Text box 1. Contributions to the literature

● Evidence on the epidemiological characteristics of special-cause burns and risk factors of burn mortality is limited in previous public health literature.

● More severe injuries, longer hospital stays and higher health care expenditures caused by special-cause burns cannot be ignored. It effectively expands current knowledge of the special cause-burn impacts.

● These findings provide empirical support for burn management from developing countries.

Introduction

Burns are a global health problem and can cause high morbidity and mortality. Globally, burns cause approximately 200,000 deaths annually and are the fourth most common type of trauma in the world [1]. In low- and middle-income countries, the burden of burns is even greater [2]. Different burns can be associated with different physiological and pathophysiological responses, therefore, in order to develop effective prevention instruments, identification of epidemiology of target burn injuries is important.

A burn is tissue damage that can be caused by heat, electricity, chemicals, radiation or friction and seriously affect human psychology and physiology that impact quality of life [3]. The classification of burns usually depends on the depth of the injury, also known as the burn degree, thus they have been categorized into (I) superficial, (II) superficial partial-, (III) deep partial- and (III) full-thickness injuries [3, 4]. In addition, according to different causes of injury, burns could be divided into thermal burns and some other non-thermal burns, such as electrical burns, chemical burns, radiation burns, etc., which are defined as special-cause burns here [5, 6]. Although the majority of burn injuries are caused by heat from thermal burns, special-cause burn injuries are associated with higher mortality and worse local and systemic damage and treatment outcomes compared to the general burn population [3, 5]. Currently, there are only some sporadic reports on special-cause burns [7, 8], however, the epidemiological studies on special-cause burns with large samples are still lacking.

According to previous researches, burn resource allocation and surveillance, are the key first steps in injury prevention [9, 10]. Burn injuries without adequate information allocation and specific guidelines often result in significant prolonged physical and psychological distress and require long periods of hospitalization [11,12,13]. Although information on burn epidemiology is critical for resource allocation and prevention, the available data are mainly from high-income countries and are directly related to access to health-care resources, environmental differences and the resources across the various health-care systems [14,15,16]. Moreover, it is worth noting that although burn injuries are decreasing in high-income countries, the incidence of burn injuries remains high elsewhere, with approximately 90% of burns occurring in low- and middle-income areas [17].

In this study, we aimed to present a retrospective investigation and analysis of the epidemiological data on burn patients specially special-cause burn at a regional burn center in China from 2004 to 2021. We hypothesized that special cause-burn patients suffer more severe injuries, and specifically provided relevant evidence for the prevention and outcomes of special-cause burns.

Materials and methods

Study design

A retrospective data analysis was performed on all hospitalized patients to the burn center at Tongren Hospital of Wuhan University (Wuhan Third Hospital). The burn center, including the burn ward and the burn intensive care unit (BICU) with 120 beds in total, is one of major specialized burn centers in central China, offering burn treatment service for all burned patients. The cause of burn injury was divided into special-cause and thermal burns. In the present study, injuries caused by electric burns, chemical burns, hot crush injury, firecracker burns, blast, radiation burns, and electrical and lightning, were considered special-cause burns, as defined previously [6]. Whereas, thermal burns included hydrothermal burns, flame burns, hot metal (solid or liquid) burns, or high-temperature gas burns.

Study population

This study included all the burn patients who were admitted to hospital for systematic treatment between January 1, 2004, and December 31, 2021 in our center. Patients diagnosed with burn including thermal burns and the above special-cause burns such as electrical burns, chemical burns, radiation injury, et al. were included. Patients suffering from scars after burning for plastic surgeries and other injuries not associated with burns as well as patients with incomplete data records were excluded from this study. This study was approved by the ethics committee of Tongren Hospital of Wuhan University & Wuhan Third Hospital (No. TR-2022042010). All methods and procedures were performed in accordance with the Declaration of Helsinki and Council for International Organizations of Medical Sciences (CIOMS) International Ethics Guidelines. In addition, all patients had a diagnosis of burn and treatment, according to the American Burn Association (ABA) criteria and Advanced Burn Life Support (ABLS).

