Episodic Alcohol Use and Risk of Nonfatal Injury

G. Borges1,2 , C. J. Cherpitel3, L. Mondragón2, V. Poznyak4, M. Peden5 and I. Gutierrez6

1 Universidad Autónoma Metropolitana–Xochimilco, Xochimilco, Mexico.
2 Instituto Nacional de Psiquiatría, Mexico City, Mexico.
3 Alcohol Research Group, Public Health Institute, Berkeley, CA.
4 Department of Mental Health and Substance Dependence, World Health Organization, Geneva, Switzerland.
5 Department of Injuries and Violence Prevention, World Health Organization, Geneva, Switzerland.
6 Hospital General Dr. Manuel Gea González, Mexico City, Mexico.

Received for publication March 31, 2003; accepted for publication October 14, 2003.


    ABSTRACT
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Usual and acute alcohol consumption are important risk factors for injury. Although alcohol-dependent people are thought to be at increased risk of injury, there are few reports suggesting that their risk is greater than that of nondependent alcohol users in a given episode of alcohol use. The authors conducted a case-crossover analysis of data on 705 injury patients from a hospital emergency department in Mexico City, Mexico, collected in 2002. The majority of the sample was male (60%) and over 30 years old (51%). With use of a multiple matching approach that took into account three control time periods (the day prior to the injury, the same day in the previous week, and the same day in the previous month), the estimated relative risk of injury for patients who reported having consumed alcohol within 6 hours prior to injury (17% of the sample) was 3.97 (95% confidence interval: 2.88, 5.48). This increase in the relative risk was concentrated within the first 2 hours after drinking; there was a positive association of increasing risk with increasing number of drinks consumed. These data suggested that relative risk estimates were the same for patients with and without alcohol use disorders.

alcohol drinking; case-control studies; risk; substance-related disorders; wounds and injuries

Abbreviations: Abbreviations: CI, confidence interval; RR, relative risk.


    INTRODUCTION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Injuries and violence are highly prevalent worldwide and entail high costs to society (1). Because injuries are preventable, they are of special relevance to public health. In 2000, injuries accounted for 9 percent of global mortality and 12 percent of the global burden of disease (2). According to data from 2001, traffic injuries were the fifth leading cause of death among Mexican males (13th among females), and homicides were the eighth leading cause of death for Mexican males (2, 3). Alcohol use and alcohol use disorders are associated with increased risks of mortality and morbidity from injury and violence, and alcohol is a prominent factor in the need for emergency department care (4, 5). Several studies conducted in the United States and abroad have estimated that 10–40 percent of patients who visit an emergency department have detectable amounts of alcohol in their blood or on their breath (4, 69). Alcohol consumption plays a role in approximately 30 percent of motor vehicle accidents and 40–56 percent of assaults. In addition, 50 percent of trauma patients are found to have been injured while under the influence of alcohol (1012).

Although alcohol consumption has been found to be a major risk factor for both intentional and unintentional injuries in emergency department settings, few studies have evaluated alcohol’s contribution to the relative risk of nonfatal injury (1315). An important limitation in obtaining risk estimates that can be used to formulate public health policy has been the limited availability of nonbiased controls in emergency department studies. However, the advent of the case-crossover study (16), a research design in which cases are used as their own controls, has circumvented this limitation to some extent. This analytical strategy provides risk estimates for intermittent alcohol use over and above the baseline risk associated with long-term alcohol consumption, and because of self-matching, traditional risk factors for injury are controlled. However, with two exceptions (17, 18), the case-crossover strategy has not been applied in emergency department settings.

In the study described here, we built on this previous case-crossover research. We report relative risk estimates for alcohol use within 6 hours prior to injury, using different time periods for control comparisons (19). Estimates of the relative risk of injury associated with increasing levels of alcohol use and with the presence of alcohol use disorders, a matter of considerable controversy and important public health implications (20), are also reported.


