Interpretation and bias in case-crossover studies

Dust storms and cardiorespiratory emergency department visits in three Southwestern United States: application of a monitoring-based exposure metric

Climate change is projected to increase the risk of dust storms, particularly in subtropical dryland, including the southwestern US. Research on dust storm's health impacts in the US is limited and hindered by challenges in dust storm identification. This study assesses the potential link between dust storms and cardiorespiratory emergency department (ED) visits in the southwestern US. We acquired data for 2005-2016 from eight IMPROVE (Interagency Monitoring of PROtected Visual Environments) sites in Arizona, California, and Utah. We applied a validated algorithm to identify dust storm days at each site. We acquired patient-level ED visit data from state agencies and ascertained visits for respiratory, cardiovascular, and cause-specific subgroups among patients residing in ZIP codes within 50 km of an IMPROVE site. Using a case-crossover design, we estimated short-term associations of ED visits and dust storms, controlling for temporally varying covariates. During 2005-2016, 40 dust storm days occurred at the eight IMPROVE sites. Mean PM10 and PM2.5 levels were three to six times greater on dust storm days compared to non-dust storm days. Over the study period, there were 2 524 259 respiratory and 2 805 925 cardiovascular ED visits. At lags of 1, 2, and 3 days after a dust storm, we observed 3.7% (95% CI: 1.0%, 7.6%), 4.9% (95% CI: 1.1%, 8.9%), and 5.0% (95% CI: 1.3%, 8.9%) elevated odds of respiratory ED visits compared to non-dust storm days. Estimated associations of dust storm days and cardiovascular disease ED visits were largely consistent with the null. Using a monitoring-based exposure metric, we observed associations among dust storms and respiratory ED visits. The results add to growing evidence of the health threat posed by dust storms. The dust storm metric was limited by lack of daily data; future research should consider information from satellite and numerical models to enhance dust storm characterization.

Differences in risk factors for flare-ups in patients with lumbar radicular pain may depend on the definition of flare

OBJECTIVES

The objective was to determine whether specific physical activity (PA) or psychological stress factors are associated with different definitions of flare-ups (pain-defined flares [PDFs]: periods of increased pain lasting at least 2 h, when pain intensity is distinctly worse than it has been recently; and non-pain-defined flares [NPDFs]: obviously uncomfortable feelings, such as fatigue, loss of function, or emotional/psychosocial fluctuations, without major fluctuations in pain intensity based on 11-point scales) among people with lumbar radicular pain.

METHODS

This was a case-crossover study. Participants with acute or subacute lumbar radicular pain completed serial face-to-face or online assessments for 6 weeks at 3-day intervals to determine whether they experienced sciatica flare-ups (PDF/NPDF) after specific types of PA or psychological stresses.

RESULTS

A total of 152 participants were enroled. There were 597 PDF and 323 NPDF case periods and 800 control periods. The odds of PDFs were increased by prolonged walking and standing, and the odds of NPDFs were increased by prolonged sitting, mental distress, and depressed mood. According to the multivariable analyses, prolonged sitting (OR: 3.0, 95% CI: 1.7-5.5), prolonged walking (OR: 6.2, 95% CI: 3.9-9.9), and prolonged standing (OR: 5.6, 95% CI: 3.3-9.5) were significantly associated with the odds of PDFs, and prolonged sitting (OR: 3.4, 95% CI: 1.8-6.2), mental distress (OR: 6.7, 95% CI: 2.5-17.5), and depressed mood (OR: 5.8, 95% CI: 2.6-12.8) associated with the odds of NPDFs.

CONCLUSIONS

Prolonged sitting, walking, and standing triggered the occurrence of PDF. Prolonged sitting, mental distress, and depressed mood triggered the occurrence of NPDF.

Best practices for interviewing applicants for medical school admissions: a systematic review

INTRODUCTION

Interviews are commonly used to select applicants for medical school, residency, and fellowship. However, interview techniques vary in acceptability, feasibility, reliability, and validity. This systematic review investigated the effectiveness of different interview methods in selecting the best qualified applicants for admission to medical school and developed a logic model to implement best practices for interviewing.

METHODS

Five electronic literature databases were searched for comparative studies related to interviewing in medical schools from inception through February 1, 2021. Inclusion criteria included publications in English that compared different methods of conducting a selection interview in medical schools with a controlled trial design. General study characteristics, measurement methodologies, and outcomes were reviewed. Quality appraisal was performed using the Medical Education Research Study Quality Instrument (MERSQI) and the Oxford Risk of Bias Scale. Based on these findings, a logic model was constructed using content analysis.

RESULTS

Thirteen studies were included. The multiple mini-interview (MMI) was reliable, unbiased, and predicted clinical and academic performance; the virtual MMI increased reliability and lowered costs. For unstructured interviews, blinding interviewers to academic scores reduced bias towards higher scorers; student and faculty interviewers rated applicants similarly. Applicants preferred structured over unstructured interviews. Study quality was above average per the MERSQI, risk of bias was high per the Oxford scale, and between-study heterogeneity was substantial.

DISCUSSION

There were few high-quality studies on interviewing applicants for admission to medical school; the MMI appears to offer a reliable method of interviewing. A logic model can provide a conceptual framework for conducting evidence-based admissions interviews.

How many crashes does cellphone use contribute to? Population attributable risk of cellphone use while driving

BACKGROUND

Cellphone distraction is a major contributing factor for traffic crashes, a leading cause of death worldwide. The novel naturalistic driving study (NDS) study with continuously collected in situ driving videos provides an opportunity to accurately estimate the safety impact of cellphone distraction.

METHODS

We apply a case-cohort study design to the Second Strategic Highway Research Program NDS, the largest NDS up-to-date with more than 3400 participants. The data include with 842 level 1-3 crashes and 19,338 randomly selected control driving segments. We propose a partial Population Attributable Risk (PAR) estimator that provides consistent and stable estimation over time and across different driving behaviors.

