The search resulted in 573 hits in the Ovid Medline database, of which 39 fulfilled the inclusion criteria [1, 3, 12–48].
Most studies excluded were "short reports" where abstracts were not given (n = 245), others had a patient-centred approach (n = 193) or focused on stress management or debriefing of ambulance personnel (n = 11). Other studies were excluded because of no relevant health outcome (n = 28), no specified ambulance sample (n = 10), a focus on leisure activities (n = 2), or not reporting original research (n = 5). Studies dealing with the aftermath of the "9/11" attack (n = 4) were excluded because of the special circumstances and the inclusion of volunteers. Several studies had a focus on infectious diseases, mainly hepatitis (n = 19). These studies have been addressed in two reviews [49, 50], which will be briefly presented here. Two studies were excluded [51, 52] because the same findings were reported in a follow-up study [53]. Fifteen of the studies were excluded because they had been reported in the previous review [7].
Only five relevant studies were identified in other databases [2, 54–57], four were known by the research group [8–11], and one other study [53] was identified in the reference lists. Thus, 49 studies were included in this review.
The studies were from the USA (21), the United Kingdom (6)/Northern Ireland (3), Sweden (4), the Netherlands (3), Canada (3), Australia (2), Wales (2), France (1) Germany (1), New Zealand (1), Japan (1) and Scotland (1). The previous review included only 23 original studies [7], whereof 15 were identified in our Medline search, and two in other databases. Although available in the searched databases, six of the studies were not identified by our search strategy because four studies did not have a specified ambulance sample [58–61], one study did not give an abstract [62], and one study was not indexed in the databases [63]. We identified four relevant studies addressing the relations between stress and strain [18, 30, 35, 42] published before 1995 that were not included in the previous review [7]. The search strategy was not reported in the previous review. However, because the identified studies overlap considerably with our review, the conclusions about the correlations between stress and strain symptoms seem to be based on most of the relevant studies published before 1995. We discuss their main findings in light of more recent research.
Post-traumatic stress disorder symptoms
Several studies have addressed the prevalence of post-traumatic stress disorder (PTSD) symptoms in the ambulance services. A study from a region in Sweden (n = 362 [sample size]/72.4% [response rate]) is the largest study, and claimed to be representative [29, 56]. The prevalence of PTSD symptoms among ambulance workers was 12% on the Post-traumatic Symptom Scale (PTSS-10), and 15% or 21.5% using different criteria on the Impact of Event Scale (IES). The authors concluded that the prevalence of PTSD symptoms among ambulance personnel (21.5%) was much higher than in the general population in Sweden (2.6%). A study from an urban area in the USA (n = 225) used the Minnesota Multiphasic Personality Inventory-2 PTSD Scale (MMPI-2 PK) and reported a 20% prevalence of PTSD symptoms among ambulance workers, which was higher than the prevalence of 5% for men and 10% for women in the general population [26]. However, none of these studies reported confidence intervals (CI) or t values, making the comparisons questionable. Similar high prevalence rates measured by the IES were reported in studies from Canada [37] and Scotland [14], and in a study from the UK that used the Post-traumatic Diagnostic Scale [1]. A slightly lower prevalence was reported in another study from Canada (15.9%) [2], and in a study from the Netherlands (12%) [45].
In conclusion, the prevalence of PTSD symptoms is consistently high in the regular ambulance services, about 20% of ambulance workers in five of seven studies. However, no study has adequately tested whether ambulance workers have a higher risk than those in other occupational groups.
Acute stressors and coping
Two of the studies focusing on acute stressors had a longitudinal design, both of which were conducted in the USA. The PTSD symptom responses of rescue workers (n = 322, including paramedics, firefighters, and police) were measured using self-administered questionnaires 1.5 years (T1) and 3.5 years (T2) after critical incidents[53]. Despite modest improvements in symptoms at follow-up, rescue workers were at risk for chronic symptomatic distress after exposure to critical incidents. The degree of exposure, peri-traumatic dissociation, fewer years of experience, external locus of control, and poor social support predicted higher levels of symptoms at T2 when the level of distress at T1 was controlled. In another study on firefighters and paramedics[16], avoidance coping was significantly associated with an increase in PTSD symptoms during a six-month prospective follow-up period. The number of duty-related traumatic incidents did not have a significant effect.
