Introduction

Injury is a major cause of death of children in China. The overall injury-related under-five mortality rate was 1.6‰ in 2015 in China, and injury is the third leading cause of under-five deaths and the first leading cause of death among children between 1 and 4 years old1. Injury is also a major cause of death of children worldwide2. The injury-related mortality rate in children is much higher in low- and middle-income countries than in high-income countries, and it is estimated that more than 95% of injury-related deaths in children occur in developing countries2,3,4,5. There is still much room for a decline in the injury-related under-five mortality rate in China.

There were some studies focused on the epidemiological characteristics of injury-related under-five deaths. E.g., in Turkey (2014–2017), injury-related under-five deaths were mainly attributed to traffic injuries (36.5%), falls (12.0%), and suffocation (10.2%). Of all injury deaths, 59.9% were males, and 52.7% occurred at home or in its close vicinity6; In Iran (2010–2015), multivariate logistic regression showed that mothers' low education level, age 1–5 years', living in a supportive center, and having financial problems increased the odds of under-5 mortality caused by injury7; In China (2009–2016), injury-related under-five deaths were mainly attributed to suffocation (34.3%), drowning (29.6%), traffic injuries (17.7%), falls (7.2%) or poisoning (4.7%)8; From 2013 to 2019 in Sichuan, China, the top three causes of total under-five deaths were accidental drowning (35.0%), accidental suffocation (32.7%), and traffic accidents (15.5%)9.

Injury is the most common cause of preventable morbidity and mortality among children10. Therefore, studies on the epidemiological characteristics of injury-related under-five deaths are important for providing evidence for future intervention11. However, the epidemiology of injury-related deaths among children under five has been rarely reported recently, and more studies need to be included in China (Fig. 1).

Figure 1
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Time trends in injury-related under-five mortality rate in Hunan Province, China, 2015–2020.

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Therefore, we investigated the epidemiology of the injury-related under-five mortality rate in Hunan Province, China, using Under Five Child Mortality Surveillance System data for the period 2015–2020. The aim of this study was to provide some information for under-five child injury intervention programs to reduce injury-related deaths.

Methods

Data sources

This study used data from the Under Five Child Mortality Surveillance System in Hunan Province, China, 2015–2020, which is run by the Hunan Provincial Health Commission and covers all under-five deaths in Hunan Province. Children’s death reports included demographic characteristics such as gender, age, primary cause of death, location of death and other key information. According to the WHO International Classification of Diseases (Tenth Revision, ICD-10), 23 injuries in this study were classified into five types: drowning (W65–W74), traffic injury (V01–V98), suffocation (W75–W84), poisoning (X44–X49), fall (W00–W19), or “other” (W20–W64, W85–W94, X00–X43, X50–X59).

Our data were derived from the Under Five Child Mortality Surveillance System. It is the second use of the data, and no further ethical approval was required for the present study.

Data quality control

To carry out surveillance, the Hunan Provincial Health Commission formulated the "Maternal and Child Health Monitoring Manual in Hunan Province". Data were collected and reported by experienced doctors. To reduce the integrity rate and information error rate, we asked the technical guidance departments to carry out comprehensive quality control each year.

Statistical analysis

The injury-related mortality rate is defined as the number of deaths from injury per 1000 live births (‰). We calculated the injury-related mortality rate and 95% confidence intervals (CI) by Poisson’s regression. Chi-square trend tests (χ2trend) were used to determine trends in mortality rates by year. Crude odds ratios (ORs) were calculated to examine the association of each epidemiological characteristic with injury-related deaths.

All statistical analyses in this study were performed using SPSS 18.0 (International Business Machines Corporation, New York City, United States).

Results

Injury-related under-five mortality rate in Hunan Province, China, 2015–2020

Our study included 4,286,087 live births, and a total of 22,686 under-five deaths occurred, including 7586 (accounted for 33.44% of all under-five deaths) injury-related deaths. The injury-related under-five mortality rate was 1.77‰ (95% CI 1.73–1.81). Table 1 shows the injury-related mortality rates and proportions by year, residence, gender, and age. (Table 1).

Table 1 Injury-related under-five mortality rate in Hunan Province, China, 2015–2020.
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Injury-related under-five mortality rate by injury type

Injury-related deaths were mainly attributed to drowning (2962 cases, 39.05%), suffocation (2300 cases, 30.32%), traffic injuries (1200 cases, 15.82%), falls (627 cases, 8.27%), and poisoning (156 cases, 2.06%). The mortality rates due to drowning, suffocation, traffic injuries, falls, and poisoning were 0.69‰ (95% CI 0.67, 0.72), 0.54‰ (95% CI 0.51, 0.56), 0.28‰ (95% CI 0.26, 0.30), 0.15‰ (95% CI 0.13, 0.16), and 0.04‰ (95% CI 0.03, 0.04), respectively. (Table 2).

