The use of epidemiological data in the control of foodborne viruses

Assessment of Food and Waterborne Viral Outbreaks by Using Field Epidemiologic, Modern Laboratory and Statistical Methods-Lessons Learnt from Seven Major Norovirus Outbreaks in Finland

Seven major food- and waterborne norovirus outbreaks in Western Finland during 2014–2018 were re-analysed. The aim was to assess the effectiveness of outbreak investigation tools and evaluate the Kaplan criteria. We summarised epidemiological and microbiological findings from seven outbreaks. To evaluate the Kaplan criteria, a one-stage meta-analysis of data from seven cohort studies was performed. The case was defined as a person attending an implicated function with diarrhoea, vomiting or two other symptoms. Altogether, 22% (386/1794) of persons met the case definition. Overall adjusted, 73% of norovirus patients were vomiting, the mean incubation period was 44 h (4 h to 4 days) and the median duration of illness was 46 h. As vomiting was a more common symptom in children (96%, 143/149) and diarrhoea among the elderly (92%, 24/26), symptom and age presentation should drive hypothesis formulation. The Kaplan criteria were useful in initial outbreak assessments prior to faecal results. Rapid food control inspections enabled evidence-based, public-health-driven risk assessments. This led to probability-based vehicle identification and aided in resolving the outbreak event mechanism rather than implementing potentially ineffective, large-scale public health actions such as the withdrawal of extensive food lots. Asymptomatic food handlers should be ideally withdrawn from high-risk work for five days instead of the current two days. Food and environmental samples often remain negative with norovirus, highlighting the importance of research collaborations. Electronic questionnaire and open-source novel statistical programmes provided time and resource savings. The public health approach proved useful within the environmental health area with shoe leather field epidemiology, combined with statistical analysis and mathematical reasoning.

Sequencing of viral genes

The use of molecular techniques in epidemiology gives a better understanding of viral transmission and diversity, and helps to define and characterizc outbreaks. By elucidating transmission patterns and defining outbreak parameters, appropriate preventive measures can be implemented in a timely fashion. Previously, the understanding of viral classification and phylogeny was difficult due to the challenges inherent in studying viruses. Automated cycle sequencing that uses fluorescently labeled nucleotides has revolutionized epidemiological studies of viruses at the molecular level. Sequencing of viral genes enables the identification and characterization of viruses, and sequence data are essential when investigating the etiology, dissemination, and transmission of viral infections as well as for disease surveillance and prevention. The present chapter focuses on the use of sequence analyses in epidemiological investigations.