A critical reminder of severe phlegmonous lesion of the hand caused by Pasteurella multocida: a case report

¹Laboratory of Microbiology, Mohammed VI University Hospital, Oujda, Morocco, ²Faculty of Medicine and Pharmacy of Oujda, Mohammed First University, Oujda, Morocco

^&Corresponding author
Fatima-Zahra Joudar, Laboratory of Microbiology, Mohammed VI University Hospital, Oujda, Morocco

Introduction    

Pasteurella multocida is a Gram-negative coccobacillus and a facultative anaerobic bacterium commonly found as a commensal organism in the aerodigestive tracts of many domestic and wild animals, including cats, dogs, and farm animals. Human infection typically occurs following animal bites or scratches or through direct contact with animal oral or nasal secretions. While P. multocida most frequently causes localized soft tissue infections such as cellulitis, it can also be responsible for more severe invasive infections, including respiratory infections, septicemia, septic arthritis, urogenital infections and more rarely, meningitis.

Severe hand infections caused by P. multocida remain uncommon, particularly those progressing to extensive tissue necrosis and requiring amputation. Delayed presentation is a major risk factor for poor outcomes. We report a case of severe hand infection due to P. multocida following a stray cat bite in a 54-year-old woman, with a delayed presentation of 10 days, ultimately leading to amputation of the fifth metacarpal and necrosectomy of the cellulofatty spaces of the hypothenar compartment of the right hand.

Patient and observation     

Clinical findings: on physical examination, the patient was conscious and hemodynamically stable. The right hand showed marked erythema and edema, associated with tense bullae containing purulent and hemorrhagic material. Purulent discharge was observed around the fifth metacarpal (Figure 1). Flexion deformity of the fingers of the affected hand was noted, suggesting deep soft tissue involvement. There were no signs of systemic sepsis at presentation.

Timeline of the current episode: on day 0, the patient sustained a bite to the right hand from a stray cat. Over the following nine days, they experienced progressive pain, swelling, and inflammatory signs. On day 10, they were admitted to the emergency department, where surgical lavage and debridement were performed and empiric antibiotic therapy was initiated. In the subsequent days, microbiological analysis identified Pasteurella multocida. The condition progressed to soft tissue necrosis and osteitis, ultimately requiring necrosectomy and amputation of the distal fifth metacarpal, after which the patient showed clinical improvement.

Diagnostic assessment: laboratory investigations revealed an elevated C-reactive protein level of 120 mg/L and an erythrocyte sedimentation rate of 45 mm in the first hour. The complete blood count showed leukocytosis at 15,000/mm³ with neutrophilia of 85%, consistent with an acute bacterial infection. Plain radiography of the hand showed no initial abnormalities (Figure 2). Deep pus samples collected intraoperatively (Figure 3) were sent for microbiological analysis. Direct Gram staining revealed numerous Gram-negative coccobacilli associated with an intense neutrophilic response. Cultures were performed on blood agar (aerobic and anaerobic), chocolate agar enriched with vitamins under CO₂ atmosphere, and in BD BACTEC™ Plus Aerobic/F and Anaerobic/F broth bottles. After 8 hours of incubation, both aerobic and anaerobic broth cultures became positive. Subsequent subcultures yielded grayish colonies measuring approximately 3 mm in diameter after 48 hours. Identification by MALDI-TOF mass spectrometry (Bruker Biotyper®) confirmed Pasteurella multocida with a high-confidence score. Antimicrobial susceptibility testing, performed according to EUCAST guidelines, showed susceptibility to penicillin G, ampicillin, amoxicillin, amoxicillin/clavulanic acid, cefotaxime, ciprofloxacin, and levofloxacin, and resistance to nalidixic acid, tetracycline, and doxycycline (Figure 4). The final diagnosis was an extensive Pasteurella multocida infection of the right hand complicated by phlegmon, necrosis of the cellulofatty spaces, and osteitis of the distal fifth metacarpal following a cat bite. Differential diagnoses included other bacterial soft tissue infections related to animal bites.

Therapeutic interventions: immediate management included surgical lavage and debridement with bilateral incisions on the palmar and dorsal surfaces of the fifth metacarpal. Pus was drained and collected for microbiological analysis. Empiric intravenous antibiotic therapy with ampicillin (1 g three times daily) was initiated for five days. Due to progression to necrosis, the patient subsequently underwent necrosectomy of the cellulofatty spaces in the hypothenar compartment and amputation of the distal fifth metacarpal. Antibiotic therapy was then switched to oral amoxicillin/clavulanic acid (1 g three times daily) for 15 days.

