S. pneumoniae drug susceptibility tracked in Japan

By Joanna Lyford, Senior medwireNews Reporter

A 12-year survey of the antimicrobial susceptibility of Streptococcus pneumoniae isolates in Miyagi Prefecture in Japan has identified important changes, including improved susceptibility to β-lactam antibiotics.

The study authors attribute the changes to the introduction of a pneumococcal vaccine, and say their findings highlight the importance of ongoing surveillance of S. pneumoniae infection.

The study was undertaken by Daiki Ozawa (Tohoku University Graduate School of Medicine, Sendai, Japan) and colleagues and focused on the drug susceptibility profile of S. pneumoniae isolates from otorhinolaryngology patients.

The team obtained 41,069 isolates from patients at 40 otorhinolaryngology outpatient clinics between 2001 and 2012. Specimens were cultured at a central laboratory and assessed for susceptibility to eight antimicrobial agents, as indicated by minimum inhibitory concentrations.

Between 2001 and 2010, susceptibility of S. pneumonia to penicillin was lowest in children aged 0 to 2 years followed by those aged 3 to 5 years. Subsequently, susceptibility improved sequentially between 2010 and 2012.

For example, the prevalence of penicillin-resistant S. pneumoniae decreased from 35.2% in 2010 to 14.6% in 2012 in rhinorrhoea specimens and from 43.4% to 14.3% in otorrhoea specimens.

Susceptibility to certain antimicrobial drugs, including cephems and carbapenems, was relatively stable over the study period overall. In the 0 to 2 age group, however, susceptibility to these agents improved slightly after 2010.

Susceptibility to macrolides decreased in all age groups during the study period and high levels of resistance were apparent until 2012. Susceptibility to lincosamides fell dramatically during the first few years of the study period; again resistance remained high until 2012.

Susceptibility to fluoroquinolones was unchanged during the study period.

Writing in the Journal of Infection and Chemotherapy, Ozawa et al note that the improvement in S. pneumonia susceptibility to penicillin occurred after the introduction of the 7-valent protein-polysaccharide conjugate vaccine in 2010. The vaccine “may have had a herd immunity effect by altering pneumococcal carriage and transmission rates,” they propose.

The team concludes: “[I]t is important to continue performing surveys in order to determine how the circumstances of S. pneumoniae infection in Japan affect the drug susceptibility profile and serotype replacement in the future.”

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