Effects of cleaning and disinfection in reducing the spread of Norovirus contamination via environmental surfaces

Abstract

A reverse transcriptase polymerase chain reaction assay was used to study the transfer of Norovirus (NV) from contaminated faecal material via fingers and cloths to other hand-contact surfaces. The results showed that, where fingers come into contact with virus-contaminated material, NV is consistently transferred via the fingers to melamine surfaces and from there to other typical hand-contact surfaces, such as taps, door handles and telephone receivers. It was found that contaminated fingers could sequentially transfer virus to up to seven clean surfaces. The effectiveness of detergent– and disinfectant-based cleaning regimes typical of those that might be used to decontaminate faecally contaminated surfaces and reduce spread of NV was also compared. It was found that detergent-based cleaning with a cloth to produce a visibly clean surface consistently failed to eliminate NV contamination. Where there was faecal soiling, although a combined hypochlorite/detergent formulation at 5000 ppm of available chlorine produced a significant risk reduction, NV contamination could still be detected on up to 28% of surfaces. In order consistently to achieve good hygiene, it was necessary to wipe the surface clean using a cloth soaked in detergent before applying the combined hypochlorite/detergent. When detergent cleaning alone or combined hypochlorite/detergent treatment failed to eliminate NV contamination from the surface and the cleaning cloth was then used to wipe another surface, the virus was transferred to that surface and to the hands of the person handling the cloth. In contrast, were surfaces where contaminated with NV-infected faecal suspension diluted to 1 in 10 and 1 in 80, intended to simulate surfaces that have become contaminated after secondary transfer, treatment with a combined bleach/detergent formulation, without prior cleaning, was sufficient to decontaminate surfaces and prevent transfer.

Introduction

Noroviruses (NVs) are a major cause of gastroenteritis, which spreads rapidly in premises such as hospitals, hotels, day-care centres, residential and domestic homes.1., 2., 3., 4., 5. NV hospital outbreaks are common, and frequently result in ward closures because of the need to prevent further spread and to facilitate environmental cleaning. The scale of the problem in the community was highlighted by a recent study of rates of infectious intestinal disease in the UK. Wheeler et al.⁶ estimated that for every one case of NV reported to national surveillance, a further 1562 cases occur in the community. Based on the number of reported cases, Evans et al.⁷ estimated the total number of cases in the community to be around 3 million per year.

The likelihood of airborne transmission of NV was demonstrated in an outbreak at a restaurant where no food source was implicated, but an analysis of the attack rate showed an inverse correlation with the distance from a person who had vomited.³ Microbiological data show that projectile vomiting associated with NV infection may distribute up to 3×10⁷ virus particles as an aerosol,⁸ whilst environmental sampling during outbreaks of vomiting and diarrhoea confirm that widespread dissemination of NV occurs on hand contact and other surfaces.2., 9. From such data and from estimates which suggest that the infective dose for NV may be as low as 10–100 particles, Caul⁸ concluded that, in addition to possible aerosol inhalation, hands and surfaces also play an important part in facilitating transfer of NV infection, either by direct faecal–oral transfer or by transfer to foods that are eaten without further cooking.

The potential for transmission of NV via environmental surfaces is also supported by epidemiological studies, the most compelling evidence coming from recurrent outbreaks of NV infection in successive cohorts of guests in hotels and on cruise ships.9., 10., 11., 12. From the patterns of infection, it is concluded that whereas aerosols are probably the main route of dissemination within a cohort of guests, contaminated fomites are the most likely factor responsible for sustaining a succession of outbreaks. Other data comes from an investigation of an NV outbreak at a wedding reception, which showed that the likely route of transmission was from a kitchen assistant who had vomited in a sink that was subsequently used for preparing vegetables eaten by the wedding guests.¹³ Analysis of risk exposure during an outbreak of NV gastroenteritis in an elderly care unit showed that areas where patients had vomited were the most significant factor for the spread of NV to staff.¹ Further evidence of environmental transfer comes from a report of two carpet fitters who became ill after removing a carpet from a hospital ward 13 days after the last case in an NV outbreak.¹⁴ The role of contaminated soft furnishings in transmission and the difficulties these pose for decontamination is highlighted by the outbreak that occurred among school children who attended a theatre in which a vomiting incident had occurred on a previous day.¹⁵ Guidelines have been issued for the control of NV outbreaks in hospitals that stress the importance of preventing staff and patient movements to other areas, thorough handwashing and effective environmental decontamination.¹⁶

Since NV is uncultivable in the laboratory, little is known about the length of time it remains infectious in the environment or the effectiveness of disinfection procedures used to inactivate the virus. The development of a broadly reactive reverse transcriptase polymerase chain reaction (RT-PCR) has facilitated the detection of the virus in both clinical and environmental samples.¹⁷ In this investigation, we have used an RT-PCR assay to study the transfer of NV from contaminated faecal material via fingers and surfaces, and compared the effectiveness of detergent-based cleaning alone with hypochlorite disinfection for eliminating NV from faecally contaminated surfaces.