A huge and unexplained "spike" in the number of suicide incidents on Toronto's subway system at the end of last year has rippled into transit-employee ranks, the agency says, helping fuel a rise in absenteeism.

Over more than a decade prior to 2017, the Toronto Transit Commission (TTC) averaged 1.54 suicide incidents – a term that includes both fatalities and attempts – in December. In the last month of 2017, it had eight such incidents.

These suicidal acts in December left at least four people dead. Three others were apprehended before they made contact with a train, according to the TTC. The eighth person was hit and lived long enough to leave the station, the agency said, although it's not known publicly if the person survived treatment.

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The unusual succession of incidents – two of them coming within 4½ hours on the last day of the year – prompted hundreds of minutes of subway delays, affecting tens of thousands of subway passengers. And they took a toll on the TTC staff involved in them.

"Absenteeism was up in December and has been for five of the past six months," TTC acting chief executive Rick Leary said in his monthly report, released on Friday. "Some long-term absences can be attributed to a spike in suicide events on the subway late last year. These are complex cases of trauma and employees receive support from all areas of the organization to assist in their recovery and ultimate return to work."

Frank Grimaldi, president of Amalgamated Transit Union Local 113, said the impact of transit suicide on staff absenteeism was likely small compared to passenger crowding and anger sparked by equipment shortcomings. However, subway suicides are a very difficult thing for staff to observe, he said, and the union is pushing for better benefits in their aftermath.

"It's a traumatic experience," he said. "Nobody's used to seeing somebody die."

TTC spokesman Brad Ross acknowledged that "priority ones" – the agency term for when someone is hit by a train – were just one factor among others.

In the whole of 2017, he said this week, a total of 32 staff were off for suicide-incident-related reasons, accounting for about 5 per cent of all lost-time days. In the second half of the year, that had edged up to 6 per cent. In January of this year, it dropped down to 4 per cent.

The rate of subway suicide incidents subsided in January, with that month falling roughly in line with recent norms, and the reason for the jump at the end of 2017 remains unknown. The Globe and Mail spent time last month looking into the December increase but decided then not to draw attention to the spike.

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Reached in January, the Office of the Chief Coroner for Ontario said it investigates each such case individually and that it could be months before any commonalities emerge. Around the same time, a spokesperson for Toronto Public Health suggested it was not its responsibility to investigate this spike.

On Friday, Mr. Ross said the agency would be keen to participate in a broader study looking at whether a profile can be created for people that choose the Toronto's subway as a suicide method. But he said that such work would be better led by mental-health professionals than a transit agency.

"The TTC doesn't have the intelligence, the research, the data," Mr. Ross said.

Studies elsewhere show that one reason subways are chosen is the mistaken belief that death is certain. But subway trains are not a sure thing, with about half of those who attempt suicide on the TTC surviving long enough to leave the station.

The TTC has trained its staff to watch for warning signs that could indicate suicidal behaviour and has installed advertising urging people to call a number that connects to a counsellor. But the only real solution, according to the agency, is to erect barriers along the edges of the platforms.

Such barriers, which slide open in concert with the doors on the train, have been shown in other transit systems to reduce suicide incidents dramatically. But the barriers can be expensive. A consultant report for the TTC recently pegged the cost at $24-million per station, for a total of more than $1.5-billion. However, that number has been called into question by TTC chief operating officer Mike Palmer, who said that, although he didn't know whether the number was too high or too low, he didn't believe it reliable.

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Note: Stories of suicide can be difficult to read. If you're dealing with mental-health concerns, help is available. If you're in crisis or in need of assistance, call 416-408-HELP, go to your nearest hospital or call 911.