Traumatic brain injury as an independent risk factor for problem gambling: a matched case-control study

PURPOSE

To assess whether traumatic brain injury (TBI) increases the risks of subsequent problem gambling.

METHODS

We conducted a matched case-control analysis of adults in Ontario, Canada. The study included those who self-reported their gambling activities in the Canadian Community Health Survey 2007-2008. Using Problem Gambling Severity Index, we defined cases as those who were problem gamblers and controls who were recreational gamblers. Cases were matched to controls 1:2 using propensity scores based on demographics, prior mental health, and self-reported behaviours. The main predictor was prior TBI defined as requiring emergency care and identified using ICD-10 codes from administrative health databases. We estimated the likelihood of prior TBI in problem gamblers compared to controls using conditional logistic regression.

RESULTS

Of 30,652 survey participants, 16,002 (53%) reported gambling activity of whom 14,910 (49%) were recreational gamblers and 4% (n = 1092) were problem gamblers. A total of 1469 respondents (5%) had a prior TBI. Propensity score matching yielded 2038 matched pairs with 1019 cases matched to 2037 controls. Case-control analysis showed a significant association between prior TBI and subsequent problem gambling (odds ratio 1.27, 95% confidence interval 1.07-1.51, P = 0.007). The increased risk was mostly apparent in men aged 35 to 64 years who reported alcohol use or smoking. The relative risk of problem gambling in those with two or more TBIs equated to an odds ratio of 2.04 (95% confidence interval 1.05-3.99).

CONCLUSIONS

We found that a prior TBI was associated with an increased subsequent risk of problem gambling. Our findings support more awareness, screening, and treating problem gambling risks among TBI patients.

Life-threatening alcohol-related traffic crashes in adverse weather: a double-matched case-control analysis from Canada

IMPORTANCE

Drunk driving is a major cause of death in North America, yet physicians rarely counsel patients on the risks of drinking and driving.

OBJECTIVE

To test whether the risks of a life-threatening alcohol-related traffic crash were further accentuated by adverse weather.

DESIGN

Double matched case-control analysis of hospitalised patients.

SETTING

Canada's largest trauma centre between 1 January 1995 and 1 January 2015.

PARTICIPANTS

Patients hospitalised due to a life-threatening alcohol-related traffic crash.

EXPOSURE

Relative risk of a crash associated with adverse weather estimated by evaluating the weather at the place and time of the crash (cases) compared with the weather at the same place and time a week earlier and a week later (controls).

RESULTS

A total of 2088 patients were included, of whom the majority were drivers injured at night. Adverse weather prevailed among 312 alcohol-related crashes and was significantly more frequent compared with control circumstances. The relative risk of a life-threatening alcohol-related traffic crash was 19% higher during adverse weather compared with normal weather (95% CI: 5 to 35, p=0.006). The absolute increase in risk amounted to 43 additional crashes, extended to diverse groups of patients, applied during night-time and daytime, contributed to about 793 additional patient-days in hospital and was distinct from the risks for drivers who were negative for alcohol.

CONCLUSIONS

Adverse weather was associated with an increased risk of a life-threatening alcohol-related traffic crash. An awareness of this risk might inform warnings to patients about traffic safety and counselling alternatives to drinking and driving.

Fracture Risk After Initiation of Use of Canagliflozin: A Cohort Study

BACKGROUND

Sodium-glucose cotransporter-2 inhibitors promote glycosuria, resulting in possible effects on calcium, phosphate, and vitamin D homeostasis. Canagliflozin is associated with decreased bone mineral density and a potential increased risk for fracture.

OBJECTIVE

To estimate risk for nonvertebral fracture among new users of canagliflozin compared with a glucagon-like peptide-1 (GLP-1) agonist.

DESIGN

Population-based new-user cohort study.

SETTING

Two U.S. commercial health care databases providing data on more than 70 million patients from March 2013 to October 2015.

PATIENTS

Persons with type 2 diabetes who initiated use of canagliflozin were propensity score-matched in a 1:1 ratio to those initiating use of a GLP-1 agonist.

MEASUREMENTS

The primary outcome was a composite end point of humerus, forearm, pelvis, or hip fracture requiring intervention. Secondary outcomes included fractures at other sites. A fixed-effects meta-analysis that pooled results from the 2 databases provided an overall hazard ratio (HR).