Follow-up and outcomes: following surgical management and adjustment of antibiotic therapy, clinical and microbiological evolution was favorable, with regression of local inflammatory signs and satisfactory wound healing. No adverse drug reactions were observed. Early rehabilitation was initiated after resolution of the acute phase and is planned to continue for several months to optimize recovery of joint range of motion and hand function (Figure 5).

Patient perspective: the patient reported significant concern regarding the rapid progression of the infection and the functional impact on her dominant hand. She expressed relief after the surgical procedures and antibiotic adjustment, noting a clear improvement in pain and local symptoms. Although distressed by the amputation, she acknowledged the necessity of the intervention to control the infection and prevent further complications.

Informed consent: written informed consent was obtained from the patient for publication of this case report and accompanying clinical information. Patient anonymity was preserved in accordance with ethical standards.

Discussion     

The first human infection caused by P. multocida was described in 1913 by Brugnatelli in the wife of a farmer suffering from puerperal fever. However, it was not until 1930 that Kapel established the link between cat bites and human infection. P. multocida is typically responsible for soft tissue infections following animal bites or scratches, predominantly caused by cats and dogs in 60 to 80% of cases. Local complications include the formation of abscesses, tenosynovitis, septic arthritis, and osteomyelitis [1]. Risk factors include immunosuppression, diabetes, advanced age, and delayed wound care, which are associated with more severe outcomes [1,2].

Pasteurella multocida is a Gram-negative coccobacillus, non-spore-forming and non-motile, and is part of the commensal flora of the nasopharynx or gastrointestinal tract of many domestic or wild animals, with rates reaching up to 90% in cats and 66% in dogs [1]. The most common P. multocida infection in humans is soft tissue infection following an animal bite. However, this organism can infect other systems or organs, leading to severe diseases with life-threatening potential [1,2]. In our case, the patient had localized inflammatory edema following a cat bite. The infectious, particularly bacterial cause, must be considered. Bite wounds encountered in clinical practice most often involve domestic animals, primarily cats and dogs [3]. Approximately one-fifth of these wounds become infected. The bacteria most frequently isolated belong to the genera Pasteurella (30 to 50% of dogs and 50 to 90% of cats are carriers), Staphylococcus, Streptococcus, and the anaerobic group. The infection may be polymicrobial [3].

Our case is distinguished by a monomicrobial infection, meaning it is caused by a single type of microorganism, in this case, P. multocida. The clinical presentation combines intense but localized inflammatory signs, with the absence of general signs and secondary septic localizations (lung, liver, spleen, heart), which argues against a rapid, fulminant sepsis as observed in more common pyogenic infections (e.g., Staphylococcus and Streptococcus) [4]. Other distinguishing factors include the interval between the bite and the onset of inflammatory signs (short in pasteurellosis), and the type of local reaction (purulent collection from pyogenic organisms, necrotic elements from anaerobes or streptococci, etc.). In this patient, the chronology of events and the clinical presentation strongly suggest pasteurellosis. This is the most common inoculation-related pathology following a domestic animal bite [5].

After a short incubation period ranging from three to twelve hours, characteristic of this bacterium, a highly inflammatory, warm, erythematous, and classically very painful edema appears. There may sometimes be a discharge of serous fluid, and more rarely, frank pus, at the bite site. As described in the literature, the infection progressed rapidly in our patient, causing intense inflammation and pain at the bite site. Infectious samples are typically obtained from pus or any potential collections, after cleaning the wound [6]. Typical presentation includes rapid-onset erythema, pain, edema, and warmth at the bite site, often within 3-12 hours. Severe manifestations can include abscess formation, tenosynovitis, septic arthritis, osteomyelitis, and, rarely, sepsis or bacteremia [6].

The diagnosis of pasteurellosis is strongly suspected when a Gram-negative bacillus is isolated from the pus sample, as observed under microscopic examination after Gram staining. Penicillin is considered the treatment of choice for Pasteurella infections. Other drugs with effective activity include ampicillin, amoxicillin-clavulanic acid, cefuroxime, and ciprofloxacin. Reports have described P. multocida strains resistant to penicillin in human infections, and strains producing β-lactamases resistant to certain β-lactams have also been documented. Alternative antibiotic options for P. multocida infections include second- and third-generation cephalosporins, tetracyclines, chloramphenicol, and fluoroquinolones, which are active against P. multocida in vitro [7]. In the case reported here, since the infection was monomicrobial, the use of aminopenicillins proved particularly effective. Although aminopenicillin was sufficient to treat a monomicrobial infection in this case, it is important to emphasize that animal bites are often polymicrobial.

