Shirin Kalimuddin1, Swaine L Chen2,3, Cindy T K Lim4, Tse Hsien Koh5, Thean Yen Tan6, Michelle Kam7, Christopher W Wong3, Kurosh S Mehershahi2, Man Ling Chau8, Lee Ching Ng8, Wen Ying Tang9, Hishamuddin Badaruddin10, Jeanette Teo11, Anucha Apisarnthanarak12, Nuntra Suwantarat12,13, Margaret Ip14, Matthew T G Holden15, Li Yang Hsu2,4, Timothy Barkham9. 1. Department of Infectious Diseases, Singapore General Hospital. 2. Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore. 3. Genome Institute of Singapore. 4. Saw Swee Hock School of Public Health, National University Singapore. 5. Department of Pathology, Singapore General Hospital. 6. Department of Laboratory Medicine, Changi General Hospital, Singapore. 7. Department of Internal Medicine, Singapore General Hospital. 8. Environmental Health Institute, National Environment Agency. 9. Department of Laboratory Medicine, Tan Tock Seng Hospital. 10. Communicable Diseases Division, Ministry of Health, and. 11. Department of Laboratory Medicine, Microbiology Unit, National University Hospital, Singapore. 12. Infectious Disease Division, Thammasat University Hospital, and. 13. Chulabhorn International College of Medicine, Thammasat University, Pathumthani, Thailand. 14. Department of Microbiology, Chinese University of Hong Kong, Shatin; and. 15. School of Medicine, St Andrews University, Scotland, United Kingdom.
Abstract
BACKGROUND: Streptococcus agalactiae (group B Streptococcus [GBS]) has not been described as a foodborne pathogen. However, in 2015, a large outbreak of severe invasive sequence type (ST) 283 GBS infections in adults epidemiologically linked to the consumption of raw freshwater fish occurred in Singapore. We attempted to determine the scale of the outbreak, define the clinical spectrum of disease, and link the outbreak to contaminated fish. METHODS: Time-series analysis was performed on microbiology laboratory data. Food handlers and fishmongers were screened for enteric carriage of GBS. A retrospective cohort study was conducted to assess differences in demographic and clinical characteristics of patients with invasive ST283 and non-ST283 infections. Whole-genome sequencing was performed on human and fish ST283 isolates from Singapore, Thailand, and Hong Kong. RESULTS: The outbreak was estimated to have started in late January 2015. Within the study cohort of 408 patients, ST283 accounted for 35.8% of cases. Patients with ST283 infection were younger and had fewer comorbidities but were more likely to develop meningoencephalitis, septic arthritis, and spinal infection. Of 82 food handlers and fishmongers screened, none carried ST283. Culture of 43 fish samples yielded 13 ST283-positive samples. Phylogenomic analysis of 161 ST283 isolates from humans and fish revealed they formed a tight clade distinguished by 93 single-nucleotide polymorphisms. CONCLUSIONS: 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.
BACKGROUND: Streptococcus agalactiae (group B Streptococcus [GBS]) has not been described as a foodborne pathogen. However, in 2015, a large outbreak of severe invasive sequence type (ST) 283 GBS infections in adults epidemiologically linked to the consumption of raw freshwater fish occurred in Singapore. We attempted to determine the scale of the outbreak, define the clinical spectrum of disease, and link the outbreak to contaminated fish. METHODS: Time-series analysis was performed on microbiology laboratory data. Food handlers and fishmongers were screened for enteric carriage of GBS. A retrospective cohort study was conducted to assess differences in demographic and clinical characteristics of patients with invasive ST283 and non-ST283 infections. Whole-genome sequencing was performed on human and fish ST283 isolates from Singapore, Thailand, and Hong Kong. RESULTS: The outbreak was estimated to have started in late January 2015. Within the study cohort of 408 patients, ST283 accounted for 35.8% of cases. Patients with ST283 infection were younger and had fewer comorbidities but were more likely to develop meningoencephalitis, septic arthritis, and spinal infection. Of 82 food handlers and fishmongers screened, none carried ST283. Culture of 43 fish samples yielded 13 ST283-positive samples. Phylogenomic analysis of 161 ST283 isolates from humans and fish revealed they formed a tight clade distinguished by 93 single-nucleotide polymorphisms. CONCLUSIONS: 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.
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