Legionella Outbreak Disneyland

“The Happiest Place on Earth?”

An outbreak of Legionnaires Disease has been widely reported across media outlets in the US during the past week.  At the time of writing, the total number of patients stands at 15 with 11 having spent time at the Disneyland Amusement Park located in California.  2 of the patients, who had not attended the park, have since died.   Following the confirmation of the cases, the presence of legionella was detected in 2 of the 18 cooling towers at Disneyland. Cooling towers are often overlooked when considering the control of Legionella at facilities, but the effects of ignoring them can have very serious consequences.

Legionnaires Disease is spread through the inhalation of contaminated water droplets or mist.  The risk of infection is easily controlled when dealing with standard hot and cold water outlets such as faucets or showers by means of tight temperature control and eliminating the potential to produce droplets or mist which can be inhaled.

Cooling towers by their nature produce a fine mist which can be carried for miles before falling back down to ground level, potentially exposing a far greater number of people.  In Hereford in 2003, following an investigation by the HSE and subsequent court case, it was determined that contaminated cooling towers were to blame for an outbreak of Legionnaires Disease resulting in 28 cases confirmed with 2 fatalities.  The company was also fined £300,000.

Cooling towers can become fouled over time due to build up of airborne dust.  As part of any Legionella risk assessment, the extent of fouling in the cooling system needs to be evaluated. Following this maintenance and cleaning procedures need to be defined at set intervals and should be incorporated as a written control scheme.  If a system can be shown to be free from fouling, i.e. the deposition of particulate material and debris, there is no need for it to be cleaned at a set time interval, rather the system should be cleaned whenever it is known or suspected to have become fouled.

Some ways of reducing the potential of contamination are as follows:

  • Corrosion control:  Many cooling towers are constructed using mild steel which is susceptible to corrosion. Corrosion and scale inhibitors should be applied continuously and be capable of producing the desired control over corrosion and scaling.
  • Chemical water treatment:  Biocides to control microbial growth and dispersants to control fouling. These may be in the form of single-function chemicals or multi-functional admixtures.
  • Alternatives:  Alternatives to the above may take the form of UV treatment, use of ozone or filtration.

It is vitally important for any facility with cooling towers to have a legionella risk assessment completed with a written legionella control scheme  based on the risk assessments findings.

The author, Ronan Sutcliffe, is a director of Environmental Efficiency, a consultancy that is dedicated to helping clients maintain environmental compliance and embrace best practice.  The views expressed are the author’s.