Odontogenic Facial Cellulitis Caused by Haemophilus aphrophilus in a Pediatric Patient: A Culture-Guided Antibiotic Switch Following Extraoral Drainage A Case Report

Technical Summary: Odontogenic Facial Cellulitis Caused by Aggregatibacter aphrophilus in a Pediatric Patient

Problem Statement
Odontogenic cellulitis is a frequent pediatric emergency requiring prompt source elimination, surgical drainage, and antimicrobial therapy. While empiric antibiotic regimens (typically amoxicillin-clavulanic acid with or without metronidazole) are standard for polymicrobial infections involving viridans streptococci and obligate anaerobes, treatment failure can occur due to antimicrobial resistance or infection by uncommon pathogens. This case report addresses the clinical challenge of managing severe odontogenic infections that do not respond to standard empiric therapy, specifically highlighting the rare occurrence of Aggregatibacter aphrophilus (formerly Haemophilus aphrophilus) as a causative agent in pediatric patients.

Methodology
The study presents a single-case report of a 10-year-old previously healthy female presenting with a four-day history of progressive chin and submental swelling, fever (38°C), and pain. The clinical workflow followed a standard diagnostic and therapeutic protocol with a specific pivot based on microbiological data:

1. Clinical Assessment: Diagnosis of odontogenic cellulitis was established based on diffuse facial swelling, tenderness, and a grossly carious mandibular left second primary molar (FDI tooth 75).
2. Surgical Intervention: The patient underwent extraction of the offending tooth and incision and drainage (I&D) of the abscess.
3. Microbiological Sampling: Purulent material was collected aseptically prior to antibiotic administration for culture and antimicrobial susceptibility testing (AST).
4. Therapeutic Trial: Empiric therapy with amoxicillin-clavulanic acid and metronidazole was initiated immediately post-procedure.
5. Adaptive Management: Upon observing limited clinical improvement after several days, the team reviewed the culture results. The isolate was identified as A. aphrophilus, which demonstrated resistance to amoxicillin but susceptibility to amikacin, meropenem, imipenem, ciprofloxacin, and other agents.
6. Targeted Therapy: Empiric antibiotics were discontinued, and the regimen was switched to intravenous amikacin based on the AST profile.

Key Results

• Microbiological Findings: Culture revealed heavy growth of Aggregatibacter aphrophilus. AST confirmed resistance to amoxicillin and susceptibility to amikacin, meropenem, imipenem, ciprofloxacin, ofloxacin, cefotaxime, chloramphenicol, levofloxacin, and ceftazidime.
• Clinical Outcome: Following the switch to intravenous amikacin, the patient exhibited rapid clinical improvement within four days. Symptoms resolved, including the normalization of body temperature, subsidence of pain, and marked reduction in facial swelling with the restoration of normal facial contour.
• Follow-up: The patient was discharged without complications and showed complete resolution of the infection at follow-up, with no recurrence or functional impairment.

Significance and Claims
The paper posits that this case underscores two primary clinical imperatives:

1. Consideration of Uncommon Pathogens: In cases of severe odontogenic infections that fail to respond to appropriate surgical management and empiric antibiotics, clinicians should consider atypical pathogens such as A. aphrophilus. The authors note that the fastidious nature of this organism often leads to under-recognition when routine microbiological investigations are omitted.
2. Value of Culture-Guided Therapy: The successful outcome demonstrates the critical value of obtaining culture and susceptibility testing in selected cases—specifically those with extensive cellulitis, systemic signs of infection, or failure to respond to initial therapy. This approach facilitates targeted antimicrobial therapy, reduces unnecessary exposure to ineffective antibiotics, and supports antimicrobial stewardship.

The authors conclude that while antibiotics alone cannot eradicate odontogenic infections with the source in situ, the combination of definitive surgical management (extraction and I&D) and culture-directed antibiotic therapy resulted in a favorable outcome. They acknowledge the limitation of generalizing findings from a single patient but assert that such reports expand knowledge regarding unusual pathogens and provide practical lessons for diagnosis and management. The paper does not propose new experimental protocols but advocates for the application of existing microbiological principles in refractory pediatric dental infections.