Variables

The following factors were included as research variables: age at diagnosis, sex, marital status, cause of burn injury, the season during diagnosis, percentage of total burn surface area (TBSA), degree of burn, burn site, surgical treatment and amputation, duration of hospital stay, total hospitalization cost, and treatment outcome. The treatment outcomes were defined as follows: cured, treatment abandoned, or death. Due to the fact that grade III and IV burns extend through the full dermis layer, while the grade I and II only involve superficial or deep partial-thickness injuries [3], in the present study we plan grade III and IV together and consider them as more severe burn degree.

Statistical analysis

In the descriptive analysis, normally distributed measurement data is expressed as mean ± standard deviation and compared by using Student’s t-test, while non-normally distributed measurement data is expressed as the median and interquartile range (IQR) and compared using Wilcoxon rank-sum test. The classification variables are expressed as numbers (percentage) and analyzed using the chi-square method. Lastly, the risk factors for treatment outcomes (death and cure) were identified by logistic regression analysis and odds ratio (OR) with 95% confidence interval (CI) to express the magnitude of risk. All the P-values were bilateral, and a P-value of < 0.05 was statistically significant. R statistical package (v. 4.2.0) was used for these evaluations.

Results

Baseline characteristics

A total of 33,619 burn patients, including 4,452 special-causes burn patients (13.3% of total burn patients), were included for analysis (Table 1). Overall, thermal burn injuries were determined to be the primary cause of burn injuries, accounting for 86.71% of all-cause burns (Fig. 1A). The hydrothermal burns were the main cause of thermal burns, accounting for 69.40% of thermal burns and 60.13% of all-cause burns (Supplementary Fig. 1A and Fig. 1A). In addition, in the special-cause burn group, electrical-related burns accounted for approximately 60.98%, which were the main cause of special-cause burns (Supplementary Fig. 1B), while only 8.10% of all-cause burns (Fig. 1A). Between 2004 and 2021, the absolute number of total burn patients admitted to the burn center showed an upward trend until 2019, but the number of total burn patients declined in 2020–2021 (Fig. 1B). Nonetheless, it can be seen that the number and rate of special-cause burn patients admitted to the burn center remained generally stable during all 2004–2021 (Fig. 1B and C).

Table 1 Baseline characteristics
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Fig. 1
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The proportion of different causes of burns (A), the number of patients with different cause burns (B), and the annual rate of different cause burns (C)

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Of the 33,619 patients, the median age at diagnosis was 23 years, and the median age of the special-cause burn cohort at diagnosis was higher compared to the thermal burn cohort (38 vs. 17 years; P < 0.001) (Table 1). Overall, 21,625 were male (64.3%) and 11,994 cases were female (35.7%), with a male to female ratio of 1.8:1. However, the proportion of male patients was more in the special-cause burns cohort than the thermal burns cohort (82.1% vs. 61.6%, P < 0.001). In addition, compared to the thermal burn group, special-cause burn group was characterized by a greater proportion of married individuals (72.8% vs. 42.0%) with III-IV degree burns (78.1% vs. 50.2%) in the upper extremity (50.8% vs. 16.5%), with burn injuries occurring mostly during summer and autumn (30.2% vs. 25.9% and 26.0% vs. 23.2%) (all P < 0.001) (Table 1).

In the thermal burn group, pediatric patients aged 0–10 were the primarily affected age group, accounting for 43.2%, followed by the 30-50-year-old population. However, people aged 41–50 were the main incidence group for the special-cause burn cohort, accounting for 23.1% of the special-cause burn cases, and the incidence rate gradually decreased since then (Fig. 2A). In addition, the population with ≤ 10% burn surface areas accounted for the vast majority in both the special-cause and thermal burns cohorts (all-cause burns: 56.9%, thermal burns: 54.9%, and special-cause burns: 71.3%) (Fig. 2B). Moreover, the 31-60-year-old patients with special-cause burns have larger burn surface area (all P < 0.05) (Supplementary Table 1).

Fig. 2
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The proportion of burn patients in different age groups (A) and with different burn surface areas (B)

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In the special-cause burn group, the patients with III-IV grade burn degree have larger burn surface area (both P < 0.05) (Supplementary Table 2). In the subgroup analysis, blast injuries in special-cause burns tend to have a large burn surface area (58.3% of the 50%+ burn area; Fig. 3A) and similarly burn degree (58.8% of grades; Fig. 3B). Besides, electrical and lightning injuries and hot crush injury in special cause burns had the largest III-IV grade burn degree proportion (99.5%; Fig. 3B) and surgical treatment proportion (78.8%; Fig. 4A), respectively.