Three cross-sectional studies have reported associations between coping, i.e. suppression of emotions at a neurotic level [46], wishful thinking [23], low sense of coherence [56], ego defence mechanisms (displacement, regression, and projection) [26], and more PTSD symptoms.
Other studies have focused on the psychosocial work environment reporting significant correlations between frequency of incident stressors and degree of organizational stress [17], degree of operational hassles [54], degree of emotional demands and poor communication [45], length of review following a critical event resulting in loss of life [2], and PTSD symptoms.
In conclusion, four studies have identified emotional ways of coping [16, 23, 46, 53, 56] significantly related to more PTSD symptoms, but no studies have been able to identify any protective coping strategies. Degree of work-related stress was related to more PTSD symptoms in three studies [17, 45, 54]. However, it is not yet possible to conclude on the relationship between psychosocial work factors and individual coping in explaining PTSD symptoms, and the specific work-related stressors and coping dimensions that reliably predict adverse stress reactions among ambulance workers are still uncertain.
Burnout
A study from the Netherlands [45] used the Maslach Burnout Inventory to investigate the prevalence of burnout in workers from 10 regions (n = 221/56%) and found a higher risk for burnout in ambulance workers (8.6%) than in the general working population (5.3%). However, the CI and significance level were not reported. The percentages of workers with high scores on the separate dimensions were reported as 12% for emotional exhaustion (EE), 18% for depersonalization (DP), and 16% for low personal accomplishment (PA). The study reported a significantly higher prevalence of fatigue (10%), as measured by the Checklist Individual Strength, in ambulance workers, but the prevalence in the reference group was not reported. A study from a single service in the USA (n = 69) reported an opposite result and concluded that the average burnout scores in ambulance workers were slightly but not significantly lower than the national average [47]. However, this conclusion was based on a small and non-representative sample. A study from a Scottish regional ambulance service (n = 160/69%) reported the percentages of workers with high scores on the Maslach Burnout Inventory for the separate scales as 26% for EE, 36% for low PA, and 22% for DP, but did not report confidence intervals [14].
Hence, no clear conclusion can be made about the prevalence of burnout in the ambulance services, and it is an open question whether burnout levels are higher than in the general working population.
Depression and anxiety
The level of anxiety and depression, as measured by Spielberger's State-Trait Anxiety Inventory, was lower in ambulance workers from a county-wide service in the USA (n = 63/81%) than in a normative sample of working males [34]. However, because these comparisons were based on a small and non-representative sample and the variance scores and prevalence were not reported, the mean scores might have obscured important individual differences between the comparison groups.
In a relatively large study from a single organization in Wales (n = 617/60%) [1], the prevalence of anxiety caseness was 22% and depression caseness was 10%, as measured with the Hospital Anxiety and Depression Scale (cut-off > 11). Three other studies reported a similarly high prevalence of psychological distress (> 20%), as measured by the General Health Questionnaire [GHQ-12] [14, 23, 43]. A lower prevalence (2.1%) of severe symptoms, as measured with Beck's Depression Inventory, was reported in a study from a single ambulance service in Canada [37].
In conclusion, four out of five studies claimed that as many as 20% of workers in the ambulance services suffer from psychopathological problems, but it is unknown whether this prevalence differs from that in the working populations in the respective countries.
Work-related and individual correlates
Both chronic and acute stressors were addressed in a one-year follow-up study of ambulance personnel from 10 regions in Holland (n = 142/36% at T2) comprising a representative sample of the rural-urban distribution [45]. Lack of support from co-workers and supervisors at T1 predicted more burnout symptoms and general fatigue at T2. These findings were significant after controlling for symptoms at T1. Self-reported acute stressors were associated with fatigue, and burnout at T1, but did not predict health symptoms at T2. Lack of autonomy and financial reward were not significant predictors. In a prospective study from the USA (n = 65/33% at T2), high work group and supervisor support predicted less work-related stress at the six-month follow-up (T2), and an increase in stress from T1 to T2 predicted an increase in psychological distress [39].
