Sandbox hemophillus

Pathophysiology

Transmission

• Transmission is by direct contact or by inhalation of respiratory tract droplets.
• Neonates can acquire infection by aspiration of amniotic fluid or contact with genital tract secretions containing the bacteria.

Seeding

• A larger bacterial load or the presence of a concomitant viral infection can potentiate the infection.
• The colonizing bacteria invade the mucosa and enter the bloodstream.
• 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.

Pathogenesis

• The antiphagocytic nature of the Hib capsule and the absence of the anticapsular antibody lead to increasing bacterial proliferation.
• When the bacterial concentration exceeds a critical level, it can disseminate to various sites, including meninges, subcutaneous tissue, joints, pleura, pericardia, and lungs.
• The antibody to the Hib capsule plays the primary role in conferring immunity.
• Newborns have a low risk of infection, likely because of acquired maternal antibodies.
• When these transplacental antibodies to the PRP antigen wane, infants are at high risk of developing invasive H influenzae disease, and their immune responses are low even after the disease.
• Therefore, they are at high risk of repeat infections since prior episodes of H influenzae do not confer immunity. By age 5 years, most children have naturally acquired antibodies.
• The Hib conjugate vaccine induces protection by inducing antibodies against the PRP capsule.
• The Hib conjugate vaccine does not provide protection against NTHi strains. Since the widespread use of the Hib conjugate vaccine, NTHi has become more of a pathogen.