RESULTS

The US population-adjusted PAR show that 8% of crashes (PAR = 0.08, 95 %CI: [0.06, 0.19]) can be reduced if cellphone distraction were switched to sober, alert, and attentive driving behavior. Young adults (age 20-29 years) and middle-aged drivers (age 30-64 years) each contribute 39% of the population level PAR. Within each age group, the PARs vary substantially from 18% for young adult drivers to 5% for middle-aged drivers. The contribution of cellphone visual-manual tasks to crashes is more than 4 times larger than cellphone talking and accounts for 87.5% of cellphone-related crashes (PAR = 0.07).

CONCLUSIONS

Cellphone distraction contributes to a considerable part of crashes. Young drivers are more susceptible to the influence of cellphone distraction and visual-manual distraction accounts for the majority of cellphone-related crashes.

Matters of the Heart: Case-Crossover Analysis of Myocardial Infarction on Valentine's Day

We studied the risk of myocardial infarction on Valentine's Day. We conducted a case-crossover study of 51,450 adults with myocardial infarctions in February, 1989-2019. The exposure was Valentine's Day, and the 2 days before and after Valentine's Day. We estimated odds ratios (OR) to compare days when myocardial infarction occurred with neighboring control days. Compared with other days, Valentine's Day was associated with lower odds of myocardial infarction the following day for men (OR 0.91, 95% confidence interval 0.85-0.98), but not for men and women combined (OR 0.95, 95% confidence interval 0.91-1.01). Risk of myocardial infarction in men is lower the day after Valentine's Day.

Methodological considerations in MVC epidemiological research

Background

The global burden of MVC injuries and deaths among vulnerable road users, has led to the implementation of prevention programmes and policies at the local and national level. MVC epidemiological research is key to quantifying MVC burden, identifying risk factors and evaluating interventions. There are, however, several methodological considerations in MVC epidemiological research.

Methods

This manuscript collates and describes methodological considerations in MVC epidemiological research, using examples drawn from published studies, with a focus on the vulnerable road user population of children and adolescents.

Results

Methodological considerations in MVC epidemiological research include the availability and quality of data to measure counts and calculate event rates and challenges in evaluation related to study design, measurement and statistical analysis. Recommendations include innovative data collection (eg, naturalistic design, stepped-wedge clinical trials), combining data sources for a more comprehensive representation of collision events, and the use of machine learning/artificial intelligence for large data sets.

Conclusions

MVC epidemiological research can be challenging at all levels: data capture and quality, study design, measurement and analysis. Addressing these challenges using innovative data collection and analysis methods is required.

Full moon and traffic accident-related emergency ambulance transport: A nationwide case-crossover study

BACKGROUND

Several studies have examined the association between environmental factors and traffic accidents. However, the role of a full moon in triggering emergency ambulance transport due to road traffic casualties is unclear. Thus, we aimed to examine whether a full moon contributes to the incidence of emergency transport due to road traffic crashes.

METHODS

We acquired nationwide data on daily emergency transport due to road traffic crashes from all 47 prefectures of Japan from 2010 to 2014. We conducted a time-stratified case-crossover study using conditional Poisson regression to examine the relationship between the occurrence of a full moon and emergency transport due to road traffic crashes for each prefecture. Prefecture-level results were combined using a random-effects meta-analysis to evaluate nation-level estimates.

RESULTS

There were 842,554 cases of emergency transport due to road traffic crashes across 1826 nights (62 full moon nights: n = 29,584; 1764 control nights: n = 812,970). On days with a full moon, the pooled adjusted relative risk (RR) of emergency transport due to traffic accidents was 1.042 (95% confidence interval [CI], 1.021-1.063). Overall, 4.03% (95% CI: 2.06-5.93) of the cases (1192 cases) were attributable to full moon nights. Stratified analyses revealed a significant increase in emergency transport due to traffic accidents on full moon nights for males, people aged ≥40 years, and before midnight.

CONCLUSIONS

Full moon nights are associated with an increase in the incidence of emergency transport due to road traffic crashes. These results indicate that public health strategies should account for full moon nights to decrease emergency transport due to traffic accidents.

Do Physical Activities Trigger Flare-ups During an Acute Low Back Pain Episode?: A Longitudinal Case-Crossover Feasibility Study

STUDY DESIGN

Prospective, longitudinal case-crossover study.

OBJECTIVE

The aim of this study was to determine whether physical activities trigger flare-ups of pain during the course of acute low back pain (LBP).

SUMMARY OF BACKGROUND DATA

.: There exist no evidence-based estimates for the transient risk of pain flare-ups associated with specific physical activities, during acute LBP.

METHODS

Participants with LBP of duration <3 months completed frequent, Internet-based serial assessments at both 3- and 7-day intervals for 6 weeks. At each assessment, participants reported whether they had engaged in specific physical activity exposures, or experienced stress or depression, during the past 24 hours. Participants also reported whether they were currently experiencing a LBP flare-up, defined as "a period of increased pain lasting at least 2 hours, when your pain intensity is distinctly worse than it has been recently." Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for associations between potential triggers during the past 24 hours, and the risk of LBP flare-ups, using conditional logistic regression.

RESULTS

Of 48 participants followed longitudinally, 30 participants had both case ("flare") and control periods and contributed data to the case-crossover analysis. There were 81 flare periods and 247 control periods, an average of 11 periods per participant. Prolonged sitting (>6 hours) was the only activity that was significantly associated with flare-ups(OR 4.4, 95% CI 2.0-9.7; P < 0.001). Having either stress or depression was also significantly associated with greater risk of flare-ups (OR 2.5, 95% CI 1.0-6.0; P = 0.04). In multivariable analyses, prolonged sitting (OR 4.2, 95% CI 1.9-9.1; P < 0.001), physical therapy (PT) (OR 0.4, 95% CI 0.1-1.0; P = 0.05), and stress/depression (OR 2.8, 95% CI 1.2-6.7; P = 0.02) were independently and significantly associated with LBP flare-up risk.

