Disasters often have an effect on the victims' health and victims present more psychological and physical health problems as a result. Within this context, several risk groups may be distinguished, as gender and age, which have been described after many disasters 1.

Most of the studies found that women present with more health problems than men in the aftermath of a disaster related to earthquakes and hurricanes 234567. Some studies showed other results, however, in which men appeared to be more vulnerable than women 89.

In her review using 160 studies about the health problems after disasters, Norris 1 concludes that in 49 studies a statistically significant gender difference was observed in post disaster stress, distress or disorder. Of these, 46 studies found female survivors to be more adversely affected, especially for developing a Posttraumatic Stress Disorder (PTSD). In a meta-analysis Brewin found that when men and women were directly compared within the same study, women were more at risk of developing PTSD holding constant the type of trauma 10. Finally, Tolin & Foa conducted a meta – analysis on sex differences in trauma and PTSD, using 290 studies published between 1980 and 2005. Their general conclusion was that females were more likely than males to meet criteria for PTSD, although females were less likely to experience potentially traumatic events 11.

Some studies on the effect of age in presenting post-disaster health problems showed that middle aged (40–65) victims were most distressed 6912 and showed a higher utilization of health care services 13. Two groups of different ages were compared in most of these studies and the results showed that the older group (65+ years) presented with fewer symptoms of distress or depression. The inoculation theory has to be mentioned in this context, viz. that victims with more experience of life and its major and minor (personal) disasters are more resilient to the effects of a "new" disaster than "inexperienced" victims 12141516. Contradictory results are found too, however, and several studies have shown elderly Japanese, Polish and Australian victims of natural disasters to be more at risk of post-disaster distress than younger groups 171819. In general, however, older victim groups are more resilient to the effects of a disaster than younger groups 1.

Almost all studies referred to above are based on designs that did not use pre-disaster data and used a cross-sectional, retrospective design with short-term follow-up, using (self-report) questionnaires. In the reviews and meta – analysis mentioned above 11011 it was suggested that the design of the study strongly influenced outcomes and results. Retrospective studies were associated with weaker effects for female gender and stronger effects for younger age and the effect size was greater when respondents were interviewed rather than given questionnaires. Epidemiological studies were associated with a significantly greater sex difference in PTSD than were convenience-sample studies.

Moreover, most studies discussed gender and age differences concerning PTSD, while in family practice (or primary care in general) this disorder is not often diagnosed. After disasters family practitioners often diagnose other psychological problems (anxiety, depression, disturbances of sleep, concentration or memory) and/or physical symptoms. In addition, we know of no studies in family practice of gender and age as possible risk factors for post-disaster health problems.

On 13 May 2000 a fireworks depot exploded in a residential area of Enschede, a city with 125,000 inhabitants in the eastern part of the Netherlands. As a result, 18 residents and 4 firemen were killed and about 1,000 people were injured. Some 1,200 victims lost their homes and personal belongings and had to be relocated for some years. Baseline data were available after the disaster, because the health problems of (future) victims and controls had already been registered by the family practitioner in the period prior to the disaster. This enabled us to investigate health problems longitudinally, therefore, with the inclusion of pre-disaster utilization rate and morbidity.

The aim of this study was to explore whether the supposed risk factors of female gender and younger age would (also) appear in a study in family practice in which a pre-disaster baseline measurement was available with a longitudinal design, without recall bias and using a comparison group.

We hypothesized that women and members of the younger age groups will have, for several years post disaster, elevated rates of psychological problems and physical symptoms and an increased utilization compared to their pre disaster baseline, to members of a comparison group and compared to men and older age groups.

The groups of affected residents and matched comparisons both contained 3164 persons, 52% of which were men (table 1). There were more women in the youngest groups and in the oldest groups (5–14 and 65+).

The aim of this study was to explore whether female affected residents were more vulnerable than male ones and whether younger age groups were more vulnerable than older groups to the effects of a man-made disaster in a longitudinal design with a pre-disaster measurement and a comparison group. Changes in service utilization and in morbidity as presented by patients in family practice were tested.

The main finding of the study is that no statistically significant differences were found between men and women and between various age-groups with regard to post-disaster increases in utilization rate, in psychological problems and in physical symptoms. We conclude, therefore, that as such, female gender and younger age were no risk factor in family practice following this disaster. The finding that women present a higher utilization than men in the second year alone was an unexpected one. It is hard to explain, because no gender differences in presenting with psychological problems were found in the same year.

This finding that female gender is not a risk factor after a disaster is in contrast with the findings of many other studies 123456727. A difference between our study and previous studies on gender differences may be that the previous studies were often based on natural disasters with a sudden and fierce impact, e.g. earthquakes or hurricanes. Such disasters may cause more extensive destruction of housing and infrastructure than the man-made disaster in the present study and these large scale disasters may have an additional impact on women as breadwinners, having to raise children, or losing social support 11.

