The average injury mortality rate of children and adolescents in Zhuhai City from 2013 to 2017 was 10.70/100,000, which was lower than the global population mortality rate (66.90/100,000) [15] higher than the HIC children and adolescents injury mortality rate (7.70/100,000), and lower than the injury mortality rate of LMIC children and adolescents (37.20/100,000) [16]; while the average injury mortality rate of children and adolescents in Zhuhai City was also lower than the total injury mortality rate of children aged 0–17 in China in 2014 (22.90/100,000) [4], and lower than the injury death rate of the entire population in Guangdong Province in 2015 (43.11/100,000) [17], injury also ranked first among all causes of death among children and adolescents aged 1–17.
Drowning and road traffic injuries were the main causes of death among children and adolescents in Zhuhai City, which is consistent with the major causes of death among children in China [18]. Road traffic injuries are the leading cause of child injury deaths worldwide, followed by drowning [3]. The main causes of child injury deaths in the United States were road traffic injuries and firearm injuries. There are differences in injury mortality patterns in different countries and regions.
Drowning is one of the leading causes of death among children aged 5 to 14 years old in China [19]. The average drowning mortality of children and adolescents in Zhuhai was 10.30/100,000, which was higher than the national average mortality (7.46/100,000) in China [4]. Drowning in Malaysia was estimated at 5 per 100,000 people, including nondeath cases [20]. The overall drowning mortality rate in Nepal was 1.90 per 100,000, but 53.00% occurred in people under 20 years old, and most drowning occurred in rivers (natural bodies of water) [21]. Drowning ranked first in injury deaths among children and adolescents in rural areas in Zhuhai City. Drowning is closely related to temperature, environmental risks, and water-related risk activities[22], especially in rural areas of Zhuhai, where there are many rivers and ponds. In addition, the factor of high temperatures lasting longer during the year was related to children and adolescents' tendency to swim in natural water.
The average death rate attributable to road traffic injuries for children and adolescents in Zhuhai was 6.57/100,000, which was slightly lower than the national death rate of road traffic injuries for children and adolescents (6.66/100,000) [4]. From 1991 to 2015, the death rate attributable to road traffic injuries among children and adolescents aged 1 to 14 years in Ireland decreased from 2.10/100,000 to 0.32/100,000 [23]. From 2006 to 2012, the incidence of road traffic injuries in Canadian children was 70.91/100,000, and the hospitalization rate for injuries decreased from 85.51/100,000 to 58.77/100,000[24]. With the implementation of the global "traffic safety promotion", the use of seat belts and appropriate child safety seats has steadily increased, and the production of safer cars, better road construction, and increased public awareness of driving risk behaviors have reduced road traffic injuries among children and adolescents[25,26]. Although road traffic injuries for children and adolescents in Zhuhai City were slightly lower than the mortality rate for children and adolescents in China, road traffic injuries were still the main cause of death, hospitalization and outpatient/emergency department visits, and there is still much more space for improvement.
The global burden of disease estimates indicate that 172 million falls result in short-term or long-term disability annually[27]. A cohort study in Brazil found that falls were the most commonly reported injuries in all age groups among children[28]. Falls among children and adolescents in Zhuhai City were the main reason for hospitalization and outpatient/emergency department visits. A large household survey covering more than one million people in Bangladesh in 2013 found that nonfatal falls were the most common injuries[29].
Animal bites were one of the main reasons for children and adolescents to visit to the outpatient/emergency department for injuries. A study showed that the incidence of animal bites in China was 245.05 per 100,000 in 2016[30]. Although animal bites are mostly minor injuries, as more and more pets enter the family, the problems caused by animal bites could not be ignored; this is especially true for dog bites as they are prone to rabies, and the potential harm is greater.
A multicountry survey of children aged 14–17 years found that 8.90% of girls and 2.60% of boys reported self-harm incidents in the past year[31]. Studies by Muehlenkamp[32]and Swannell[33] showed that self-harm/suicide behavior was prevalent in adolescents in clinical and community samples. The suicide mortality rate of children and adolescents in Zhuhai City was 1.69/100,000. Most of them were older children aged ≥ 12 years, and the suicidal tendency increased with age. The self-harm/suicide rates of children and adolescents are rising in many high-income countries[34,35,36]. The development trajectory, cultural background, risk factors and mechanisms, and independent diagnosis of self-harm/suicide among children and adolescents in China will be the focus of future research.
Studies in several countries have shown that rural children and adolescents have higher injury mortality rates than urban children[37,38]. Rural children and adolescents in Zhuhai had an injury mortality rate of 13.57 per 100,000, which was 1.60 times that of urban areas. Road traffic injuries were the leading cause of injury deaths among children and adolescents in urban areas and drowning injuries were the leading cause of injury deaths among children and in rural areas. These urban-rural differences could be caused by environmental factors, residents' behavioral factors, different infrastructure investments, and differences in access to emergency medical services[39].
