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Control of norovirus outbreaks in areas of potential infection

17 June 2014

To critically review the management of norovirus outbreaks, Hygiena International ATP test systems(involving a hand-held SystemSURE luminometer and UltraSnap swabs) have been used to evaluate the effectiveness of cleaning procedures.

Norovirus is the most prevalent cause of infectious gastroenteritis in the UK, and the ATP Bioluminescence technique has been used for many years to identify potential sources of contamination in the food chain, in production and preparation areas as well as many other industrial and commercial applications such as restaurants and hotels etc. It has also been utilised more recently to monitor surface cleanliness, and used in conjunction with varying infection control measures to monitor many other areas of potential infection. These include confined environments as found in care homes and hospitals, where secondary or subsequent outbreaks often re-occur even after initial cleaning and sanitation procedures have been undertaken. Other potential areas of application include schools, or wherever food is prepared or consumed by the general public.

Any cleaning procedure is designed to remove residues of food and body fluids such that the subsequent application of disinfectants can function correctly and inactivate residual microbial contamination. Foods and body fluids contain large amounts of ATP i.e. adenosine triphosphate (the universal energy carrier) such that residues of ATP remaining on surfaces after cleaning provide a direct, objective measure of the efficacy of the cleaning process and residual contamination risk.

The Hygiena UltraSnap swabs contain a reagent known as luciferase/luciferin in the bulb of the swab. Once the swab is snapped and the bulb squeezed, an oxidation reaction takes place with any ATP present, emitting light. The light produced is directly proportional to the amount of ATP in the area tested. This is a rapid method showing a strong correlation between ATP and microbial cells, with results measured in relative light units (RLU) can be obtained within 15 seconds.

The key to preventing the spread of norovirus is thorough and effective cleaning combined with disinfection during and after an outbreak, and the effectiveness of decontamination should be evaluated by Health Officers. The Hygiena SystemSURE test procedure is swift, provides a PASS/CAUTION/FAIL result and can be undertaken by personnel after only minimal training.

Previous research on outbreaks of norovirus (including on cruise ships), have inadequately described the control measures implemented. Other more specific detection methods for norovirus are also expensive and it can take some time before results become available. With the SystemSURE equipment, samples were taken in infected areas and toilets and all points of regular personal contacts (eg handrails, door knobs/levers etc) including some adjacent non-infected areas and points of contact following deep cleaning. The areas swabbed were random and taken from various sampling points immediately after cleaning, and focusing on typical high hand touch areas which can transmit infection. This study was moderate in size with 601 swabs/sampling sites measured in the case of two outbreaks. A benchmark of 100 RLU was used as the maximum acceptable safe reading, since previous studies showed that this is achievable in hospital near patient areas as well as at commercial catering establishments. Accordingly a traffic lights system was adopted of Pass (green) indicating <50 RLU, Caution (orange) representing 51 – 100 RLU being present and Fail (red) where >100 RLU existed.
Post-cleaning data was generated after both outbreaks which indicated that most of the surfaces tested were actually cleaned to a high standard (generally <50 RLU). However, a small number of unclean surfaces were identified with very high RLU values of 1600 – 6946 which suggested that these locations were either poorly cleaned or not cleaned at all. The highest failure rate and highest RLU values were associated with handrails, toilet area taps and shower holders with average RLU values of 182, 468 and 978 respectively.

Additional figures showed that a better level of cleaning was achieved after a second infection outbreak. In the first outbreak involving 812 personnel, a total of 62 persons became ill with norovirus over 10 days. Three months later, at the same location only 36 from a total of 948 people became ill over 6 days. Any higher attack rates or prolonged outbreaks could be linked to greater residual environmental contamination. ATP testing performed at the infected site generally showed good cleaning after the first outbreak with low average ATP results. Sample sites included hand rails, hand contact areas in washrooms, restaurants and bars, and the Internet centres. However, several other areas of poor cleaning were identified including worktops, restaurant trolley handles, ice machines and taps. The café at the site location had the highest recorded result of public areas sampled at 4635 RLU – taken from the men’s toilet taps.

There had been many failures in implementing the established control measures. However, it seems clear that enhanced hygiene measures can significantly reduce norovirus transmission in outbreaks by as much as 85% when properly implemented to ensure of breaking the chain of infection and so reducing the transmission potential. For effective decontamination of points of common or regular personal contact to avoid subsequent or successive outbreaks, some areas of public access may have to be isolated for a short period following an outbreak.

Clearly the consistency and thoroughness of the delivery of cleaning and decontamination services are crucial to managing and preventing norovirus outbreaks. Organising dedicated teams to clean specific areas in a controlled manner is often advantageous, e.g. bathrooms and washrooms where vomiting incidents have or are likely to have occurred. Environmental sampling is recommended in all areas of outbreaks to evaluate the efficacy of control measures. ATP swabs are not a substitute for microbiological culturing methods, they are an invaluable tool for the rapid assessment of cleaning standards. They have served to identify areas and surfaces regularly inadequately cleaned, resulting in public service locations changing their cleaning procedures.

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