Haemophilus influenzae type b as an important cause of culture-positive acute otitis media in young children in Thailand: a tympanocentesis-based, multi-center, cross-sectional study

BACKGROUND Streptococcus pneumoniae (S. pneumoniae) and Haemophilus influenzae (H. influenzae) are considered major causes of bacterial acute otitis media (AOM) worldwide, but data from Asia on primary causes of AOM are limited. This tympanocentesis-based, multi-center, cross-sectional study assessed bacterial etiology and antimicrobial susceptibility of AOM in Thailand. METHODS Children 3 to 59 months presenting with AOM (< 72 hours of onset) who had not received prescribed antibiotics, or subjects who received prescribed antibiotics but remained symptomatic after 48-72 hours (treatment failures), were eligible. Study visits were conducted from April 2008 to August 2009. Bacteria were identified from middle ear fluid collected by tympanocentesis or spontaneous otorrhea swab sampling (< 20% of cases). S. pneumoniae and H. influenzae serotypes were determined and antimicrobial resistance was also assessed. RESULTS Of the 123 enrolled children, 112 were included in analysis and 48% of the 118 samples were positive for S. pneumoniae (23% (27/118)), H. influenzae (18% (21/118)), Moraxella catarrhalis (6% (7/118)) or Streptococcus pyogenes (3% (4/118)). The most common pneumococcal serotypes were 19F (26%) and 14 (22%). The majority of H. influenzae isolates were encapsulated (18/21), with 13 type b (Hib) representing 62% of all H. influenzae isolate or 11% of all samples (13/118), and there were only 3 non-typeable isolates. Despite high antibiotic resistance, amoxicillin/clavulanate susceptibility was high. No pneumococcal vaccine use was reported. CONCLUSIONS S. pneumoniae and H. influenzae, both frequently antibiotic resistant, were leading causes of bacterial AOM and there was an unexpectedly high burden of Hib in this population unvaccinated by any Hib conjugate vaccine. Conjugate vaccines effective against pneumococcus and H. influenzae could potentially reduce the burden of AOM in this population.