Emergency dispatchers answering 911 calls can develop symptoms of post-traumatic stress disorder even if they are not directly witnessing tragic events, a new study shows.

One in 30 surveyed dispatchers reported symptoms after taking emergency calls severe enough to merit a PTSD diagnosis, according to the survey of 171 current dispatchers across 24 U.S. states.

Surveyed dispatchers reported near-traumatic distress on average from 32 percent of emergency calls including suicidal callers or calls about the injury or death of a child, according to the research.

Northern Illinois University psychologist Michelle Lilly and former 911 dispatcher Heather Pierce surveyed the dispatchers and reported their findings on Thursday in the Journal of Traumatic Stress.

Pierce said in a statement the results show the need to provide these workers with prevention and intervention support as is currently provided for their frontline colleagues.

Lilly and Pierce argue that their research supports a broader definition of a traumatic event since 911 dispatchers can experience emotional distress working away from the emergency scene and talking with strangers under duress.

How to define PTSD is a bone of contention among psychologists, experts say. New PTSD guidelines are set to appear in May 2013 when the American Psychiatric Association releases the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders.

Detractors say loosening the criteria for a traumatic event will result in just about anyone being eligible for a PTSD diagnosis, leading to a strain on mental health resources.

In a 2005 letter to the British Journal of Psychiatry, American psychologists Jon Elhai, Todd Kashdan and B. Christopher Frueh questioned a study that equated the loss of livestock by farmers with a PTSD-level traumatic event.

With the current trajectory all negative experiences will be synonymous with traumatic events, trivializing the experiences of real trauma victims, the trio wrote.

The National Comorbidity Survey Replication, which examines the prevalence of mental disorders in the U.S., estimates that 6.8 percent of all adult Americans will experience PTSD at some point in their lifetime with women more than twice as likely as men to have the disorder.

A 2008 survey conducted by the RAND Corporation examined 1,938 U.S. service members that had been deployed in Iraq and Afghanistan and found that 13.8 percent of them had PTSD.