Authorities are now trying to track down as many as 400 people who might have come into contact with the infected health worker.

The caregiver had visited six locations while contagious on the West Island, St-Laurent and Town of Mount-Royal from May 11 to May 14. In particular, nurses plan to give shots to any unvaccinated children or workers at a T.M.R. daycare.

Authorities are also taking the extraordinary step of offering free measles vaccines from Friday to June 14 to anyone who has not received the standard two doses.

To date, Montreal has reported seven cases of the measles this year, up from an annual average of four. What distinguishes the two new cases from the others is that the individuals contracted the measles in the city and not abroad.

“With the measles, for us, one (secondary) case is an outbreak,” Dr. Mylène Drouin, director of the Montreal Public Health Department, told reporters at a hastily-called news conference Thursday afternoon.

“The secondary cases tell us that we have a transmission that is going on, and of course, the collective immunity is not enough to stop the transmission,” Drouin explained. “That’s why we’re preoccupied.”

The health worker who cared for the infected girl had previously received the two doses against the measles, yet contracted the disease anyway, Drouin added, noting that the two shots confer 95 per cent protection, but are not foolproof.

Authorities have already retraced the girl’s contacts, but they’ve concluded that it’s impossible to do so fully in the case of the health worker. As a result, authorities have posted a list of all the places the health worker visited. The locations and times are the following:

On Saturday, May 11:

— École Des Sources (Iranian Cultural Society of the West Island), 2900 Lake St. in Dollard-des-Ormeaux, from noon to 1:05 p.m.

— A Tim Hortons outlet at 3760 Sources Blvd. in Dollard-des-Ormeaux, from 12:15 p.m. to 1:25 p.m.

— A Royal Bank branch at 4400 Sources Blvd. in Dollard-des Ormeaux, from 12:25 p.m. to 1:35 p.m.

— Esthéticienne Manju beauté at 3637 Sources Blvd. in Dollard des Ormeaux, from 2 p.m. to 5 p.m.

On Sunday, May 12:

— The Hôtel Courtyard Marriott (entry hall and pool), 7000 Robert-Joncas Place in St-Laurent, from 3 p.m. to 5:30 p.m.

On Tuesday, May 14:

— The Garderie Aventuriers d’Outremont, 196 Bates Rd, second floor in T.M.R., from 4:30 p.m. to 5:35 p.m.

“What is important is to ask yourself is whether you were in any of those specific places at the times indicated,” Drouin said. “Those are the times we considered that the virus was in the air.”

“If the answer is yes, the second question to ask yourself is, are you protected? You are considered protected if you were born before 1970 or if you have the two doses of vaccine.”

Those who are at high risk of complications from the measles are children under the age of one, pregnant women and those with weakened immune systems. Drouin encouraged those who have doubts about whether they’ve been vaccinated to call the 811 Info-Santé phone line.

Drouin estimated that between 200 to 400 people might have been exposed to the contagious health worker. The measles virus can spread to others through coughing and sneezing. It can live up to two hours in the air when an infected individual coughs.

Thursday’s declared outbreak follows three measles exposure alerts since February. In all three cases, the individuals picked up the measles while travelling to Europe and the Caribbean.

The two secondary infections arose from the third measles alert. An unvaccinated individual returned to Montreal with the measles on April 26 from a trip to Paris.

That person, in turn, unwittingly transmitted the virus to a female family member in Montreal. The girl then spread the measles to an inoculated health worker, underscoring the highly contagious nature of the virus. Read more at Montreal Gazette