CONCLUSION

Among participants with acute LBP, prolonged sitting (>6 hours) and stress or depression triggered LBP flare-ups. PT was a deterrent of flare-ups.

LEVEL OF EVIDENCE

2.

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.

Development and validation of a set of six adaptable prognosis prediction (SAP) models based on time-series real-world big data analysis for patients with cancer receiving chemotherapy: A multicenter case crossover study

Background

We aimed to develop an adaptable prognosis prediction model that could be applied at any time point during the treatment course for patients with cancer receiving chemotherapy, by applying time-series real-world big data.

Methods

Between April 2004 and September 2014, 4,997 patients with cancer who had received systemic chemotherapy were registered in a prospective cohort database at the Kyoto University Hospital. Of these, 2,693 patients with a death record were eligible for inclusion and divided into training (n = 1,341) and test (n = 1,352) cohorts. In total, 3,471,521 laboratory data at 115,738 time points, representing 40 laboratory items [e.g., white blood cell counts and albumin (Alb) levels] that were monitored for 1 year before the death event were applied for constructing prognosis prediction models. All possible prediction models comprising three different items from 40 laboratory items (₄₀C₃ = 9,880) were generated in the training cohort, and the model selection was performed in the test cohort. The fitness of the selected models was externally validated in the validation cohort from three independent settings.

Results

A prognosis prediction model utilizing Alb, lactate dehydrogenase, and neutrophils was selected based on a strong ability to predict death events within 1–6 months and a set of six prediction models corresponding to 1,2, 3, 4, 5, and 6 months was developed. The area under the curve (AUC) ranged from 0.852 for the 1 month model to 0.713 for the 6 month model. External validation supported the performance of these models.

Conclusion

By applying time-series real-world big data, we successfully developed a set of six adaptable prognosis prediction models for patients with cancer receiving chemotherapy.

Climate and the eye: Case-crossover analysis of retinal detachment after exposure to ambient heat

BACKGROUND

Retinal detachment is an important cause of visual loss, but the association with outdoor heat exposure has not been studied. Our objective was to determine the relationship between acute exposure to high outdoor temperature and risk of retinal detachment.

MATERIALS AND METHODS

We analysed 14,302 individuals with inpatient procedures for retinal detachment from April through September between 2006 and 2013 in the province of Quebec, Canada. Using a time-stratified case-crossover study design, we examined the association of retinal detachment with outdoor summer temperature the preceding week. We estimated odds ratios (OR) and 95% confidence intervals (CI) for mean weekly temperature according to subtypes of retinal detachment (traction, serous, rhegmatogenous, breaks), and assessed associations by age and sex.

RESULTS

Exposure to elevated temperature the preceding week was associated with a higher likelihood of traction detachment, but not other forms of retinal detachment. Associations were stronger at <75 years of age in both men and women. Relative to 15°C, a mean weekly temperature of 25°C was associated with an OR for traction detachment of 2.71 (95% CI 1.56-4.71) before 55 years, 2.73 (95% CI 1.61-4.64) at 55-64 years, and 1.98 (95% CI 1.30-3.02) at 64-75 years.

DISCUSSION

Elevated outdoor temperatures may be associated with an increased risk of traction retinal detachment. In light of climate change, a better understanding of the impact of heat waves on the eye and other sensory organs is needed.

Who really gets strep sore throat? Confounding and effect modification of a time-varying exposure on recurrent events

Unmeasured confounding is the fundamental obstacle to drawing causal conclusions about the impact of an intervention from observational data. Typically, covariates are measured to eliminate or ameliorate confounding, but they may be insufficient or unavailable. In the special setting where a transient intervention or exposure varies over time within each individual and confounding is time constant, a different tack is possible. The key idea is to condition on either the overall outcome or the proportion of time in the intervention. These measures can eliminate the unmeasured confounding either by conditioning or by use of a proxy covariate. We evaluate existing methods and develop new models from which causal conclusions can be drawn from such observational data even if no baseline covariates are measured. Our motivation for this work was to determine the causal effect of Streptococcus bacteria in the throat on pharyngitis (sore throat) in Indian schoolchildren. Using our models, we show that existing methods can be badly biased and that sick children who are rarely colonized have a high probability that the Streptococcus bacteria are causing their disease. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

A case-crossover study of transient risk factors influence on occupational injuries: a study protocol based on a review of previous studies

BACKGROUND

The occupational injury incident rate remains relatively high in the European Union. The case-crossover study gives a unique opportunity to study transient risk factors that normally would be very difficult to approach. Studies like this have been carried out in both America and Asia, but so far no relevant research has been conducted in Europe.

METHOD

Case-crossover studies of occupational injuries were collected from PubMed and Embase and read through. Previous experiences concerning method, exposure and outcome, time-related measurements and construction of the questionnaire were taken into account in the preparation of a pilot study. Consequently, experiences from the pilot study were used to design the study protocol. Approximately 2000 patients with an occupational injury will be recruited from the emergency departments in Herning and Odense, Denmark. A standardised questionnaire will be used to collect basic demographic data and information on eight transient risk factors. Based on previous studies and knowledge on occupational injuries the transient risk factors we chose to examine were: time pressure, performing a task with a different method/using unaccustomed technique, change in working surroundings, using a phone, disagreement, feeling ill, being distracted and using malfunctioning machinery/tools or work material. Exposure time 'just before the injury' will be compared with two control periods, 'previous day at the same time of the injury' (pair match) and the previous work week (usual frequency).

DISCUSSION

This study protocol describes a unique opportunity to calculate the effect of transient risk factors on occupational injuries in a European setting.

Till receipts - a new approach for investigating outbreaks? Evaluation during a large Salmonella Enteritidis phage type 14b outbreak in a north west London takeaway restaurant, September 2009

Binary file ES_Abstracts_Final_ECDC.txt matches

The exposure-crossover design is a new method for studying sustained changes in recurrent events

OBJECTIVES

To introduce a new design that explores how an acute exposure might lead to a sustained change in the risk of a recurrent outcome.

