Disturbing Suicide Cluster Prompts CDC to Start Investigation in Palo Alto One California community is trying to stop suicides from becoming "contagious."

 -- Shawna Chen recalled the unsettling response she got when she was in middle school and she told friends that she was going to attend the elite Henry M. Gunn High School in Palo Alto, California.

"'That's the school with suicides," Chen, 18, recalled her friends saying. "I don't think I understood what that meant or the gravity of what that meant."

The disconcerting comment stemmed from a horrific period between 2009 and 2010 during which five students or recent graduates from the school died by suicide, according to a report from the Palo Alto Unified School District. The deaths signaled a "suicide cluster," defined by the U.S. Centers for Disease Control and Prevention as three or more suicides in close proximity in regards to time and space.

During her first two years at the high school, Chen said she didn't think too much about the suicide cluster there as she focused on her academics at the school, which has been ranked as one of the best high schools in the nation by U.S. News and World Report.

But then, as Chen and her classmates juggled college visits, SAT tests and AP classes, they also had to grapple with a second cluster between 2014 and 2015, the occurrence of which was noted during a school board meeting. These are sometimes called an "echo cluster," according to the CDC.

Police and officials from the CalTrain commuter line confirmed that four local teens died from October 2014 to March 2015. CalTrain tracks run near the school and some of the students who died by suicide did so on those tracks, officials said. Chen said three of the deaths were students at Gunn or recent graduates. At least one other student from nearby Palo Alto High School also reportedly died by suicide during that time, according to local reports.

"It was a huge shock and there was a silent tension on campus on the following days," she told ABC News of her experience during that time. "It was hard for people to wrap their heads around it."

Palo Alto is not the only community to be affected by suicide clusters in recent years. In the last five years, the CDC has also investigated incidents in Fairfax County, Virginia, and two counties in Delaware where suicide clusters affected teens and young adults.

In Palo Alto, members of the CDC's epidemiological assistance team are scheduled to begin an investigation this week on the "suicide contagion" risk in a similar way they may investigate a viral or bacterial outbreak that spreads through a community. As federal officials arrive in Palo Alto, they will face a community that is trying to find innovative ways to combat suicide when it becomes a "contagion."

Learn more about the CDC investigation in Palo Alto during ABC News' "Nightline" airing tonight at 12:35 a.m. ET

Suicide may seem to be the ultimate individual act, but a single suicide has the potential to cause a ripple effect with further deaths following in its wake, experts said, noting that these "suicide clusters" occur almost exclusively among teens and young adults.

Madelyn Gould, a professor of psychiatry and epidemiology at the Columbia University Mailman School of Public Health, explained that teens are at a unique point in their life where their core relationships are changing and they are more impulsive than adults.

"Their relationships with other teens really start to play much more of a role than their relationships with their parents, and so they influence each other more," she explained. "Between both the social influences and biological influences, it makes them much more vulnerable to being influenced by somebody else's suicide."

Gould has studied at least 50 suicide clusters throughout the U.S. and said one of the only constant threads that connect those at risk is age.

"There's no such thing as a 'suicide town,'" Gould told ABC News. "It crosses every socio-economic community from impoverished to wealthy, black to white, Native American. It really crosses all divides in the United States."

The CDC even wrote a response plan in the 1980's to "combat" and "prevent" clusters. In that report, the agency estimated that clusters account for 1 to 5 percent of suicides in adolescents and young adults.

Suicide is the second-leading cause of death for Americans between the age of 15 to 24 and the third-leading cause of death for those between the ages of 10 to 15, according to the CDC.

In Palo Alto, the string of suicides prompted the community to act. Both local government leaders and school officials had already worked to address suicide risk after the 2009 to 2010 cluster. The Palo Alto Unified School District and the Santa Clara Health Department both organized and coordinated community responses and initiatives aimed at protecting students based on materials provided by the CDC.

Denise Herrmann has been the principal of Gunn High School for 18 months, and she said she has already had to attend three funerals for students. And she has grappled with how to help students heal after the deaths, she said.

"Nightline" co-anchor Byron Pitts traveled to Palo Alto recently and spoke to Herrmann about how students have worked together to cope with the tragedy.

Efforts to deal with the suicide cluster include a program to teach students techniques to handle stress through yoga and breathing exercises, a program that brings in recent alumni to talk about life after high school and one that matches incoming freshman with adults so that they can meet throughout the year and get one-on-one attention, Herrmann said.

And it's not just the administrators who are stepping up to help, but the students as well, she told Pitts.

