It’s not often you read an article where an investigation has been halted because the source of an infection cannot be found, but that seems to be the case in Toronto. For an unknown reason there has been a 78% increase in the number of Torontonians testing positive for Mycobacterium avium – to put that number into perspective that equates to 66 new cases each month between June 2014 and June 2015!
While there is cause for concern, there is no need for people to panic. Most people who become infected by M. avium have underlying conditions such as age, HIV-positive and those with pre-existing lung problems. The unfortunate truth is that most people who become ill end up with lung damage and develop reoccurring lung infections, as the main symptoms are similar in nature to Tuberculosis. M. avium is ubiquitous in nature and has been isolated from fresh and salt water worldwide. The common environmental sources include; aerosolized water, piped hot water systems (including household and hospital water supplies), house dust, soil, birds, farm animals and cigarette components (e.g., tobacco, filters, paper).
Transmission is generally thought to be due to inhalation of environmentally derived airborne organisms rather than person to person, however, oral ingestion may also be a route of infection but is generally considered more likely in the immunocompromised host. Because it is primarily transmitted by inhaling droplets of water, municipal water supplies are often the original source – but it’s important to understand that drinking water is not how you’re going to get it. Total eradication of the bacteria from municipal water supplies is virtually impossible as the bacterium tends to grow in biofilms that are known to line the large water pipes used in municipal water distribution systems.
While this current situation is associated with humans, M. avium can also cause infections in pigs, domestic and wild birds, cattle, sheep, goats, cats and dogs. However, the mechanism of transmission and type of infection can vary greatly. Domestic and wild birds become infected by ingesting contaminating food and/or soil. Similarly, other animals can be infected by ingesting contaminated soil or infected poultry. The long and the short is that due to the ubiquitous nature of this bacterium it’s impossible to avoid being exposed to the bacteria. The best way to prevent developing the disease is to keep your immune system strong.
As for Toronto, numerous experts want to see the spike in cases investigated further. While there does not seem to be a specific area of the city impacted more than others or clustering of cases that could be associated with environmental exposure, it is obvious that by the sudden spike in cases in June of last year that there was a tipping point when something changed and it certainly would be nice to get to the bottom of it!