Small gram ⊝ coccobacillary rod. - Aerosol transmission. - Produces IgA protease. - Culture on chocolate agar, which contains factors V (NAD⁺) and X (hematin) for growth. - Can also be grown with S aureus, which provides factor V via RBC hemolysis.- Capsule is composed of the polymer polyribosylribitol phosphate (PRP). It protects bacterium against phagocytosis and complement-mediated lysis by binding factor H, a circulating regulator protein that normally prevents complement (C3b) deposition on host cells

Can cause:- Epiglottis: "cherry red" in children; "thumbprint sign" on lateral neck x-ray- Meningitis: epidemic in unvaccinated children ages 3 months to 2 years- Otitis media: usually nontypeable strains- Pneumonia

Diagnosis: blood or CSF culture on chocolate agar; PCR; antigen detection of capsule

- Vaccine contains type b capsular polysaccharide conjugated to diphtheria toxoid. Given between 2 and 18 months of age.

Treatment: cefotaxime or ceftriaxone; use rifampin if still colonized