Presentation and treatment of animal and human bite injuries at a Swiss tertiary emergency department: a cross-sectional study

BACKGROUND: Animal and human bite injuries are a relevant health problem worldwide. With the increasing number of pets, bite injuries are becoming more frequent. Previous studies on animal and human bite injuries in Switzerland were completed several years ago. The aim of the present study was to provide a detailed overview of patients with bite injuries admitted to a tertiary emergency department in Switzerland in terms of demographics, injury patterns and treatment strategies. METHODS: A 9-year cross-sectional analysis of patients presenting to the emergency department of Bern University Hospital in the period January 2013 to December 2021 following an animal or human bite injury. RESULTS: A total of 829 patients with bite injuries were identified, including 70 for postexposure prophylaxis only. Their median age was 39 (IQR 27–54) years and 53.6% were female. Most patients were bitten by a dog (44.3%), followed by cats (31.5%) and humans (15.2%). Most bite injuries were mild (80.2%); severe injuries were mainly found in dog bites (28.3%). Most patients were treated within six hours after human (80.9%) or dog (61.6%) bites; after cat bites, patients often presented with a delay (74.5%) and signs of infection (73.6%). Human bite wounds were superficial in the majority of cases (95.7%), rarely showed signs of infection (5.2%) at the time of presentation and hospitalisation was never required. CONCLUSIONS: Our study provides a detailed overview of patients admitted to an emergency department of a tertiary Swiss University Hospital after an animal or human bite. In summary, bite injuries are common among patients who present to the emergency department. Therefore, primary and emergency care clinicians should be familiar with these injuries and their treatment strategies. The high risk of infection, particularly in cat bites, may warrant surgical debridement in the initial treatment of these patients. Prophylactic antibiotic therapy and close follow-up examinations are recommended in most cases.


Introduction
Animal and human bite injuries are a significant global health problem [1][2][3]. The frequency and nature of animal and human bite injuries depend on geographic location, level of industrialisation and cultural factors [4]. Whereas in industrialised countries bite injuries are more likely to result in localised injuries and infections, human rabies remains an important zoonotic disease in many developing countries, especially in Asia and Africa [5].
In the USA, an estimated 50% of people will be bitten by an animal or another person during their lifetime and bite injuries account for 1% of all emergency department visits [3,6,7]. According to the literature, dog bites are the most common animal bites (60-80%), followed by cat bites (20-30%) and rodent bites (2-3%) [2,[8][9][10]. Human bites are the third most common source of bites, accounting for 3.6% to 23% of all bite injuries [1,11].
Wound characteristics depend on the species, the bite source dentition and the anatomical location of the injury [2]. The most frequent locations are the hands and extremities in 70-80% of cases and the head and neck in 10-30% of cases [4]. Most bite wounds can be treated in the emergency department [1]. Adequate and prompt management with irrigation and removal of necrotic tissue is important in lowering complication risk [1,12,13]. The incidence of wound infection is high compared with other traumatic wounds. The relative risk is determined by animal species, site of bite, host factors and local wound care [12]. Human bites can also transmit hepatitis B, hepatitis C and HIV; postexposure prophylaxis should be considered in every human bite [14].
In Switzerland, animal bites are frequent and represent a public health problem of increasing importance due to the steadily growing pet population [15]. The true incidence of bite injuries in general is difficult to determine because not all patients with bite injuries seek medical attention; this is especially common for human bites [2,12]. In Switzerland, 20 years ago, an annual incidence rate of medical consultations following vertebrate bites and scratches was found to be 325 per 100,000 people [15]. In regard to socioeconomic changes in Switzerland including the growing pet population in recent years, the present study aimed to provide an up-to-date overview of animal and human bite injuries in patients admitted to a tertiary emergency department in Switzerland in terms of demographics, injury patterns and treatment strategies for bite injuries of different sources.

Study design
This cross-sectional study was conducted at the Department of Emergency Medicine for Adults of the Inselspital, Bern University Hospital, Switzerland, a tertiary emergency department, from 1 January 2013 to 31 December 2021.

Search strategy and eligibility criteria
A full-text keyword search was performed on the medical reports of all adult patients (≥16 years) admitted to our emergency department within the given time period using the defined keyword "bite". The medical reports of the identified consultations were then manually reviewed for an actual human or animal bite injury by two experienced physicians (MK and LM). Patients without a recent bite wound diagnosis, cases with incomplete clinical data in the manual full-text analysis and patients who refused to give general consent for the use of their anonymised data or subsequently withdrew it were excluded from the study. Follow-up consultations after the emergency department visit were not evaluated. Patients who visited the emergency department only for postexposure prophylaxis were analysed separately (postexposure prophylaxis-specific) due to often undocumented bite information in the reports.

