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| Journal of the New Zealand Medical Association,
10-September-2004, Vol 117 No 1201
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Dog bite injuries
Louise Marsh, John Langley, Robin Gauld
Results of recent studies around the World have shown
increasing trends in the incidence of fatal, hospitalised, and emergency
department presentations of dog bites.1
The only previously published study in New Zealand on the
incidence of dog bites was by Langley in
19922—that study outlined the increasing
incidence rate of hospitalisations for dog bites over a 10-year period (1979 to
1988). Interest in dog control heightened in February 2003 when several serious
attacks were described in the media. Consequently, there were calls for a review
of legislation pertaining to dog control.
In New Zealand there is a lack of recent and relevant data
to determine the current extent of the problem and to make an informed decision
about preventive methods to address the issue. The research described here
sought to update earlier work—by determining trends in the incidence of
serious dog bites in New Zealand from 1989 to 2001, inclusive.
MethodsWe adopted a similar strategy
to Langley2 for the identification of serious
cases. This involved identifying fatal and public hospital inpatient victims
from New Zealand Health Information Service’s (NZHIS) electronic mortality
and morbidity data files using the external cause of injury and poisoning codes
(E codes). Readmission for the same injury were excluded.
The NZHIS databases include a free text narrative of up
to 70 characters for hospitalisations, and up to 90 characters for fatalities
describing the circumstances of injury. The proportion of injury
hospitalisations with useful information in this field has been low since 1995.
Hospitalisations were restricted to those with a principal diagnosis of injury.
Patients not staying at least one night, readmissions, and in-hospital deaths
were excluded.
From 1989 to June 1999, the circumstances of injury
were classified using ICD-9 E-Codes.3 For that
period, cases with an E-Code of ‘E906.0:
Other injury caused by animals – dog bite’ or a free text
narrative including the words
‘dog’ and
‘bite’ were identified as
dog bite injuries.
For the period 1989 to 1994, the number of struck by
dog hospitalisations was estimated by identifying all cases with an E-Code of
E906, or
E906.9 where the free text narrative
included the word ‘dog’ but
not the word ‘bite’. From
July 1999 onwards, the circumstances of injury were classified using ICD-10
codes.4
For the period 1989 to 1994, cases with a code of
‘W54: Bitten or struck by
dog’ were identified as dog bite injuries. The proportion of these
dog bite cases were estimated as being equal to the proportion of bitten- or
struck-by-dog cases from 1989 to 1994. Estimates of the total New Zealand and
Maori populations, by gender and age group, were obtained from Statistics New
Zealand.5
The inpatient data was analysed using Stata 7.0 and
SPSS software. Rates and 95% confidence intervals were calculated using negative
binomial regression analyses. Rate ratios, calculated from the exponential of
the beta coefficients from the negative binomial regression were used to compare
rates between categories. Pearson’s Chi-squared analysis was used to test
for differences in the distribution of categorical data.
The natural log was taken to normalise the distribution
of the number of days stayed in hospital. The mean days stay and confidence
limits were calculated on the logged scale and then back transformed by taking
the anti log—this provides an estimate of the geometric mean and
confidence limits on the original scale. Regression analysis was used to compare
the mean number of days stayed by anatomical location of injury. Since the
outcome variable had been log transformed, the exponential of the beta
coefficients provide estimates of ratios of geometric means.
The distribution of age varies between Maori and
non-Maori. Therefore direct standardisation was used to compare inpatient dog
bite rates between Maori and non-Maori.
ResultsFrom 1989 to 2001, 3119 potential
dog bite hospitalisations and 1 dog bite fatality were identified. Of these 3119
incidents, 94 hospitalisations were estimated to have resulted from being struck
by a dog rather than being bitten. Hence, for the period 1989 to 2001, there
were an estimated 3025 hospitalisations and 1 fatality as a result of dog bites.
The incidence rates of dog bite hospitalisations by year are
given in Figure 1. Rates for 1999 to 2001 have been adjusted to allow for the
proportion of cases that were a result of being struck by rather than bitten by
a dog. All other rates presented below were derived from the population of
potential dog bites (n=3119) and, as such, are likely to be slight
overestimates. Small numbers precluded reliable adjustments to these
rates.
The data for ethnicity of dog
bite victims was analysed for the years 1996 onwards (due to a different
definition of ethnicity prior to this date). There were 1588 victims during this
time, and New Zealand European victims represent 52% of the total bite victims,
Maori 28%, and all other groups 20%. The age-adjusted incidence rates for Maori
and non-Maori were 10.6 (9.4–11.7) and 5.9 (5.6–6.3)
respectively.
