MONTREAL One of the province s worst COVID-19 oubreaks has swept quickly through a long-term care home in Île-Perrot, infecting more than 80 people in just two weeks. The speed of the outbreak first left the local health board (CISSS) stumped, and the union representing the workers raising alarms over ventilation problems. In response, the CISSS brought in an external firm Monday to review the ventilation system for the Laurent-Bergevin long-term care home (CHSLD), it said and that didn t solve the mystery, though it did suggest some areas for improvement. The causes of the spread of the virus within the CHSLD are not yet known despite the extensive investigation underway, said Jade St-Jean, the spokesperson for the Monteregie West CISSS, which oversees the home.