Data collection and extraction
The following data were extracted automatically or manually (MK and LM) from the database of the patient management system (E. care; Mesalvo Turnhout BV, Turnhout, Belgium) of the Department of Emergency Medicine for Adults of Bern University Hospital, Switzerland: -Patient characteristics: sex and age.
-Consultation characteristics: date of admission, time to consultation, patient destination (discharge from the emergency department or inpatient admission), department of admission.
-Bite characteristics: source (animal species or human) and context of the bite (relationship to the source, accident during leisure time, accident at work, situation in detail).
-Wound characteristics: anatomical site and severity of injury (according to Rueff's classification [16]: 0 = no visible lesion; grade I = superficial skin lesion, torn skin, scratched skin, bite canal, crushing injury; grade II = wound extending from the skin to the fascia, muscle or cartilage; grade III = wound with tissue necrosis or tissue loss). The presence of infection was determined based on the description in the emergency report (case history, clinical exam, antibiotic therapy).
-Therapy: type of wound treatment (disinfection: superficial wounds were disinfected; wound irrigation: deep wounds were rinsed [normally with sterile water -in-formation not always available] and disinfected; suturing [simple, complex]; wound revision); location of wound treatment (in the emergency department, in the operating theatre or polyclinic); antibiotic treatment (prophylactic antibiotics, secondary antibiotics, i.e. prescribed because of wound infection); postexposure prophylaxis: tetanus, rabies, HIV, hepatitis B. Simple suturing was defined as superficial wound care of the skin performed with single stitches; complicated suturing was that done for deeper wounds, for example when hand surgeons or plastic surgeons were consulted.

Statistical analysis
The statistical analysis was performed with Stata® 16.1 (StataCorp LLC, College Station, Texas, USA). For the descriptive analysis, the distribution of continuous variables, such as age, were described with the median and interquartile range (IQR) as most continuous variables were not normally distributed. The distribution of categorical data was described with the total number accompanied by the percentages. P values were obtained using the Chi-squared test for categorical variables and the Kruskal-Wallis test for continuous variables; variables with a p value <0.05 were considered significant.

Ethical considerations
The study was approved by the regional ethics committee of the Canton of Bern, Switzerland (KEK:2019-00628).

Results
From 1 January 2013 to31 December 2021, a total of 9560 out of 407,278 patients referred to our emergency department were identified in the medical database using our search strategy. Ultimately, 829 patients met all inclusion criteria. Of these, 70 (8.4%) patients visited the emergency department only for postexposure prophylaxis treatment and were analysed separately; hence 759 (91.4%) patients were included in the overall study analysis (figure 1).

Treatment of animal and human bite injuries
For the majority of patients, wound treatment was provided in the emergency department (n = 562, 74.0%); one fifth of the patients (n = 164, 21.6%) required treatment in the operating theatre or by a specialist in the polyclinic, e.g. hand surgery or plastic surgery. In the majority of cases, wound treatment was restricted to cleaning measures only (n = 402, 53.0% superficial disinfection; n = 112, 14.8% with additional wound irrigation with sterile water). Simple suturing was performed in 60 (7.9%) patients, complicated suturing in 39 (5.1%) patients. Patients with cat bites needed a wound revision in 41.4% (n = 99) of cases. Half

Context of animal and human bites
Bites most frequently occurred during leisure time (n = 609, 80.2%), regardless of the source of the bite. In more than half of all bite categories (n = 453, 59.7%), the animal or person biting was known to the victim. Human bites happened most frequently during acts of aggression (n = 88, 76.5%); in 27 cases (23.5%), the bite occurred under the influence of alcohol or other drugs. The reasons for animal bites were manifold (table 5).

