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INTRODUCTION
Road traffic injury (RTI) is one of top five causes of all-cause mortality globally, and the incidence is increasing as the number of vehicles increases (12). In Korea, the mortality rate from RTI was on the rise until the 2000s and started to decrease; however, it still accounted as the second leading cause of death among youth and the ninth in all ages in 2013 (3). RTI is predicted to result in more severe functional impairment as well as higher case-fatality compared to other blunt trauma (4). Even though several strategies to prevent RTI such as public campaign and legislation were implemented, the incidence and mortality of RTIs increased especially in developing countries (5).
Education, enforcement, and engineering are known to be highly effective in preventing injuries including RTI (678910). Seat belt, when properly used, is accounted as one of the most effective modalities to save lives and reduce the extent and number of injuries (789). Proper seat belt use prevents 25%-50% of fatal injuries, 25%-45% of serious injuries, and 20%-25% of minor injuries (11). However, seat belt use remains low at 4% to 72% (121314). According to the 2013 National Health Statistics of Korea, the seat belt use rates for male and female drivers continuously decreased since 2001 from 82.8% to 63.5% and 91.5% to 74.1%, respectively; for male and female front seat passengers, the use rates decreased from 76.3% to 51.7% and 80.5% to 61.5%, respectively (15).
Driving status and passenger seating positions are also associated with case-fatality and severe injury (16). It is known that front seat passengers have higher case-fatality from RTI (17); on the contrary, there is only minimal risk difference when both driver and the front seat passenger are belted (18). Moreover, rear seat passengers are less likely to die compared to front seat passengers; however, unbelted rear seat passengers are not only at increased risk, but also pose harmful effects on belted front seat passengers (16192021).
The seat belt use rates are different among drivers and non-driving passengers, and the clinical outcomes are affected by both of seat belt use and driving status. Studies comparing the preventive effects of seat belt on clinical outcomes between drivers and non-driving passengers are limited. We hypothesize that the preventive effects of seat belt on case-fatality and severe injury would be bigger in magnitude for drivers than for non-driving passengers among injured patients from RTI. This study aimed to describe the seat belt use among patients who sustained RTI, to evaluate the preventive effects of seat belt, and to compare the effects across drivers and non-driving passengers.
MATERIALS AND METHODS
Study design and setting
This is an observational study using the Emergency Department based Injury In-depth Surveillance (EDIIS) database in Korea. The EDIIS is a nationwide, prospective database of injury patients visiting the emergency department (ED), which gathers injury-related information for planning national policy in injury prevention. The EDIIS project was organized and financially supported by the Korea Centers for Disease Control and Prevention (CDC). The Ministry of Health and Welfare designated EDs into three levels according to the resources and functional requirements; level 1 (n=19) and level 2 (n=110) EDs have more resources and better facilities for emergency care and must be staffed by emergency physicians 24 hr a day and 365 days a year.
Data source and collection
The EDIIS was designed based on the core dataset of the International Classification of External Causes of Injuries (ICECI) proposed by the World Health Organization. The database collects patients' demographic information, injury-related information, prehospital emergency medical service records, clinical findings, diagnostic assessment and medical treatment in the ED, ED disposition, and patient outcome after admission if the patient was admitted (22).
Primary surveillance and data collection was performed by general physicians, and most of the recorded information was supervised and corrected by emergency medicine physicians and trained research coordinators on a daily basis. All research coordinators were required to complete training prior to project participation and regularly input surveillance data into a web-based database system of the Korea CDC. The data was reviewed every month by the quality management committee of this project, who provided regular feedback to maintain the data quality.
Study population
The study population was all adult patients who sustained RTI in vehicle (drivers and non-driving passengers) and visited any of the 17 tertiary academic teaching hospitals' EDs (10 level 1 EDs and 7 level 2 EDs) between January 2011 and December 2012, excluding cases resulting from out-of-vehicle RTI, 10-or-more passenger vans, or had unknown information on seat belt use and/or clinical outcomes. Patients who visited EDs for recurrent complications after injury were not included in this study.
