A mixed methods approach to elucidate SARS-CoV-2 transmission routes and clustering in outbreaks in native workers and labour migrants in the fruit and vegetable packaging industry in South Holland, the Netherlands, May to July 2020.

Boogaard, Laura H; Sikkema, Reina S; van Beek, Janko; Brockhoff, Henricus J; Dalebout, Eva; de Heus, Barry; Niemansburg, Sophie L; Nieuwenhuijse, David; Stougje, Danny; Verspui, Ellen; Oude Munnink, Bas B; Koopmans, Marion; Fanoy, Ewout

OBJECTIVES To obtain insight in SARS-CoV-2 clustering and transmission routes during outbreaks in the predominantly migrant workforce of the fruit and vegetable packaging industry of South Holland, the Netherlands, May to July 2020. DESIGN This mixed methods study applied direct observation and interviews, epidemiologic investigation, source and contact data analysis and whole-genome sequencing. RESULTS We detected 46 SARS-CoV-2 cases and four outbreaks with a proportional representation of labour migrant and native workers in six unrelated facilities. Complete viral genome sequences revealed at least three clusters of native workers and labour migrants, two within and one between facilities. On-site inspections found adequate implementation of preventative measures, that both native workers and labour migrants showed suboptimal adherence to. Being a labour migrant was associated with living in shared housing, but not with more contacts or different sources. CONCLUSIONS The fruit and vegetable packing industry gave the impression of sufficient preparedness and control. Suboptimal adherence to the facilities' preventative guidelines could have facilitated work-floor transmission. Community and household transmission are likely to have contributed to outbreaks. We encourage further research into risk factors for transmission in labour migrants and application of these insights into targeted public health policy.