Fourteen workers renovating an old house in Quebec, Canada developed a respiratory disease from inhaling hazardous materials, according to the Centers for Disease Control and Prevention (CDC), which warns employers to provide appropriate protective equipment during such work.

The workers contracted histoplasmosis, caused by exposure to fungus spores. Bats and birds can excrete the organism in their droppings and it persists in the environment for several years. Outbreaks can occur when demolition work produces dust containing bird or bat droppings.

Approximately 30 workers and residents were exposed to dust from bird or bat droppings previously hidden in the brick walls.

Two of the affected workers were hospitalized.

The CDC says there’s a strong link between illness and high exposure to dust during demolition of the exterior walls, and with the handling of contaminated debris away from the work site.