RESULTS

79 964 patients initiating use of canagliflozin were identified and matched to 79 964 patients initiating use of a GLP-1 agonist. Mean age was 55 years, 48% were female, average baseline hemoglobin A1c level was 8.7%, and 27% were prescribed insulin. The rate of the primary outcome was similar for canagliflozin (2.2 events per 1000 person-years) and GLP-1 agonists (2.3 events per 1000 person-years), with an overall HR of 0.98 (95% CI, 0.75 to 1.26). Risk for pelvic, hip, humerus, radius, ulna, carpal, metacarpal, metatarsal, or ankle fracture was also similar for canagliflozin (14.5 events per 1000 person-years) and GLP-1 agonists (16.1 events per 1000 person-years) (overall HR, 0.92 [CI, 0.83 to 1.02]).

LIMITATION

Unmeasured confounding, measurement error, and low fracture rate.

CONCLUSION

In this study of middle-aged patients with type 2 diabetes and relatively low fracture risk, canagliflozin was not associated with increased risk for fracture compared with GLP-1 agonists.

PRIMARY FUNDING SOURCE

Brigham and Women's Hospital, Division of Pharmacoepidemiology and Pharmacoeconomics.

Association of Duration of Surgery With Postoperative Delirium Among Patients Receiving Hip Fracture Repair

IMPORTANCE

Postoperative delirium in older adults receiving hip fracture surgery is associated with morbidity and increased health care costs, yet little is known of potential modifiable factors that may help limit the risks.

OBJECTIVE

To use population-wide individual-level data on the duration of hip fracture surgery to determine whether prolonged surgical times and type of anesthesia are associated with an increased risk of postoperative delirium.

DESIGN, SETTING, AND PARTICIPANTS

This retrospective population-based cohort study analyzed patients aged 65 years and older receiving hip fracture surgery between April 1, 2009, and March 30, 2017, at 80 hospitals in Ontario, Canada. Generalized estimated equations with logistic regression analysis were used to determine the relationship between procedure duration, type of anesthesia, and the occurrence of postoperative delirium. Restricted cubic splines were also generated to visualize this relationship. Data analysis was conducted from July to October 2018, revision in January 2019.

EXPOSURE

Surgery duration, measured as the total time in the operating room.

MAIN OUTCOMES AND MEASURES

A diagnosis of postoperative delirium during hospitalization.

RESULTS

Among 68 131 patients with surgically managed hip fracture (median [interquartile range] age, 84 [78-89] years; 72% women) identified, 7150 patients experienced postoperative delirium. In total, 26 853 patients (39.4%) received general anesthesia. Receiving general anesthesia was associated with a slightly higher rate of postoperative delirium compared with not receiving general anesthesia (2943 [11.0%] vs 4207 [10.2%]; P = .001). The risk for delirium increased with increased surgical duration-every 30-minute increase in the duration of surgery was associated with a 6% increase in the risk for delirium (adjusted odds ratio, 1.06; 95% CI, 1.03-1.08; P < .001). Prolonged surgical duration was associated with a higher incidence of postoperative delirium, and the risk was higher was in patients who had received general anesthesia (adjusted odds ratio, 1.08; 95% CI, 1.04-1.12; P < .001) than in those patients who did not receive GA (adjusted odds ratio, 1.04; 95% CI, 1.01-1.08; P = .01).

CONCLUSIONS AND RELEVANCE

Among older adults receiving hip fracture surgery, both an increased duration of surgery and receiving a general anesthetic were associated with an increased risk for postoperative delirium.

Pedestrian Fatalities Associated With Halloween in the United States

This study examines 42 years of National Highway Traffic Safety Administration data to establish whether Halloween is associated with an increased rate of pedestrian fatalities.

