A child with cellulitis following water exposure

CASE PRESENTATION

An 11-year-old previously healthy and vaccinated female presented to our centre with a 2-day history of left foot edema associated with tenderness, erythema, and inability to bear weight on the affected foot. She had no fever. She was seen in an outpatient clinic 2 days prior to her presentation and started on oral cephalexin; however, her symptoms worsened and erythema had ascended rapidly.

On examination, she was clinically well and afebrile. Puncture wound was present between her left fourth and fifth toe with a large amount of white watery discharge coming through the wound. She had significant pitting edema and erythema of her left foot extending up to left distal tibia with warmth, tenderness, and normal ankle joint range of motion (Figure 1).

Figure 1.

Picture of left foot.

Her initial blood work showed a white blood cell count of 12.4 × 10⁹/L, with an absolute neutrophil count of 7.6 × 10⁹/L, C-reactive protein of 43 mg/L (<5.00), and normal creatinine kinase (CK) level.

Upon further questioning, the mother mentioned that the patient was swimming in a lake the day prior to the start of symptoms and stepped on a sharp object in the lake. The patient was admitted for parenteral antibiotic therapy. A bacterial culture from the foot discharge revealed the diagnosis.

DISCUSSION

The wound culture grew Aeromonas species, a gram-negative, facultatively anaerobic bacteria that is a known cause of skin and soft tissue infection (SSTI) after freshwater (rivers and lakes) and brackish water exposure as well as medicinal leech exposure (Hirudotherapy). They can cause sepsis in patients with end-stage liver disease and in immunocompromised hosts. The usual presentation is self-limiting diarrheal disease and SSTI in immunocompetent patients.

SSTI is one of the three classic syndromes caused by Aeromonas. The other two include: (1) gastrointestinal tract syndromes (e.g., enteritis, colitis, and hemolytic-uremic syndrome) and (2) bacteremia (1). Traumatic wounds are the most common predisposing factor in invasive aeromonad infection leading to cellulitis which can progress rapidly to myonecrosis, necrotizing fasciitis, and fulminant sepsis. Given the rapid progression of cellulitis observed in our patient, the CK level was measured and a surgical consult was done to rule out myonecrosis and necrotizing fasciitis.

Aeromonas infections are monomicrobial in most cases. However, polymicrobial infections can occur in cases of traumatic injury. Our patient had growth of Citrobacter freundii in addition to Aeromonas jandaei on cultures of the discharge.

Detailed clinical history-taking in cases of cellulitis is key to identifying potential infectious etiologies and will help in deciding empiric antimicrobial treatment. There are no clinical symptoms and signs that distinguish Aeromonas infections from other uncommon gram negative rods associated with aquatic exposure. Table 1 shows the differential diagnosis for SSTI associated with aquatic and other exposure histories.

Table 1.

Skin and soft tissue infection associated with aquatic exposure and unique exposure history

Exposure, and setting, or location	Likely organisms
Brackish, freshwater, and floodwater	Aeromonas spp., Vibrio vulnificus
Swimming pool or aquarium water	Mycobacterium marinum
Poultry, fish, crab, and shrimp	Erysipelothrix rhusiopathiae
Dog or cat bite	Pasteurella spp., Capnocytophaga
Human bite	Eikenella corrodens
Penetrating trauma and burn	Pseudomonas and Staphylococcus aureus
Neutropenia	Gram-negative rods including pseudomonas
Varicella infection	Group A Streptococcus
Immunocompromised	Cryptococcus neoformans/gattii

Mortality rate for Aeromonas sepsis can be 33% or higher (1). Thus, it is important to have a high index of suspicion when evaluating patients with cellulitis after water exposure who are at risk of developing septicemia. Aeromonas species can produce inducible β-lactamases, including extended-spectrum-β-lactamases and chromosomal CphA metallo-β-lactamases which specifically hydrolyze carbapenems (1,2). They are uniformly resistant to penicillin and ampicillin, are often resistant to cefazolin, and have variable susceptibility to third-generation cephalosporins, piperacillin-tazobactam, and carbapenems (2).

Empirical treatment with fluoroquinolones in mild to moderate cases of Aeromonas infections is recommended with the addition of an aminoglycoside for severe infections (sepsis, tissue necrosis). It is important to know that antimicrobial resistance can develop on therapy, there is emerging resistance to fluoroquinolones in some Aeromonas strains, and polymicrobial infection can often occur in traumatic cases requiring polymicrobial therapy.

Our patient’s bacterial culture susceptibility result revealed intermediate sensitivity to meropenem, resistance to ertapenem, and sensitivity to ciprofloxacin, gentamicin, and piperacillin-tazobactam. She had significant improvement of cellulitis and was discharged after 48 h of starting piperacillin-tazobactam and ciprofloxacin. She was discharged on oral ciprofloxacin for 10 days as it was an attractive single oral antimicrobial agent that would ensure excellent drug bioavailability and would cover for both organisms (Citrobacter freundii and Aeromonas jandaei).

CLINICAL PEARLS

• Aeromonas infections are associated with freshwater and brackish water exposure. Traumatic injury is often the portal of entry.

• Cellulitis is a common diagnosis. Aquatic exposure history should raise clinical concern of unusual gram negative organisms which are often resistant to conventional SSTI antimicrobials.

• The development of cellulitis with rapid progression should alert the clinician for possible myonecrosis or necrotizing fasciitis.

INFORMED CONSENT

Family consent has been obtained to publish this case.

FUNDING

There are no funders to report.

POTENTIAL CONFLICTS OF INTEREST

All authors: No reported conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.