Depression after exposure to stressful events: lessons learned from the severe acute respiratory syndrome epidemic

1. Introduction

The history of humanity has been marked by the impact of many fearsome epidemics of infectious disease. At the start of the 21st century, the international community experienced a similarly frightening public health emergency, on a global scale, with the spread of severe acute respiratory syndrome (SARS). Severe acute respiratory syndrome was an unusual corona virus-based pneumonia that spread rapidly [1]. The SARS epidemic demonstrated that one effect of globalization has been to make it possible for an infectious disease to travel from one continent to another in a matter of hours and highlighted the importance of international coordination of efforts to respond to novel outbreaks of infectious disease. It was first detected in November 2002 in China's Guangdong province and eventually affected more than 25 countries. China was one of the most severely affected countries, and Beijing was among the world's most heavily affected cities, according to the World Health Organization's summary report [2], [3].

Because of the high infectious potential and mortality rate of the disease, the disaster of the SARS epidemic led to panic and anxiety in the affected countries [3], [4], [5], [6]. Health care workers were at elevated risk of becoming infected with SARS and represented more than 20% of those who actually contracted the disease [3].

Studies of the SARS outbreaks that occurred in Canada, Taiwan, and Hong Kong found that the enormous emotional burden carried by those health care workers who were on the front lines of the battle against the disease led to psychologic morbidity for many of them [4], [7], [8]. The mental disorder that is most commonly linked, in the literature, to disaster-related experiences is posttraumatic stress disorder (PTSD), but studies have also found that, among those with PTSD after a disaster, comorbid depression is common [9], [10]. A few studies [7], [11], [12], [13], including one of Hong Kong's SARS outbreak [7], have specifically examined levels of depressive symptoms among health care workers affected by disaster. Health care workers in Hong Kong who had worked closely with patients with SARS during the SARS outbreak were found to have relatively high levels of depressive symptoms 1 year later [7].

Subjective perceptions regarding the degree of danger to which one is being exposed can differ widely among individuals with objectively similar levels of disaster exposure. These subjective perceptions may be more strongly associated with an individual's subsequent psychologic morbidity than more objective measures of danger [14]. In a study of individuals exposed to an oil spill, for example, individuals' subsequent levels of depression and anxiety were more strongly related to their perceptions regarding the degree to which the spill had posed a threat to their health than to their actual degree of exposure to the oil [15]. Previous studies of the SARS epidemic, however, have not examined the relationship between subjective perceptions of outbreak-related risk and subsequent levels of depressive symptoms.

In general, little is known about which factors may be associated with protection against depression after a disaster. Although altruistic intent to help has been shown to be protective against postdisaster PTSD [16], [17], [18], the few studies that have looked at its effects on postdisaster depression have produced inconsistent findings [19], [20].

To help fill the research gaps described above, the present study (1) examines the relationship between specific types of exposure of Beijing hospital employees to the city's SARS outbreak and their subsequent levels of depressive symptoms and (2) assesses the role of perceived SARS-related risk and altruistic acceptance of risk in levels of depressive symptoms 3 years later, controlling for other factors including levels of PTSD symptoms.

2. Methods

3. Results

4. Discussion

Using data from a survey of the employees of a hospital in Beijing that was affected by the 2003 SARS outbreak, this study examined hospital employees' levels of depressive symptoms, 3 years after the outbreak, in relation to the levels and types of outbreak exposures that they experienced during the outbreak and to their perceptions at that time of SARS-related risk.

Of our 4 trauma exposure measures, representing exposures either to the outbreak or to other potentially traumatic experiences, we found that 3, that is, having worked in locations where exposure to patients with SARS was common, having been quarantined during the outbreak, and having been exposed to a violent incident or disaster before the outbreak, were significantly predictive of current level of depressive symptoms. A relative or friend having contracted SARS, on the other hand, was not found to be predictive of a respondent's current level of depressive symptoms. In the regression analyses, when the effects of these types of exposures were examined simultaneously, 2, that is, having been quarantined and pre-SARS trauma exposure, emerged as significant predictors of high levels of depressive symptoms. Their effects still held even after the PTSD symptom level and current high-stress job variables were also controlled for.

That quarantining was found to be predictive of a high level of depressive symptoms, even 3 years after the outbreak, in this sample is consistent with the results of previous studies examining the mental health effects of SARS outbreak exposures. Studies of health care workers affected by the SARS outbreaks in Toronto, Canada, and in Taiwan found quarantining experience to be predictive of subsequent general psychologic distress [32], [34], [35], [36], [37]. In these studies, increased SARS-related fear, loss of social support, and increased stigmatization by individuals who now saw these health care workers as more likely, compared even with other health care workers, to be sources of disease infection [34] were found to be aspects of the quarantine experience that helped to explain quarantined individuals' elevated levels of psychologic distress [32], [34], [37], [38].

It is likely that in Beijing, too, these aspects of quarantining helped lead to quarantined hospital workers' higher depressive symptom levels 3 years after the outbreak. In China, as in Canada and Taiwan, selection, during the SARS epidemic, of health care staff for quarantining generally resulted from a judgment, on the part of the responsible authorities, that the selected individuals were at relatively high risk for actually contracting SARS—either because their work assignments brought them into close contact with infected individuals or because they had exhibited some of the symptoms of SARS. Employees' own fears of dying from the disease and of losing family members to it would, thus, have tended to be especially strong at the time when they were quarantined.