Table 2 Injury-related under-five mortality rate by injury type.
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Injury-related under-five mortality rate by year

From 2015 and 2020, the injury-related mortality rates were 1.78‰, 1.77‰, 1.60‰, 1.78‰, 1.80‰, and 1.98‰, respectively, and showed an upward trend (χ2trend = 7.08, P = 0.01). The mortality rates from suffocation, falls, and poisoning showed increasing trends, too (P < 0.05). (Table 3).

Table 3 Injury-related under-five mortality rate by year.
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Injury-related under-five mortality rate by age

The injury-related mortality rates were lower in children aged 0–11 months than in those aged 12–59 months (0.52‰ vs. 1.25‰, OR = 0.41, 95% CI 0.39–0.44). Injury-related deaths due to drowning (OR = 0.02, 95% CI 0.02–0.03), traffic injuries (OR = 0.10, 95% CI 0.08–0.12), falls (OR = 0.18, 95% CI 0.14–0.22), and poisoning (OR = 0.27, 95% CI 0.18–0.39) were more common in children aged 12–59 months, while deaths due to suffocation were more common in children aged 0–11 months (OR = 4.03, 95% CI 3.64–4.47). (Table 4).

Table 4 Injury-related under-five mortality rate by age.
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Injury-related under-five mortality rate by residence

The injury-related mortality rates were lower in urban than rural areas (1.57‰ vs. 1.88‰, OR = 0.84, 95% CI 0.80–0.88). Injury-related deaths due to drowning (OR = 0.89, 95% CI 0.82–0.96), suffocation (OR = 0.79, 95% CI 0.73–0.87), and traffic injuries (OR = 0.81, 95% CI 0.72–0.92) were more common in rural areas. (Table 5).

Table 5 Injury-related under-five mortality rate by residence.
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Injury-related under-five mortality rate by gender

The injury-related mortality rates were higher in males than females (2.05‰ vs. 1.45‰, OR = 1.42, 95% CI 1.35–1.49). Injury-related deaths due to drowning (OR = 1.80, 95% CI 1.66–1.94), suffocation (OR = 1.22, 95% CI 1.12–1.33), traffic injuries (OR = 1.13, 95% CI 1.01–1.27), and falls (OR = 1.35, 95% CI 1.15–1.58) were more common in males. (Table 6).

Table 6 Injury-related under-five mortality rate by gender.
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Proportions of injury-related under-five deaths by injury types and epidemiological characteristics

Table 7 showed the following epidemiological characteristics of injury-related deaths: (1) The number of injury-related deaths decreased with children’s age. (2) Injury-related deaths happened more frequently in cold weather (around February). (3) Almost half (49.79%) of injury-related deaths occurred at home. (4) Most (69.01%) children did not receive treatment after suffering an injury until they died, and most (60.98%) injury-related deaths did not receive treatment because it was too late to get to the hospital.

Table 7 Proportions of injury-related under-five deaths by injury types and epidemiological characteristics.
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The epidemiological characteristics of some injury subtypes differed from those described above: (1) Most (71.94%) deaths due to drowning occurred in children aged 12–35 months, and were more common in July. (2) Most (80.13%) deaths due to suffocation occurred in children aged 0–11 months, and were more common in January. (3) Most deaths due to traffic injuries happened on the way to the hospital (41.58%) and in the hospital (34.08%) (Table 7).

Discussion

Overall, we found that drowning and suffocation were the most common injury types for under-five deaths. Injury-related under-five deaths were more common in children aged 12–59 months, those living in rural areas, and males. In addition, we found that injury-related under-five deaths were associated with some epidemiological characteristics.

The overall injury-related under-five mortality rate (1.77‰) in our study is consistent with the reported mortality rate in China (1.6‰ in 2015)1. Several comprehensive studies showed that the injury-related under-five mortality rate in China is higher than in developed countries2,4. The following are injury-related under-five mortality rates reported in some regions: 9.1/100,000 in Turkey in 20176; 39.5/100,000 in Pakistan, 2006–200712; 302/100,000 in India in 200513; 48.96/10,000 in Hunan Province, China, 2009–201414; 1.7–3.8‰ in Sichuan Province, China, 2009–201715. There are major differences between them. It may indicate that there are large geographical differences in injury-related under-five mortality rates, and that injury-related under-five mortality rates are changing over time. In this study, the proportion of injury-related under-five deaths in total under-five deaths increased steadily from 2015 to 2020, and the injury-related under-five mortality rate showed an upward trend, while some previous studies showed downward trends15,16. It suggested that injuries were gradually becoming the leading cause of under-five deaths in Hunan Province, China. Therefore, it deserves our special attention.