Fig. 3
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The proportion of burn surface areas (A) and burn degree (B) caused by different burn causes

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Fig. 4
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Proportion of surgical treatment (A), amputation (B), cure rate (C) and median total cost (D) for different burn reasons

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Treatment and outcomes

We found that 67.6% of all burn patients were treated with non-surgical conservative treatments, while 32.4% of patients received surgical treatment (Table 2), and about 1.4% of all patients underwent amputation. In addition, we also found that the surgical (57.2 vs. 28.6%, P < 0.001) and amputation (6.2 vs. 0.6%, P < 0.001) rates were higher in the special-cause burn cohort compared to the thermal burn cohort. Moreover, the median duration of hospital stays (15 vs. 11 days, P < 0.001) and the median cost of treatment (RMB 13,372 vs. 9665, P < 0.001. The RMB, also known as the Chinese Yuan, is the official currency of the People’s Republic of China) were higher for the special-cause burn group than for the thermal burn group. Notably, the proportion of blast injury patients in special cause burns was highest in amputation (19.2%), mortality (9.5%) and median total treatment costs (177,520 RMB) among all burns (Fig. 4B, C and D). With regard to mortality, the post-treatment mortality rate in the general population was 0.7%, with no statistical difference observed between the mortality rates of the two cohorts (P = 0.768).

Table 2 Outcomes of patients
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Through logistic regression analysis (Table 3), we found that burn patients belonging to the following variables: older (OR: 1.06, 95%CI: 1.05–1.07, P < 0.001); male (OR: 1.75, 95% CI: 1.24–2.48, P = 0.002); unmarried (OR: 0.33, 95%CI: 0.20–0.55, P < 0.001); winter (OR: 1.66, 95%CI: 1.08–2.54, P = 0.02); III-IV burn degree (OR: 4.24, 95%CI: 1.68–10.72, P = 0.002); ≥3 burn sites (OR: 5.50, 95%CI: 2.49–12.13, P < 0.001); and ≥ 10% TBSA (OR for 10–29%: 3.22, 95%CI: 1.67–6.20; OR for 30–49%: 13.21, 95%CI: 7.02–24.88; and OR for ≥ 50%: 63.33, 95%CI: 35.23-113.86; all P < 0.001) were at an increased risk of mortality. However, special-cause burn was not a risk factor for increased mortality (P = 0.695).

Table 3 Predictors of mortality
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Discussion

Although the majority of burn injuries are caused by thermal burns, special-cause burn injuries are usually more severe and difficult to manage and often contribute to higher mortality [5, 18]. This population-based analysis characterizes the burden of major burn injury in a major regional burn center in central China, providing critical epidemiologic data for future resource planning and injury prevention efforts. We characterized the epidemiological characteristics of special-cause burn, and determined the risk factors associated with the mortality of burn patients. Overall, older age, male, unmarried, winter, III-IV degree of burn, ≥ 3 burn sites, and larger TBSA were significantly associated with higher burn mortality, and special cause-burn patients suffer more severe injuries, resulting in longer hospital stays and higher health care expenditures.

Special-cause burns often occur in specific environments such as industrial production, disasters and accidents, wars, and terrorist attacks. Moreover, they are often mass injuries and attract high social attention. There were several groups of burn victims of industrial production or traffic accidents in this study, for instance, one such incident was caused by the explosion and combustion of yellow phosphorus during transportation, causing chemical burns to more than 80 onlookers, fire officers, and soldiers [4]. Notably, as a result of the COVID-19 pandemic and China government-imposed lockdown measures from 23/3/2020, which advised people to stay at home [19], reductions in outdoor activities and lifestyle changes contributed to a decrease in the incidence of burns. Our data confirm that the total number of patient visits for burns decreased in 2020 and 2021, and the number of visits for thermal burn patients decreased by nearly 50%, consistent with a prior study [19].

