Acute
otitis media (AOM) is the most common disease seen in childhood. Streptococcus pneumoniae, non-typeable Haemophilus influenzae (NTHi), and Moraxella catarrhalis are the most frequent pathogens of all AOM episodes. The high prevalence of drug-resistant pathogens such as
penicillin-resistant S. pneumoniae (PRSP) and betalactamase producing or nonproducing
ampicillin-resistant H. influenzae (BLPAR or BLNAR) is causing serious clinical problems worldwide. PRSP and BLNAR have become important risk factors for intractable clinical outcome of AOM. PRSP causes a three times higher incidence of intractable AOM than susceptible strains. BLNAR strains show
penicillin-binding protein gene mutation and are not only resistant to
ampicillin, but also have reduced susceptibility to
cephalosporin. The resistant H. influenzae pathogen has shown clonal dissemination in Japan in ways different from those of
penicillin-resistant S. pneumoniae. Protection against AOM due to these pathogens may depend on pathogen-specific
antibodies. Pneumococcal capsular
polysaccharides (PCPs) are type specific and poorly immunogenic in children younger than 2 years old. Approximately 50% of
otitis-prone children showed subnormal levels of anti-PCP
IgG2 antibody. In our immunological study in children with
otitis media, however,
otitis-prone children were not unusually vulnerable to
infections except those resulting in
otitis media. This fact seems to refute the presence of a broad immunological deficit in these children. Some pathogen-specific
antibodies may be directed against
protein immunogens such as
pneumococcal surface protein A (PspA) of S. pneumoniae, P6 of NTHi, and UspA of M. catarrhalis. The levels of antibody to P6 of NTHi in healthy children were significantly higher than those in the
otitis-prone children after the age of 18 months. In general, individual antibody levels in
otitis-prone individuals did not have an age-dependent rise. The failure to develop a good antibody response to common
antigens such as PspA and P6 may enable the pathogen to cause persistent or recurrent disease.