Tropical Australia Animal Bites: Clinical Outcomes and Management Strategies
Aug 28, 2024
2024/8/26
A comprehensive retrospective audit titled “Animal Bite Wounds and Their Management in Tropical Australia” provides critical insights into the microbiologic characteristics and clinical management of animal bites in tropical Australia. The study highlights the types of animals responsible for bite injuries and evaluates the efficacy of current Australian antimicrobial guidelines in managing such cases.
1. The study analyzed 1,745 hospitalizations due to animal bites and penetrating injuries between 2013 and 2020, finding that snakes (42%), dogs (29%), and cats (9%) were the most common culprits.
2. Delayed hospital presentation (>24 hours) was strongly associated with increased infection risk, especially for cat-related injuries, which accounted for a substantial proportion of late-presenting cases.
3. The empirical antimicrobial regimens recommended by Australian guidelines were deemed appropriate in nearly all cases, with only 12 cases (0.7%) requiring adjustments due to pathogens not covered by the standard guidelines.
4. Significant tissue trauma and deep infections at presentation were linked to higher rates of complications, with a 6% primary outcome rate that included ICU admissions, amputations, and unplanned rehospitalizations.
Introduction
Animal bites are a major public health concern in tropical Australia, where encounters with both domestic and wild animals frequently result in serious injuries. This study examines the outcomes of bite-related hospitalizations in Cairns Hospital, which serves a vast population in northern Queensland. By analyzing data from 2013 to 2020, the study aims to assess the effectiveness of current Australian antimicrobial guidelines and to identify risk factors for infection and severe outcomes in animal bite cases.
In a tropical environment with diverse fauna, including venomous snakes, large mammals, and marine life, bite management requires careful consideration of both the animal involved and the type of injury. The study offers an in-depth look at how timely medical intervention and appropriate antibiotic therapy can reduce complications and improve patient outcomes.
Method
This retrospective audit was conducted at Cairns Hospital, a tertiary referral center in tropical Australia. The study reviewed the medical records of 1,745 patients hospitalized for animal bites or penetrating injuries between December 2013 and October 2020. Demographic data, clinical presentation, microbiologic results, and outcomes were collected using a standardized pro forma. Only cases that resulted in hospital admission were included, and blunt trauma or superficial abrasions were excluded.
The study categorized animal encounters based on species and injury type, with particular attention to delayed presentations (greater than 24 hours after the bite). The researchers also examined the appropriateness of antimicrobial therapy according to the Australian Therapeutic Guidelines. Statistical analysis, including logistic regression, was used to identify risk factors for infection and complicated clinical courses. The primary outcome was a composite of severe complications, including ICU admission, amputation, and unplanned rehospitalization.
Microbiological sampling and culture results were analyzed to identify pathogens responsible for infections. The study also explored the frequency of primary versus secondary wound closure and its impact on infection rates and patient outcomes. Data was processed using STATA statistical software, and results were stratified based on animal type and clinical presentation.
Result
1. Animal Encounters and Bite Incidence
Snakes were the leading cause of animal-related hospitalizations, accounting for 42% of cases, followed by dogs (29%) and cats (9%). Male patients were disproportionately affected, representing 59% of cases, particularly in incidents involving snakes and aquatic animals. Notably, livestock-related injuries, while less common, had a high incidence of severe tissue trauma.
Delayed presentation was a significant risk factor for infection. The study found that 73% of cat bite patients presented more than 24 hours after the encounter, and nearly all of these cases (96%) were associated with an infected wound. In contrast, only 18% of snakebite cases presented late, and these were less likely to develop infections due to prompt medical attention and the use of antivenom.
A wide variety of animals contributed to bite injuries, with notable cases involving jellyfish (7%), crocodiles, and other marine animals. However, despite the tropical setting, infections caused by exotic pathogens were rare, and Australian antimicrobial guidelines provided adequate coverage for almost all cases. Late presentation, particularly for cat bites, was strongly associated with a higher risk of infection.
2. Infection and Risk Factors
The study identified that 20% of all hospital admissions involved infections present at the time of hospital arrival. Delayed presentation was the most significant predictor of infection, with a 68-fold increase in risk for those presenting after 24 hours. Cat bites were particularly prone to infection, with an odds ratio of 22.20 (95% CI: 11.18-44.08) for developing an infection compared to other animals.
Superficial cellulitis and lymphangitis were the most common infections, but more serious deep infections, such as septic arthritis and osteomyelitis, were also reported. Notably, the study found that surgical interventions, such as wound debridement and removal of foreign bodies, were often necessary for deep infections. Empiric antimicrobial therapy was prescribed in 49% of cases, with amoxicillin-clavulanate being the most commonly used regimen.
Microbiological culture identified common pathogens such as Pasteurella multocida in dog and cat bites, while Staphylococcus aureus and Streptococcus species were common in other types of injuries. Only 0.7% of cases required changes in the antimicrobial regimen due to unexpected pathogens. Delayed presentation and cat-related injuries were the strongest predictors of infection in this cohort.
3. Complications and Surgical Outcomes
The primary outcome (severe complications such as ICU admission, amputation, or unplanned rehospitalization) occurred in 6% of cases. Significant tissue trauma, particularly from livestock and marine animals, was independently associated with a ninefold increase in the risk of a complicated course. Surgery was required in 35% of cases, with primary closure used in about a third of surgical procedures.
Infections were relatively rare in post-operative cases, with only 1.1% of surgical patients developing an infection. Primary closure was found to be safe for selected wounds, particularly those with minimal contamination, and led to better cosmetic outcomes in some cases. However, primary closure was avoided in cases with high risk of infection, particularly cat bites and deep puncture wounds.
Despite the variety of animals involved, the overall clinical outcomes were favorable, with a low rate of mortality (0.1%) and only a few cases requiring amputation. Three deaths occurred due to snake envenomation, highlighting the importance of timely access to antivenom and critical care for snakebite victims. Significant tissue trauma and deep infections were key predictors of severe complications in animal bite cases.
Conclusion
This study underscores the importance of timely medical review and appropriate antimicrobial therapy in managing animal bites in tropical Australia. Delays in seeking care, particularly for cat bites, significantly increase the risk of infection and complications. Australian antimicrobial guidelines provide comprehensive coverage for most pathogens, and surgical interventions, when required, result in favorable outcomes. Continued efforts to educate the public on the importance of early presentation and proper wound care are crucial for reducing the risk of infection and improving patient outcomes.
Paper URL: https://doi.org/10.1016/j.ijid.2022.02.026
