Severe Lower Extremity Cellulitis Caused by an Unusual Pathogen: Haemophilus Influenzae Type F

Area of Science:

• Infectious Diseases
• Bacteriology
• Immunology

Background:

• * Cellulitis is a common bacterial skin infection, typically affecting the lower extremities.
• * Invasive infections caused by non-typeable or non-vaccine-preventable strains of *Haemophilus influenzae* are increasingly recognized.
• * The emergence of capsular type F *Haemophilus influenzae* (HiF) presents a novel challenge, particularly in immunocompromised populations.

Observation:

• * A 64-year-old female with well-controlled human immunodeficiency virus (HIV) presented with severe, painful lower extremity cellulitis.
• * Initial imaging (CT scan) excluded gas or deep tissue collections, ruling out necrotizing fasciitis.
• * Blood and wound cultures identified *Haemophilus influenzae* type F (HiF) as the causative agent.

Findings:

• * The patient's cellulitis was confirmed to be caused by *Haemophilus influenzae* type F.
• * This case represents an unusual presentation of cellulitis due to this specific pathogen.
• * The identification of HiF underscores its role as a newly emergent pathogen.

Implications:

• * This case highlights the potential for *Haemophilus influenzae* type F to cause invasive infections beyond the typical respiratory tract.
• * Clinicians should consider HiF in the differential diagnosis of severe cellulitis, especially in immunocompromised patients.
• * The rise of HiF emphasizes the need for ongoing surveillance and potential updates to vaccination strategies against *Haemophilus influenzae*.