"We want to make sure that everyone knows it's okay to seek help if you're feeling blue, down, anxious," she said. "So, students have made sure they've written stories, they've done videos. Actually, some of our students teamed up to do a documentary."

One of the students who wanted to share her story was Chen. As the editor of the student newspaper, she said she knew she wanted to do something to help, especially after seeing how many media stories focused on why the cluster happened and not how to recover.

When a suicide happened after Chen started attending Gunn High School, "a lot of the media came in and were investigating and said 'Why are these kids killing themselves?'" Chen recalled. "It was being prodded apart, like a wound."

Chen said she came up with a new idea for sharing positive student stories after hearing Madelyn Gould speak at a community meeting about how the stories of recovery can reach those who are suicidal.

"We have research that shows stories about resilience and coping and dealing with suicidal thoughts in ways that are engaging ... they are not only inspiring, they can prevent somebody else's suicide attempt," Gould told ABC News.

Chen said after hearing Gould speak, she knew she wanted to provide an outlet for students. "What about if we provide that in the student paper?'" Chen recalled thinking.

Chen started a new section for the paper this year called "Changing the Narrative," aimed at having students at the elite school share essays of their fears and anxieties.

"The website went up and they said 'Thank you for sharing it,'" she said of her fellow students.

Two other high school seniors, Christian Leong and Andrew Baer, at Palo Alto High School also shared their story in a documentary called "Unmasked," talking about the pressures of academic life.

The school board last year approved funding so that two licensed therapists could be at both Gunn High School and Palo Alto High School full time. There have been multiple community meetings to address concerns about the high stress environment at Gunn High School and potential risks to students' well-being if they take multiple advanced placement courses. The school board now recommends that students take no more than two AP classes.

In addition, Gunn High School started "block" scheduling this year -- meaning the class period is longer but they have fewer classes in a day. And school officials are also working to combat "academic bullying" on social media so that there is a less competitive atmosphere on campus.

"Any time you are trying to intimidate, it doesn't matter if it's with strength or other things, if it's intimidating others with academic strength it still could have a negative or harmful impact," Herrmann said.

Dr. Meg Durbin, a family physician in Palo Alto, had three sons who attended Gunn High School during the first suicide cluster. The deaths galvanized her and others in the medical community to make mental health a consistent topic, she told ABC News, noting that students have learned to expect questions about their mental health during every checkup.

Durbin helped co-found HEARD -- the Health Care Alliance for Response to Adolescent Depression -- and also helped create a program to facilitate getting teens to mental health care providers.

Even in an affluent community like Palo Alto, "people are keen to have their health care covered by insurance. They're not keen on spending a couple hundred dollars for psychiatrists," Durbin said.

Access to child psychiatrists are rare across the country, creating a serious issue when teens experience a mental health crisis. To help cut down on the time it can take to find a provider, HEARD put together a vetted list of providers who will take on patients. They also have volunteers, who work with multiple families, to find care for at-risk youth.

She's even had insurance companies call her to confirm that a patient is getting mental health care, Durbin said.

While there have been multiple steps taken to protect students, some groups had other recommendations about how to best help the students.

Teacher Marc Vincenti said he thinks there needs to be an epidemiological study into the suicides and more focus on the root causes for academic stressors. He started the "Save the 2,008" initiative, with more than 400 supporters, aimed at helping students in the district. The number 2,008 refers to the number of students at Gunn High School after the string of suicides happened.

The goal is to make sure "the environment that we send our kids to every day is more humane, is more forgiving, is more compassionate, and is more likely to serve as a safety net to those kids who are especially in despair," Vincenti said.

Vincenti said he's concerned that all these new initiatives give students even more work to do, and he wants people to focus on connecting with children and cut down class sizes.

Durbin and Chen both say they hope the community could become an example for others about how to combat a suicide cluster. Durbin pointed out that a tool-kit developed by mental health leaders in Palo Alto, including by members of HEARD, was adopted by across the state.

She said in her own family, one of the new programs has helped her son grapple with the past tragedy. Her oldest son graduated just two days after the first student died by suicide in 2009.

"He wanted to get out of there," she recalled of his graduation. But now with the alumni program, he has reconnected with his old school.

Though suicide clusters can arise anywhere, Gould said a community can take concrete steps to diminish the risk of a cluster and that she has been "extremely impressed" by what Palo Alto has done.

"They have engaged the entire community to embrace their responsibility," she told ABC News. "That is the first thing that is very, very effective."

Resources for suicide prevention and mental illness concerns can be found here.

Michael Nedelman, a medical student at Stanford and the current Stanford–ABC News Global Health Media Fellow, assissted with this article.