Of those where a location was
given (42%), 30% of the victims were bitten while at a home (not necessarily
their own). For 6% of the victims, the bite occurred on the street or highway,
and 1% were bitten while on a farm.
The upper limb, head, and
lower limb were the most common regions to be injured, with the most common site
of injury being the face. The results show evidence of a difference in the
distribution of injury location by age group (Figure 2). Injuries to the head
were significantly more common for the younger age groups; injuries to the upper
limb most commonly occurred in those aged over 15 years, and lower limb injuries
were more consistently spread through the age groups.
Males, and children less than
9 years of age (Table 1) had the highest rates of injury.
Table 1. Demographic characteristics of dog bite
victims in New Zealand (1989–2001)
The total number of hospital
inpatient days incurred as a result of dog bites for the 13-year period was
9,450, with 3 days being the mean number of days in hospital. The longest time
spent in hospital for a dog bite injury was 56 days. For a 1 year increase in
age, there was an estimated 1% (1.0–1.3) increase in the number of days
stayed (p=0.001). Victims with injuries to the lower limb were more likely to
stay in hospital the longest, with a mean number of 5.6 days.
Figure 1. Incidence rates of dog bites in New Zealand
(1989–2001)
Figure 2. Age of victim and the main body region
injured (1989–2001)
 DiscussionOne death occurred during the study
period (1988–2001). This represents the only fatality identified in New
Zealand since 1979. This result is consistent with other developed countries
where death due to a dog bite has been very rare. The rates of serious dog bite
injuries resulting in hospitalisations continued to increase following those
reported by Langley2 for the period 1979
to1988. Subsequent to the introduction of the Dog Control Act 1996, the rate
dropped for the following 3 years but then increased to nearly pre-1996
levels.
The decrease in incidence rates from 1996 could be
attributed to the public responding to publicity around dog control around this
time coupled with the introduction and enforcement of strict dog control law in
1996. The elevated risk for 2000 and 2001 could represent a real change in risk
or be an artefact of coding changes or a combination of both.
The overall incidence rate was similar to that observed in
Australia of 7.7 for 1995 to 1996,1 but is much
higher than the Canadian inpatient rate of 2.3 for
1993.6 Direct comparison with overseas studies
may be limited, however, by the use of different research methods and different
treatment/service delivery practices (which influence what is counted as a
case).
The epidemiological characteristics of dog bite injuries
over the period studied were similar to those found in other
studies7—with males and young children,
particularly those under 10 years of age, disproportionately represented. High
rates among children can probably be explained by their lack of physical
strength or motor skills to ward off an attacking
dog.8 Immaturity and lack of judgement may also
sometimes lead children to act in ways that animals perceive as threatening or
aggressive.6 Furthermore, it has been suggested
that (prior to their injury) children under 5 years of age are significantly
more likely to provoke animals than older
children.9
While younger victims did not stay in hospital as long as
older victims, their injuries were often sustained to the head region, with very
few being to the limbs. Data from elsewhere shows similar
patterns.1 It may be that parents of injured
children are more likely to seek medical attention, and young children and
victims sustaining head injuries may be more likely to be admitted to hospital
than other groups.
Victims aged 20 to 24 had the highest number of injuries to
their upper limbs in this study. Other studies found this to be a common injury
site, and the leg was also particularly likely to be injured for those in the 20
to 25 age group.10
This study showed the Maori inpatient rate was 1.8 times the
non-Maori rate. Previous research in New Zealand found the Maori rate to be 2.6
times that of non-Maori for the period 1979 to
1988.2 The rates ratios may be a real change or
be a function differences in ethnicity classification over time.
Dog bites continue to be a significant problem—so
ongoing monitoring is required to demonstrate whether dog control procedures are
reducing injury.
Author information:
Louise Marsh, PhD Student, Department of Preventive and Social Medicine, Dunedin
School of Medicine, University of Otago, Dunedin; John Langley, Director, Injury
Prevention Research Unit, Department of Preventive and
Social Medicine, Dunedin School of Medicine, University of Otago, Dunedin;
Robin Gauld, Senior Lecturer in Health Policy, Department of Preventive and
Social Medicine, Dunedin School of Medicine, University of Otago,
Dunedin
Acknowledgements:
The authors thank Jo McKenzie and Shaun Stephenson for their statistical
assistance.
Correspondence: John
Langley, Injury Prevention Research Unit, Department of Preventive and Social
Medicine, Dunedin School of Medicine, PO Box 913, Dunedin. Fax: (03) 479 8337;
email: John.Langley@ipru.otago.ac.nz
References:
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