Source of Legionnaires' outbreak that killed two and hospitalized 30 continues to elude investigators

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Initially confirmed by the Middlesex-London Health Unit (MLHU) in early August, the source of an outbreak of Legionnaires’ Disesase continues to elude investigators.

From May 1 to September 30, a total of 30 confirmed cases were reported to the MLHU. All 30 were admitted to hospital at one point, nine were admitted to the ICU, and two died. Four cases remain in hospital today.

Despite extensive searches and sampling from 17 cooling tower sites in proximity to the cases, no samples of legionella bacteria have yet been matched to the outbreak.

“It is common in an investigation such as this one that the source of the legionella bacteria that has caused the outbreak cannot be found. We conducted our search based on the location of the cases, wind and weather patterns and the types of cooling towers in the region. Unfortunately, while some legionella was identified, none of it linked back to the cases,” explained Dr. Joanne Kearon, Acting Medical Officer of Health for the Middlesex-London Health Unit.

Legionnaires disease is a respiratory illness caused by Legionella bacteria, with symptoms of high fever, chills, dry cough, shortness of breath and potential for pneumonia. Symptoms usually begin within two to ten days of exposure.

The bacteria is found naturally in the environment, usually in water like hot tubs, plumbing systems or pats of an air conditioning system. If the bacteria become airborne and are inhaled by humans, it can cause Legionnaires Disease, although most people exposed will not become ill. Older people, or individuals with compromised immune systems are at greater risk for developing severe symptoms.

Legionella is not transmissible from person to person, through public water, or through contaminated food.

“It’s frustrating. We all like situations like this to come to a satisfying conclusion. Instead, what we can emphasize is the importance of prevention. We ask that all businesses and property managers with cooling towers or other susceptible pieces of equipment ensure they are properly maintained throughout the year,” added Kearon.

Although MLHU has yet to pin down the source of the outbreak, transmission is tapering off, and it is likely that the outbreak will be declared over soon.