Nontypeable Haemophilus influenzae in Carriage and Disease

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Abstract
Haemophilus influenzae causes a number of diseases in humans, including both localized and systemic infections.1 Early work established that not all isolates of this gram-negative bacterium possess the same pathogenic potential. Lower respiratory tract infections caused by nontypeable H influenzae (NTHi) strains are responsible for significant mortality in both infants and children in developing countries.2 They also represent a major cause of morbidity in both developed and developing countries. In general, carriers of NTHi are healthy but occasionally develop localized acute respiratory tract infections (eg, otitis media, sinusitis, pneumonia, and conjunctivitis). In addition, NTHi is associated with exacerbations of underlying lung disease (eg, chronic bronchitis, bronchiectasis, and cystic fibrosis). Less frequently, it has been reported to cause septicemia, endocarditis, epiglottitis, septic arthritis, and meningitis, illnesses more usually associated with H influenzae type b (Hib).3 Also, NTHi is reported as causal in female genital tract infection and postpartum and neonatal infection (including septicemia).4 Brazilian purpuric fever is the most serious disease exclusively caused by strains of NTHi.5