever yielded a solution that eluded your at first, as it did for McDade? Please leave your answers in the comments. 

The AIHA guideline Recognition, Evaluation, and Control of Legionella in Building Water Systems is available for purchase in the AIHA Marketplace. CDC’s toolkit, Developing a Water Management Program to Reduce Legionella Growth and Spread in Buildings, is freely available via the agency’s website.


Kay Bechtold is assistant editor of The Synergist.








Ed Rutkowski is editor-in-chief of The Synergist​.

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