Streptococcus pneumoniae and Haemophilus influenzae at the initial stage of influenza

Background: Streptococcus pneumoniae and Haemophilus influenzae infections in children with influenza have been noted because of the severity of co-infection. In Japan, vaccination against S. pneumoniae and H. influenzae infections has been listed in the vaccine program in 2008, but the characteristics of the two organisms, colonizing at the initial stage of influenza infection, have not been investigated in detail. Methods: Nasopharyngeal swabs from children with influenza (flu+) (n = 236; mean age, 6.2 years) were examined for bacterial pathogens, including S. pneumoniae and H. influenzae. They were then examined for serotypes, drug susceptibilities, and resistance genes (or gene mutations). As a reference, children with upper respiratory tract infection (URTI+, flu-; n = 189; mean age, 6.2 years) were also examined. Results: S. pneumoniae, beta-streptococci (groups A, B, and G), methicillin-susceptible and -resistant S. aureus, Moraxella catarrhalis, and H. influenzae were isolated. For S. pneumoniae, nine serotypes were detected with prevalent types of 3, 6, 19 and 23. Penicillin resistance was detected in types 19 and 23, while resistance to macrolide and clindamycin was found in various types. For H. influenzae, only b serotype was detected, with marked ampicillin resistance. The majority was non-typeable. Very similar results were obtained even in URTI+ (flu-) cases. Conclusion: Multiple drug-resistant S. pneumoniae with major serotypes, for example, 19 and 23 and H. influenzae with serotype b were already present at the initial stage of influenza infection, similar to URTI+ flu- cases. They could be prevented by current vaccines, but drug-resistant non-typeable H. influenzae is troubling.