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Risk Factors for Injury among Veterinarians

Gabel, Christine L.; Gerberich, Susan G.


Work-related injuries among veterinarians are a major problem, but little is known of the specific risk factors involved. The purpose of this nested case-control study, conducted from a comprehensive population-based study of practicing Minnesota veterinarians, was to identify risk factors for job-related injuries. We questioned cases (N = 193) on exposures occurring in the month before their injury, and we questioned controls (N = 495) on exposures occurring in a randomly selected month. We used logistic regression to model the dependence of veterinary work-related injury on each exposure of interest and associated confounders. We observed increased rates for prior injuries (RR = 1.7, 95% CI = 1.1–2.6), participation in sports (RR = 1.7, 95% CI = 1.05–2.6), no sharps boxes present (RR = 1.8, 95% CI = 1.01–3.2), current smoking (RR = 4.1, 95% CI = 1.8–9.1), and 6 or fewer hours of sleep (RR = 1.8, 95% CI = 1.0–3.3). We identified a dose response for lifting patients, as follows: lifting 41–75 lb (RR = 3.1, 95% CI = 1.6–5.9), lifting 76–100 lb (RR = 3.2, 95% CI = 1.6–5.9), and lifting more than 100 lb (RR = 6.1, 95% CI = 2.5–15.0). Decreased rates were observed for participation in aerobic activities (RR = 0.6, 95% CI = 0.4–0.99), perception of lower risk (RR = 0.4, 95% CI = 0.2–0.9), and experience (RR = 0.6, 95% CI = 0.4–0.9).

From the Regional Injury Prevention Research Center, Center for Violence Prevention and Control, and Occupational Injury Epidemiology and Control Program, Division of Environmental and Occupational Health, School of Public Health, University of Minnesota, Minneapolis, MN.

Address correspondence to: Susan G. Gerberich, Regional Injury Prevention Research Center, Center for Violence Prevention and Control, and Occupational Injury Epidemiology and Control Program, Division of Environmental and Occupational Health, School of Public Health, University of Minnesota, Mayo Mail Code 807, 420 Delaware Street SE, Minneapolis, MN 55455;

Support for this effort was provided in part by the Regional Injury Prevention Research Center, Division of Environmental and Occupational Health, School of Public Health, University of Minnesota; Occupational Injury Epidemiology and Control Program, Midwest Center for Occupational Health and Safety, University of Minnesota (T42/CCT 510422); and Midwest Veterinary Supply Inc (Russell R. Wiley, president).

Submitted October 2, 2000; final version accepted June 1, 2001.

Occupational injuries are a major source of morbidity and mortality among all workers; among the approximately 65,000 practicing veterinarians in the United States, little is known of the extent of risk factors for work-related trauma. Based on previous studies, the injury rate for veterinarians is at least 10 per 100 veterinarians per year 1–4 and was shown to be 23 per 100 in the comprehensive study that served as the basis for the current effort. 5

Reporting of such injuries is limited. Although workers’ compensation claims might be a source of data for those who claim these benefits, many veterinarians treat their own injuries; from one study, it was estimated that two-thirds of those injured treated themselves with methods beyond first aid such as suturing or antibiotics. 2

There are few studies of injuries to veterinarians. Those that exist are descriptive and of limited value owing to varying definitions of injury and low response rates. 1–4

In the overall study, 5 there were two primary aims: (1) to identify the rates of injury among veterinarians who practiced in Minnesota during 1996 and (2) to ascertain the specific risk factors involved. The research design used an initial comprehensive survey followed by a nested case-control study among the cohort of veterinarians. In this paper, information is presented from the case-control effort.

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Subjects and Methods


We studied the cohort of all veterinarians licensed to practice veterinary medicine in Minnesota during 1996. A list of all licensed veterinarians in Minnesota (N = 2,687) was obtained from the State Veterinary Licensing Board. An initial comprehensive survey was mailed during February 1997 to determine active practice status of the respondents, whether or not they were injured during 1996, details of any injuries, demographic data, and practice information; follow-up to nonrespondents 1 month later served to improve response. From these mailings a total of 1,023 practicing veterinarians who sustained a total of 351 injuries was identified. Injuries were approximately uniform throughout all months (6.1–9.5%), except for a slight increase in December (13.6%). About 95% of respondents worked in any given month. Comprehensive data are described elsewhere. 5

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Selection of Cases and Controls

All animal-related injury events (N = 287) reported by veterinarians in the initial survey were identified as cases; persons were identified as many as four times as cases. To select controls, all persons in the cohort were given up to 12 numbers from 1 to 12 to represent the months of 1996 in which they were practicing; for cases, the injury month and the month before the injury were eliminated as control months. Then, controls (N = 720) were randomly selected from all eligible person-months. Thus, control persons could have reported no animal-related injury or could have sustained their animal-related injury in a month other than the one selected as a control. Control persons could be selected several times; most persons were selected only once or twice.

