Ad Hoc Group on Foodborne Viral Infections meeting 14 September 2011

Summary of the fifth meeting of the ad hoc group on Foodborne Viral Infections

1. Introduction

At this meeting the group considered Environmental Health Officers’ (EHO) perspectives on prioritising and dealing with norovirus incidents and outbreaks, Health Protection Units’ (HPU) response to notifications of norovirus incidents, environmental monitoring and testing for norovirus and control options at all stages of the food chain.

2. EHO perspective on prioritising and dealing with norovirus incidents and outbreaks

Members received presentations from two EHOs on dealing with incidents relating to norovirus in oysters. Investigations into previous norovirus outbreaks associated with oysters were summarised and some of the difficulties associated with investigating and tracing the source of the illness were highlighted. These included difficulties in taking enforcement actions due to lack of agreed standards and validated testing methods, the use of private investigators in investigating outbreaks, and delays in notification and reporting of outbreaks. Difficulties were also encountered with traceability of produce as oysters sometimes come from several different suppliers. In terms of future developments it was noted that the need to set viral limits in bivalves and in water had been recognised and advances in detection methods were promising.

3. HPU response to notifications of norovirus incidents

Members were briefed on the HPU response to notifications of norovirus incidents and the systems for statutory notification were outlined; these included a list of notifiable diseases and a list of notifiable organisms. Laboratories are required to notify positive findings and clinicians are required to notify diseases. It was noted that norovirus is not on the list of notifiable infections and is not specifically on the list of notifiable diseases but could be considered to come under food poisoning which is a notifiable disease.

HPUs have to make a judgement on whether reported cases are food related or result from person to person spread. Challenges in defining the source of illness were highlighted. HPUs then gather basic information about the cases and provide infection control advice or may perform a visit if the outbreak is prolonged.

Members noted that the extension to the IID2 study is looking at the extent to which norovirus is foodborne. Research in the Netherlands has suggested more than 40% is due to food, in the UK the most recent estimate was 11% and in the US the estimate is higher. It was agreed there were significant difficulties in conducting such an analytical study and including illness known only to be foodborne.

4. Environmental contamination testing

Members received a presentation on environmental monitoring and detection of norovirus and the results of a study to look at environmental contamination of surfaces such as door handles, toilets, fridges, etc. in different catering premises were presented. The results of a study to look at norovirus in a hospital environment were also presented. Toilets, equipment, computers and fittings were all examined post outbreak and post-cleaning. Members were informed that norovirus is readily detected in the environment and strains found in the population match those found in the environment. Characterisation of the P2 domain could be used to link environmental contamination and norovirus cases.

5. Options for control at all stages of the food chain

Members were briefed on options for prevention and control of virus at all stages of the food chain. Both procedural controls (such as education of food handlers about microbial safety guidelines and hygiene rules) and physical controls (such as chemical disinfection and temperature control) were discussed. The practicalities and effectiveness of different control options on different viruses and foods were outlined.

6. Work Programme

Members reviewed the work programme and agreed to focus on Hepatitis E at their next meeting.