Haemophilus influenzae Infection

Haemophilus influenzae disease is a name collectively used for any kind of infection caused by the bacteria called Haemophilus influenzae. They are broadly classified into encapsulated and non-encapsulated types. The encapsulated bacterium is further subdivided into ‘a’ through ‘f’ subtypes based on capsule type. The most familiar and predominant form is H. influenzae type b (Hib), which infects mostly children and immunocompromised individuals. Other types such as type a, e and f are also isolated but less commonly than type b. Only rarely type c and d are identified. All of the serotypes, particularly type b, are common etiological agents in lower respiratory tract infections such as pneumonia. They can also cause many other types of serious infections such as meningitis, epiglottitis, cellulitis, septic arthritis, and even empyema and bacteremia.

The Hib conjugate vaccine is effective for protection against capsular polysaccharide type ‘b’ and has decreased the rate of Hib infections to a greater extent. Currently, non-encapsulated H. influenzae, also called non-typeable H. influenzae (NTHi), is responsible for the majority of cases of otitis media, sinusitis, and pneumonia in patients that have already been immunized with the vaccine. The mode of transmission is through inhalation of respiratory secretion droplets from infected individuals or by direct close contact.