STUDY DESIGN AND SETTING

The exposure-crossover design uses self-matching to control within-person confounding due to genetics, personality, and all other stable patient characteristics. The design is demonstrated using population-based individual-level health data from Ontario, Canada, for three separate medical conditions (n > 100,000 for each) related to the risk of a motor vehicle crash (total outcomes, >2,000 for each).

RESULTS

The exposure-crossover design yields numerical risk estimates during the baseline interval before an intervention, the induction interval immediately ahead of the intervention, and the subsequent interval after the intervention. Accompanying graphs summarize results, provide an intuitive display to readers, and show risk comparisons (absolute and relative). Self-matching increases statistical efficiency, reduces selection bias, and yields quantitative analyses. The design has potential limitations related to confounding, artifacts, pragmatics, survivor bias, statistical models, potential misunderstandings, and serendipity.

CONCLUSION

The exposure-crossover design may help in exploring selected questions in epidemiology science.

Lack of adjustment latitude at work as a trigger of taking sick leave-a Swedish case-crossover study

OBJECTIVES

Research has shown that individuals reporting a low level of adjustment latitude, defined as having few possibilities to temporarily adjust work demands to illness, have a higher risk of sick leave. To what extent lack of adjustment latitude influences the individual when making the decision to take sick leave is unknown. We hypothesize that ill individuals are more likely to take sick leave on days when they experience a lack of adjustment latitude at work than on days with access to adjustment latitude.

METHODS

A case-crossover design was applied to 546 sick-leave spells, extracted from a cohort of 1 430 employees at six Swedish workplaces, with a 3-12 month follow-up of all new sick-leave spells. Exposure to lack of adjustment latitude on the first sick-leave day was compared with exposure during several types of control periods sampled from the previous two months for the same individual.

RESULTS

Only 35% of the respondents reported variations in access to adjustment latitude, and 19% reported a constant lack of adjustment latitude during the two weeks prior to the sick-leave spell. Among those that did report variation, the risk of sick leave was lower on days with lack of adjustment latitude, than on days with access (Odds Ratio 0.36, 95% Confidence Interval 0.25-0.52).

CONCLUSIONS

This is the first study to show the influence of adjustment latitude on the decision to take sick leave. Among those with variations in exposure, lack of adjustment latitude was a deterrent of sick leave, which is contrary to the à priori hypothesis. These results indicate that adjustment latitude may not only capture long-lasting effects of a flexible working environment, but also temporary possibilities to adjust work to being absent. Further studies are needed to disentangle the causal mechanisms of adjustment latitude on sick-leave.

Assessing the risk of stroke from neck manipulation: a systematic review

BACKGROUND

Strokes, typically involving vertebral artery dissection, can follow cervical spinal manipulative therapy, and these types of stroke occur rarely. There is disagreement about whether a strong association between neck manipulation and stroke exists. An earlier systematic review found two relevant studies of association that used controls, which also discussed the limitations of the two papers. Our systematic review updates the earlier review, and aims to determine whether conclusive evidence of a strong association exists.

METHODS

PRISMA guidelines for systematic reviews were followed, and the literature was searched using a strategy that included the terms 'neck manipulation' and 'stroke' from the PubMed, Embase, CINAHL Plus and AMED databases. Citations were included if they met criteria such as being case-control studies, and dealt with neck manipulation and/or neck movement/positioning. Papers were scored for their quality, using similar criteria to the earlier review. For individual criteria, each study was assigned a full positive score if the criterion was satisfied completely.

RESULTS

Four case-control studies and one case-control study, which included a case- crossover design, met the selection criteria, but all of them had at least three items in the quality assessment that failed to be completely positive. Two studies were assessed to be the most robustly designed, one indicating a strong association between stroke and various intensities of neck movement, including manipulation, and the other suggesting a much reduced relative association when using primary care practitioners' visits as controls. However, potential biases and confounders render the results inconclusive.

CONCLUSION

Conclusive evidence is lacking for a strong association between neck manipulation and stroke, but is also absent for no association. Future studies of association will need to minimise potential biases and confounders, and ideally have sufficient numbers of cases to allow subgroup analysis for different types of neck manipulation and neck movement.

Adverse events from spinal manipulation in the pregnant and postpartum periods: a critical review of the literature

BACKGROUND

The safety of spinal manipulation during pregnancy and the postpartum periods has been a matter of debate among manual therapists. Spinal manipulative therapy during these periods is a commonly performed intervention as musculoskeletal pain is common in these patients. To date there has not been an evaluation of the literature on this topic exclusively.

METHODS

A literature search was conducted on PubMed, CINAHL and the Index to Chiropractic Literature along with reference searching for articles published in English and French in the peer-reviewed literature that documented adverse effects of spinal manipulation during either pregnancy or postpartum. Case reports, case series, and any other clinical study designs were deemed acceptable for inclusion, as were systematic reviews. The appropriate Scottish Intercollegiate Guidelines Network (SIGN) tools were used to rate included articles for quality when applicable.

RESULTS

Five articles identifying adverse events in seven subjects following spinal manipulation were included in this review, along with two systematic reviews. The articles were published between 1978 and 2009. Two articles describing adverse effects from spinal manipulation on two postpartum patients were included, while the remaining three articles on five patients with adverse effects following spinal manipulation were on pregnant patients. Injury severity ranged from minor injury such as increasing pain after treatment that resolved within a few days to more severe injuries including fracture, stroke, and epidural hematoma. SIGN scores of the prospective observational cohort study and systematic reviews indicated acceptable quality.

CONCLUSIONS

There are only a few reported cases of adverse events following spinal manipulation during pregnancy and the postpartum period identified in the literature. While improved reporting of such events is required in the future, it may be that such injuries are relatively rare.

A case-crossover study of transient risk factors for occupational traumatic hand injuries in Incheon, Korea

OBJECTIVES

A case-crossover study was conducted to identify transient risk factors for occupational acute hand injuries.