Therefore, the use of broad-spectrum antibiotics is generally recommended, especially to cover other commonly involved bacteria, such as Staphylococcus aureus and anaerobic bacteria [6,7]. In our case, the antibiotic treatment was expanded with amoxicillin/clavulanic acid, primarily aimed at preventing secondary infection of the surgical site while maintaining its effectiveness against P. multocida. Our patient presented to the hospital 10 days after the bacterial inoculation, which represents a notably long delay compared to the typical rapid progression of pasteurellosis. This delay allowed P. multocida to fully exert its virulence factors [7]. This prolonged period was likely the primary cause of the progression from a localized infection to osteoarticular complications. Additionally, the immunosuppression caused by diabetes was a significant risk factor for pasteurellosis [7].

Infections caused by P. multocida have been observed in both immunocompromised patients and healthy individuals. The increasing frequency of P. multocida infections may be attributed to more frequent contact with domestic animals. It is essential to inform immunocompromised patients about the risks associated with P. multocida infection and animal exposure to prevent the spread of the infection. The diagnosis of P. multocida infections requires a thorough collection of the patient's animal contact history, which must be communicated to the clinical microbiology laboratory. Both prevention and diagnosis are key to controlling the spread of P. multocida infections [8,9]. The speed of intervention is crucial to limit local damage and prevent the systemic spread of the infection, which may require more intensive hospital management, including additional surgical interventions or prolonged treatment. The rapid identification of the pathogen using advanced microbiological techniques, such as MALDI-TOF mass spectrometry, is essential for ensuring an accurate diagnosis and tailoring antibiotic treatment based on the isolated strain.

Another important aspect in the treatment of P. multocida infections is post-animal bite prophylaxis. While appropriate antibiotic therapy is essential following a bite, it is also crucial to assess the risks of delayed complications, such as soft tissue and bone infections, and plan for rigorous follow-up to detect any unexpected progression. In the absence of early intervention, the progression to sepsis or systemic infection becomes a major threat. Current guidelines for the management of animal bites also highlight the importance of tetanus prophylaxis depending on the circumstances of the bite and the patient's vaccination history. The prognosis of P. multocida infections is generally favorable if treated promptly with appropriate antibiotics. Delays in intervention, immunocompromised status, or severe local complications can lead to necrosis, osteomyelitis, or, rarely, amputation, as observed in our patient.

Finally, it is relevant to discuss recent advancements in research on P. multocida antibiotic treatments. While traditional antibiotics such as penicillin and amoxicillin remain the treatments of choice, recent studies on antibiotic resistance and the emergence of resistant strains in certain settings, particularly in hospital environments, emphasize the need to continue monitoring epidemiological trends and reevaluate therapeutic protocols to ensure the effectiveness of treatments [10].

Conclusion     

This case describes a hand phlegmon following a stray cat bite caused by Pasteurella multocida, which required surgical debridement and targeted antibiotic therapy after microbiological identification. It highlights that even seemingly minor cat bites can rapidly progress to severe hand infections, underscoring the importance of early clinical evaluation, prompt surgical management when indicated, and appropriate empiric antibiotic therapy guided by exposure history.

Competing interests     

The authors declare no competing interests.

Authors' contributions     

Patient management: Fatima-Zahra Joudar and Abderazzak Saddari. Data collection: Fatima-Zahra Joudar, Abderazzak Saddari and Said Ezrari. Manuscript drafting: Mohammed Lahmer. Manuscript revision: Abderazzak Saddari, Adil Maleb and Said Ezrari. All authors read and approved the final version of the manuscript.

Figures     

Figure 1: clinical images of the right hand showing extensive soft tissue infection: A) palmar view; B) dorsal view of the right hand demonstrating extensive hand phlegmon with bullae containing purulent and hemorrhagic exudate; C) associated finger flexion deformity

Figure 2: lateral radiograph of the right hand (lateral radiograph of the right hand showing soft tissue swelling without evidence of bone involvement)

Figure 3: intraoperative view of the right hand showing soft tissue necrosis (intraoperative image demonstrating necrosis of the cellulofatty tissues adjacent to the fifth metacarpal bone)

Figure 4: culture on blood agar and antibiogram from the same patient (bacterial growth on culture medium showing smooth, grayish colonies compatible with Pasteurella multocida, antibiotic susceptibility testing by disk diffusion method demonstrating inhibition zones around multiple antibiotic disks and indicating susceptibility of the isolate)

Figure 5: image of the patient's hand 6 months after recovery

References