Two nationwide cross-sectional studies were identified. In a recent study from Sweden (n = 1189/79%) [12], worry about job conditions and psychological demands for both genders, and low social support for men only, were significantly associated with more sleeping problems, headache- and stomach symptoms. Unfortunately, the health data was not based on standardized instruments. A study from New Zealand (n = 686/46%, 232 ambulance workers) [54] showed that stress levels did not differ significantly between police, firemen, and ambulance workers. Operational stressors were associated with more trauma symptomatology and psychological strain in all groups. In contrast, organizational hassles were not significantly correlated with psychological strain in ambulance personnel.
In accordance with these results, three cross-sectional studies have reported significant relations between high job stress and psychological strain [15, 17, 19]. Four studies have reported low social support to be associated with more mental health problems [3, 15, 17, 57]. However, in a study from Canada, social support was not significantly associated with mental health problems when individual factors were included in the multiple regression models [2].
A few studies have focused on individual factors and two prospective studies were identified. In a follow-up study (n = 70) in the ambulance service in North England, external control and type A personality predicted more mental health symptoms at the six-month follow-up, but work-related stressors had no significant effect on symptoms [48]. A one-month follow-up study from the USA reported that coping was more highly correlated with psychological strain at T2 than with frequency of events, but the data were not presented [19]. The highest significant correlations were between accepting responsibility (self-criticism and self-blame), escape-avoidance coping, confrontive coping (i.e., handling stressors with aggression and hostility), and psychological strain; correlation coefficients ranged from 0.3 to 0.4.
In conclusion, work-related stress was associated with mental health problems in seven studies [12, 15, 17, 19, 39, 45, 54]. However, two studies reported that personality factors [48] and coping [20] were more highly correlated with psychological strain than work- related stress were. Low support was associated with mental health problems in six studies [3, 15, 17, 39, 45, 57]. In one study, separate analysis for men and women showed a significant association only for men [12], and one study found no significant effect of social support when coping was adjusted for [48].
Medical impairment and early retirement
A regional study between 1988 and 1992 in Northern Ireland reported a high standardized rate of early retirement for medical reasons, after controlling for age and sex, among ambulance workers (636, 95%CI: 558–714) compared with the group with the second highest ratio, manual workers (164, 95%CI: 149–179), non-manual workers (38, 95%CI: 25–52), and nursing workers (91, 95%CI: 75–107) [40]. The main causes of retirement were musculoskeletal, circulatory, and mental disorders, although the main causes did not differ significantly between occupational groups. However, ambulance personnel were more likely to retire because of circulatory and mental problems, especially alcohol abuse, than manual workers [41].
A register-based study from Sweden found that paramedics had a higher rate of permanent medical impairment (2.2 per 1000 gainfully employed people per year) than other health service workers (mean 0.38 per 1000), but the incidence measured in paramedics was based on a small sample size of five [9].
Hence, ambulance workers seem to be at a relatively higher risk of permanent medical impairment and early retirement on medical grounds than other occupational groups.
Somatic health
A large study from Japan (n = 1551/76.9%) addressed self-reported physical health problems. Two-thirds of the emergency medical technicians reported lower back problems, compared with one-quarter of the general working population. Nearly one-third of workers in the ambulance services also reported problems with the neck, shoulders, and knees [36]. In a study from the UK, ambulance workers (n = 52) reported more physical health problems on average (15.1 v. 13.8) than the general working population[55]. Unfortunately, none of the studies reported confidence intervals (CI) or t values, making the comparisons questionable.
A small study from the USA, based on a convenience sample, found that 48% reported back pain within the last 6 months, but not all (39%) was related to emergency- work [22]. In a recent nationwide representative study from Sweden (N = 1189/79%), one-fourth of the female and one-fifth of the male ambulance personnel reported two ore more health complaints (headache, stomach symptoms, and sleeping problems) sometimes or often. However, no comparative data was reported [12].