Increased Risk of Traffic Injury After a Cerebrovascular Event

Background and Purpose- We aimed to determine the long-term risks of a motor vehicle collision after a cerebrovascular event and whether the risks were similar after left- or right-hemispheric events. Methods- We used a population-based registry to identify patients diagnosed with a transient ischemic attack or stroke (hemorrhagic or ischemic) between 2003 and 2013 in Ontario, Canada. Hemispheric laterality was determined using radiological and clinical findings. We identified subsequent serious injuries involving the patient as a driver using linked administrative data. Secondary outcomes included serious injuries involving the patient as a pedestrian, as a passenger, or other traumatic events (fall, fracture, ankle sprain). We used proportional hazard models accounting for death as a competing risk to test the association of hemispheric laterality and outcomes with and without adjustment for age, sex, discharge modified Rankin Scale score, home location, and prior driving record. Patients were followed through to 2017. Results- Among 26 144 patients with hemispheric cerebrovascular events, 377 subsequent serious traffic injuries as a driver (2.2 per 1000 person-year) were identified over a median follow-up of 6.4 person-years. The rate did not differ by laterality (adjusted hazard ratio, 1.00; 95% CI, 0.82-1.23). The risk of a serious traffic injury as a pedestrian was significantly higher after a right-sided than left-sided event (adjusted hazard ratio, 1.27; 95% CI, 1.02-1.58). Subsequent risks for other traumatic injuries did not differ by laterality of cerebrovascular event. Conclusions- The risk of a serious traffic injury as a pedestrian is substantially higher after a right-hemispheric cerebrovascular event compared with a left-sided event. Walking should be promoted for exercise in survivors of a stroke or transient ischemic attack, but these vulnerable road users may benefit from additional poststroke rehabilitation to optimize safety.

Death and readmissions after hospital discharge during the December holiday period: cohort study

OBJECTIVE

To determine whether patients discharged from hospital during the December holiday period have fewer outpatient follow-ups and higher rates of death or readmission than patients discharged at other times.

DESIGN

Population based retrospective cohort study.

SETTING

Acute care hospitals in Ontario, Canada, 1 April 2002 to 31 January 2016.

PARTICIPANTS

217 305 children and adults discharged home after an urgent admission, during the two week December holiday period, compared with 453 641 children and adults discharged during two control periods in late November and January.

MAIN OUTCOME MEASURES

The primary outcome was death or readmission, defined as a visit to an emergency department or urgent rehospitalisation, within 30 days. Secondary outcomes were death or readmission and outpatient follow-up with a physician within seven and 14 days after discharge. Multivariable logistic regression with generalised estimating equations was used to adjust for characteristics of patients, admissions, and hospital.

RESULTS

217 305 (32.4%) patients discharged during the holiday period and 453 641 (67.6%) discharged during control periods had similar baseline characteristics and previous healthcare utilisation. Patients who were discharged during the holiday period were less likely to have follow-up with a physician within seven days (36.3% v 47.8%, adjusted odds ratio 0.61, 95% confidence interval 0.60 to 0.62) and 14 days (59.5% v 68.7%, 0.65, 0.64 to 0.66) after discharge. Patients discharged during the holiday period were also at higher risk of 30 day death or readmission (25.9% v 24.7%, 1.09, 1.07 to 1.10). This relative increase was also seen at seven days (13.2% v 11.7%, 1.16, 1.14 to 1.18) and 14 days (18.6% v 17.0%, 1.14, 1.12 to 1.15). Per 100 000 patients, there were 2999 fewer follow-up appointments within 14 days, 26 excess deaths, 188 excess hospital admissions, and 483 excess emergency department visits attributable to hospital discharge during the holiday period.

CONCLUSIONS

Patients discharged from hospital during the December holiday period are less likely to have prompt outpatient follow-up and are at higher risk of death or readmission within 30 days.

Eczema and subsequent suicide: a matched case-control study

OBJECTIVE

To assess the association of eczema with a patient's subsequent risk of death from suicide. We hypothesised that persistent eczema would be associated with an increased risk for death from suicide.

DESIGN

Double matched case-control study.

SETTING

General population of Ontario, Canada.

PARTICIPANTS

Patients 15-55 years old. We identified cases of suicide from coroners' reports between 1 January 1994 and 31 December 2014 and matched 1:2 with alive controls based on age, sex and socioeconomic status.

EXPOSURE

The primary predictor was a history of persistent eczema, defined as five or more physician visits for the diagnosis over the preceding 5 years.

MAIN OUTCOME AND MEASURE

Logistic regression to estimate the association between eczema and death from suicide.

RESULTS

We identified 18 441 cases of suicide matched to 36 882 controls over the 21-year accrual period. Persistent eczema occurred in 174 (0.94%) suicide cases and 285 (0.77%) controls yielding a 22% increased risk of suicide associated with persistent eczema (OR 1.22, 95% CI 1.01 to 1.48, p=0.037). In mediation analyses, this association was largely explained through major suicide risk factors. Two-thirds of patients with eczema who died from suicide had visited a physician in the month before their death and one in eight had visited for eczema in the month before their death. Among patients who died by suicide, jumping and poisoning were relatively more frequent mechanisms among patients with eczema.