METHODS

In total, 98 subjects were recruited from a hospital specializing in occupational accidents and trauma. Patients who had injured fingers, hands or wrists during work were interviewed within 30 days after their accidents.

RESULTS

The relative risks for each factor were as follows: 22.9 for unusual or malfunctioning machines (95% confidence interval [CI] 14.4-36.4), 3.3 for wearing gloves (95% CI 1.9-5.7), 5.7 for unusual tasks (95% CI 3.8-8.8), 12.1 for altered work methods (95% CI 8.4-17.6), 4.1 for rushing (95% CI 2.6-6.3), 12.9 for being distracted (95% CI 7.9-20.9), 1.2 for feeling ill (95% CI 0.4-3.6) and 1.0 for working overtime (95% CI 0.6-1.6).

CONCLUSION

The results suggest that some transient risk factors were associated with occupational acute hand injuries. These risk factors are probably preventable, and modifying unsafe or unusual conditions is important to reduce occupational traumatic hand injuries.

Association of episodic physical and sexual activity with triggering of acute cardiac events: systematic review and meta-analysis

CONTEXT

Evidence has suggested that physical and sexual activity might be triggers of acute cardiac events.

OBJECTIVE

To assess the effect of episodic physical and sexual activity on acute cardiac events using data from case-crossover studies.

DATA SOURCES

MEDLINE and EMBASE (through February 2, 2011) and Web of Science (through October 6, 2010).

STUDY SELECTION

Case-crossover studies investigating the association between episodic physical or sexual activity and myocardial infarction (MI) or sudden cardiac death (SCD).

DATA EXTRACTION

Two reviewers extracted descriptive and quantitative information from each study. We calculated summary relative risks (RRs) using random-effects meta-analysis and absolute event rates based on US data for the incidence of MI and SCD. We used the Fisher P value synthesis method to test whether habitual physical activity levels modify the triggering effect and meta-regression to quantify the interaction between habitual levels of physical activity and the triggering effect.

RESULTS

We identified 10 studies investigating episodic physical activity, 3 studies investigating sexual activity, and 1 study investigating both exposures. The outcomes of interest were MI (10 studies), acute coronary syndrome (1 study), and SCD (3 studies). Episodic physical and sexual activity were associated with an increase in the risk of MI (RR = 3.45; 95% confidence interval [CI], 2.33-5.13, and RR = 2.70; 95% CI, 1.48-4.91, respectively). Episodic physical activity was associated with SCD (RR = 4.98; 95% CI, 1.47-16.91). The effect of triggers on the absolute rate of events was limited because exposure to physical and sexual activity is infrequent and their effect is transient; the absolute risk increase associated with 1 hour of additional physical or sexual activity per week was estimated as 2 to 3 per 10,000 person-years for MI and 1 per 10,000 person-years for SCD. Habitual activity levels significantly affected the association of episodic physical activity and MI (P < .001), episodic physical activity and SCD (P < .001), and sexual activity and MI (P = .04); in all cases, individuals with lower habitual activity levels had an increased RR for the triggering effect. For every additional time per week an individual was habitually exposed to physical activity, the RR for MI decreased by approximately 45%, and the RR for SCD decreased by 30%.

CONCLUSION

Acute cardiac events were significantly associated with episodic physical and sexual activity; this association was attenuated among persons with high levels of habitual physical activity.

Real-world personal conversations using a hands-free embedded wireless device while driving: effect on airbag-deployment crash rates

A wireless device embedded in the vehicle allowed the user to engage in a personal hands-free conversation (HFC), and automatically placed an emergency notification call to an OnStar call center if the vehicle was involved in a crash in which its airbag deployed. A database stored the exact counts, start timestamps, and billed durations of all HFC and airbag notification calls. In 30 months of naturalistic driving, there were 91 million HFC calls from an average of 323,994 drivers per month who made calls. There were 14 airbag deployments in 276 million driver-minutes of HFC conversation for an exposed incidence rate of 5.08 airbag crashes per 100 million driver-minutes. There were 2,023 airbag deployments in an estimated 24.7 billion driver-minutes of no HFC conversation for a not-exposed incidence rate of 8.18 airbag crashes per 100 million driver-minutes. The crash incidence rate ratio (IRR) is the ratio of these two rates or 0.62 (95% C.I. 0.37 to 1.05). Sensitivity analyses controlled for the impact on the crash IRR of estimated time spent driving per day and calls by passengers. Counting all crashes as much as 20 minutes later than a call as related to that call gave similar results. We conclude that for personal conversations using a hands-free embedded device the risk of an airbag crash is somewhere in a range from a moderately lower risk to a risk near that of driving without a recent personal conversation. These results are not consistent with the large increase in crash risk reported in epidemiological studies using the case-crossover method.

Alcohol sales and risk of serious assault

BACKGROUND

Alcohol is a contributing cause of unintentional injuries, such as motor vehicle crashes. Prior research on the association between alcohol use and violent injury was limited to survey-based data, and the inclusion of cases from a single trauma centre, without adequate controls. Beyond these limitations was the inability of prior researchers to comprehensively capture most alcohol sales. In Ontario, most alcohol is sold through retail outlets run by the provincial government, and hospitals are financed under a provincial health care system. We assessed the risk of being hospitalized due to assault in association with retail alcohol sales across Ontario.

METHODS AND FINDINGS

We performed a population-based case-crossover analysis of all persons aged 13 years and older hospitalized for assault in Ontario from 1 April 2002 to 1 December 2004. On the day prior to each assault case's hospitalization, the volume of alcohol sold at the store in closest proximity to the victim's home was compared to the volume of alcohol sold at the same store 7 d earlier. Conditional logistic regression analysis was used to determine the associated relative risk (RR) of assault per 1,000 l higher daily sales of alcohol. Of the 3,212 persons admitted to hospital for assault, nearly 25% were between the ages of 13 and 20 y, and 83% were male. A total of 1,150 assaults (36%) involved the use of a sharp or blunt weapon, and 1,532 (48%) arose during an unarmed brawl or fight. For every 1,000 l more of alcohol sold per store per day, the relative risk of being hospitalized for assault was 1.13 (95% confidence interval [CI] 1.02-1.26). The risk was accentuated for males (1.18, 95% CI 1.05-1.33), youth aged 13 to 20 y (1.21, 95% CI 0.99-1.46), and those in urban areas (1.19, 95% CI 1.06-1.35).

