Confirmed Legionnaires’ Disease Cases in the Middlesex-London Region

The Middlesex-London Health Unit is providing an update to the community following the declaration of an outbreak of Legionnaires’ Disease.
Please note: Data will be updated each week on Tuesday afternoons.

Outbreak-Associated Case Details

Notes to accompany map:

• This map shows the general area of confirmed cases (home addresses) of Legionnaires’ disease reported to the Middlesex-London Health Unit in 2025.
• Areas are shaded to represent the estimated number of reported cases to the Middlesex-London Health Unit. Darker shading indicates higher concentrations of cases, while lighter areas reflect lower numbers.
• The inner blue circle represents a 3-kilomtre and the outer bule circle represents a 6-kilometre radius around the average location of all home addresses for reported cases, helping to illustrate where most cases are generally residing.
• This map represents a snapshot in time and should be interpreted in the context of ongoing case and environmental investigations.
• To maintain patient confidentiality, no individual homes or exact addresses of specific cases, or other identifying geographic features, are shown.
• The 3- and 6-kilometer radius may not reflect the actual distribution or movement patterns of individuals affected by the outbreak.
• Although this map shows where the greatest density of cases reside, there are confirmed Legionnaires’ cases outside of this area.
• The map is subject to change as more information becomes available as investigations continue. The map reflects the data available at the time of publication.
• The outbreak case definition may change as more information becomes available. Changes in the outbreak definition may increase or decrease the case count and as a result may impact the area shown in the map.

The Health Unit is still working in close partnership with Public Health Ontario and the Public Health Ontario Laboratories to investigate and identify the source of the outbreak. Environmental sampling of potential sources of Legionella is ongoing. If you are aware of a location that may be relevant to the investigation, please contact us at health@mlhu.on.ca.

For more information including, symptoms, risk, diagnosis, and prevention click here.