MLHU declares end of deadly legionnaires disease outbreak in the region

The Middlesex-London Health Unit (MLHU) declared the end of the legionnaires disease outbreak that killed two people and infected 30 in total, all of whom spent time in hospital, Friday.

The outbreak was first declared in July after reports of the illness began to mount. Cases in the outbreak were contracted between May 1 and Sept. 26, according to the MLHU.

One person remains in hospital, health officials said, and nine others were admitted to local intensive care units.

"The date when the last case started feeling unwell was September 14. Now that 24 days have passed since any new cases have developed, the outbreak is considered over," a spokesperson for the health unit wrote in a statement.

The bacteria that cause the disease, Legionella bacteria, are usually found in water environments like hot tubs, cooling towers, large plumbing systems or parts of an air-conditioning system. If misted into the air through wind or fans, people can breathe the bacteria and become unwell. 

The disease is not transmitted from people, or through contaminated foods or public waterworks.

Last week, MLHU officials announced the second death in the outbreak and said they had been unable to find the source of the contamination.

In Friday's announcement, officials reiterated that despite collecting samples from 18 cooling towers in the 5-kilometre area in which all the cases were believed to have come from, no samples detected legionella that matched what was identified in the infected people.

Still, the MLHU's statement said some test results are still in the possession of a Public Health Ontario lab.

"It remains possible that a source could be found. If the source is found the community will be informed that the source has been found and sanitized."

The MLHU's Associate Medical Officer of Health, Dr. Joanne Kearon, told CBC last week that roughly half of legionella outbreaks resolve without a source being found.

The Canadian government says the average number of reported cases of legionnaires' disease in this country is generally under 100 per year, but the actual number of cases may be much higher as many people with pneumonia may not be tested for legionella.