Previous studies showed that the leading injury types worldwide for under-five deaths were traffic injuries, drowning, burn, suffocation, and falls4. Chen et al. reported that the leading injury types for under-five deaths were traffic accidents (57.44%) and drowning (35.53%) in China, 2006–201716. It is different from our study. And many other studies also reported different injury types for under-five deaths14,15,17,18,19,20,21,22. It indicated that there are differences in injury types for under-five deaths in different areas, and also that the leading injury types for under-five deaths are changing over time.

In this study, drowning was the leading cause of injury-related under-five deaths, which may be mainly related to open bodies of water, such as rivers and lakes. And it is more common in rural areas. It is consistent with some previous studies9,23,24,25. For most open bodies of water in rural areas, there were no protective measures and little reliable adult supervision for children. And it may increase the risk of drowning. Suffocation was the second-leading cause of injury-related under-five deaths and the leading cause of injury-related deaths for children aged 0–11 months. It is consistent with previous studies9. We have looked at the causes of suffocation and found most deaths due to suffocation occur in bed and through the inhalation of milk. It is consistent with previous studies26,27. It may be mainly related to the negligence and poor first-aid knowledge of caregivers27,28,29. From 2015 to 2020, the injury-related mortality rate due to suffocation increased year over year, while Wang et al. reported a steady suffocation mortality rate among children under five in China, 2006–201628. One possible explanation is China’s two-child policy since 201430, which increases caregivers' burden. It may require further, in-depth research.

Overall, we found injury-related under-five mortality rates were higher in children aged 12–59 months than those aged 0–11 months, higher in rural than urban areas, and higher in males than females. It is consistent with previous studies15,23,24,25,31,32,33,34,35,36. Although the injury-related mortality rate was higher in children aged 12–59 months than those aged 0–11 months, the number of injury-related deaths decreased with age by year. It is consistent with previous studies37. It may be associated with the poor self-protection ability of young children24. Higher injury-related mortality rates in rural areas may be related to the poor living environment, residents' safety literacy, and first-aid ability32,38,39,40. Higher injury-related mortality rates in males may be related to differences in biological temperament, cognitive strategies, exposure opportunity, and gender socialization15.

However, some injury subtypes were inconsistent with the overall injuries in terms of epidemiology. e.g., the mortality rate due to suffocation was higher in children aged 0–11 months than in those aged 12–59 months. Most deaths due to suffocation occurred in bed or through the inhalation of milk, as mentioned in the previous paragraph. It may be mainly related to the negligence and poor first-aid knowledge of caregivers. There were no statistically significant differences in mortality rates from falls and poisoning between urban and rural areas or in the mortality rate due to poisoning between males and females. It has been less well reported. Brito et al. found that use of the high net, the presence of stairs or steps without a handrail, and exits and passages kept with toys, furniture, boxes, or other items that may be obstructive were associated with the risk of falls in children under five years of age41. Children’s falls and poisoning injuries are more often the result of accidents than suicide.

In addition, some other epidemiological characteristics are associated with the injury-related under-five mortality rate. And some of them were rarely covered in previous studies. E.g., total injury deaths happened more often in cold weather (around February), while drowning deaths were more common in July. It is consistent with previous studies9,42,43. It is related to several factors: first, bad weather and poor road conditions in cold weather increase the risks of traffic accidents, and a large number of people travel to celebrate the Chinese Spring Festival (mostly celebrated in February), which also increases the risks of traffic accidents; Second, people take measures to keep warm in cold weather, which increases the risks of suffocation and gas poisoning; Third, higher temperatures in July increase the risks of children's exposure to water and drowning, and summer vacations in July and August also increase the risks of children's exposure to water and drowning. Most deaths due to drowning, suffocation, and poisoning occur at home. It is the result of most injuries occurring suddenly at home, and children receive no treatment until they die because it is too late to go to the hospital44. Instead, most deaths due to traffic injuries and falls occurred in hospitals or on the way to hospitals. It is the result of the fact that most traffic injuries and falls do not cause immediate deaths, leading to a large number of outpatient and hospitalized patients.

Some things could be improved in our study. As such, we did not analyze some epidemiological features due to data limitations, including economic conditions and educational levels of children’s parents.

Conclusion

In summary, our data indicated that the injury-related mortality rate was relatively high, and we have described its epidemiological characteristics. Several mechanisms have been proposed to explain these phenomena. Our study is of great significance for under-five child injury intervention programs to reduce injury-related deaths.