Burns in Sweden: An analysis of 24538 cases during the period 1987–2004

1. Introduction 

Besides being a personal catastrophe for the patient, a severe burn is also a medical problem and an economical burden on the national health services. Burns are among the most expensive of the non-fatal injuries [1] and account for a substantial direct economic loss [2], [3]. In the United States, burns are the fourth leading cause of death from accidental injury [4]. The morbidity after a large burn is considerable compared with other injuries [5], [6], and it is often associated with loss of quality of life and the risk of developing depression or post-traumatic stress disorder [6], [7], [8]. Recent studies have shown a reduced incidence of burns in several countries [9], [10], [11], [12], [13], [14], [15]. Earlier calculations of the incidence of burns have been made, indicating that about 0.4% of the Scandinavian population seek medical care for burns each year [16]. Taking the present number of inhabitants in Sweden, this extrapolates to about 36000 burns treated each year.

A previous Swedish study found that between the years 1987–1996 there was a 16% reduction in the number of patients admitted to hospital with burns as their primary diagnosis [14]. During the same period there was a 70% decrease in mortality, and at the end of the period about 2 people/million inhabitants died each year in Swedish hospitals with burns as their main diagnosis [14]. Overall, men seem to be most prone to burns as several studies have reported that most of such patients are male [1], [2], [3], [17].

Several authors have also previously described a double-peaked age distribution of burns, among the age groups 0–4 years and 15–44 years of age, with some variation depending on the chosen intervals [1], [3], [14].

Like other intensive care units, our occupancy rate varies, and in order to be able to manage the uneven flow of patients we have a well-developed cooperative plan between burn centres in Scandinavia. This means that Swedish centres will accept burned patients from other Scandinavian countries, and will also send their own patients abroad for treatment when needed. However, foreign patients have not been included in this study.

Developments in burn care move fast and new protocols for treatment, preventive measures, and a rapidly-growing scheme to treat people with burns as outpatients continue. However, current epidemiological data are often difficult to grasp and published papers consist mostly of reports from single units or from the United States. We therefore wished to form a clear, updated, picture of the epidemiology of burns in Sweden. We wanted to look into possible changes in incidence, mortality, and distribution according to sex and age by using data from a Swedish nation-wide database. The purpose of this study was therefore to present an epidemiological picture of burns that require hospital care in Sweden.

2. Patients and methods 

In Sweden, all patients’ names and personal birth number (social security number) are recorded, and reported to the National Swedish Board of Health and Welfare (NSBHW). The patient's diagnosis was given according to the International Classification of Diseases-9 (ICD-9) during the years 1987–1996 and ICD-10 from 1997 onwards. The data from all Swedish patients who were admitted to hospital with a diagnosis of burns (primary or secondary) according to ICD-9/10 (Table 1) during the years of 1 January 1987 to 31 December 2004 were obtained from the NSBHW. The patients were divided into age groups of five years (such as 0–4 years, 5–9 years, and so on), and other variables requested are given in Table 2.

Table 1. Diagnostic groups studied. (Swedish versions)

	(A) ICD-9 (1987–96)
	940	Burns confined to eye area
	941	Burns of face, head, and neck
	942	Burns of trunk
	943	Burns of upper limb (except wrist and hand)
	944	Burns of wrist and hand
	945	Burns of lower limb
	946	Burns of multiple specified sites
	947	Burns of inner organ
	948	Burns classified according to size on body
	949	Surface area burn, unspecified
	(B) ICD-10 (1997 onwards)
	T20	Burns of head and neck
	T21	Burns of trunk
	T22	Burns of upper limb and shoulder (except wrist and hand)
	T23	Burns of wrist and hand
	T24	Burns of hip and lower limb (except ankle and foot)
	T25	Burns of ankle and foot
	T26	Burns of eye
	T27	Burns of respiratory system
	T28	Burns of internal organs
	T29–T30	Burns of multiple unspecified sites

Table 2. Information requested from NSBHW

	Sex
	Age (years)
	Year of discharge
	Date of admission
	Date of discharge
	Time of admission
	Clinical code
	Clinic
	Primary diagnosis
	Secondary diagnosis (1–7)
	Cause (1–2)
	Operation (1–12)
	Age at death
	Cause of death
	Time of death (year, month)

Each patient's name could appear on more than one occasion in the original records as a new record was started every time a patient changed clinics or was discharged and readmitted. The length of stay was defined as the number of uninterrupted days spent in hospital after the first admission, regardless of any change of clinics. When the patient had been discharged for more than one day the admission was regarded as interrupted and the length of stay calculated. All subsequent records for the same patient were then omitted, so no patient could appear more than once, and only the first admission is included in the study.