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Data Collection

A conceptual model was used in developing the survey instruments and in analyzing and interpreting the data. This model was based on knowledge of the veterinary working environment, consultation with other veterinarians, previous published information, and information about injury occurrence mechanisms. Potential risk factors were grouped into categories to aid in development of questions (Table 1). The overall model of injury included all potential sources of injury; the current effort concerns only animal-related injury outcomes.

Table 1

Table 1

All persons selected were mailed a comprehensive survey in July 1997 asking about exposures in the month before their injury (cases) or the randomly selected month (controls). Separate questionnaires encoded for the respective month, along with explanatory letters, were sent to all participants. Persons who received more than one questionnaire (ie, were selected as controls more than once, or sustained multiple injuries) were allowed to indicate “same” in relevant portions of the questionnaires if they felt the information remained unchanged from the first questionnaire they completed. Information was collected on a variety of exposures as determined from the conceptual model (Table 1).

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Several exposures, determined through the conceptual model, were identified as factors of primary interest for the analysis. These included: availability and utilization of technical assistance; use of safety measures in the usual working environment; type of practice/animals treated; fatigue factors including hours of sleep, emergency coverage, and hours worked per week; and lifting and physical fitness. We used unconditional logistic regression to calculate crude rate ratios for each exposure of interest and to model the dependence of animal-related injury among practicing veterinarians on each exposure of interest along with the pertinent confounders.

For each exposure of interest, we used the conceptual model to identify potential confounders 6 to enter into the analysis. Each analytic model was evaluated using Proc Logistic in SAS 7 to determine the relevant rate ratios. Several variables in the models were continuous in nature and were assessed both as continuous and categorical: age, years of experience, body mass index, hours worked, hours of sleep, and percentages of time engaged in emergency work and time spent in various activities.

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Among the 287 cases and 720 controls who were sent surveys, 193 cases (67%) and 495 controls (69%) responded. Characteristics of the 193 cases and 495 controls are shown in Table 2. In Table 3, environmental safety measures present in the working environment are shown for cases and controls.

Table 2

Table 2

Table 3

Table 3

In Table 4, we present crude and multivariate rate ratios for variables included in the final model. Increased rates were found for those veterinarians who had 5 or fewer years of experience (RR = 3.1, 95% CI = 1.4–6.8) and 6–10 years (RR = 1.9, 95% CI = 0.9–4.0), compared with more than 20 years; smoked currently (RR = 4.1, 95% CI = 1.8–9.1); incurred prior injuries (RR = 1.7, 95% CI = 1.1–2.6); slept 6 or fewer hours per night on average (RR = 1.8, 95% CI = 1.0, 3.3); sat less than 1 hour per day (RR = 3.2, 95% CI = 1.6–6.3); stood less than 1 hour per day (RR = 1.7, 95% CI = 0.9–3.0); and participated in any type of sports (RR = 1.7, 95% CI = 1.0–2.6).

Table 4

Table 4

We found a dose-response effect in weight of patients lifted without assistance. Compared with lifting ≤40 lb, increasing rates were seen for lifting 41–75 lb (RR = 3.1, 95% CI = 1.6–5.9), 76–100 lb (RR = 3.2, 95% CI = 1.6–5.9), and >100 lb (RR = 6.1, 95% CI = 2.5–15.0). Those who did not use hydraulic lifts experienced a slight increase in risk (RR = 1.3, 95% CI = 0.7–2.5), and those who said the lifts were not needed experienced a large increase (RR = 5.9, 95% CI = 2.3–15.0). A decreased rate of injury was seen for the perception of low risk of injury in the work, compared with the perception of a high risk of injury (RR = 0.4, 95% CI = 0.2–0.9).

Availability of technician assistance was also considered an important potential risk factor to examine. There were higher rates for those who answered “frequently” or “sometimes” compared with those who said they always had assistance when working with animals (RR = 1.8, 95% CI = 0.9–3.9, and RR = 1.9, 95% CI = 0.9–4.1, respectively). A similar result was seen when veterinarians were asked about the availability of sharps boxes used for disposal of needles in their usual work environment. Those who responded “not available” had increased rates of injury (RR = 1.8, 95% CI = 1.0–3.2); those who responded “not applicable” had an even greater rate (RR = 4.8, 95% CI = 2.2–10.4).