CONCLUSIONS

Patients with persistent eczema have a modestly increased subsequent risk of death from suicide, but this is not independent of overall mental health and the absolute risk is low. Physicians caring for these patients have opportunities to intervene for suicide prevention.

Medical Emergencies in Farmers

BACKGROUND

Agricultural work involves hazards that may harm long-term well-being. We evaluated the risk of long-term disability and death for agricultural workers compared to construction workers with similar demographics. We hypothesized that delays to emergency care and subsequent long-term disability following injury might be worse for agricultural workers compared to those injured in construction.

METHODS

We evaluated all adults severely injured on farms or on construction sites in Ontario, Canada, between April 1, 2009, and March 31, 2012, according to the Ontario Trauma Registry. We excluded individuals living outside of the province, those missing a valid health card number, or youth less than 17 years old. Our primary outcome was death or the subsequent application for disability support.

RESULTS

In total, 353 patients were injured on a farm or construction site during the study period. Delays to emergency care exceeding 12 hours were more frequent for agricultural workers compared to construction workers (43% vs 23%, P <.001). After a 5-year follow-up, agricultural workers had a death or disability rate marginally higher than construction workers (23% vs 14%, P = .068), equivalent to a hazard ratio of 1.62 that was marginally statistically significant (95% confidence interval 0.96-2.75, P = .072). The risk of death and disability was greatest for patients who had the longest delays to emergency care.

INTERPRETATION

Agricultural workers experience a substantial delay in receiving emergency care and a marginally higher risk of death or disability in the years following injury compared to construction workers.

Mediation analysis with a time-to-event outcome: a review of use and reporting in healthcare research

BACKGROUND

Mediation analysis tests whether the relationship between two variables is explained by a third intermediate variable. We sought to describe the usage and reporting of mediation analysis with time-to-event outcomes in published healthcare research.

METHODS

A systematic search of Medline, Embase, and Web of Science was executed in December 2016 to identify applications of mediation analysis to healthcare research involving a clinically relevant time-to-event outcome. We summarized usage over time and reporting of important methodological characteristics.

RESULTS

We included 149 primary studies, published from 1997 to 2016. Most studies were published after 2011 (n = 110, 74%), and the annual number of studies nearly doubled in the last year (from n = 21 to n = 40). A traditional approach (causal steps or change in coefficient) was most commonly taken (n = 87, 58%), and the majority of studies (n = 114, 77%) used a Cox Proportional Hazards regression for the outcome. Few studies (n = 52, 35%) mentioned any of the assumptions or limitations fundamental to a causal interpretation of mediation analysis.

CONCLUSION

There is increasing use of mediation analysis with time-to-event outcomes. Current usage is limited by reliance on traditional methods and the Cox Proportional Hazards model, as well as low rates of reporting of underlying assumptions. There is a need for formal criteria to aid authors, reviewers, and readers reporting or appraising such studies.

Association of Cataract Surgery With Traffic Crashes

Importance

Cataracts are the most common cause of impaired vision worldwide and may increase a driver's risk of a serious traffic crash. The potential benefits of cataract surgery for reducing a patient's subsequent risk of traffic crash are uncertain.

Objective

To conduct a comprehensive longitudinal analysis testing whether cataract surgery is associated with a reduction in serious traffic crashes where the patient was the driver.

Design, Setting, and Participants

Population-based individual-patient self-matching exposure-crossover design in Ontario, Canada, between April 1, 2006, and March 31, 2016. Consecutive patients 65 years and older undergoing cataract surgery (n = 559 546).

Interventions

First eye cataract extraction surgery (most patients received second eye soon after).

Main Outcomes and Measures

Emergency department visit for a traffic crash as a driver.

