a Instituto Nacional de Salud Publica, Cuernavaca, Mexico.
b Southern California Injury Prevention Research Center, University of California, Los Angeles, CA, USA.
Reprint requests to: Jess F Kraus, Southern California Injury Prevention Research Center, UCLA School of Public Health, 10833 Le Conte Avenue, Los Angeles, CA 900951772, USA. E-mail: jkraus{at}ucla.edu
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Abstract |
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Methods Using LA County and Mexico City death certificate data for 1994 and 1995, injury deaths were classified according to the International Classification of Diseases Ninth RevisionClinical Modification external cause of injury codes. Crude, gender-, and age-adjusted annual fatality rates were calculated and comparisons were made between the two regions.
Results Overall and age-adjusted injury death rates were higher for Mexico City than for LA County. Injury death rates were found to be higher for young adults in LA County and for elderly residents of Mexico City. Death rates for motor vehicle crashes, falls, and undetermined causes were higher in Mexico City, and relatively high rates of poisoning, homicide, and suicide were found for LA County. Motor vehicle crash and fall death rates in Mexico City increased beginning at about age 55, while homicide death rates were dramatically higher among young adults in LA County. The largest proportion of motor vehicle crash deaths was to motor vehicle occupants in LA County and to pedestrians in Mexico City.
Conclusions These findings illustrate the importance of primary injury prevention in countries having underdeveloped trauma care systems and should aid in setting priorities for future work. The high frequency of pedestrian fatalities in Mexico City may be related to migration of rural populations, differing vehicle characteristics and traffic patterns, and lack of safety knowledge. Mexico City's higher rate of fall-related deaths may be due to concurrent morbidity from chronic conditions, high-risk environments, and delay in seeking medical treatment.
Keywords Mortality, injury deaths, external cause, rates
Accepted 2 February 2000
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Introduction |
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Other differences were noted by Langlois et al.4 in method of suicide and homicide rates and a few other external causes.
The importance of cross-national comparisons of injury mortality findings prompted the US National Centers for Disease Control and Prevention, National Center for Health Statistics, to initiate the International Collaborative Effort (ICE) on Injury Statistics. The goal of ICE is to foster improvements in the quality and international comparability of injury data.5 Recent findings from 11 participating ICE countries, using similar methods of cause (mechanism) of death coding, showed injury deaths rates to be highest in France and Denmark compared with England, Wales and Israel, which had the lowest rates. In addition, remarkable differences in rates were noted for several specific external causes such as poisonings where the death rate for Denmark was higher than the US rate largely due to the significant differences in suicide poisoning in Denmark.6
Prompted by the desirability of identifying differences in injury death rates (and possible causal explanations) we undertook a comparison of injury death rates between Los Angeles (LA) County, California and Mexico City DF, Mexico for 19941995.
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Methods |
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Data sources
Death certificate data for residents of LA County were obtained from the California Department of Health Services, Office of the Registrar. The data are found in the California Master Mortality database and provide detailed information on age, race, gender, cause of death, and whether the person was injured at work or not. In 1994 and 1995, there were 9930 injury deaths among LA County residents.
Death certificate data from Mexico City were available from the Instituto Nacional de Estadistica Geografia e Informatica (INEGI) database for 1994 and 1995. These data provide detailed information on deaths by age, gender, cause of death, place of occurrence and whether the person was injured at work or not. In 1994 and 1995, there were 9253 injury deaths among Mexico City residents.
We identified all LA County and Mexico City deaths involving an injury using the International Classification of Diseases Ninth RevisionClinical Modification (ICD-9-CM) external cause of injury codes (E-codes) E800E999. We excluded therapeutic misadventures (870879), and deaths from drugs, medicinal and biological substances causing adverse effects in therapeutic use (930949). Injury fatalities were classified into 11 mutually exclusive external cause groups: motor vehicle-related (810825, 929.0), falls (880888, 929.3), drownings (830, 832, 910), fires/burns/explosions (890899, 923925, 929.4), poisonings (850869, 929.2), homicides/legal intervention (960978), suicides (950959), other transportation (800809, 826829, 831, 833848, 929.1), non-homicide firearms (922), undetermined causes (980989), and all other causes (900909, 911921, 926928, 929.5, 929.8, 929.9, 990999). Motor vehicle-related injuries were further subset into vehicle occupants, pedestrians, motorcyclists, and pedal cyclists.
Los Angeles County population estimates by age, gender, and race for 1994 and 1995 were obtained from the California Department of Finance (Race/Ethnic Population Estimates with Age and Sex Detail, 19901996. Sacramento, CA: January 1998). This data file covers state- and county-wide intercensal population estimates from 1990 to 1996 for residents of California.
Mexico City population estimates by age and gender for 1994 and 1995 were obtained from the Centro de Estudios Sobre Población y Salud de la Secretaría de Salud. This data file covers state- and delegation-wide intercensal population estimates from 1990 to 1996 for residents of Mexico City.
Analytical methods
Crude annual injury fatality rates as well as gender- and age-adjusted rates per 100 000 population (and 95% CI) were calculated for LA County and Mexico City. The standard used to obtain adjusted rates was the sum of the two populations by age and gender. The Mantel-Haenszel test for no association between injury fatality and population area was used for comparison analysis between the two regions. Race was not evaluated in the analyses because Mexico City has a very homogeneous population and stratified cell sizes for minority ethnic groups would fall below the threshold for meaningful analysis, and hence, rate estimates would not be robust. Specific rates by Hispanic ethnic group for LA County were compared with Mexico City.
Microsoft Excel and SAS statistical software were used for data management.
