Rinsing contaminated fingers with water alone, or with triclosan-containing soap and water, was considerably more effective for removing Norwalk virus than was using an alcohol-based hand sanitizer, but the antibacterial soap showed no advantage over water alone, according to a report in the January Applied and Environmental Microbiology (76:394-399). These findings are from the first known direct test of an alcohol-based hand sanitizer against a human norovirus strain, according to Christine Moe and Pengbo Liu of the Rollins School of Public Health at Emory University in Atlanta, Georgia, and their collaborators there and at North Carolina State University, Raleigh.

"Our findings have greatest significance for food service and health care settings because over-reliance on alcohol- based hand sanitizers may put them at greater risk for norovirus outbreaks," Moe says. Noroviruses spread readily through fecal contamination of food, water, hands, and surfaces, notably those involved in food preparation. An estimated 23 million cases occur annually in the United States, affecting about 8% of the population, according to a 1999 report from the Centers for Disease Control and Prevention in Atlanta. Norwalk virus, named for an Ohio municipality which had an outbreak of the virus in 1968, causes nausea, vomiting, diarrhea, and abdominal cramps, often accompanied by headache and fever.

Moe, Liu, and their collaborators compared the effectiveness of liquid soap and alcohol hand sanitizers in removing or killing viruses on finger pads, following methods developed by the American Society for Testing and Materials. After finger pads were inoculated with norovirus and then washed, the researchers used quantitative reverse transcriptase PCR to measure viruses that remained. In another set of tests, sodium hypochlorite (bleach) eliminated virus, while ethanol, regardless of concentration, did little to reduce virus titer. In vivo rinsing either with water or with antibacterial, triclosan-containing soap proved about equally effective in reducing viruses on finger pads.

These results suggest that protection comes from mechanically removing the virus from the hands, rather than from inactivating the virus, says Stuart Levy of Tufts University in Boston, Massachusetts, who was not involved in this research. Elaine Larson of Columbia University in New York, N.Y. agrees. "It is likely that much of the viral removal from hands is more related to mechanical friction than to antiviral product activity," she says. "It's likely that plain soap would perform as well as an antibacterial product, but more data are needed."

"Human hands play an important role in person-to-person transmission of noroviruses, and effective hand hygiene is an important way to interrupt this transmission route," say Moe and Liu. Remarkably, dose-response, humanchallenge studies show noroviruses to be the most infectious agents ever described, Moeadds. Avoiding infection is a challenge because some hosts lack symptoms, while others can excrete infectious particles for several weeks after symptoms subside. Virus concentrations can be extremely high in feces, she says. "There are examples of outbreaks where a single food service worker with dirty hands made contaminated food items that resulted in hundreds, even thousands of cases of norovirus illness." Regarding the apparent ineffectiveness of alcohol, Moe says that some viruses, including norovirus, lack envelopes, making them relatively insensitive to alcohol and, thus, "tough little pathogens." Meanwhile, however, alcohol inactivates many kinds of bacteria as well as viruses with envelopes.

Moe and her collaborators are continuing to test commercially available hand-hygiene products to see how they perform against human noroviruses. Some new alcohol-based sanitizers "seem much more effective [than those tested earlier] in reducing noroviruses on finger pads," she says. "These findings highlight the need for evidencebased, decision making about hand-hygiene products in settings where norovirus outbreaks occur."

David C. Holzman
David C. Holzman is the Microbe Journal Highlights Editor.