China's quarantining policies were, however, somewhat different from Taiwan's, and considerably different from Canada's, in ways that may have led Chinese health care workers to have even higher levels of SARS-related fear, compared with their Canadian counterparts, and might also have affected their perceptions of social support somewhat differently. Unlike in Canada, quarantining in China was often a group affair. Healthy hospital staff could be selected to be quarantined together with hospital patients and were often required to continue working, caring for those patients, while quarantined [39]. These quarantined health care staff would have known that, even if they had not already been infected with SARS, they would, because of being placed in these situations, remain at high risk of eventually becoming infected because of their continued contact with patients with SARS. However, those who continued working in these settings may also have experienced the satisfaction of knowing that they continued to play an important role in society that would have been valued by many of the patients they worked with. Again unlike their Canadian counterparts, however, most of the quarantined hospital employees in our sample experienced a period of at least 10 days of being unable to see or be with their families at all. (The median length of the quarantine periods was 14 days.) This aspect of their quarantining may have led to especially severe distress, but its effects are difficult to measure with any precision.

Stigmatization has been shown to potentially have long-term effects on individuals' psychologic well-being. Robertson et al [34] found that some of the health care workers who had experienced stigmatization during Toronto's SARS outbreak continued, even after the outbreak ended, to worry that others would continue to react to them as they had during the outbreak. Among bereaved parents, stigmatization experienced in the aftermath of a child's death has been found to be predictive of the parents' depressive symptom levels even 10 years later [40].

Thus, it is likely that the relatively high post-outbreak levels of depressive symptoms found among the quarantined respondents in the current study resulted from several factors associated with quarantining, including the elevated sense of danger associated with being quarantined, reduced social support, and increased stigmatization.

Pre-outbreak traumatic experience was also found, in our study, to be predictive of post-outbreak level of depressive symptoms. This is somewhat in contrast to the finding of our previous study of the same hospital employee population [18], which focused on post-outbreak symptoms of PTSD. In that study, pre-SARS traumatic experience was not found to be predictive of later SARS-related PTSD symptom levels. On the surface of it, the direction of this contrast seems surprising because traumatic experiences have frequently been found to be more strongly predictive of PTSD than of depression [41], [42], [43], [44]. It must be noted, however, that the IES-R, the instrument that we used to measure PTSD symptoms, was, like most instruments, designed to measure only PTSD symptoms associated with memories of a single specific event or set of events—in this case, the SARS outbreak. The respondents were not asked about PTSD symptoms they might currently be having because of sudden or violent traumas experienced before the SARS outbreak. It should also be noted that although the SARS outbreak was indeed a highly stressful, often traumatic, and life-threatening experience for those affected by it, the types of stressful events it engendered were somewhat different in nature from those mentioned in the instrument that was used to measure traumas had before SARS. The instrument had been adapted from one used in previous disaster research [23], [45]. The events described in the prior trauma instrument are generally sudden, noisy, and violent ones, unlike SARS, which caused harm to its victims in ways that were long-term rather than short-term and comparatively subtle, slow, and quiet. In this sense, the stresses caused by the SARS epidemic would not be expected to be evocative of the types of stresses mentioned in the prior trauma questions. Thus, perhaps it is not really surprising to find that the prior trauma items were, in our sample, predictive of respondents' later depressive symptoms but unrelated to their later symptoms of SARS-related PTSD. Some of our respondents may, unbeknownst to us, have been having either clinical-level or subthreshold PTSD syndromes linked to their memories of events that occurred before the SARS outbreak, which in turn may have been contributing to their relatively high levels of depressive symptoms. Future studies examining the psychologic effects of both recent and less recent traumatic experiences should consider the similarities and differences found between various types of traumatic experiences in designing their survey instruments.

The associations of perceived risk and altruistic acceptance of risk with level of depressive symptoms were also examined in this study. Previous studies conducted in Canada, Hong Kong, and Singapore found perceived SARS risk to be associated with subsequent outbreak-related PTSD symptoms [46], [47], [48]. In the current study, perceived risk was found to be associated with higher levels of depressive symptoms 3 years after the outbreak, even when controlling for PTSD symptom level. Reported altruistic acceptance of risk, on the other hand, was found to decrease the odds of having a high current level of depressive symptoms, even with control for exposure, PTSD symptoms, and sociodemographic factors, suggesting a buffering effect of altruistic acceptance of risk on the development of depressive symptoms after exposure to the outbreak.

This study is limited by its cross-sectional nature; in addition, it was not possible for us to perform a true control-group comparison because no employee of the hospital—or 2003 Beijing resident—was completely without exposure to the SARS outbreak. It is also limited by its use of the CES-D to measure depressive symptoms because this measure is not actually diagnostic of major depression.

The findings do, however, provide valuable information for policy makers and mental health professionals worldwide regarding the psychologic impact of an infectious disease outbreak. Our results support previous research indicating that hospital staff and other individuals who, spend time in quarantine because of an infectious disease outbreak, may be at elevated risk for depression, even over the long term. Appropriate mental health treatment services should be offered to such individuals.