    MATERIALS AND METHODS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
The data analyzed were obtained from a hospital emergency department in Mexico City, Mexico. Mexico City was one site in the WHO Collaborative Study on Alcohol and Injuries, a multicountry epidemiologic study sponsored by the World Health Organization. The WHO Collaborative Study on Alcohol and Injuries was carried out in 12 emergency departments in the following countries: Argentina, Belarus, Brazil, Canada, China, Czech Republic, India, Mexico, Mozambique, New Zealand, South Africa, and Sweden.

Sample selection
A sample of adult patients (age >=18 years) admitted to the emergency department of the Hospital General Dr. Manuel Gea González and reporting an injury was drawn from emergency department admission forms, reflecting consecutive patient arrival in the emergency department over a 6.5-week period (January–February 2002). All eligible patients were approached for interview (with informed consent) as soon as possible after admission to the emergency department. Patients who were too severely injured to be interviewed in the emergency department were interviewed in the hospital after their condition had stabilized.

During the data collection period, a total of 744 patients were approached, of whom 39 (5.2 percent) did not participate. Primary reasons for nonparticipation were patient refusal (2.2 percent) and transfer of the patient before an interview had been obtained (1.7 percent). One patient was admitted to the emergency department alive but subsequently expired, and two others were too severely injured to be interviewed.

Data collection
Data were collected using a questionnaire that took approximately 25 minutes to complete and was administered by trained interviewers. Among other items, the interviewer obtained data on the condition that had brought the patient to the emergency department, the patient’s use of alcohol within the 6 hours prior to the event, the number of drinks consumed, and the amount of time between consumption of the last drink and injury. Information on alcohol use during the same time period was also obtained for the day prior to the injury, the same day in the previous week, and the same day in the previous month. Data on the quantity and frequency of usual drinking, alcohol use disorders in the previous 12 months, and demographic characteristics were also obtained.

Alcohol use disorders were measured according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (21), criteria for alcohol abuse and dependence. A positive response to any of several questions on the consequences of drinking qualifies as alcohol abuse, while a positive response in at least three of seven domains (tolerance, withdrawal, drinking more than intended, unsuccessful efforts to control use, giving up pleasures or interests in order to drink, spending a great deal of time in drinking activities, and continuing to use alcohol despite problems) qualifies as alcohol dependence.

We used a quantity-frequency typology for drinking during the past year that was developed in prior studies carried out in the same emergency department (22). It is based on the frequency of usual drinking and whether the patient reported consuming either 12 or more drinks or 5–11 drinks on one occasion. Frequency of drinking was defined as low (less than once a month), moderate (at least once a month but less than three times per week), or high (three or more times per week). Quantity was defined as low (never consuming five drinks at one time), moderate (consuming at least five but less than 12 drinks at one time), or high (consuming 12 or more drinks at one time). Five alcohol use categories were developed from this typology: 1) abstainer (no drinking during the past year); 2) infrequent drinking (low frequency/any quantity); 3) light drinking (moderate or high frequency/low quantity); 4) moderate drinking (moderate or high frequency/moderate quantity or moderate frequency/high quantity; and 5) heavy drinking (high frequency/high quantity).

Scales for measuring usual alcohol use, alcohol use prior to the injury, and alcohol use disorders have been validated previously in emergency department studies in Mexico (23, 24).

Data analysis
Patients who reported drinking at any time within the 6 hours prior to injury were considered exposed cases. We analyzed the volume of alcohol consumed during the 6-hour period by converting the numbers and sizes of drinks of wine, beer, spirits, and local beverages to pure ethanol and using a standard drink size of 16 ml as a common volume measure across beverages. Two analytical strategies were used in these analyses, the pair matching approach and the usual frequency approach (19).

Pair matching
We performed pair matching comparing, for each patient, his or her reported use of alcohol during the 6 hours prior to injury with his/her use of alcohol during the same time period on the day prior to injury, on the same day in the previous week, and on the same day in the previous month. For alcohol use during the 6 hours prior to injury, the question posed was: "In the 6 hours before and up to your having your injury/accident, did you have any alcohol to drink, even one drink?" (yes/no). Information on alcohol use at the same time in the previous week was elicited as follows: "In this next section, I am going to ask you about what you were doing exactly 1 week ago. Think about the time you had your accident (today) and remember the same time a week ago. Last week at the same time, did you have any alcohol to drink in the 6 hours leading up to this time?" (yes/no). We asked similar questions to obtain data on alcohol use on the day prior to injury and on the same day in the previous month.

