What is the pathophysiology of nonencapsulated (NTHi) strains Haemophilus influenzae infections?

Updated: Jun 11, 2021
  • Author: Joseph Adrian L Buensalido, MD; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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The NTHi strains colonize the nasopharynx in up to 80% of individuals. The spread of bacteria by direct extension to the eustachian tubes causes otitis media. Spread to the sinuses leads to sinusitis. Spread down the respiratory tract results in bronchitis and pneumonia. Eustachian tube dysfunction, antecedent viral upper respiratory tract infection (URTI), foreign bodies, and mucosal irritants, including smoking, can promote infection. In patients with underlying chronic obstructive pulmonary disease (COPD) or cystic fibrosis (CF), NTHi frequently colonizes the lower respiratory tract and can exacerbate the disease.

NTHi strains form biofilm in vitro and ex vivo and have been implicated in chronic infection such as otitis media, sinusitis, and bronchitis. NTHi biofilm formation was found in patients with CF on the apical surface of airway epithelia with decreased antibiotic susceptibility. Studies into the nature of this biofilm structure and proteins will help develop strategies to fight chronic infections. Persons at risk for invasive H influenzae disease include those with asplenia, sickle cell disease, complement deficiencies, Hodgkin disease, congenital or acquired hypogammaglobulinemia, and T-cell immunodeficiency states (eg, HIV infection).

NTHi infection appears to disturb epithelial integrity and barrier function owing to the destruction of cell-cell contacts, which is believed to be a prominent feature in NTHi infection and has been related to a decrease in both E-cadherin mRNA and protein-levels in lung epithelial cells from patients with chronic bronchitis. [9]

Children younger than 4 years and contacts (eg, household and daycare) of individuals with Hib disease are at higher risk of infection. More research is needed to determine the risk factors for non–type B H influenzae and NTHi. However, persons with sickle cell disease, individuals with asplenia, individuals with HIV infection, persons with immunoglobulin deficiencies and complement component deficiencies, hematopoietic stem cell transplant recipients, patients undergoing chemotherapy or radiation therapy for malignant neoplasms, and American Indians and Alaska Natives are at higher risk for invasive H influenzae disease. [10]

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