Some residents of Lac-Mégantic, Que., are traumatized by sunsets. The sight of a glowing orange orb, so beautiful to most people, causes them anxiety to the point of making them sick.

The fiery sight reminds them of the night when an oil-laden train derailed and exploded in a fireball in the heart of their town, taking 47 lives with it. "For them, orange becomes something catastrophic," says Normand Grimard, a social worker who has treated many witnesses of the tragedy. "It symbolizes explosions."

Sunsets, slamming doors, real trains and even toy trains – ordinary and everyday things still trigger responses of distress in the people of Lac-Mégantic evidence of alarming rates of post-traumatic stress in the town of 6,000. According to findings released by public-health authorities on Thursday, 67 per cent of residents of Lac-Mégantic continue to suffer "moderate to severe" post-traumatic stress, 2 1/2 years after the flames went out

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The glare of public attention has moved elsewhere, but, according to health authorities, the well-being of the Méganticois is getting worse, not better. One in three in the health study admitted to psychological distress. One in eight felt unsafe in their neighbourhood. One in six reported a rise in alcohol consumption over the past two years.

"We noted no improvement and even a deterioration in the global and psychological health of the population of Lac-Mégantic," Mélissa Généreux, director of public health for the region, said in an interview. "That was a surprise to me."

One of the reasons for residents' persistent suffering is that they cannot escape the aftermath of the calamity. The heart of the town remains under reconstruction. A train continues to roll through one to two times a day; though it is not allowed to carry crude oil for now, its mere presence remains a daily and at times disturbing reminder of the deadly train of July 6, 2013.

"I can't look at trains anymore. When I see one it gives me shivers," says Louise Couture, 50, whose daughter, Kathy Clusiault, perished in the 2013 explosion. A toy train that Ms. Couture kept in her home for visiting children is now left in its box. She remains anxious, and thoughts of her daughter come to her as she tries to sleep. "Sometimes the horror comes back into my head," she says.

In some ways, Ms. Couture is getting better. For weeks after the disaster, she kept a purse on her kitchen table near the door with enough money to survive a few days, in case she had to flee again in the middle of the night.

She has been in group and individual therapy since the events. The nightmares have stopped, but she knows her recovery will take time. "A great sadness invades us, there is still anger, incomprehension," Ms. Couture says. "It's almost three years and I'm still sad. It's going to take a long time to get better."

The study by provincial public-health authorities of 1,600 people in Lac-Mégantic and the surrounding region indicates that, even though some health markers are worsening, fewer people are seeking professional help than in the past. Extensive support has been made available to residents in the aftermath of the disaster, but consultations have dropped by half since 2014.

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This suggests residents may be trying to move on with their lives, even though they still need help, health officials say. "We want to tell people: It's possible you still need help after 2 1/2 years, and we don't want you to isolate yourselves, that would be the worst reflex. With a trauma like this, you have to talk about it," said Carol Filion, a deputy director at the health authority.

The mayor of Lac-Mégantic, Jean-Guy Cloutier, says he finds the rates of stress in the study surprisingly high, but he acknowledges he sees evidence of it; some town employees have taken leave for burnout. "It's a small community. We all know each other. Just to look at some people's faces, I see their stress and I know they're not well," Mr. Cloutier said in an interview. He says a rail bypass – so trains can skirt the town centre – will be essential in helping people recover.

"When people hear the train whistle, it takes them back to square one," he said. "As long as we don't have it [the bypass], people will not be 100-per-cent healthy."