The use of different control time periods helps to balance for the presence of any episodic or usual patterns of drinking in the population. We also combined these three control periods for multiple (3:1) matching. The number of drinks consumed on each of the three control occasions was obtained and transformed into a measure of volume, as described above. Conditional logistic regression was used to calculate matched pair relative risks and 95 percent confidence intervals (16).

Usual frequency
The usual frequency approach uses the quantity and frequency of drinking during the past 12 months to define person-time at risk. We estimated the amount of person-time of exposure to alcohol by multiplying the reported usual annual frequency and quantity of alcohol consumption by the duration of its hypothesized physiologic effect (1 hour per drink). We then calculated unexposed person-time by subtracting the exposed person-time in hours from the number of hours in 1 year. With this approach only, it was possible to calculate 1-hour relative risks for each hour, from 1 hour between the last drink and the injury to 6 hours between the last drink and the injury. We used techniques for analyzing sparse person-time data to calculate relative risks and 95 percent confidence intervals, as described by Maclure (16).

Data on demographic characteristics and alcohol use for exposed and unexposed cases are presented in table 1. Relative risk estimates derived from case-crossover analysis for any alcohol use across different control periods are presented in table 2 (16). Relative risk estimates from dose-response analyses and results of trend tests (25) are shown in table 3, and relative risk estimates for alcohol use disorders and results of chi-squared tests for heterogeneity (25) are shown in table 4. Relative risks for any alcohol use in the 6 hours prior to injury are presented on an hour-by-hour basis in figure 1.


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TABLE 1. Characteristics of a study population of emergency department injury patients according to alcohol use within 6 hours prior to injury, Mexico City, Mexico, 2002
 

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TABLE 2. Risk of injury according to alcohol use within 6 hours prior to injury, Mexico City, Mexico, 2002
 

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TABLE 3. Risk of injury according to alcohol use within 6 hours prior to injury and number of drinks consumed, Mexico City, Mexico, 2002
 

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TABLE 4. Risk of injury according to alcohol use within 6 hours prior to injury and diagnosis of alcohol use disorders, Mexico City, Mexico, 2002
 


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FIGURE 1. Relative risk of injury according to alcohol use within 6 hours prior to injury, by time of consumption, Mexico City, Mexico, 2002. Bars, 95% confidence interval.

 

    RESULTS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Of the 705 injury patients who agreed to participate, 122 (17 percent of the sample) reported having consumed alcohol within 6 hours prior to injury. As table 1 shows, the prevalence of alcohol use within this period was higher among males, younger patients, those who were single, those with higher incomes, and those who visited the emergency department because of an intentional self-inflicted injury or an intentional injury inflicted by someone else. Among patients with unintentional injuries (the largest group of patients), 54 percent of injuries were from falls and approximately 14 percent were from blunt force or the result of a stab, cut, or bite (not shown). Less than 10 percent of patients were victims of vehicular accidents. Sixty percent of heavy drinkers and 55 percent of those meeting the criteria for alcohol use disorders reported having used alcohol within 6 hours prior to injury.

As table 2 shows, there was an increase in the relative risk of injury for all control time periods with both the matched pair approach and the usual frequency approach. The highest estimated relative risk of injury was obtained with the usual frequency approach; it was well above the estimates obtained from all matched pair analyses. The lowest relative risk estimate was for drinking on the same day in the previous month. The multiple matching approach, which takes all three matched pair time periods into account, provided an intermediate relative risk estimate.