Some studies on gender, however, demonstrated results resembling those in our study. In a study on gender effects after 9/11 28, a lifetime risk of post-traumatic stress disorder (PTSD) in women was found that showed that PTSD was not directly related to the attacks. In another study on 9/11, an excess burden of PTSD was attributed to female behavioural factors (e.g. acting as primary care-giver, experience of peri-event panic attacks) and biographical factors (e.g. previous unwanted sexual contact, recent history of mental problems) 29. The disaster itself seemed to play a limited role in these studies. Another study concerning the effect of an air show disaster showed that gender did not act as a risk factor on post-traumatic stress symptoms 30. These three studies were controlled for pre-disaster morbidity. One 9/11 study about female victims without a pre-disaster assessment found a relationship between social and economic circumstances and PTSD suggesting that women are not more vulnerable to PTSD than men 31.

After studying reviews and meta-analyses 11011 we concluded that results of studies about gender being a risk factor for post-disaster utilization and morbidity (or not) were influenced by the study design. Retrospective studies were associated with weaker effects for female gender and the effect size was greater when respondents were interviewed rather than given questionnaires10. Epidemiological studies were associated with a significantly greater sex difference in PTSD than were convenience-sample studies 11. Our design was not retrospective, no respondents were used (no 'recall bias') and epidemiological methods were applied. Based on the literature mentioned we hypothesized (strong) effects for women, although our study did not concern PTSD, but stress reactions, depressive feelings/disorders and anxiety feelings/disorders and physical symptoms. Moreover, the effect of demographic characteristics can not be thoroughly understood without controlling exposure and/or subjective appraisal characteristics. As mentioned before, privacy rules made it impossible to be 100% certain about the amount of exposure and subjective characteristics were not available because existing registries were used.

In our study, all five separate age groups presented post-disaster increases in psychological problems and utilization. These increases did not differ from one another, however, and so it appeared that all age groups were equally vulnerable to the effects of the disaster. This is in contrast with the finding of Norris in her review, which was that 88% of all studies of adult victims showed that younger adults were more adversely affected by disaster than older adults 1. We found no results, therefore, to support the inoculation theory as presented in several studies showing a stronger resilience of elderly victims to the effects of a disaster 141516. In contrast to the present study, however, these studies were performed after natural disasters and two of them included high proportions of older adults 1415. High age elderly were compared with young age elderly, but these groups were pooled in one 65+ group in our study, because of the low numbers of victims in these groups. One of the flood studies was controlled for pre-disaster morbidity15. Age was studied in an adult group of victims in the study of an air show disaster referred to above, which was controlled for pre-disaster symptoms. Like gender, age did not appear to be a risk factor for post-disaster psychological problems in this study 30.

In summary, gender and (younger) age as such are not risk factors for presentation of post-disaster utilization or morbidity in the present study. Of the few studies that confirm our findings, two had a "pre-disaster" design similar to our study 1530. The studies that showed female gender and younger age to be risk factors were mostly based on large scale natural disasters and they did not perform pre-disaster assessments and or used a comparison group.

In conclusion, the fireworks disaster appears to have dispersed its impact equally among male and female affected residents of all ages. In specific terms, neither women nor any particular age group were at increased risk of suffering the detrimental health effects of this man-made disaster in a residential area. In other studies concerning this specific disaster, it was found that having a pre-disaster history of psychological problems and disorders appeared to be the most important risk factor for post-disaster psychological as well as physical health problems 242526. In the first three years post-disaster being relocated due to the disaster appeared to be another strong indicator for disaster related health problems. Risk factors which appear in 'normal' primary care (gender, age, insurance type, ethnicity) did not have any extra effect of the disaster: post-disaster differences between these groups may be explained by pre-disaster differences.

After disasters family practitioners do not have to focus specifically on gender or on any age group post-disaster, but especially on those with psychological problems before the disaster and patients who lost their houses and personal belongings. As Freedy mentioned 37, after disaster 'family practitioners are key agents for providing information, remaining empathic, encouraging patients to seek and accept assistance (...) and repeatedly checking on disaster victims for up to (at least) 12 months'

Our study is one of the first which used a pre-post design and a longitudinal control-comparison design, using existing registries in family practice. It is important that this alternative design will be implemented after another disaster, collecting exposure data as well.

The authors declare that they have no competing interests.

RJHS originated and wrote the article, and assisted with the analysis. CJY supervised all aspects of the study. PS completed the analysis. TALML-J, WJHMvdB and JvdZ originated the study and provided feedback and suggestions throughout. All authors helped to develop ideas, interpret findings and review drafts of the manuscript.