What is the role of S pneumoniae 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

S pneumoniae is the most common etiologic agent responsible for AOM and for invasive bacterial infections in children of all age groups. [11] It is a gram-positive diplococcus with 90 identified serotypes (classified on the basis of the polysaccharide antigen), the frequency of which varies between age groups and geography. On direct culture, various studies have shown these bacteria to be responsible for 29-40% of isolates, but additionally pneumococcal antigens are recovered from approximately a third of those cultures classified as sterile.

Pneumococcal infections are probably responsible for at least 50% of AOM episodes. Serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F are responsible for most invasive pneumococcal disease in America; in ear aspirates from patients with AOM, serotypes 19 (23%), 23 (12.5%), 6 (12%), 14 (10%), 3 (8.5%), and 18 (6%) are isolated most commonly. The polyvalent pneumococcal vaccine confers immunity to approximately 85% of those serotypes responsible for AOM.

S pneumoniae was once susceptible to almost all common antibiotics, including penicillin G, erythromycin, and most sulfonamides. Alteration of the cell wall’s penicillin-binding protein (the antimicrobial target) has led to the appearance of multidrug-resistant S pneumoniae (MDRSP), which is resistant to beta-lactam compounds, macrolides, and sulfonamides. Resistance rates as high as 40% have been reported for these 3 antimicrobial groups. Serotypes 6B, 9V, 14, 19A, 19F, and 23F have the highest frequency of penicillin resistance.

Ceftriaxone, cefotaxime, rifampin, and vancomycin still appear to have therapeutic efficacy, as does immunization with polyvalent pneumococcal vaccine for prevention. Unfortunately, polysaccharide antigens are not immunogenic early in life. To overcome this problem, conjugated antigens, in which the polysaccharide antigen is attached to a protein carrier, may be administered to induce production of antibodies to these polysaccharides. Some conjugated antigens (eg, vaccinations for H influenzae type b [Hib]) are in widespread use.

A heptavalent vaccine for S pneumoniae is now in widespread use and appears to have made an impact on the number of cases of invasive pneumococcal disease. This vaccine confers long-term immunity to 7 of the most common and invasive strains. Emerging evidence suggests that other serotypes are beginning to be recovered more frequently in ear and sinus infections. This might render the vaccine less useful in future years. In North America, this vaccine has now been replaced by an updated 13-valent vaccine that contains conjugated antigenic material for 6 of those additional serotypes of the pneumococcus.


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