Relative risk of injury was also estimated for subgroups of patients on the basis of the multiple matching approach for any alcohol use during the exposure period and the three comparison periods (not shown). The relative risk for females was 1.9 (95 percent confidence interval (CI): 0.9, 3.8), as compared with 4.8 (95 percent CI: 3.3, 6.9) for males (chi-squared test for homogeneity of the relative risks: {chi}2 = 5.29; p = 0.02). The relative risk for patients under age 30 years was 5.0 (95 percent CI: 3.3, 7.6), as compared with 2.6 (95 percent CI: 1.5, 4.4) for older patients ({chi}2 = 3.77; p = 0.05). Patients with an unintentional injury had a relative risk of 2.5 (95 percent CI: 1.7, 3.7), as compared with risks of 12.8 (95 percent CI: 1.5, 108.9) for those with an intentional self-inflicted injury and 9.9 (95 percent CI: 4.9, 19.8) for those with an injury inflicted by someone else ({chi}2 = 12.69; p = 0.005).

We also performed sensitivity analyses for the usual frequency approach, changing the hypothesized physiologic effect of alcohol from 1 hour per drink to 2 hours per drink and one-half hour per drink (not shown). Relative risks were 6.2 (95 percent CI: 5.5, 7.0) and 28.1 (95 percent CI: 22.3, 35.6), respectively.

We analyzed the dose-response relation between alcohol drinking and injury risk using the three control periods and multiple matching (table 3). For all time periods, there appeared to be a general trend of an increase in the estimated relative risk with an increase in alcohol consumption above one drink during the 6-hour period prior to injury.

We evaluated whether alcohol use disorders (abuse or dependence) were effect modifiers of the risk associated with any alcohol use, across all control periods. As table 4 shows, relative risks were similar regardless of the presence of alcohol use disorders, and p values associated with the chi-squared test for heterogeneity were high, suggesting that relative risk estimates were homogenous for all control periods. The usual frequency approach, however, showed a higher relative risk among patients who were free of alcohol use disorders (relative risk (RR) = 15.92) in comparison with patients with alcohol dependence (RR = 9.97) or abuse (RR = 9.20), though the p value for the test of heterogeneity (p = 0.133) was not significant. However, given the low power of this test (25), the lack of significance should be interpreted with caution.

Analysis of the risks of injury associated with alcohol abuse and dependence according to the amount of alcohol consumed was not possible because of sparse data. Therefore, categories for alcohol abuse and dependence were collapsed, as were categories for alcohol consumption (0–1 drink was the reference category). We found a dose-response relation similar to the one presented in table 3. Relations were similar for patients with and without alcohol use disorders, and there was no evidence of heterogeneity of relative risks across alcohol use disorders and numbers of drinks (not shown).

Figure 1 shows relative risk estimates on an hour-by-hour basis obtained with the usual frequency approach. The largest effect was found for alcohol consumption during the first hour preceding injury (RR = 6.26, 95 percent CI: 4.89, 8.02), followed by a decrease in relative risk during the second hour (RR = 1.76, 95 percent CI: 1.15, 2.70). The relative risk became null for alcohol consumption more than 2 hours prior to injury, suggesting that the induction time for the effect of alcohol use on injury risk is concentrated within the first 2 hours after drinking.


    DISCUSSION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
In this study, we used the case-crossover analytical strategy to assess the relative risk of sustaining an injury within 6 hours following alcohol consumption. Approximately 17 percent of the study sample reported using alcohol during the exposure period, and the estimated relative risk was 3.97 with a multiple matching approach. This result is consistent with findings from previous case-crossover and cross-sectional studies (17, 26). Most of the increase in the relative risk was concentrated within the first 2 hours after drinking, a finding compatible with the relative risk of 4.3 reported previously (18) but divergent from the finding of Vinson et al. (17), who reported no difference in relative risk on an hour-by-hour basis. While patients who reported consuming only one drink prior to injury generally had no increase in risk, increases in consumption were associated with increasing relative risks of injury, ranging from 3.5 for 2–3 drinks during the 6-hour period to 8.0 for six or more drinks, using a multiple matching approach. Dose-response estimates obtained here for low-level drinking were well below the risk level reported previously in a population-based case-control study (15).

