Nosocomial outbreak of multidrug-resistant Streptococcus pneumoniae serotype 15A (non-vaccine serotype) in a community hospital

Multidrug-resistant Streptococcus pneumoniae (MDRSP) showing resistance to β-lactams, macrolides, and fluoroquinolones poses a significant clinical challenge, with increasing prevalence of non-vaccine serotypes (NVT) such as 15A and 35B following the introduction of pneumococcal conjugate vaccines. Here, we report an outbreak of serotype 15A MDRSP isolated from four patients at a community hospital. A nosocomial outbreak occurred in an acute care ward and affected four unvaccinated elderly patients (aged 62-91 years). All isolates were identified as serotype 15A and showed resistance to β-lactams, fluoroquinolones, and macrolides. The isolates belonged to a single-locus variant of sequence type (ST) 292 and showed amino acid alterations in the transpeptidase domains of penicillin-binding proteins (PBPs; PBP1a, 2b, and 2x), and mutations causing amino acid changes in the quinolone resistance-determining regions of gyrA, parC, and parE. Additionally, they harbored both ermB and mefA/E genes. These findings indicate a clonal outbreak. A retrospective analysis suggests possible associations with frequent sputum suctioning, tube feeding, low body mass index, and prolonged hospitalization. MDRSP likely spread via healthcare workers working within the vicinity of the patients. The outbreak was contained within 24 days by the implementation of contact precautions, cohorting, and the use of closed suction systems. This report describes the first documented nosocomial outbreak of MDRSP ST292 lineage in Japan, highlighting several important points: the emergence of multidrug-resistant NVT in healthcare settings, the effectiveness of basic infection control measures in prevention, and the importance of serotyping in understanding pathogenicity and resistance patterns.