2015 Epidemic of Severe Streptococcus agalactiae Sequence Type 283 Infections in Singapore Associated With the Consumption of Raw Freshwater Fish: A Detailed Analysis of Clinical, Epidemiological, and Bacterial Sequencing Data

Abstract

ST283 is a zoonotic GBS clone associated with farmed freshwater fish, capable of causing severe disease in humans. It caused a large foodborne outbreak in Singapore and poses both a regional and potentially more widespread threat.

Group B Streptococcus Infections Caused by Improper Sourcing and Handling of Fish for Raw Consumption, Singapore, 2015–2016

“…Fish and water strains from 1 clade were nearly identical to clinical strains from this outbreak (Figure 4). The small variability of 0–2 SNPs and 0–12 indels between fish and water strains and the reference human outbreak strain (SG-M1) is equivalent to variability observed in 131 clinical strains from the same outbreak reported elsewhere (0–5 SNPs from the SG-M1 reference) ( 12 ). Strains from a second clade of GBS ST283 had a difference of 57–71 SNPs and 11–33 indels when compared with the SG-M1 genome.…”

“…The first clade included 12 isolates from 6 fish from a food stall, a fresh produce market and a port, and 4 fish tank water samples from a port. Genome sequencing showed that these 12 isolates were nearly identical (0–2 SNPs and 0, 1, and 12 indels all in homopolymeric runs of > 4 nt) compared with the 2.1-Mbp genome of the reference human outbreak strain, SG-M1, isolated from a meningitis patient during the GBS outbreak in Singapore during 2015 ( 12 , 17 ). Isolates that clustered into the second clade were 20 isolates from 12 fish and 2 fish tank water samples and did not include any human isolates either from this outbreak or from previous reports of human GBS infecting isolates.…”

“…Among the 20 GBS PCR-positive samples from food stalls, 5 yielded isolates; these isolates were of serotype II ST652, serotype III ST283, serotype III ST335, and serotype V ST1 (Technical Appendix Table 3). The GBS ST283 isolated was from a RTE sliced fish sample sold as grass carp collected from a food stall linked to a human case, as described ( 12 ). We did not detect GBS ST283 in samples from restaurant/snack bars; however, we did find a range of other GBS, including serotypes Ia ST7, Ia ST103, Ia ST485, III ST651, III ST861, V ST1, V ST24, VI ST167, and VII ST1.…”

“…Patients with GBS ST283 infections during this outbreak were more likely to show development of meningoencephalitis, septic arthritis, and spinal infection than were persons with non–GBS ST283 infections ( 12 ). Although this study suggested Malaysia as a source of the strain, the finding of the same ST in Hong Kong and Thailand ( 10 , 11 ) suggested that GBS ST283 is generally prevalent throughout the region.…”

“…GBS ST283 had previously been isolated from tilapia in Thailand ( 10 ) and in adult human cases in Hong Kong ( 11 ). However, GBS ST283 has not been reported to colonize the human gastrointestinal tract, although to date only 1 study of fish mongers and fish handlers has specifically looked for colonization by this strain ( 12 ). …”