Contrary to previous research (18), in both the matched pair and usual frequency analyses described here, we found no significant effect modification across levels of alcohol use disorders. These data suggest that all patients, regardless of the presence of alcohol abuse or dependence, are at similar risks of sustaining an injury following short-term alcohol exposure. Large variations in relative risk were found by cause of injury, with a greater relative risk among intentional injuries, especially those that were self-inflicted. It is unlikely that similar mechanisms are involved in the proposed relation between acute alcohol exposure and injury occurrence across all types of injury. We are planning to conduct future analyses using the full set of data from all emergency departments participating in the WHO Collaborative Study on Alcohol and Injuries. These analyses will enable us to provide more accurate estimates for a wider range of injury types (motor vehicle accidents, violence-related injuries, etc.). We also plan to take into account types of alcoholic beverages across emergency department sites.

Because we used the case-crossover study design, the increase in the relative risk of injury reported here cannot be attributed to between-person confounding, such as confounding by age, gender, or other fixed variables that are more difficult to define and measure in the context of injury, such as risk-taking behavior. Confounding by transient factors within an individual can occur if these factors are associated with the time at which drinking takes place, but it is unlikely that such factors could account for all of the associations reported here. On the other hand, relative risk estimates from case-crossover studies should be interpreted only as reflections of short-term change in the baseline risk associated with alcohol use and should not be confused with the chronic effect that alcohol consumption may have on injury occurrence (27).

This study was limited to a single emergency department in Mexico City. Although the study design provided us with a representative sample of patients from that facility, those patients may not be representative of other emergency departments in the city or the country. As with other emergency department studies, these cases also cannot be assumed to be representative of injured persons who do not seek medical attention. Because of the sample size, analysis of numbers of drinks consumed and specific alcohol use disorders was precluded. All results reported here were based on the patient’s self-reported alcohol consumption for differing time frames, and it is possible that patients were more likely to recall with exactitude their consumption immediately prior to an injury event than for any other previous period. On the other hand, there is no reason why patients would overestimate their drinking prior to an injury, as compared with any other time period asked about here. An effort was made to try to compensate for possible recall bias by using four different control time periods, ranging from the day prior to the injury to the usual frequency and quantity of drinking in the past 12 months. Nevertheless, results were similar across all time periods, which suggests that findings of an increased relative risk of injury for persons who reported drinking prior to the injury are robust.

These findings could have important public health ramifications by introducing a time dimension into prevention messages addressing alcohol use and its short-term consequences. This may have particular relevance in the prevention of traffic injuries, where educational and community-based interventions designed to reduce driving under the influence of alcohol and well-enforced drunk-driving laws have been successful strategies. If a person decides to drink alcohol, the consumption of increasing amounts may have pronounced effects on his/her risk of triggering an injury. This risk is concentrated mainly within a short-term period (1–2 hours); thus, efforts should be made to provide a safe environment during this time. According to the 2002 World Health Report (3), a 25 percent reduction in alcohol use could result in approximately 15 million fewer disability-adjusted life years in 2010 (3). Since injuries and violence contribute significantly to disability-adjusted life years, this reduction would have a major impact on the magnitude of alcohol-related injuries worldwide.


    ACKNOWLEDGMENTS
 
This study was funded in part by the World Health Organization, the Mexico National Institute of Psychiatry (grant 4275P), the Mexico National Council for Science and Technology (grant CONACYT-39607-H), and the US National Institute on Alcohol Abuse and Alcoholism (grant AA13750-02).

The authors appreciate the efforts and support of the Board of Directors and staff of the Hospital General Dr. Manuel Gea González.

This paper was partially based on data obtained during the WHO Collaborative Study on Alcohol and Injuries. A full list of study investigators and staff is available from the World Health Organization.


    NOTES
 
Correspondence to Dr. Guilherme Borges, Instituto Nacional de Psiquiatría y Universidad Autónoma Metropolitana, Calzada Mexico Xochimilco no. 101, Mexico Distrito Federale CP 10610, Mexico (e-mail: guibor@imp.edu.mx). Back


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 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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