Abstract

BackgroundPneumococcal disease outbreaks of vaccine preventable serotype 4 sequence type (ST)801 in shipyards have been reported in several countries. We aimed to use genomics to establish any international links between them. MethodsSequence data from ST801-related outbreak isolates from Norway (n = 17), Finland (n = 11) and Northern Ireland (n = 2) were combined with invasive pneumococcal disease surveillance from the respective countries, and ST801-related genomes from an international collection (n = 41 of > 40,000), totalling 106 genomes. Raw data were mapped and recombination excluded before phylogenetic dating. ResultsOutbreak isolates were relatively diverse, with up to 100 SNPs (single nucleotide polymorphisms) and a common ancestor estimated around the year 2000. However, 19 Norwegian and Finnish isolates were nearly indistinguishable (0–2 SNPs) with the common ancestor dated around 2017. ConclusionThe total diversity of ST801 within the outbreaks could not be explained by recent transmission alone, suggesting that harsh environmental and associated living conditions reported in the shipyards may facilitate invasion of colonising pneumococci. However, near identical strains in the Norwegian and Finnish outbreaks does suggest that transmission between international shipyards also contributed to those outbreaks. This indicates the need for improved preventative measures in this working population including pneumococcal vaccination.

Highlights

  • Outbreaks of invasive pneumococcal disease (IPD) in shipyard workers have been observed in multiple European countries in recent years; Northern Ireland (2015), Norway (2019), Finland (2019) and France (2020) [1,2,3,4]

  • The Public Health Agency, Health Protection Service, Northern Ireland (PHA-NI) defined outbreak cases as: individuals who worked at the Belfast shipyard after 11th January 2015 AND for a confirmed case: a clinical diagnosis of IPD or pneumococcal pneumonia AND at least one of the following: S. pneumoniae isolated from a normally sterile site, pneumococcal DNA or antigen detected in fluid from a normally sterile site or pneumococcal antigen detected in urine

  • Illumina sequence data was available from Norwegian Institute of Public Health (NIPH) for the 17 Norwegian outbreak isolates belonging to clonal complex (CC)801 isolated in January-April 2019 [2] and a further five CC801 isolates from routine IPD surveillance between 2005 and 2018

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Summary

Introduction

Outbreaks of invasive pneumococcal disease (IPD) in shipyard workers have been observed in multiple European countries in recent years; Northern Ireland (2015), Norway (2019), Finland (2019) and France (2020) [1,2,3,4]. These European outbreaks all involved serotype 4 though other serotypes were reported (3, 8, 9 N and 12F) [1,2,3,4]. Near identical strains in the Norwegian and Finnish outbreaks does suggest that transmission between international shipyards

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