All patients who died during the study period were recorded in the original data, and there was no correlation between diagnosis of a burn and date of death (for example, a patient could have died 10 years after the burn, of cardiac failure, and still be mentioned in the register). To limit the number of deaths to patients who died as a direct cause of their burn, only patients whose death occurred during their first hospital admission were included in the group who died (which meant that they died within a year of the burn). Patients found dead on the scene of the accident, or who were dead on arrival to hospital, are not included in this material, but those very severely burned patients that were admitted to hospital receiving only comfort care are included. The mortality data for 2004 were not available from the NSBHW at the time of this study. The remaining data were analysed using descriptive measures, Spearman rank correlation, and simple regression. To assess factors that affected length of stay in hospital, a forward stepwise multiple regression was done using length as the dependent variable, and sex, age, and year of treatment as independent variables. Incidence and mortality were standardised to the actual Swedish population for each year. Probabilities of less than 0.05 were considered significant, and descriptive data are expressed as mean (S.D.) unless otherwise stated.

3. Results 

A total of 24538 patients were admitted to Swedish hospitals with burns between 1987–2004, giving a mean of 1363/year. The fewest were admitted in 2000 and 2004 (n=1181 each) and the most in 1987 (n=1611). Of all the patients admitted, 16945 (69%) were male and 7593 (31%) were female, giving a male:female ratio of 2.23:1 (Fig. 1). Men predominated in all age groups.

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Fig. 1. Distribution of age and gender in burned patients admitted to hospital in 1987–2004. Black bars – men, grey bars – women.

Standardising the number of patients to the population did not affect the results (Table 3). Children aged 0–4 years were the most likely to be admitted to hospital, and accounted for 27% of the entire study material during the period of analysis. Among the other age groups, 20–24 year olds were the largest, but only slightly so (7%) (Fig. 1).

Table 3. Number of patients admitted to hospital with burns in 1987–2004/million population.

	Year	Male	Female	Total
	1987	275	110	191
	1988	257	103	179
	1989	270	101	183
	1990	237	102	168
	1991	237	99	168
	1992	234	96	165
	1993	235	89	161
	1994	230	100	164
	1995	228	99	163
	1996	208	93	150
	1997	210	97	153
	1998	208	97	152
	1999	208	89	145
	2000	182	85	133
	2001	183	84	133
	2002	182	99	140
	2003	174	94	133
	2004	179	84	131
	Mean	219	96	156
	Median	219	97	157
	Range	174–275	84–110	131–191

There was a highly significant reduction in numbers admitted over the years (p<0.0001). This was significant for both genders, but was more pronounced among male patients, for whom the regression coefficient showed an almost linear trend over time.

When we analysed the numbers in each age group separately we found that there were significantly fewer admissions in all age groups up to 50 years of age except for 30–34 and 35–39 year olds. There was also a decreasing trend in the age groups 70–74 and 75–79 years. However, the group of 85–89 year olds had increased significantly over time (p=0.03). The remaining age groups showed no significant variation.

The median length of stay was 3 days (mean 10.6 (29.8), range 0–1573). Women stayed in hospital slightly longer than men; median 4 days (mean 11.7 (27.8), range 0–704) compared with median 3 days (mean 10.0 (30.6), range 0–1573). Children between 0–4 years of age had the shortest hospital stay (median 3 days (mean 6.0 (10.0), range 0–385), and 70–74 year olds the longest (median 13 days (mean 27.8 (68.9), range 0–1302). The median length of stay shortened over time (p<0.0001).

We used a forward stepwise multiple regression analysis to assess factors that may have affected length of stay. Length was used as the dependent variable, and gender, age, and year of treatment as independent variables. At a probability of less than 0.01, all factors: gender (0.2), age (0.1), and year of treatment (−0.05) were found to be significant. (β values given in brackets).

During the years 1987–2003 a total of 740 people died with burns as a primary or secondary diagnosis, resulting in a mean of 4.99 deaths/million inhabitants/year. Of those who died 453 (61%) were male and 289 (39%) were female. The mortality for men was 2.7% and for women 3.8% (p=0.22) giving an overall mortality of 3%. There was an overall significant reduction in mortality over time in both absolute numbers and when standardised to population (p<0.001 and p<0.0007, respectively) (Fig. 2).

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Fig. 2. Mortality at hospitals due to burn/million inhabitants/year.

However, when we separated the genders we found that it was the male population that accounted for the reduction (Fig. 3). Among men there was a highly significant reduction in mortality (p<0.0006) whereas among women there was no difference.

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Fig. 3. Number of deaths at Swedish hospitals, with a burn injury diagnosis, 1987–2003. Black bars – men, grey bars – women, line – total number of deaths.

4. Discussion 

To our knowledge this is the largest published nation-wide epidemiological study of burned patients. Even though Miller et al. [18] and Pegg [19] reported large studies with important information they have not had access to such a complete and homogenous patient-base as we have had. For instance, the National Burn Repository published by Miller et al. [18] is based on voluntarily contributed patient-data that is not nation-wide and cannot be verified for contribution bias.

