Preventing norovirus outbreaks on wards

In the US, around 23 million people suffer acute gastroenteritis due to noroviruses each year – while, in the UK, the Health Protection Agency has estimated that it costs the NHS in England over £100 million every year, with 75% of all reported outbreaks occurring in healthcare settings. Although noroviruses are not normally dangerous, they can lead to complications in patients who are young, elderly or vulnerable due to other health problems. At the annual congress of the Infection Prevention Society, Dr Christine Moe, a professor at Emory University in the US, presented clinical evidence to explain why these viruses thrive in healthcare settings, along with new data on the efficacy of preventative measures. Dr Moe explained that human noroviruses have been proven to be the most infectious pathogens known, with a 45% attack rate: “noroviruses are members of the Calciviridae family and can be transmitted through faecal contamination of food and water, surfaces and hands. They are very successful and persistent pathogens, with only a small amount of the virus needed to infect humans,” she explained. “They are also uniquely enduring, surviving on surfaces for up to four to six weeks. There is a very short incubation period of around 24 hours, and symptoms normally last 12 to 72 hours, while carriers can excrete the virus long after they recover from symptoms.” Providing an overview of the epidemiology of the virus, she explained that, in the US, most outbreaks tend to be food borne and occur in restaurants. To a lesser extent, they also occur in care homes, cruise ships and schools. In contrast to the US, however, most outbreaks in the UK are associated with healthcare – with 20% of cases linked to hospitals and 39% with residential care facilities. In the UK, research suggests there are around 130 to 215 norovirus outbreaks reported each year, with around one million cases per year. She suggested that the trend for more private rooms, with smaller numbers of patients, and less shared bathrooms in the US, is likely to account for some of the differences in epidemiology. However, in both countries, it appears that incidence is increasing. Whether this is due to better surveillance, diagnostics and awareness, or the arrival of new strains (which appear to be more virulent) is unclear, she pointed out. Some of the risk factors include the fact that there is a large proportion of highly susceptible population in healthcare settings – noroviruses tend to affect the elderly and to a lesser extent the young. Shared hospitals wards, multiple beds in the same room, higher patient to staff ratios, inadequate hygiene and inadequate use of disinfectants are also contributing factors. In the case of outbreaks in the healthcare setting, the virus is usually introduced into the environment by faecal contamination, projectile vomiting or contaminated food or water. Once in the environment it is spread by direct and indirect contact by patients and staff – either by hands, or through contact with contaminated surfaces. Norovirus outbreaks typically involve both patients and staff, with high reported attack rates. Multiple wards are often affected during outbreaks – usually due to the same strain – resulting in ward closure, staff shortages and major disruption to hospital activities. Outbreaks in the healthcare setting tend to be smaller in size than those in the restaurant setting and are most likely to be due to person-to-person transmission. Higher mortality rates and longer duration are also associated with the healthcare setting.

Norovirus research

Dr Moe revealed that a number of studies have been conducted to investigate factors such as environmental and person-toperson transmission. This has included the testing of surfaces, such as ceramic, formica and stainless steel, using two norovirus strains – at staged intervals over a four to six-week period. The most reduction in virus was found on the ceramic surface, but the noroviruses were found to be very persistent on all these surfaces – surviving longest at cooler temperatures. Hand hygiene is considered a critical component of interrupting person-toperson transmission, but Dr Moe warned that hospitals need to be wary of assuming that any sanitising agent will work against the virus. She revealed that the first ever study of the human norovirus, using human volunteers, showed variations in the effectiveness of hand hygiene agents. The groundbreaking fingerpad method study, which she led at the Rollins School of Public Health at Emory University in the US, was the first to abandon traditional surrogate animal viruses and test actual human noroviruses collected from the stool of infected volunteers. Samples of the virus were applied to the hands of human volunteers and topical antimicrobial products evaluated against them. In comparing different sanitising and handwashing agents, each with different formulations and alcohol levels, the laboratory found marked differences in the levels of effectiveness. An initial study showed that a 62% ethanol-based sanitiser was ineffective against Norwalk virus on human fingerpads. This was compared to liquid antibacterial soap and water rinse. “In this first study, we found that the most effective agent was the liquid triclosan soap but there was only a 1 log (90%) reduction. This has important implications as hospitals are vulnerable to outbreaks and tend to rely on alcoholbased sanitisers.” Other products were also tested, including two hand sanitisers by Gojo Industries. This included Purell VF 447 which comprised 70% ethanol, along with additional potentiators. (The product was not launched in the EU). Data showed that this provided better virus removal than other products tested with a log reduction of 1.7. However, the most effective was the Purell hand sanitising gel, VF481, which reduced the virus by over 99.9% (3 log reduction) after a 15-second contact. The hand sanitiser was tested using a modified American Society of Testing Materials method, using the sanitiser at exposure times of 30 seconds and 15 seconds. The fingerpad studies using Norwalk virus were approved by the Emory University Institutional Review Board and included 5 to 12 adult volunteers. Each participant was asked to wash, disinfect and dry their hands, then 10 μl of a 20% stool suspension containing Norwalk virus was inoculated onto fingerpads of both hands. Virus was immediately eluted from one fingerpad in order to measure input concentration of the virus. After drying for 20 minutes, virus from another finger was eluted to measure the remaining amount of virus after drying. The dried virus on the fingerpads were then exposed to 1mL of the sanitiser for either 30 seconds or 15 seconds. Any remaining virus was then eluted off the fingerpads. Norwalk virus RNA was measured by quantative real-time RT-PCR using Norwalk virus-specific primers and probes. Log reductions of virus were calculated to examine the efficiacy of the sanitiser against the virus. The research team concluded that Purell hand sanitising gel, VF481, is an effective sanitiser against Norwalk virus with a log reduction between 2.8 and 3.1 after 30 second contact time and 3.7 after 15 second contact time. Although the observed mean log reduction after 15 seconds contact time was slightly greater than the mean log reduction after 30 seconds contact time, the researchers said that this was likely to be due to variability between experiments. However, efficacy was not decreased when the exposure time was reduced from 30 seconds to 15 seconds. Dr Moe concluded from the research that the most reliable regime to reduce norovirus on hands is the use of alcoholbased hand sanitisers containing additional ingredients to potentiate the alcohol, adding that efficacy data should be carefully considered when selecting ways to prevent human norovirus risk. Dr Moe said that different strains of norovirus had also been tested and the research had found that some are more persistent than others, such as genogroup 2 noroviruses, which are reported most frequently in outbreaks and have proven more resistant to disinfection methods.