Discussion
In this single-centre study, 829 of 407,278 emergency department patients were evaluated for bite injuries from 2013 to 2021. In line with the literature, dog bites were the most frequent animal bite injuries, followed by cat and human bites [4].
The literature shows that men are more often affected by bite injuries in general; and, specifically, that dog bites are more common in young males; conversely, injuries from cats are significantly more frequent in females and older people [4,8,17,18]. In our present study, the number of female patients overall was higher than male patients due to a high number of cat bites, whereas the number of dog bites was comparable between both sexes. Cat bite injuries were more than twice as likely to affect women, and human bites were more common in men.
Animal bites are mainly caused by pets [19,20] and often occur in the context of a distressed animal: 50% to 80% of all patients are bitten by a familiar animal [3,21], up to even 90% in the case of dog bites [1,[8][9][10]. Our results underline these findings: two thirds of the patients knew the animal and an animal in distress was present in one third of the cases. Bite injuries caused by humans are frequently related to aggressive behaviour, often associated with alcohol and other drugs or during sexual and athletic activities, occupational interventions (e.g. dental) or are self-inflicted [1]. In our present study, in almost two thirds of human bites the source of the bite was known to the victim and in more than 70% of the cases aggression was involved, in almost one quarter alcohol or other drugs.
In line with previous data [17], the arm and hand were by far the most frequently injured body sites. Dog bites led to the most severe primary injuries, whereas the majority of human and cat bites were deemed superficial injuries according to Rueff's classification.
Surgical debridement with appropriate irrigation can effectively eradicate bacterial flora [22]. Nevertheless, 10-20% of bite wounds become infected, including 30-50% of cat bites, 5-25% of dog bites and 20-25% of human bites [4,[23][24][25][26]. Therefore, most experts recommend early prophylactic antibiotic treatment for fresh, deep wounds; injuries in critical body areas such as hands, feet and around joints, the face and genitalia; and for people at increased risk of infection due to immune disorders [3,4,[25][26][27]. However, this remains a controversial issue in the literature. Meta-analyses found no evidence for a reduction in infection rates with prophylactic antibiotics, except in hand bite wounds caused by cats and humans [28][29][30].
In this study, 60% of patients with dog bites and 80% of patients with human bites presented to the emergency department within 6 hours. Two thirds of these patients received prophylactic antibiotic therapy. Consistent with prompt presentation, less than one fifth of dog bite patients and only a few human bite patients showed signs of infection at emergency department presentation. Dogs typically cause crush injuries when they bite [1]; in contrast cat bites result in small puncture wounds that appear harmless on the surface and the true depth of the injury is often underestimated by the patient and the physician [4]. Therefore, cat bites are often considered minor injuries, even though there is a high risk of infection due to deep bacterial inoculation. Initially, many of them might not even be treated medically. As our data show, the majority of patients with cat injuries presented to the trauma centre when complications occurred: over 70% of patients with cat bites presented with a delay of more than six hours after the bite event and showed signs of infection. This is in line with the liter-  [12].
The high rate of infections after cat bites is certainly related to the tertiary care role of our emergency department, as many patients are referred for hand or plastic surgery due to complications after bite injuries. Consequently, more than one third of patients were hospitalised after cat bites compared to 16.4% of patients after dog bites, although the initial bite injury by dogs was more often classified as severe. Patients with human bite wounds had only superficial wounds and hospitalisation was not required.
Only 4 of the 115 human bite patients received HIV postexposure prophylaxis and 17 patients received hepatitis B postexposure prophylaxis. This low rate may be due to the fact that the source was known to many patients and the risk of transmission of infectious diseases could be assessed. Nevertheless, careful evaluation of the indication for HIV postexposure prophylaxis, hepatitis B postexposure prophylaxis and hepatitis C infection follow-up is warranted after all human bite injuries.

Strength and limitations
The strength of this study is the consecutive inclusion of all admissions of animal and human bite injuries in a large emergency department over a 9-year time period. This study has some limitations. As with all retrospective data analyses, we cannot rule out documentation bias or missed patients, despite careful data extraction and analysis. This is a single-centre study and many patients with minor bite injuries are likely to be treated in surrounding hospitals and by general practitioners and are not seen at the tertiary emergency department. In addition, patients presenting primarily for a bite injury and those presenting as a result of a complication following a bite injury were included in this cohort. In view of this and the fact that no follow-up data were collected, no general statements can be made about the association between the source of the bite and the risk of infection in this patient population.

Conclusion
Animal and human bites, although preventable, are common consultations in the emergency department. Dog bites were the most common, followed by cat and human bites. Dog bites were associated with the most severe primary injuries. Patients with dog and human bites often presented primarily to the emergency department, whereas patients with cat bites frequently presented with a delay and signs of infection. In summary, primary and emergency care physicians must be aware of the high risk of infection after bite injuries, especially after cat bites. Surgical debridement in the initial treatment needs to be considered. Prophylactic antibiotic therapy and close follow-up examinations are recommended in most cases.