Biphasic Outbreak of Invasive Group A Streptococcus Disease in Eldercare Facility, New Zealand

Area of Science:

• Infectious Disease Epidemiology
• Genomic Epidemiology
• Microbiology

Background:

• Invasive group A Streptococcus (iGAS) outbreaks in eldercare facilities pose significant mortality risks.
• A 3-month iGAS outbreak in an eldercare facility resulted in 5 deaths and exhibited a biphasic pattern.
• Initial chemoprophylaxis contained the first phase, but a second outbreak phase emerged after infection control measures ceased.

Purpose of the Study:

• To retrospectively investigate the genomic epidemiology of a biphasic invasive group A Streptococcus outbreak.
• To identify the specific clone responsible for the outbreak and its genetic characteristics.
• To understand the role of genomic elements in the outbreak's persistence and spread.

Main Methods:

• Whole-genome sequencing (WGS) of Streptococcus pyogenes isolates from the outbreak and during the response.
• Bioinformatics analysis to determine phylogenetic relationships and identify genetic markers.
• Comparison of outbreak isolates with non-outbreak strains to detect unique genetic features.

Main Results:

• Analysis confirmed a single clone of Streptococcus pyogenes emm81 responsible for the outbreak among residents and staff.
• Outbreak isolates possessed an integrative conjugative genomic element absent in non-outbreak emm81 strains.
• This element carried the macrolide resistance determinant erm(TR), indicating potential for antimicrobial resistance spread.

Conclusions:

• Retrospective, high-resolution genomic investigation successfully identified the clonal origin and spread of the iGAS outbreak.
• The outbreak demonstrated rapid transmission within a closed facility, challenging standard infection control procedures.
• Complete clearance of the outbreak was not achieved solely by infection control measures, underscoring the need for integrated genomic surveillance.