in health-care environments, the prevention of nosocomial infections involves routine and terminal cleaning. nonflammable alcohol vapor in co2 systems is used in health care environments where medical electronics would be adversely affected by aerosolized chlorine or other caustic compounds. in 2011, the cdc published a clinical practice guideline addressing strategies for the prevention and control of norovirus gastroenteritis outbreaks in health-care settings. based on a systematic review of published scientific studies, the guideline presents 51 specific evidence-based recommendations, which were organized into 12 categories: 1) patient cohorting and isolation precautions, 2) hand hygiene, 3) patient transfer and ward closure, 4) food handlers in healthcare, 5) diagnostics, 6) personal protective equipment, 7) environmental cleaning, 8) staff leave and policy, 9) visitors, 10) education, 11) active case-finding, and 12) communication and notification. the guideline also identifies eight high-priority recommendations and suggests several areas in need of future research. vaccine trials ligocyte announced in 2007 that it was working on a vaccine and had started phase 1 trials. the company has since been taken over by takeda pharmaceutical company. as of 2019, a bivalent (nov gi.1/gii.4) intramuscular vaccine had completed phase 1 trials. in 2020 the phase 2b trials were finished. the vaccine relies on using a virus-like particle that is made of the norovirus capsid proteins in order to mimic the external structure of the virus. since there is no rna in this particle, it is incapable of reproducing and cannot cause an infection. persistence the norovirus can survive for long periods outside a human host depending on the surface and temperature conditions: it can survive for weeks on hard and soft surfaces, and it can survive for months, maybe even years in contaminated still water. a 2006 study found the virus remained on surfaces used for food preparation seven days after contamination. detection in food routine protocols to detect norovirus in clams and oysters by reverse transcription polymerase chain reaction are being employed by governmental laboratories such as the food and drug administration (fda) in the us. treatment there is no specific medicine to treat people with norovirus illness. norovirus infection cannot be treated with antibiotics because it is a virus. treatments aim to avoid complications by measures such as the management of dehydration caused by fluid loss in vomiting and diarrhea, and to mitigate symptoms using antiemetics and antidiarrheals. epidemiology annual trend in reports of norovirus infection in england and wales (2000–2011). source: hpa laboratory reports of norovirus infections in england and wales 2000–2012. source: hpa, nb testing methods changed in 2007 norovirus causes about 18% of all cases of acute gastroenteritis worldwide. it is relatively common in developed countries and in low-mortality developing countries (20% and 19% respectively) compared to high-mortality developing countries (14%). proportionately it causes more illness in people in the community or in hospital outpatients (24% and 20% respectively) as compared with hospital inpatients (17%) in whom other causes are more common. age and emergence of new norovirus strains do not appear to affect the proportion of gastroenteritis attributable to norovirus. norovirus is a common cause of epidemics of gastroenteritis on cruise ships. the cdc through its vessel sanitation program records and investigates outbreaks of gastrointestinal illness—mostly caused by norovirus—on cruise ships with both a us and foreign itinerary; there were 12 in 2015, and 10 from 1 january to 9 may 2016. an outbreak may affect over 25% of passengers, and a smaller proportion of crew members. human genetics epidemiological studies have shown that individuals with different abo(h) (histo-blood group) phenotypes are infected with nov strains in a genotype-specific manner. gii.4 includes global epidemic strains and binds to more histo-blood group antigens than other genogroups. fut2 fucosyltransferase transfers a fucose sugar to the end of the abo(h) precursor in gastrointestinal cells and saliva glands. the abh-antigen produced is thought to act as a receptor for human norovirus: a non-functional fucosyltransferase fut2 provides high protection from the most common norovirus strain, gii.4. homozygous carriers of any nonsense mutation in the fut2 gene are called non-secretors, as no abh-antigen is produced. approximately 20% of caucasians are non-secretors due to g428a and c571t nonsense mutations in fut2 and therefore have strong – although not absolute – protection from the norovirus gii.4. non-secretors can still produce abh antigens in erythrocytes, as the precursor is formed by fut1. some norovirus genotypes (gi.3) can infect non-secretors. history the norovirus was originally named the "norwalk agent" after norwalk, ohio, in the united states, where an outbreak of acute gastroenteritis occurred among children at bronson elementary school in november 1968 (although an outbreak had already been discovered in 1936 in roskilde, denmark, where it is commonly known as "roskilde syge" or "roskilde illness"). in 1972, electron microscopy on stored human stool samples identified a virus, which was given the name "norwalk virus". numerous outbreaks with similar symptoms have been reported since. the cloning and sequencing of the norwalk virus genome showed that these viruses have a genomic organization consistent with viruses belonging to the family caliciviridae. the name "norovirus" (norovirus for the genus) was approved by the international committee on taxonomy of viruses (ictv) in 2002. in 2011, however, a press release and a newsletter were published by ictv, which strongly encouraged the media, national health authorities and the scientific community to use the virus name norwalk virus, rather than the genus name norovirus, when referring to outbreaks of the disease. this was also a public response by ictv to the request from an individual in japan to rename the norovirus genus because of the possibility of negative associations for people in japan and elsewhere who have the family name "noro". before this position of ictv was made public, ictv consulted widely with members of the caliciviridae study group and carefully discussed the case. in addition to "norwalk agent" and "norwalk virus", the virus has also been called "norwalk-like virus", "small, round-structured viruses" (srsvs), spencer flu and "snow mountain virus". common names of the illness caused by noroviruses still in use include "roskilde illness", "winter vomiting disease", "winter vomiting bug", "viral gastroenteritis", and "acute nonbacterial gastroenteritis".