In a study from an ambulance service in Northern Ireland [18], ambulance workers had significantly higher average systolic and diastolic blood pressure (n = 105/46%) than the general population. Twenty-one percent of the ambulance workers had systolic blood pressure > 140 mm Hg and seven percent had systolic blood pressure > 160 mm Hg, the high-risk threshold; however, caseness was not presented for the general population.
Three studies described the associations between work-related stressors and physiological stress symptoms. Ambulance workers exhibited higher physiological arousal (e.g., elevated heart rate and blood pressure) [42], salivary cortisol response [10], and noradrenalin and adrenalin levels [30] when running calls and during more severe emergency incidents than during less severe incidents.
A review from 2001 on the risk of acquiring hepatitis B or C among public safety workers included 72 studies. Fulltime EMS providers were reported to have rates of parenteral (needlestick) and nonparenteral exposure to blood and body fluids similar to those of other health care workers, including doctors and nurses. The authors concluded that EMS personnel, including firefighters, may be at risk of contracting hepatitis B as a result of their work exposure, although the risk was low. Data did not support increased prevalence of hepatitis C. Most studies were based on a convenience sample, and therefore the data might not be representative [49]. The same conclusion was made in a recent unsystematic review without reporting the number of included studies [50].
In conclusion, three studies have reported that ambulance personnel have more somatic health problems, i.e., higher blood pressure [18] and more self-reported musculoskeletal [36] and physical health [55] problems than the general population. There is no clear evidence for a heightened risk of hepatitis in ambulance personnel.
Mortality, fatal accidents and injuries
The largest study on mortality among ambulance workers is from the UK and covers the period 1979–83 [8]. Ambulance workers (n = 714) had a slightly higher standardized mortality rate (SMR; 109, 95%CI: 101–117) compared with the national average (100). However, the SMR in ambulance workers was slightly lower than that of the general population within the same social class (121, 95%CI: 21–122). Ambulance workers had a significantly higher risk of dying from ischemic heart disease, the most frequent cause of death among ambulance personnel, and all cancers than the national average. Another study based on national databases in the USA over the period 1992–97 found a relatively higher number of fatal accidents among ambulance workers (12.7 per 100,000) than in the general working population (5 per 100,000), and at levels similar to those in police (14.2 per 100,000) and firefighters (16.2 per 100,000) [31]. Most accidents were ground transportation related and air ambulance crash fatalities. There were, however, some uncertainties about both the coding of injuries and the estimates of the total number of ambulance workers.
A study from the USA of occupational injuries among fulltime ambulance personnel in two urban areas, reported a total injury-rate of 34.6 per 100 fulltime workers. The relative risk for injury was slightly higher compared to firefighters (RR = 1.5, 95%CI: 1.35–1.72), and higher than the average in the health services (RR = 5.8, 95%CI: 5.12–6.49), and the national average (RR = 7.0, 95%CI: 6.22–7.87). Sprains and strains was the leading case type, and the back was most often injured [64]. In two other studies from urban US settings, an injury rate of 50 cases per 100 fulltime workers for men and 86 cases per 100 fulltime workers for women [28], and an injury rate of 115 per 100 fulltime worker were reported [25]. Musculoskeletal injuries and low back pain were the most commonly reported injuries.
A study from Philadelphia, USA reported that 4% of all injuries were caused by assaults (2.3% from intentional assaults), of which 32% resulted in time lost from work [33]. A study from Paris found that one or more assaults were recounted by 23% of the ambulance personnel during their career, 4% resulted in sick leave and 4% resulted in PTSS therapy [27].
In conclusion, two studies suggest that ambulance workers have a higher risk of mortality and fatal accidents than the general working population. One study indicates a higher relative risk for injury among ambulance workers compared to the national average and the health services in USA, whereas, two studies report high injury rates without comparative data. However, different case definitions make it difficult to compare across the studies.
