What is the role of H influenzae in the etiology of acute otitis media (AOM)?

Updated: Sep 25, 2019
  • Author: John D Donaldson, MD, FRCSC, FACS; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

In middle ear aspirates from patients with AOM, H influenzae is the second most frequently isolated bacterium and is responsible for approximately 20% of episodes in preschool children. [12] The frequency may be higher in otitis-prone children, older children, and adults who have received the pneumococcal vaccine.

A study by Martin et al looking at AOM cases between 1999 and 2014 in children aged 6-23 months found that, while nasopharyngeal colonization with S pneumoniae has reportedly decreased since pneumococcal conjugate vaccines (PCVs) were introduced, colonization with H influenzae in the study subjects initially increased before dropping back to levels seen prior to routine administration of 7-valent PCV (PCV7). The investigators obtained nasopharyngeal cultures from four cohorts of children with AOM. The first cohort was cultured in 1999-2000, before routine PCV7 use, while in the second (2003-2005) and third (2006-2009) cohorts, two or more doses of PCV7 were administered to 93% and 100% of children, respectively, and in the fourth cohort (2012-2014), 100% of the children received two or more doses of 13-valent PCV (PCV13). Nasopharyngeal colonization with H influenzae in cohorts 1, 2, 3, and 4 occurred in 26%, 41%, 33%, and 29% of children, respectively. [13]

The bacterium is a small, pleomorphic, gram-negative coccobacillus. Those bacteria encapsulated with a polysaccharide coating are classified into 6 distinct types (a-f); nonencapsulated types are referred to as nontypeable and are responsible for the great majority of AOM episodes. (The nonencapsulated strains have been subtyped biochemically and antigenically, but, to date, this classification has limited clinical application.)

Traditionally, Hib has been found responsible for most invasive illnesses attributed to these bacteria and for meningitis, epiglottitis, and septicemia. Hib accounts for only 10% of all episodes of AOM in which H influenzae is recovered. In areas of the world where the aforementioned Hib-conjugated vaccine is administered early in life, risks from this potentially lethal strain have greatly diminished.

Antimicrobial resistance in Hib is conferred almost exclusively (95%) by the formation of a single enzyme, triethylenemelamine 1 lactamase, which, in some series, is secreted by as many as 40% of all nontypeable strains. This resistance is overcome relatively easily by using blocking agents, extended-coverage cephalosporins, broad-spectrum macrolides, or sulfonamides.

H influenzae may participate more widely in head and neck infections than was once believed. One of the principal mechanisms is related to the ability of the bacterium to hide and recover from antibiotic action by forming a mucous complex known as a biofilm. Research has focused on enhancing penetration of or dissolving the protective biofilm.


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