CONCLUSIONS

The risk of being a victim of serious assault increases with alcohol sales, especially among young urban men. Akin to reducing the risk of driving while impaired, consideration should be given to novel methods of preventing alcohol-related violence.

Impact of extended-duration shifts on medical errors, adverse events, and attentional failures

BACKGROUND

A recent randomized controlled trial in critical-care units revealed that the elimination of extended-duration work shifts (> or =24 h) reduces the rates of significant medical errors and polysomnographically recorded attentional failures. This raised the concern that the extended-duration shifts commonly worked by interns may contribute to the risk of medical errors being made, and perhaps to the risk of adverse events more generally. Our current study assessed whether extended-duration shifts worked by interns are associated with significant medical errors, adverse events, and attentional failures in a diverse population of interns across the United States.

METHODS AND FINDINGS

We conducted a Web-based survey, across the United States, in which 2,737 residents in their first postgraduate year (interns) completed 17,003 monthly reports. The association between the number of extended-duration shifts worked in the month and the reporting of significant medical errors, preventable adverse events, and attentional failures was assessed using a case-crossover analysis in which each intern acted as his/her own control. Compared to months in which no extended-duration shifts were worked, during months in which between one and four extended-duration shifts and five or more extended-duration shifts were worked, the odds ratios of reporting at least one fatigue-related significant medical error were 3.5 (95% confidence interval [CI], 3.3-3.7) and 7.5 (95% CI, 7.2-7.8), respectively. The respective odds ratios for fatigue-related preventable adverse events, 8.7 (95% CI, 3.4-22) and 7.0 (95% CI, 4.3-11), were also increased. Interns working five or more extended-duration shifts per month reported more attentional failures during lectures, rounds, and clinical activities, including surgery and reported 300% more fatigue-related preventable adverse events resulting in a fatality.

CONCLUSIONS

In our survey, extended-duration work shifts were associated with an increased risk of significant medical errors, adverse events, and attentional failures in interns across the United States. These results have important public policy implications for postgraduate medical education.

Transient risk factors for acute traumatic hand injuries: a case-crossover study in Hong Kong

OBJECTIVES

To identify the remediable transient risk factors of occupational hand injuries in Hong Kong in order to guide the development of prevention strategies.

METHODS

The case-crossover study design was adopted. Study subjects were workers with acute hand injuries presenting to the government Occupational Medicine Unit for compensation claims within 90 days from the date of injury. Detailed information on exposures to specific transient factors during the 60 minutes prior to the occurrence of the injury, during the same time interval on the day prior to the injury, as well as the usual exposure during the past work-month was obtained through telephone interviews. Both matched-pair interval approach and usual frequency approach were adopted to assess the associations between transient exposures in the workplace and the short-term risk of sustaining a hand injury.

RESULTS

A total of 196 injured workers were interviewed. The results of the matched-pair interval analysis matched well with the results obtained using the usual frequency analysis. Seven significant transient risk factors were identified: using malfunctioning equipment/materials, using a different work method, performing an unusual work task, working overtime, feeling ill, being distracted and rushing, with odds ratios ranging from 10.5 to 26.0 in the matched-pair interval analysis and relative risks ranging between 8.0 and 28.3 with the usual frequency analysis. Wearing gloves was found to have an insignificant protective effect on the occurrence of hand injury in both analyses.

CONCLUSIONS

Using the case-crossover study design for acute occupational hand injuries, seven transient risk factors that were mostly modifiable were identified. It is suggested that workers and their employers should increase their awareness of these risk factors, and efforts should be made to avoid exposures to these factors by means of engineering and administrative controls supplemented by safety education and training.

Association between infectious diseases and type 1 diabetes: a case-crossover study

BACKGROUND

To investigate the role of infectious diseases in the development of type 1 diabetes, this study estimated the relative risks of type 1 diabetes immediately after infectious diseases.

RESEARCH DESIGN AND METHODS

A case-crossover design was employed. Information on infectious diseases during 407 d before the onset of type 1 diabetes was collected from medical records and parents' interviews for 260 patients in Chinese type 1 diabetes registry. The frequency of infectious diseases in 42 d before the onset of type 1 diabetes was compared with either the usual frequency of infectious diseases over the past year or the actual frequency of infectious diseases in a comparable 42-d control period.

RESULTS

Forty-eight (18%) patients were reported to have infectious diseases during this period based on medical records and interviews with parents. The relative risk of type 1 diabetes onset was markedly elevated to 10.1 (5.6, 17.9) immediately after infectious diseases, suggesting the role of infections as a precipitator. The relative risk decreased gradually before and after 42 d and was similar between male and female patients.

CONCLUSION

The results showed that infectious diseases are associated with a large and transient increase in the risk of type 1 diabetes during 42 d after the infection.

Differential Misclassification of Exposure in Case-Crossover Studies

The aim of this study is to examine 2 types of differential misclassification of exposure in case-crossover studies. The first is the outcome-dependent misclassification of exposure, meaning that if an event has occurred, it could affect the reporting of exposure. The second is differential misclassification of exposure as a result of fading memory over time, which arises if the length of the recall period for case and control windows differs. We use empirical data from a case-crossover study of triggers of attacks in Ménière's disease. The study applied the matched-pair interval control window sampling approach. We examined misclassification in relation to 2 different types of exposures: emotional stress and salty food intake. The study covered repeated events reported by the same patients and involved the sampling of many control windows. Because some of these windows were related to case events and some unrelated, we were able to conduct both case-crossover and control-crossover analyses. Although this group of Ménière patients are well aware of their disease, and many of them have definite ideas regarding what triggers attacks, neither outcome-dependent misclassification nor differential misclassification of exposure resulting from fading memory over time seemed to be a major problem.