Results

Of the 559 546 patients, mean (SD) age was 76 (6) years, 58% were women (n = 326 065), and 86% lived in a city (n = 481 847). A total of 4680 traffic crashes (2.36 per 1000 patient-years) accrued during the 3.5-year baseline interval and 1200 traffic crashes (2.14 per 1000 patient-years) during the 1-year subsequent interval, representing 0.22 fewer crashes per 1000 patient-years following cataract surgery (odds ratio [OR], 0.91; 95% CI, 0.84-0.97; P = .004). The relative reduction included patients with diverse characteristics. No significant reduction was observed in other outcomes, such as traffic crashes where the patient was a passenger (OR, 1.03; 95% CI, 0.96-1.12) or pedestrian (OR, 1.02; 95% CI, 0.88-1.17), nor in other unrelated serious medical emergencies. Patients with younger age (OR, 1.27; 95% CI, 1.13-1.14), male sex (OR, 1.64; 95% CI, 1.46-1.85), a history of crash (baseline OR, 2.79; 95% CI, 1.94-4.02; induction OR, 4.26; 95% CI, 2.01-9.03), more emergency visits (OR, 1.34; 95% CI, 1.19-1.52), and frequent outpatient physician visits (OR, 1.17; 95% CI, 1.01-1.36) had higher risk of subsequent traffic crashes (multivariable model).

Conclusions and Relevance

This study suggests that cataract surgery is associated with a modest decrease in a patient's subsequent risk of a serious traffic crash as a driver, which has potential implications for mortality, morbidity, and costs to society.

The April 20 Cannabis Celebration and Fatal Traffic Crashes in the United States

This data analysis examines the association between the April 20 cannabis celebrations in the United States and a population-level increase in the risk of fatal traffic crash involvement.

Optical illusions and life-threatening traffic crashes: A perspective on aerial perspective

Aerial perspective illusion is a feature of visual perception where landscapes appear relatively close in clear light and distant in dim light. We hypothesized that bright sunlight might cause drivers to perceive distant terrain as relatively close and misinterpret the approach speed of surrounding landscape as unduly slow. This hypothesis would mean, in turn, that drivers in bright sunlight may underestimate their progress on the road, compensate by traveling at a faster baseline speed, and ultimately increase the prevailing risk of a life-threatening traffic crash. We conducted three pilot studies to illustrate how the illusion might contribute to a life- threatening traffic crash. The first illustration used a questionnaire to demonstrate that most respondents were mistaken when judging the distance between simple balls in different positions. The second illustration involved an experimental manipulation to assess whether aerial perspective influenced judgments about the relative positions of vehicles in traffic. The third illustration analyzed a segment of high-volume fast-speed traffic and found an increased frequency of speeding under bright sunlight. Together with past work based on the visual arts, these examples illustrate how an aerial perspective illusion can affect distance perception, may appear in realistic traffic situations, and could potentially contribute to the risk of a life-threatening traffic crash. An awareness of this hypothesis might lead to applications on how optical illusions could extend to everyday traffic and might potentially inform safety warnings to prevent life- threatening crashes.

Methods for analyzing matched designs with double controls: excess risk is easily estimated and misinterpreted when evaluating traffic deaths

OBJECTIVES

To demonstrate analytic approaches for matched studies where two controls are linked to each case and events are accumulating counts rather than binary outcomes. A secondary intent is to clarify the distinction between total risk and excess risk (unmatched vs. matched perspectives).

STUDY DESIGN AND SETTING

We review past research testing whether elections can lead to increased traffic risks. The results are reinterpreted by analyzing both the total count of individuals in fatal crashes and the excess count of individuals in fatal crashes, each time accounting for the matched double controls.

RESULTS

Overall, 1,546 individuals were in fatal crashes on the 10 election days (average = 155/d), and 2,593 individuals were in fatal crashes on the 20 control days (average = 130/d). Poisson regression of total counts yielded a relative risk of 1.19 (95% confidence interval: 1.12-1.27). Poisson regression of excess counts yielded a relative risk of 3.22 (95% confidence interval: 2.72-3.80). The discrepancy between analyses of total counts and excess counts replicated with alternative statistical models and was visualized in graphical displays.

CONCLUSION

Available approaches provide methods for analyzing count data in matched designs with double controls and help clarify the distinction between increases in total risk and increases in excess risk.

Patterns in Patient Access and Utilization of Online Medical Records: Analysis of MyChart

BACKGROUND

Electronic patient portals provide a new method for sharing personal medical information with individual patients.

OBJECTIVE

Our aim was to review utilization patterns of the largest online patient portal in Canada's largest city.