Main outcomes
The primary endpoint was in-hospital mortality, defined as death in ED or during initial admission resulting from the injury event regardless of the duration from injury to death, determined at discharge from ED or hospital. The secondary endpoint was intracranial injury, defined as diagnosis of ICD-10 code S06.1-S06.9 as recorded on discharge summary after ED and/or hospital admission. The tertiary endpoint was clinically important injury, defined as admission to general ward or intensive care unit or mortality in ED as results of the injury event, determined at discharge from ED.
Variables and measurements
The main exposure of interest was seat belt use, as detected by the EDIIS registry.
Driving was divided into two classes including drivers and non-driving passengers. We collected information on demographic factors (age, gender, and past medical history), injury-related factors (time of injury, day of injury, alcohol-related injury), prehospital factors (emergency medical services [EMS] use and time from injury to ED arrival), hospital factors (initial vital status and ED disposition), and clinical outcomes.
Statistical analysis
Descriptive analysis was performed to examine the distribution of the study variables; counts and proportions were used for categorical variables, and median and quartile values were used for continuous variables. Continuous variables were compared using the Wilcoxon rank sum test or Kruskal-Wallis test, and categorical variables were compared using the chi-square test.
Adjusted odds ratio (AOR) with 95% confidence intervals (95% CIs) of seat belt use for the study endpoints were calculated using multivariable logistic regression analysis with no seat belt use as reference. The adjusted model controlled for age, gender, past medical history (hypertension and diabetes mellitus), day and time of injury, alcohol use, and driving status.
To calculated the AOR (95% CIs) according to the driving status (driver and non-driving passenger), we developed an interaction model with an interaction term (seat belt use*driving status) as the final multivariable logistic regression model for the outcomes. All statistical analysis was performed using SAS software, version 9.4 (SAS Institute Inc., Cary, NC, USA). P values were based on a two-sided significance level of 0.05.
RESULTS
Seat belt use of road traffic injuries
Of 386,774 injured patients, 23,698 (6.1%) patients were eligible for study inclusion, excluding other mechanisms of injury (n=320,078), out-of-vehicle injuries (n=15,017), injuries occurring in 10-or-more passenger vans (n=22,067), pediatric patients (n=3,238), and patients with unknown information of seat belt use (n=530) or clinical outcomes (n=2,146) (Fig. 1).
Table 1 shows the demographic characteristics by seat belt use. Among 23,698 eligible patients, 15,304 (64.6%) were wearing seat belts. Driver, middle-aged (30-44 yr old), male, and daytime injury patients were more likely to wear seat belts (all P<0.001). In terms of clinical outcomes, no seat belt group had a higher proportion of case-fatality, intracranial injury, and clinically important injury compared to seat belt group (all P<0.001).
Table 2 shows the demographic characteristics by driving status. From 23,698 eligible patients, 14,465 (61.0%) were drivers. Among drivers, 76.7% (n=11,091) were wearing seat belts, whereas 45.6% (n=4,213) among non-driving passengers used seat belts (P<0.001). In terms of clinical outcome, drivers group had a higher proportion of case-fatality and clinically important injury (both P<0.001).
Multivariable logistic regression analysis
Compared to no seat belt group, the AOR (95% CI) of the seat belt group for case-fatality was 10.43 (7.75-14.04); 2.68 (2.25-3.19) for intracranial injury; and 2.19 (2.04-2.36) for clinical important injury, respectively. In comparison, the AOR (95% CI) of the driver group was 2.95 (2.21-3.94) for case-fatality; 1.34 (1.11-1.62) for intracranial injury; and 1.41 (1.30-1.53) for clinical important injury respectively, in reference to the non-driving passenger group (Table 3).