The mechanisms of injury deaths, injury hospitalizations, and outpatient/emergency department injury visits showed obvious age characteristics, and there were differences in the injury spectra at different stages of child development. A study in the United States showed that drowning was the most common cause of death for children aged 1 to 4 years, and the causes of death from injuries among those aged 10 to 19 years was mainly road traffic injuries, firearm injuries and suffocation[40]. The main mechanisms of injury hospitalizations for children aged 0–16 years in Australia were violence, poisoning, burns and road traffic injuries[41]. Falls were the most common mechanisms of nonfatal injuries to children in Nepal, followed by burns in preschool children, and road traffic injuries were the most likely mechanisms of injury during adolescence[42]. For outpatient/emergency department injury visits and injury hospitalizations, falls were the leading cause of injury for all age groups in Zhuhai City. Children in the younger age group had more outpatient/emergency department visits because of burns and animal bites. In the older age group, there were more blunt injuries and cuts. Drowning was the main cause of injury death among young children, and road traffic injuries were the main cause of injury death among children and adolescents in older age groups.
As a model for injury research, the injury pyramid can visually show the relative effects of fatal and nonfatal injuries [43]. This study showed that, for every injury death among children and adolescents in Zhuhai, there were 59 injury hospitalizations and 1,047 outpatient/emergency department visits for injuries. Similar to the injury pyramid (1: 36: 1014) described by Lee [9] for children and adolescents ≤ 19 years old living in Massachusetts, USA, Ballesteros [44]also found that every injury death among children in the United States was accompanied by approximately 1,000 injury-related outpatient/emergency department visits. Compared with the injury pyramid for South Korean adolescents (1: 162: 492) [10], for every injury death, the percentage of injury hospitalizations of children and adolescents in Zhuhai City was small, while the proportion of outpatient/emergency department visits was high. This difference may be due to different medical guarantees in different countries, and China may have a relatively heavy burden of hospitalization costs, which limits hospitalizations. In addition, the severity of the injury and the timeliness of treatment can also affect hospitalizations.
Compared with the whole population injury pyramid, the rate of outpatient/emergency department injury visits among children and adolescents was greater. The injury pyramid ratio for unintentional injuries among the entire South Korean population was 1: 54: 231 [8]. The injury pyramid ratio in the entire population in Missouri and Nebraska was 1: 10: 147 [11]. The injury pyramid ratio Iran, based on a household survey, was 1: 50: 646 (deaths / hospitalizations / all injuries) [12]. Studies in the same country still showed a higher rate of injury among children and adolescents seen in the outpatient/emergency departments. For example, the injury pyramid ratio for children who were ≤ 10 years old and came from Alberta, Canada, was 1: 73: 1612 [45], and the injury pyramid ratio for children who were ≥ 12 years old and came from Ontario, Canada, was 1: 25: 363[46]. Fatal injuries were at the top of the injury pyramid, but minor nonfatal injuries were more common in children and adolescents than adults, and the burden of minor nonfatal injuries cannot be ignored.
This study showed that rural children and adolescents had higher injury mortality rates than urban children and adolescents, while the incidence of outpatient/emergency department visits for injuries was higher in urban areas than in rural areas. Compared to the urban injury pyramid (1: 74: 1618), the rural injury pyramid has a narrower shape (1: 46: 593), which was related to the difference between injury-related death rates, hospitalization rates, and injury mechanisms in urban and rural areas. Incidence/mortality was higher at all levels in boys than in girls. The frequency of fatal and nonfatal injuries was higher in males than in females. Research in South Korea found that the injury pyramid of children and adolescents aged 0 to 6 years (1: 151: 3657), 7 to 12 years (1: 280: 3011), and 13 to 18 years (1: 132: 594) showed that the younger the age, the wider the bottom of the pyramid [8]. This study showed that the bottom of the injury pyramid was the widest among participants aged 6 to 11 years; with each injury death that occurred, there were the most injury hospitalizations and outpatient/emergency department injury visits. The highest injury mortality was observed in children aged 0 to 2 years, and this injury pyramid had the narrowest bottom (1: 39: 753). The rest of the children aged 3 to 5 years (1: 55: 1160), 12 to 14 years (1: 70: 1049), and 15 to 17 years (1: 72: 1007) had similar pyramid shapes. Injuries were more lethal to children in younger age groups.
Wadman MC [47] proposed 3 types of pyramids (A / B / C) based on different lethalities. The ratio of injury pyramid of self-harm/suicide among South Korean youth was 1:7:15 [10], showing a steep pyramid (type C); this was similar to the injury pyramid of self-harm/suicide among children and adolescents in Zhuhai City (1:1.2:10), indicating that self-harm/suicide had considerable lethality. The drowning injury pyramid was in the shape of an inverted triangle, indicating that, for every outpatient/emergency department injury visit that occurred; there were 1.3 injury hospitalizations and 5 injury deaths. It was observed that self-harm/suicide and drowning had a very high mortality rate, but the number of outpatient/emergency department visits for this mechanism was very small, resulting in a steep and narrow pyramid.
The mortality rate of road traffic injuries among South Korean youth was 3.00 / 100,000, with an injury pyramid ratio of 1:195:341[10]. The death rate of road traffic injuries for children and adolescents in Zhuhai was 6.57 / 100,000, and the injury pyramid ratio was 1: 17: 149. The shape of the injury pyramid for road traffic injuries was type A, indicating that the mortality rate was low, but the degree of injury was high. Type A injury pyramids have a cumulative effect on the use and cost of the medical system that is far greater than type C. The injury pyramid ratio for falls among children and adolescents in Zhuhai was 1:105:2609. Falls had a low mortality rate, but the outpatient/emergency department visits were large in scale, forming a type B pyramid. An injury mechanism with high lethality can reduce the occurrence of the injury itself through primary prevention; however, although the fatality rate of falls was very low, the scale of occurrence was large, and the consumption of medical resources may be more serious.