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Legionnaire’s Disease Outbreak at Disneyland

Disneyland is a magical place that people love to visit. But on November 12, 2017, Orange County health officials confirmed that nine people contracted Legionnaire’s disease at Disneyland in California. An additional three people, who had not been to the theme park, have also contracted Legionnaire’s disease in September after visiting Anaheim, a city in the Los Angeles metropolitan area. Out of the 12 people infected, 10 were hospitalized and an individual who had previous health issues has died.

On November 1, the amusement park shut down two out of 18 cooling towers for disinfection and testing in response to elevated levels of Legionella, the bacteria responsible for Legionnaire’s disease. The cooling towers were reopened November 5, but were again taken out of service two days later.

This grabs plenty of attention because of the high profile brand of Disneyland, and no doubt everyone wants to solve the problem quickly, but careful questions need to be asked and investigated when it comes to determining the source of Legionella which caused their illnesses. It’s important to follow a rigorous scientific process that includes the proper investigation and genetic sequencing.

Legionella is everywhere; naturally found in surface-water and groundwater, major sources of public water systems. It grows in biofilms, which line the inside of pipes of the water distribution systems. If there is a disturbance, this biofilm can break loose and enter the building water system, which can seed premise (residential and commercial) plumbing systems. Water treatment facilities add chemicals, such as chlorine, in an attempt to disinfect the supply and control the growth and spread of Legionella. Despite this, often times the amount of chlorine added isn’t sufficient enough to keep potable water safe by the time it reaches the tap or other downstream building systems.

While the Disneyland cooling towers reportedly showed elevated levels of the bacteria, based on Cogency’s analysis, the origin or source of the exposure is still uncertain:

  • Legionnaire’s disease is not contagious; yet, three people who had not been to the theme park also contracted the disease.
  • The three people who contracted the disease could not have contracted it by contact with those who were reportedly infected at the park.
  • This could mean that the point of exposure may be outside the park, somewhere in Anaheim along the public water system.
  • Due to the ubiquity of the Legionella bacteria, DNA and genomic matching is recommended to identify the specific strains or sequence based typing of the strain that caused the human infections. Otherwise, finding the presence of Legionella in any particular environmental sample may demonstrate presence of the Legionella but it does not establish a match with the virulent strain that caused the outbreak.

When reading news articles about Legionella, beware of the easy answers. Ask questions and critically evaluate.

For more information about Legionella, Legionnaire’s disease outbreaks and how to reduce your facility’s risk, contact the experts at Cogency at

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