METHODS

We conducted a 4-year time-trend analysis of aggregated anonymous utilization data of the MyChart patient portal at Sunnybrook Health Sciences Centre in Ontario, Canada, from January 1, 2012, through December 31, 2015. Prespecified analyses examined trends related to day (weekend vs weekday), season (July vs January), year (2012 vs 2015), and an extreme adverse weather event (ice storm of December 20-26, 2013). Primary endpoints included three measures of patient portal activity: registrations, logins, and pageviews.

RESULTS

We identified 32,325 patients who registered for a MyChart account during the study interval. Time-trend analysis showed no sign of attenuating registrations over time. Logins were frequent, averaged 734 total per day, and showed an increasing trend over time. Pageviews mirrored logins, averaged about 3029 total per day, and equated to about 5 pageviews during the average login. The most popular pageviews were clinical notes, followed by laboratory results and medical imaging reports. All measures of patient activity were lower on weekends compared to weekdays (P<.001) yet showed no significant changes related to seasons or extreme weather. No major security breach, malware attack, or software failure occurred during the study.

CONCLUSIONS

Online patient portals can provide a popular and reliable system for distributing personal medical information to active patients and may merit consideration for hospitals.

The full moon and motorcycle related mortality: population based double control study

OBJECTIVE

To test whether a full moon contributes to motorcycle related deaths.

DESIGN

Population based, individual level, double control, cross sectional analysis.

SETTING

Nighttime (4 pm to 8 am), United States.

PARTICIPANTS

13 029 motorcycle fatalities throughout the United States, 1975 to 2014 (40 years).

MAIN OUTCOME MEASURE

Motorcycle fatalities during a full moon.

RESULTS

13 029 motorcyclists were in fatal crashes during 1482 relevant nights. The typical motorcyclist was a middle aged man (mean age 32 years) riding a street motorcycle with a large engine in a rural location who experienced a head-on frontal impact and was not wearing a helmet. 4494 fatal crashes occurred on the 494 nights with a full moon (9.10/night) and 8535 on the 988 control nights without a full moon (8.64/night). Comparisons yielded a relative risk of 1.05 associated with the full moon (95% confidence interval 1.02 to 1.09, P=0.005), a conditional odds ratio of 1.26 (95% confidence interval 1.17 to 1.37, P<0.001), and an absolute increase of 226 additional deaths over the study interval. The increase extended to diverse types of motorcyclists, vehicles, and crashes; was accentuated during a supermoon; and replicated in analyses from the United Kingdom, Canada, and Australia.

CONCLUSION

The full moon is associated with an increased risk of fatal motorcycle crashes, although potential confounders cannot be excluded. An awareness of the risk might encourage motorcyclists to ride with extra care during a full moon and, more generally, to appreciate the power of seemingly minor distractions at all times.

Direct medical costs of motorcycle crashes in Ontario

BACKGROUND

There is no reliable estimate of costs incurred by motorcycle crashes. Our objective was to calculate the direct costs of all publicly funded medical care provided to individuals after motorcycle crashes compared with automobile crashes.

METHODS

We conducted a population-based, matched cohort study of adults in Ontario who presented to hospital because of a motorcycle or automobile crash from 2007 through 2013. For each case, we identified 1 control absent a motor vehicle crash during the study period. Direct costs for each case and control were estimated in 2013 Canadian dollars from the payer perspective using methodology that links health care use to individuals over time. We calculated costs attributable to motorcycle and automobile crashes within 2 years using a difference-in-differences approach.

RESULTS

We identified 26 831 patients injured in motorcycle crashes and 281 826 injured in automobile crashes. Mean costs attributable to motorcycle and automobile crashes were $5825 and $2995, respectively (p < 0.001). The rate of injury was triple for motorcycle crashes compared with automobile crashes (2194 injured annually/100 000 registered motorcycles v. 718 injured annually/100 000 registered automobiles; incidence rate ratio [IRR] 3.1, 95% confidence interval [CI] 2.8 to 3.3, p < 0.001). Severe injuries, defined as those with an Abbreviated Injury Scale ≥ 3, were 10 times greater (125 severe injuries annually/100 000 registered motorcycles v. 12 severe injuries annually/100 000 registered automobiles; IRR 10.4, 95% CI 8.3 to 13.1, p < 0.001).

INTERPRETATION

Considering both the attributable cost and higher rate of injury, we found that each registered motorcycle in Ontario costs the public health care system 6 times the amount of each registered automobile. Medical costs may provide an additional incentive to improve motorcycle safety.