Multivariable logistic regression analysis with interaction term
In the interaction model, AORs (95% CIs) of seat belt use for case-fatality were 11.71 (8.45-16.22) in drivers and 5.52 (2.83-14.76) in non-driving passengers. When a driver did not wear seat belt, the odds for case-fatality was 11.71 times higher relatively to when a driver wore seat belt. Furthermore, when a non-driving passenger did not wear seat belt, the odds were 5.52 times higher compared to the odds of case-fatality in a seat belt-wearing non-driving passenger. In terms of intracranial injury, AORs (95% CIs) comparing the seat belt group and no seat belt group were 3.05 (2.47-3.75) in drivers and 2.06 (1.54-2.76) in non-driving passengers. In terms of clinically important injury, AORs (95% CIs) of seat belt group compared with no seat belt group were 2.64 (2.41-2.90) in drivers and 1.61 (1.43-1.81) in non-driving passengers (Table 4).
DISCUSSION
A nationwide injury surveillance data identified significant preventive effects of seat belt on case-fatalities, intracranial injuries, and clinically important injuries requiring hospital admission. Only two thirds of injured patients from RTI were wearing seat belts, and the case-fatality was high at 2.8% in unbelted and 0.4% in belted respectively. The preventive effects on study outcomes of belted occupants compared to unbelted were higher in drivers than in non-driving passengers.
Seat belt use is the most effective modality for reducing case-fatality and severe injury from RTI, as numerous evidences support the association between seat belt use and reduced occupant case-fatality and health-related cost (789). Seat belt use would be lessen the impact from primary collision and prevent second collision of human body to vehicles. Among patients who sustained RTI in this study, any unbelted vehicle occupants, regardless of driver or passenger, had 10 times higher odds for case-fatality compared to those who were belted, 2.5 times higher for intracranial injury, and 2.2 times higher for hospital admission, respectively. Intracranial injury is one of the most fatal anatomical locations from RTI with 9.5% case-fatality rate, and is known to cause substantial disability and sequelae (23).
In terms of seating positions, we observed stronger preventive effects of seat belt on case-fatality in drivers compared to non-driving passengers (OR, 11.71 vs. 5.52, respectively). The risk is higher in unbelted drivers than in unbelted passengers where the crude case-fatality rate was 5.1% in unbelted drivers and 1.3% in unbelted non-driving passengers. On the contrary, when both the driver and front seat passenger were belted, the risk difference of severe injury between drivers and front seat passengers was diminished (18).
Seat belt legislation has been enforced in many countries including Korea where seat belt use has been made compulsory to all vehicle occupants in the vehicle; however, the seat belt use rate has not increased drastically (12131415). Despite the legislative measures to enforce seat belt use, we observed seat belt use in 76.7% among drivers and only 45.6% among non-driving passengers, which may have led to increased mortality and health burden from RTI. Seat belt legislation has been reported to reduce the severity and sequelae of traumatic brain injuries related to RTI, ultimately reducing the overall health burden (24). Primary enforcement seat belt laws mandate seat belt use and are reported to result in higher seat belt use rates and lower RTI case-fatality rates among youth and adults, compared to secondary enforcement seat belt laws (2526). Such results indicate stronger law enforcement is required for effective regulation of seat belt use.
Evidence-based strategies to increase seat belt use should be developed and implemented to increase seat belt use and reduce preventable mortality from RTIs, including extensive public advocacy and campaign, legislation and strong enforcement of related laws, and engineering and developing of new technology such as smart seat belt reminders (27). Monitoring, assurance, and development of legal remedies are necessary to enhance the seat belt use for not only the drivers, but all vehicle occupants.
This study has several limitations. First, this is an observational study, not an intervention trial. There may a potential confounding issue that exerted an impact. Second, the seat belt use, which was the main exposure variable, was measured by face-to-face interview by general physicians. This is subject to over- or under-estimation, which can result in bias. Third, we only had information on whether the vehicle occupant was the driver or a non-driving passenger, but could not distinguish whether the passenger was seated in front or rear. Injury-related information on the specific seating position, mechanism of collision, the speed at the time of injury, level of blood alcohol level were limited and not fully adjusted.
In conclusion, seat belt use among patients injured from RTI has preventive effects on case-fatality and intracranial injury. The preventive effects were significant both in drivers and passengers. Public health efforts including public campaign, advocacy, and multidisciplinary approaches to increase seat belt use would help reduce health burden from RTIs.
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