Decreased rates were identified for increasing age (36–45 years, RR = 0.6, 95% CI = 0.4–0.9; 46–55 years, RR = 0.4, 95% CI = 0.3–1.0; 56–80 years, RR = 0.3, 95% CI = 0.2–1.3), male gender (RR = 0.5, 95% CI = 0.3–0.8), use of alcohol (RR = 0.6, 95% CI = 0.4–0.9), sitting from 1 to <4 hours per day vs ≥4 hours (RR = 0.6, 95% CI = 0.3–1.2), and participation in aerobic activities (RR = 0.6, 95% CI = 0.4–1.0).

To evaluate potential selection bias, we sent a brief questionnaire to all nonresponding cases (N = 91) and controls (N = 168). The return rate for this brief survey was 35% for cases and 37% for controls. A sample of the original cohort that had not responded in the initial phase of the study was also contacted (N = 110). In Table 5, results for one variable (hours of sleep) are shown from this substudy. This information was used to evaluate the potential effect of nonresponse bias. Specifically, this bias may influence the effect estimates if it is nonrandom with respect to injury and exposure status (for example, if exposed cases were more likely to respond than the other groups). It appears that exposed cases, and unexposed controls to a lesser extent, were more likely to participate in the study than were unexposed cases and exposed controls. This selection would appear to exaggerate the effect estimates that we report.

Table 5

Table 5

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Limitations of the study include the fact that data were collected retrospectively and required the participants to recall events that had occurred in the past. Cases had the opportunity to be reminded of the injury they had reported in the initial comprehensive survey and reply regarding the month before this event. Controls were randomly assigned a month and thus did not have a marker event to stimulate their memories. In many veterinary environments, the activities and species of animals treated vary throughout the year, so it was important to account for the seasonal variation by focusing on a 1-month period, even though results in the initial survey found slightly increased proportions of injuries only in December and comparable numbers of veterinarians working in each month. Participants who were selected more than once as a control were allowed to indicate “same” on questionnaires if they felt the exposures were similar to those identified in the first questionnaire they completed. This prompting may have resulted in imprecision in measuring the differences among months. Few participants took advantage of this option and completed each questionnaire separately. Because cases who were also picked as controls were allowed to indicate “same” on these questionnaires if they perceived that the information did not vary, this option may have decreased our ability to distinguish differences in exposures between the cases and controls.

Because the relevant hazard period for injuries is usually very short, immediately preceding the injury, asking about average exposure history for the prior month may miss important short-term changes. For exposures that are more stable through time, such as type of practice or demographic characteristics, this issue should be less problematic. There is also a potential for information bias when asking about exposures several months after the incident; those injured may recall more details, or remember specific incidents, whereas the controls may have less specific memory triggers.

It was not possible to control for some important confounders, especially the behavior of a veterinarian toward a particular animal involved in an injury or toward animals in general and the behavior of the animal involved in the injury. For the veterinarian’s behavior, there is no good, reliable measure of this item; for the animal’s behavior, comparable control information cannot be readily obtained.

Veterinarians may change jobs or tasks fairly often, which may blur the determination of past exposures. There also is a difference in exposure assessment between the small-animal practitioner, who is in the same setting each day, and the large-animal practitioner, who spends much of the day traveling among a variety of farms and sales barns and also works in a clinic.

The finding of an increased rate for current smoking behavior has some substantiation from previous studies, including increased injury risk from motor vehicle crashes 7,8 and other sources. 9,10 Potential behavioral differences between smokers and nonsmokers and the possibility of carbon monoxide effects 8,9,11,12 have been reported.

Although the association of decreased alcohol use and injury appears contrary to the known relation between alcohol use and injury outcomes, 13 most of the available data are case-based and do not consider the overall population exposures. The finding from the current effort is consistent with two case-control studies that addressed farming-related injuries 14 and dairy operation-related injuries. 15

Increasing years of experience were associated with decreasing rates of injury. This effect may reflect the position within the practice, owner vs associate, and learning to work better with patients and their owners over time. It may also reflect the type of work done, as the more experienced veterinarian may be involved in more specialty-type practices. The increased rate of injury with 6 or fewer hours of sleep per night is consistent with earlier data from Belloc and Breslow, 16 who examined the relation between amount of sleep and general health.

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We thank George Maldonado, Division of Environmental and Occupational Health, School of Public Health, University of Minnesota, for his important contributions to design, analysis, and interpretation.

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injury; veterinarian injuries; risk factors; occupational injuries

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