Our study shows that the burn patients were predominantly male, with burns occurring primarily in the upper limbs. Additionally, patients in the age groups 20–30, 30–40, and 40–50 years old are more afflicted than those of other age groups. The above characteristics reveal that special-cause burns are closely associated with occupation-upper limbs are more likely to be injured during work, men are more likely to engage in dangerous work than women, and people of working age have more chances of injury. Since there is an increased incidence of construction and agricultural workload in Wuhan during summer and autumn, and the working hours are long and the work intensity is high during these seasons, most burns incidents analyzed in our study occurred during summer and autumn. However, the timing of burn injuries varies with season or month in different studies, which may be associated with the working environment and industries in those regions [20,21,22,23]. Mirmohammadi et al. investigated the epidemiology of work-related burns and found that 17.1% of people have occupational burns [21], consistent with our study in Wuhan and other studies conducted in other places [24,25,26,27].

Most burn patients had small burn surface areas, but special-cause burn patients had more severe burn degrees, which are difficult to treat. Most special-cause burn patients had ≤ 10% burn surface areas, and the proportion of patients with burn degrees was significantly higher in the special-cause burns cohort than in the thermal burn cohort, during the same period. This could be, in the special-cause burns cohort, the electrical burn was the most common cause (accounting for 63.93% of all special-cause burn patients), followed by chemical burns, thermal crush injuries, fireworks and firecrackers, and radiation burns. As industrialization progressed, the incidence of electrical burns increased substantially [28]. Electrical burns and hot crush injuries often cause destructive deep burns involving tendons, nerves, bones, and other important structures, with a high rate of amputation and disability [29,30,31,32]. Whereas, chemical burns not only cause large local damage, but are also often combined with poisoning, and sometimes even small chemical burns can be fatal [33, 34]. Furthermore, injuries from fireworks and firecrackers can occur not only in the production process but also during transportation and use, often causing extensive burns. Further, the setting off of fireworks and firecrackers often causes burns in important body parts, such as hands and eyes [35]. Radiation burns are more common after tumor radiation therapy, and the wounds caused by radiation are often difficult to heal, requiring prolonged treatment and hospitalisation [36, 37], which is consistent with our study results that special cause-burn patients suffer more severe injuries, resulting in longer hospital stays. Collectively, the common characteristics of these special-cause burns are relatively deep wound that are difficult to heal, the injuries that may require surgery, high amputation rate (specially fingers and toes), long duration of treatment, and the overall high treatment costs.

Special-cause burns accounted for 13.2% of all hospitalized burn patients from January 1, 2004, to December 31, 2021. The electrical burn was determined to be the primary cause of burns among these patients, accounting for 60.9% of all special-cause burns. This may be associated with the socio-economic development of one region [38, 39]. Socioeconomic risk factors are generally highly correlated and can therefore not be individual causal components [40]. With the economic development and increasing application of electrical and chemical products in production and everyday life, the incidence of special-cause burns has also increased. Although increasing attention has been paid to safety production and labor protection, the incidence of special-cause burns has not decreased significantly, and the harm and impact of special-cause burns related to industrial production, transportation, and disasters and accidents are still prevalent; indicating that more work is required for the prevention of special-cause burns. This issue also urgently requires the joint attention of the medical institutions, government, management, and society.

The limitation of this study is that the source of data is only the epidemiological investigation of inpatients in a single burn center. Nevertheless, since the relatively sample sizes in most single-center epidemiological studies on burns and the constraint on data consistency in multicenter research, many results in the previous reports were discrepant and the risk factors of burn injury were still not clear or specific [41]. As the only burn center in Wuhan populated over 11 million and the capital of Hubei province, our center receives patients from a vast surrounding region in central China and this extensive dataset spanning 18 years could provide a potentially accurate reflection of the special-cause burn situation. If a multicenter large-scale survey including outpatients could be conducted in conjunction with other units for future research, it would provide a relatively better and more comprehensive reference for the prevention and treatment of special-cause burns.

Conclusions

Our study summarizes the epidemiological characteristics and treatment outcomes of all burn patients. Thermal burns were determined to be the main cause of burns among burn patients. Although the proportion of special-cause burns was small, special-cause burn patients suffer more severe injuries, resulting in longer hospital stays and higher health care expenditures than thermal burn patients. However, special-cause burn did not significantly increase the mortality risk.