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Results |
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Discussion |
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The high frequency of pedestrian fatalities in Mexico City may relate to the influx of rural migrants into the City who are not accustomed to heavy vehicular traffic and the conventions of pedestrian behaviour with that traffic. Hijar7 recently reported that 55% of deaths in traffic injuries were to pedestrians while in the US the percentage was only 12.6 in 1997.8 Likewise, there may be less exposure to Mexico City residents as occupants of motor vehicles in terms of vehicle miles driven. Vehicle characteristics and patterns of vehicular traffic differ between the two regions. In addition, there is a lack of road use safety knowledge in Mexico City. Since specific vehicle use exposure measures (such as miles driven) are not available in either region it is not possible to make strict comparisons of the findings from this study.
The primary prevention of pedestrian-related fatal injuries in Mexico City may best be addressed by expanded efforts in providing more compatible environments for pedestrians. In developing countries it has been reported that pedestrians do not always check for oncoming traffic before crossing streets and drivers fail to slow down or even stop for pedestrians who are in the street.912 Crossing streets outside of crosswalks or at mid-block is quite prevalent in most countries.13 This factor, coupled with the lack of enforcement of existing laws, leads to hazardous exposure for pedestrians, regardless of age, in Mexico City. Our observation of the high prevalence of unmarked crosswalks, the practice of crossing roads other than at crosswalks, lack of traffic signs or lack of handicapped access to sidewalks may contribute to the high frequency of exposure of pedestrians to motor vehicle crash impacts. The development of road median fences to prevent crossing other than at designated crosswalks, pedestrian-friendly walkways, broader public education on the use of roads by drivers and pedestrians might be a worthwhile initial effort to address this problem in urban Mexico City and adjacent regions.
Fall deaths involve a number of different exposures. Most common in the US are injury deaths due to falls among the elderly resulting in hip fracture.14 In Mexico City fall-related deaths also occur frequently in the older age groups and may be related to domestic exposures. In addition, the high rate of fall-related injury deaths may be due to concurrent morbidity from chronic conditions, high-risk environments, and delay in seeking medical treatment.15,16
The higher frequency of fall injury deaths in Mexico City may be the result of a delay in arrival of emergency medical services or the failure to seek medical attention after a fall as well as the differences in exposure of individuals to the possibility of falls, particularly in the local environment. Specific in-depth studies, possibly of a case-control variety, may be essential in determining the specific exposures and risk factors involved in these falls, and the nature of the environmental, behavioural or lifestyle measures that may be necessary to primary prevention.
Los Angeles County had more intentional injury deaths (homicides and suicides) than Mexico City during 19941995. The lower intentional injury deaths in Mexico City may be due to the strong religious presence in Mexico. Approximately 90% of the Mexican population are Roman Catholic, and suicide and homicide are considered mortal sins.17
The differences in death rates between Hispanics in LA County and Mexico City reflect not only many environmental differences between the two regions but also socioeconomic influences as well. We were not able to control for these confounding factors in the analysis and they should be considered in future comparisons of regions with disparate living conditions, economies, etc.
External cause of death coding is mandatory for all injury-related deaths in California. All sudden, violent, or unusual deaths are coroner's cases in California and in most cases involve an autopsy to determine the cause and manner of death. While the autopsy rate has declined annually to 11% of all deaths in 1989 in the US,18 the proportion of autopsies performed for homicides was 97% and 50% of all unintentional injury, poisoning, and suicide deaths were autopsied.19
While external cause of death coding is not mandatory in Mexico City, a substantial number are coded each year. For purposes of this research project, all injury deaths were reviewed by one of us (MH) and, where necessary, causes of death were coded to the appropriate external cause categories following training on use of the ICD (CM) Ninth Revision.
Undetermined external causes of injury deaths are four to five times more frequent in proportion in Mexico City compared with LA County. In the latter, less than one per cent of all injury deaths have undetermined intention (i.e. unintentional, homicide or suicide), whereas in Mexico City almost 13% of injury deaths are of undetermined origin. Undetermined cause of death is a coroner designation in both LA County and Mexico City. Inquiry by one of the authors (MH) failed to ascertain the exact basis for this high proportion of undetermined cause of deaths but the reason may relate to the lack of information available to the medical examiner on the specific details on the mechanism of death.17 While 95% of all injury deaths are included in coroner jurisdictions in Mexico City, in many cases the information necessary to precisely classify cause of death is not available.*
The differences in poisoning death rates between LA County and Mexico City may be due to a difference in conventions of coding certain fatal events related to drug abuse. For example, Fingerhut et al.6 point out that within the US the rules for coding deaths from non-dependent overdose of drugs could be confused by assigning ICD 305 code (non-dependent abuse of drugs) instead of ICD E850858 (accidental poisoning by drugs). Hence, explanations for the differences in rates observed here could be procedural, not exposure related, and this explanation should be further investigated.
Results of this study show the benefit of sharing international experiences and provide good examples to aid in priority setting for strategies for future work. For example, our data illustrate the importance of the primary prevention of injury in countries having underdeveloped trauma care systems. In a recent report16 on this question, data on injury deaths were compared in Kumasi, Ghana, Monterrey, Mexico, and Seattle, Washington, representing low to high socioeconomic development. In the former region, there is lack of emergency medical services (EMS), while in Monterrey only basic EMS are available and in Seattle advanced EMS are provided. Injury deaths decline with increased sophistication of EMS. In Kumasi more than half of all severely injured people died in the field while in Seattle the proportion was 21%. Efforts to develop or enhance emergency service provision will no doubt affect the occurrence of some pre-hospital deaths, but the importance of primary prevention must be stressed.
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Acknowledgments |
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Notes |
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References |
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