Development of Posttraumatic Stress Disorder in Urban Emergency Medical Service Workers

Michael Blumenfield, MD, Daniel W. Byrne, MS


Medscape Psychiatry & Mental Health eJournal. 1997;2(5) 

In This Article


During the 28-month study period (9/14/90 to 1/8/93) a total of 2051 NYC EMS employees answered the questionnaire for the first time while enrolled in 1 of 84 EMS training classes (Table I).

Of the 2051 questionnaires, 225 (11.0%) had less than 80% of the PTSD questions answered. These were considered invalid for that part of the analysis. Of the 1826 subjects with valid PTSD data, 169 (9.3%) met the strict DSM-III-R criteria for PTSD if it were assumed that all the subjects experienced an event that is "outside of the range of usual experience and that would be markedly distressing to almost anyone." We made this assumption based on the nature of EMS work. Another 183 subjects (10%) had the required number and combination of symptoms for PTSD, but these symptoms had not persisted for the 1 month required by the DSM-III-R criteria. Thus, a total of 19.3% of subjects who completed the survey were shown to be suffering from PTSD.

Background statistics on the subjects who had PTSD are presented in Table II. Subjects who were separated or divorced were more likely to have had posttraumatic stress than were single and married subjects (P<0.001). Divorced subjects had significantly higher rates of PTSD, especially those in the age groups 25 through 29 years and ages 35 years and over. Subjects who were separated had the highest percentage of PTSD between the ages of 30 and 34. Married and single people had relatively low rates.

The prevalence of PTSD was significantly lower among subjects 18 through 24 years of age (P=0.001), and the mean age of the 169 subjects with PTSD was higher than those without PTSD (33% vs. 31.4%; P=0.008). Multivariate analysis of the data showed that age was not a strong independent predictor of PTSD.

The interaction between age and several other factors, however, was significant. For example, subjects between the ages of 18 and 24 who graduated from a rural high school were nearly 3 times as likely to have PTSD as those from urban or suburban high schools (11.1% vs. 4.4%, P = 0.060). From ages 25 through 34 the prevalence of PTSD was slightly higher in those from rural high schools (13.7% vs. 8.4%, P = 0.100), but at ages 35 and older there was no association between the location of high school attended and PTSD (P = 0.522).

Workers who had previous police, firefighting, volunteer ambulance, or private ambulance experience were no more likely to suffer from PTSD than those who did not have these prior experiences. However, subjects who indicated "other 911 ambulance system experience" * (P<0.001) and other previous medical or emergency work experience (P=0.015) were statistically more likely to have PTSD than those who did not. The prevalence of PTSD increased significantly with the total number of previous medical emergency work jobs (P=0.003).

* It is recognized that in reality certain volunteer ambulance and private ambulance services do use the "911 system," and there is a trend for more of these services to switch over to it. However, these questions probably reflect that "911 systems" are more likely to be found in areas where there are busier and more active emergency services.

Workers with war zone military experience were 40% more likely to have PTSD; subjects with Vietnam war zone military experience were 70% more likely to have PTSD. Although the P values from the univariate analysis were not less than 0.05 for these 2 variables, an evaluation of the outliers and analysis of the interactions among potential risk factors demonstrated that these factors were significantly associated with PTSD. For example, among the cadets, those with war zone military experience were 6.3 times more likely to have PTSD than those without it. Among the 141 divorced employees, the Vietnam veterans were at 2.3 times greater risk for PTSD (36.4% vs. 18.5%; P=0.153). Within the group of employees with 3 or fewer years of emergency work experience (prior to NYC EMS), Vietnam veterans were 2.3 times at greater risk for PTSD (17.4% vs. 7.6%; P=0.016; chi-square statistical analysis). Among the 785 employees who worked 40 or fewer hours per week or less, those with war zone military experience had twice the prevalence of PTSD as those without this experience (12.1% vs. 6.5%, P=0.089). Because of the significance of war zone military experience in these interactions, this factor was included in the cumulative risk model.

The cumulative effect of the 5 predisposing factors (divorce, rural high school, military war zone experience, 911 ambulance experience, and previous emergency work experience) found to correlate with PTSD was then analyzed. Of the 854 subjects with none of these risk factors, 6.0% had PTSD--the prevalence of PTSD increases to 9.6% with 1 risk factor, 17.1% with 2 risk factors, and 19.7% with 3 or more risk factors (Fig. 1).

Percent employees with PTSD by total number of predisposing risk factors (rural high school, divorce, military war zone experience, 911 ambulance experience, >3 years prior emergency experience). There was significant association between cumulative effect of pre-NYC EMS experience and presence of PTSD.

Current work experience, as defined by the total years with NYC EMS more than 4 years, total cumulative EMS experience more than 7 years, rank, level of class, and hours of work per week each showed statistical correlation with PTSD. The length of time with NYC EMS statistically correlated with PTSD independent of age. The prevalence of PTSD was 3.5% in the employees who were new to NYC EMS (<=2 months). It then reached a plateau of around 10% for those with 2 months to 6 years of experience. It then rose to 15.9% for those who had between 7 and 10 years of experience and then dropped for those with more than 10 years of experience.

A cumulative effect of these 5 factors correlated with the development of PTSD. A significant trend was noted for the development of PTSD as the work-related factors were combined (Fig. 2). The combined effect of the 5 predisposing factors and the 5 work-related factors provides 3 distinct groups of risk (0%, 1%-10%, and >10%; Fig. 3). The high-risk group, defined as employees with 4 or more risk factors, comprised 40.2% of the sample and had a PTSD prevalence of 15.2%. After controlling for age, using logistic regression analysis, the 10 factors were each significant independent predictors of PTSD.

Percent employees with PTSD by total number of NYC EMS work-related risk factors (NYC EMS experience, >4 years with NYC EMS, >7 years in any emergency work, rank higher than EMT, average of more than 40 hours/week). There was significant association between cumulative effect of NYC EMS work-related factors and presence of PTSD.


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