NTHi

Non-typeable Haemophilus influenzae (NTHi) is a Gram-negative, pleomorphic coccobacillus in the Haemophilus genus. Unlike encapsulated strains such as Haemophilus influenzae type b (Hib), NTHi lacks a polysaccharide capsule and is typically untypeable. It is a common inhabitant of the human nasopharynx and a frequent cause of mucosal infections.

NTHi requires X (hemin) and V (NAD) factors for growth on artificial media and is cultured on chocolate or specialized media. Virulence factors include IgA protease, outer membrane proteins, and lipooligosaccharide; it forms biofilms and can survive within the respiratory tract.

Clinical significance: NTHi is a leading cause of acute otitis media and sinusitis in children and also contributes to conjunctivitis and bronchitis. In individuals with chronic lung disease, it can cause exacerbations and chronic colonization. Invasive disease is less common than Hib but can occur, particularly in at risk populations.

Diagnosis and treatment: Diagnosis is made by culture or molecular testing of appropriate specimens (middle ear fluid, sinus aspirates, sputum, or nasopharyngeal swabs). Many NTHi strains produce beta-lactamase, reducing susceptibility to penicillins; antibiotic choice often includes amoxicillin-clavulanate or a second- or third-generation cephalosporin. Severe disease may require parenteral therapy such as ceftriaxone.

Prevention and vaccine status: The Hib vaccine protects against encapsulated type b disease but does not cover NTHi. No licensed vaccine currently prevents NTHi infections; vaccine development targets conserved protein antigens with ongoing research.