On Wednesday, Sept. 12, 2001, this column noted some of the changes already occurring in households far from Ground Zero: “Husbands and wives hug as they go off to work, holding each other for an extra moment, saying ‘Drive carefully’ with a new gravity.”

That morning, as they left for school and work, families seemed apprehensive — and more appreciative of moments together.

The column continued, “All children are bound to ask, ‘What happened?’ and ‘Why?’ “

To deal with their feelings, adolescents were already searching for hope and ways to help. For some, those heightened moments have been defining. Among the high school students who admired the firefighters, police officers, rescue workers and other helpers, many have since chosen to follow in their footsteps.

Briefly a nation of people seemed to come together — a united front to comfort the victims’ families and to honor the first responders’ heroism. Yet this sense of unity proved to be short-lived.

Extreme and extraordinary events that kill many and injure many others traumatize the survivors. Witnessing violence is traumatic, whether up close or on TV. Survivors may be traumatized by the loss of loved ones, or simply by the fact that something unimaginable actually happened — and, having happened once, could happen again. Fear and expectations of danger may take on new dimensions in the minds of survivors. All of us who were alive at the time of the 9/11 attacks are survivors.

A child may be traumatized by a single instance of abuse. The experience may change how the child interacts with others, even with once-trusted family members and teachers. A brief moment of unexpected, overwhelming violence can take on a life of its own within those who survive it, making it difficult for them to hope for their future and to trust others.

When a person is severely harmed by any unexpected cause that is capable of harming others, fear can spread from the first victim’s family to the entire community.

A trauma on the scale of 9/11 can be expected to course through the bloodstream of an entire society, altering beliefs and behavior.

Such contagion can also seep into society’s DNA and contaminate future generations. Mental health professionals speak of the “historical trauma” that affects, for example, not only survivors of genocide but also their offspring.

Terrorism’s calculated goal is far more ambitious than an isolated moment of violence. It is designed to spread fear and hatred beyond the immediate site of chaos and into the future. Terrorism triumphs when trust, cooperation and compromise — all protections against future violence — break down. Along with climate change and food and water scarcity, terrorism’s capacity to perpetuate and amplify violence to affect whole populations is a serious threat to human survival.

As physicians, we are concerned about a paralyzing polarization we see in the United States today that may be, at least in part, a contagion effect of 9/11 — 10 years later. The current lack of good faith and commitment to seeking common ground jeopardizes our future.

In the days following 9/11, the late Fred Rogers, the beloved host of the public television program “Mr. Rogers’ Neighborhood,” reassured young children and their parents by urging them to look to the helpers who stand ready to put others’ lives and futures before their own.

You see these helpers in the aftermath of the tsunami and earthquake in Japan, the shootings in Norway, the tornadoes in Missouri and other calamities. They are the rescuers, the rebuilders, the healers — those who find hope wherever it seems to have been lost.

Victims of terrorism still need to look to the helpers. Focusing on them, emulating them and trying to live up to them are part of the healing process — and perhaps one of the best ways to cure terrorism’s contagion.

Questions or comments should be addressed to Dr. T. Berry Brazelton and Dr. Joshua Sparrow, care of The New York Times Syndicate, 620 Eighth Ave., 5th Floor, New York, N.Y. 10018. Questions may also be sent by email to: [email protected] 

— New York Times Syndicate