Comparison of time series and case-crossover analyses of air pollution and hospital admission data

BACKGROUND

Time series analysis is the most commonly used technique for assessing the association between counts of health events over time and exposure to ambient air pollution. Recently, case-crossover analysis has been proposed as an alternative analytical approach. While each technique has its own advantages and disadvantages, there remains considerable uncertainty as to which statistical methodology is preferable for evaluating data of this type.

METHODS

The objective of this paper is to evaluate the performance of different variations of these two procedures using computer simulation. Hospital admission data were generated under realistic models with known parameters permitting estimates based on time series and case-crossover analyses to be compared with these known values.

RESULTS

While accurate estimates can be achieved with both methods, both methods require some decisions to be made by the researcher during the course of the analysis. With time series analysis, it is necessary to choose the time span in the LOESS smoothing process, or degrees of freedom when using natural cubic splines. For case-crossover studies using either uni- or bi-directional control selection strategies, the choice of time intervals needs to be made.

CONCLUSIONS

We prefer the times series approach because the best estimates of risk that can be obtained with time series analysis are more precise than the best estimates based on case-crossover analysis.

Violence prevention and control through environmental modifications

Violence traditionally had been considered a problem exclusively within the criminal justice domain, although it is now widely viewed as a public health issue as well. Public health has brought new and complementary tools for understanding and preventing violence. Whereas public health has long recognized the environment as a determinant of disease and injury, it has paid less attention to the environment when considering violence prevention strategies. For several decades though, some criminologists and others have been researching environmental factors in crime prevention. This article aims to discuss the main environmental crime-prevention strategies, provide examples of promising interventions, review public health literature that uses these strategies, discuss what public health can contribute, and suggest public health research to test the hypothesis that violence can be prevented and controlled through environmental modifications.

Traffic-law enforcement and risk of death from motor-vehicle crashes: case-crossover study

BACKGROUND

Driving offences and traffic deaths are common in countries with high rates of motor-vehicle use. We tested whether traffic convictions, because of their direct effect on the recipient, might be associated with a reduced risk of fatal motor-vehicle crashes.

METHODS

We identified licensed drivers in Ontario, Canada, who had been involved in fatal crashes in the past 11 years. We used the case-crossover design to analyse the protective effect of recent convictions on individual drivers.

FINDINGS

8975 licensed drivers had fatal crashes during the study period. 21501 driving convictions were recorded for all drivers from the date of obtaining a full licence to the date of fatal crash, equivalent to about one conviction per driver every 5 years. The risk of a fatal crash in the month after a conviction was about 35% lower than in a comparable month with no conviction for the same driver (95% CI 20-45, p=0.0002). The benefit lessened substantially by 2 months and was not significant by 3-4 months. The benefit was not altered by age, previous convictions, and other personal characteristics; was greater for speeding violations with penalty points than speeding violations without points; was no different for crashes of differing severity; and was not seen in drivers whose licences were suspended.

INTERPRETATION

Traffic-law enforcement effectively reduces the frequency of fatal motor-vehicle crashes in countries with high rates of motor-vehicle use. Inconsistent enforcement, therefore, may contribute to thousands of deaths each year worldwide.

Case-crossover study of partner and situational factors for unprotected sex

OBJECTIVES

To identify situational and partner characteristics associated with unprotected sex among women at risk for HIV infection.

METHODS

The most recent unprotected and protected sexual encounters were compared using a case-crossover design among 1,647 women enrolled in a prospective cohort study conducted in six U.S. cities. Information collected via audio computer-assisted self-interview included detailed situational and partner characteristics for participants' most recent sexual encounters, with and without condom use. Paired odds ratios (ORs) and 95% confidence intervals were calculated for situational or partner characteristics that may differ between unprotected and protected sexual encounters, using conditional logistic regression.

RESULTS

In the adjusted analysis, partner age of older than 40 years (OR = 2.42), partner type (OR = 2.45 for a "steady" partner), partner use of alcohol (OR = 1.67) and drugs within 2 hours (OR = 1.42) of the sexual encounter, time since the encounters (OR = 0.41, 0.33, and 0.19), and exchange of sex for money or drugs (OR = 0.68) remained significantly associated with women's most recent unprotected sexual encounter.

CONCLUSIONS

Considerations related to partner and relationship characteristics should provide information for the development of interventions for women.

Factors associated with non-fatal heroin overdose: assessing the effect of frequency and route of heroin administration

AIMS

To examine risk factors associated with non-fatal heroin overdose, particularly frequency and route of heroin administration.

DESIGN

Data from cross-sectional surveys were analysed as a case-control and as a case cross-over design.

SETTING AND PARTICIPANTS

2556 subjects treated for heroin dependence in 164 outpatient facilities in Spain.

MEASUREMENTS

Prevalence of overdose involving emergency care in the 12 months before treatment admission. CASE CONTROL DESIGN: Odds ratio (OR) adjusted by logistic regression. CASE-CROSSOVER DESIGN: Estimated relative risk (RR) of transient risk of injecting heroin.

FINDINGS

The prevalence of overdose was 10%. In the case control analysis the cumulative risk of overdose increased as the frequency of heroin use decreased. However, among daily heroin users this risk increased as the frequency of heroin injection rose, with an OR of 6.0 (95% CI: 3.9-9.6) for daily injectors versus non-injectors. Sniffers had a higher risk than smokers among non-daily users, but not among daily users. Other factors associated with increased risk of overdose were: tranquilizers, alcohol or cocaine use, living in certain regions and being long-term HIV+ 0. In the case-crossover analysis, the RR for injecting heroin versus using other routes immediately before overdose was 15.9 (95% CI: 9.5-26.6), and was much higher for non-daily heroin users than for daily users.