All inhabitants of Sweden have a personal birth number that they are legally required to specify when being treated in hospital, and which is noted in the NSBHW records. Illegal aliens and foreigners who seek medical care are provided with a temporary (but exclusive) personal birth number. This makes it virtually impossible for a patient to have been treated at a Swedish hospital without being recorded in the database from which we obtained the raw data for this study. This, and the fact that the study spans 18 consecutive years make the data particularly reliable and interesting.

The number of burned patients admitted to hospital in Sweden is relatively low compared with some other European countries [15], [17], the yearly incidence being roughly 1400 patients. When the data are standardised to the number of inhabitants of Sweden this corresponds to about 155 patients/million inhabitants/year.

We found far more burns among men in every age group, a pattern that has also been seen in other studies [1], [2], [3], [14], [17]. The higher number of men can probably be explained by their different attitude to risk, and a higher exposure to risks in traditionally male professions, for example, within heavy industry.

There is also a great variation in incidence in relation to age; several previous studies have also shown that the youngest age group (0–4 years) is over-represented [1], [3], [14]. This age group is interesting from several aspects; besides having the far greatest incidence (27% of the entire study material) this group also has the shortest length of stay. This could be explained by the fact that people are more inclined to care for small children. Scalds are the most common causes of burns at this age [3], [14] and these usually result in a less severe burn that rarely requires lengthy treatment, and so stay in hospital is kept short.

It is evident that the largest reduction in admissions, during the study period, is in the male group; which probably is a consequence of men being in majority. However, why the decrease is seen only in the younger age groups is not clear. A possible reason could be changes in safety regulations in schools and at work, a concentration of preventive measures that would mainly affect the younger population. Unfortunately, the data on burn size and depth was not usable as a large number of patients in the database lacked such information and the registrations in other aspects were found inconsistent. This is also in line with the experience from our own burn unit, where, if not detailed prospective protocols are used for these measures, the data generated becomes less accurate. Also, training of the registering doctor in this aspect is important in order to generate good data. As a significant number of patients were treated outside the two designated Swedish burn units such protocols have been lacking.

Sweden displays a relatively short length of stay compared with other countries [1], [3], [17], and the number of days spent in hospital decreased considerably over time. This could possibly be a consequence of changes in surgical and anaesthetic methods during the 1990s with the introduction of early excision, improved fluid resuscitation, monitoring of vital signs, and developments in outpatient care. This is well in line with what has been documented at one of the two national burn units of Sweden for the latter part of the time period studied [20]. The shorter length of stay in Sweden is probably also a reflection of the fact that we excluded patients after their first discharge and ignored any further days of admission. Length of hospital stay is longer in the older age groups, and women tend to stay slightly longer than men. This is probably a consequence of the larger number of elderly women, something that could also explain why they also have a somewhat higher mortality.

Surprisingly, we found a much higher mortality than a previous report from Sweden that covered the first 10 years of this study (almost 5 patients/million inhabitants/year compared with 2 in the earlier series) [14]. This is despite the continuing reduction in both admissions and mortality over time in our study. However, the previous study defined patients as those for whom burns was only the primary diagnosis. In the present study we defined patients as all who had burns as their primary or secondary diagnosis.

Furthermore, it has been shown that the number of patients dying on the scene of a fire accident, and thus never are admitted to hospital, in Sweden is quite stable; yearly close to 110 deadly fires occur killing close to 125 persons [21].

During the period of the study there was a continuous reduction in the number of patients admitted over time, a development that also has been seen in other countries [9], [10], [11], [12], [13], [14], [15]. The reason for this is not clear, but could possibly be explained by preventive measures that have resulted in a safer environment in general, and the public being made more aware of the dangers. However, one should bear in mind that this series covers only those patients with burns who were admitted to hospital. The reduction could therefore be partly a result of a better-developed outpatient organisation that took care of more patients, as well as an actual decrease in numbers.

We think that the reduction in mortality, in number of admissions, and length of hospital stay is a combination of successful preventive work and expanding outpatient facilities that have been able to take care of patients who previously required hospital treatment.

In summary, this report describes the epidemiological situation for inpatient care of almost 25000 burn injured patients for the last 18 years in Sweden. Coming from Sweden, which has a well organized health care system based on socialized medicine from which this information has been gathered suggests a high reliability of the data. The most interesting findings for this time period are that there is a clear reduction in the number of burn patients that need to be admitted to hospital for treatment and that the length of stay is continually decreasing. We believe this to be due to improvements both in the prevention of burn injuries as well as in the burn treatment itself. The data show a continuously decreasing mortality and a significant shortening of the length of stay. Unfortunately, the data on burn size and depth in the database were not found consistent and usable. Therefore, a more detailed analysis in this respect was not feasible.