CONCLUSIONS

These findings suggest that the rapid entry of a large quantity of heroin into the blood (as occurs when injecting) involves a high risk of overdose, especially when the heroin tolerance level is low (as occurs in sporadic users).

Case-crossover studies of occupational trauma: methodological caveats

OBJECTIVES

The case-crossover study design was developed to examine triggers for the onset of myocardial infarction. This paper seeks to examine selected methodological issues when applying the case-crossover method to the study of traumatic injuries in the work environment.

METHODS

Researchers known to be working on occupational case-crossover studies were invited to present at a workshop held at the National Occupational Injury Research Symposium in October 2000. Data from ongoing studies were used to illustrate various methodological issues involved in case-crossover studies of occupational injury.

KEY FINDINGS AND ISSUES IDENTIFIED

To utilize the case-crossover design, investigators must clearly define the time during which a worker is at risk of injury, the period of time during which a particular transient exposure could cause an injury and carefully select control time periods that estimate the expected frequency of exposure. Other issues of concern are changing work tasks over time, correlated exposures over time and information bias.

CONCLUSIONS AND FUTURE RESEARCH NEEDS

More case-crossover studies of occupational injury are needed to compare results from multiple studies. The validation of the timing of transient exposures relative to injury onset, whether done in a laboratory or field setting, should be conducted. Nested case-crossover designs in other epidemiological studies (case-control or cohort) can examine both transient and fixed risk factors for occupational injury, and should be attempted.

Major trauma in elderly adults receiving lipid-lowering medications

BACKGROUND

Some clinical trials, laboratory experiments, and in vitro studies suggest that lipid-lowering medications predispose a person to traumatic injury.

METHODS

We used population-based administrative database analysis to study adults age 65 years or more over a 5-year interval (n = 1,348,259).

RESULTS

About 12% of the cohort received a prescription for a lipid-lowering medication and about 88% did not. The two groups had similar distributions of age, gender, and income. Overall, 2,557 (0.2%) were hospitalized for major trauma. Those who received a lipid-lowering medication were 39% less likely to sustain a major trauma than those who did not receive such medication (95% confidence interval, 29 to 47). Similar results were observed after adjustment for age, gender, and income; cardiac and neurologic medications; and lethality. No other cardiac or neurologic medication was associated with an apparent safety advantage.

CONCLUSION

Lipid-lowering medications do not lead to a clinically important increase in the absolute risk of major trauma for elderly patients in the community.

Should we use a case-crossover design?

The first decade of experience with case-crossover studies has shown that the design applies best if the exposure is intermittent, the effect on risk is immediate and transient, and the outcome is abrupt. However, this design has been used to study single changes in exposure level, gradual effects on risk, and outcomes with insidious onsets. To estimate relative risk, the exposure frequency during a window just before outcome onset is compared with exposure frequencies during control times rather than in control persons. One or more control times are supplied by each of the cases themselves, to control for confounding by constant characteristics and self-confounding between the trigger's acute and chronic effects. This review of published case-crossover studies is designed to help the reader prepare a better research proposal by understanding triggers and deterrents, target person times, alternative study bases, crossover cohorts, induction times, effect and hazard periods, exposure windows, the exposure opportunity fallacy, a general likelihood formula, and control crossover analysis.

The use of the case-crossover design in studying illicit drug use

The case-crossover design was developed to study time-varying exposures that cause transient excess risk of acute health events. It is a variant of case-control and subject-as-own-control research designs, involving use of information about exposure history of each case to estimate the transient effect. This kind of self-control design can help to reduce sampling bias otherwise introduced in the selection of controls, as well as confounding bias that might be derived from enduring individual characteristics, especially personality traits and other long-standing inherited or acquired vulnerabilities. When the subject is used as his or her own control, these personal vulnerabilities are matched. In this paper we discuss strengths and weaknesses of the case-crossover design and suggest applications of the case-crossover design in epidemiologic studies on suspected hazards of illicit drug use, and in studies of drug use and co-occurring psychiatric disturbances. We conclude that the case-crossover design can play a useful role, but it discloses a need to secure fine-grained measurements in epidemiologic research on psychiatric comorbidity. As explained in the paper, we also believe the case-crossover method may be of use to criminologists who study the drugs-crime nexus, to services researchers and clinicians who seek to understand treatment entry and compliance behavior, and to etiologists interested in polydrug use.

Cost-effectiveness of regulations against using a cellular telephone while driving

PURPOSE

To evaluate the cost-effectiveness of regulations that prohibit using a cellular telephone while driving a motor vehicle.

DESIGN

Decision analysis of risks and benefits related to cellular telephones and driving.

SETTING

United States population in 1997.

MEASURES

Health benefits measured as the quality-adjusted life years potentially saved. Financial benefits measured as health care and other services potentially averted. Costs of regulation measured as the lost productivity derived from willingness to pay for cellular telephone calls.

RESULTS

Under base-case conditions, cellular telephone calls in the United States each day accounted for about 984 reported collisions, 1,729 total collisions, 2 deaths, 317 persons with injuries, 99 lost years of life expectancy, 161 lost quality-adjusted life years, $1 million in health care costs, and $4 million in property damage and other costs. This reflected a total of about 35 million telephone calls while driving, 70 million calling minutes, and $33 million in total value to society. The estimated cost-effectiveness ratio for a regulation restricting cellular telephone usage while driving was $300,000 per quality-adjusted life year saved, but ranged from $50,000 to $700,000 under alternative assumptions and interpretations of data. Regulations applied to teenage males could be cost-saving to society if the value of a call fell below 37 cents per minute.

CONCLUSIONS

Regulations restricting cellular telephone usage while driving are less cost-effective for society than other safety measures. Nevertheless, regulations may be justifiable because the benefits and harms do not always involve the individual who has the cellular telephone. Increasing the price of a call (or adding a supplementary tax) might decrease the number of discretionary calls, be cost-saving for society, and be life-saving for individuals.