Gastrointestinal Flu: Norovirus in Health Care and Long-Term Care Facilities
- Robert A. Weinstein, Section Editor
- Division of Infectious Diseases, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland
- Reprints or correspondence: Dr. Cynthia L. Sears, Divs. of Infectious Diseases and Gastroenterology, 1550 Orleans St., CRBII, Ste. 1M.05, Baltimore, MD 21231 (csears{at}jhmi.edu).
Abstract
Noroviruses, recognized as the leading global cause of viral gastroenteritis and a major contributor to food-borne illness, present a growing challenge in health care and long-term care facilities. The virus spreads easily and by multiple routes. A visitor to a ward might initiate an outbreak by person-to-person contact, vomiting staff members or patients can disseminate the virus by airborne means, and contaminated surfaces, such as doorknobs and computer keyboards, can sustain an epidemic. In addition, although self-limited in healthy hosts, the virus can cause increased morbidity in more-vulnerable people. The GII.4 strain of the virus now dominates in multiple recent worldwide epidemics as well as in health care and long-term care facilities. Much like the influenza virus, norovirus appears to evolve by antigenic drift and evading the immune system, causing waves of global epidemics. Previous attempts at controlling outbreaks, both in the community and in closed facilities, provide guidance about the vigilance and action required by the health care community to diminish the clinical impact of norovirus infection.
Once given the diminutive name “small, round structured viruses,”; noroviruses have emerged as a growing threat in the community and in health care facilities. Noroviruses are now recognized as the leading cause of viral gastroenteritis, estimated to affect at least 23 million people yearly in the United States alone [1] and to contribute to an expanding number of outbreaks in hospitals and long-term care facilities.
Noroviruses were originally named for the places where they were identified, but these single-stranded, nonenveloped RNA viruses are now grouped within the Caliciviridae family and are classified into 5 genogroups; groups I, II, and IV affect humans. Genogroups are further divided into genotypes (or clusters) and then strains; group I contains ⩾8 genotypes, group II contains 17 genotypes, and group IV contains 1 genotype [2, 3]. Characterized by diarrhea, vomiting, abdominal pain, malaise, and, typically, a low-grade fever, norovirus illnesses quickly resolve, most often on their own. However, viral shedding may be protracted [4, 5]. Prolonged asymptomatic shedding, noroviral persistence in the environment, and a low infectious dose contribute to the sustained transmission of these viruses.
Traditionally, the illness caused by this group of viruses has been diagnosed clinically. The Kaplan criteria for diagnosis of presumptive norovirus infection, developed in 1982, include stool cultures negative for bacterial pathogens, vomiting in ⩾50% of cases, an incubation period of 24–48 h, and a mean or median illness duration of 12–60 h [6]. Specific diagnosis can be made through use of electron microscopy and ELISA, although these methods lack sensitivity. The benchmark for diagnosis is RT-PCR, developed for norovirus in the 1990s. With this method, the Kaplan criteria have been found to have a sensitivity of 68% and a specificity of 99% [7].
For years, noroviruses have remained under the radar for most clinicians. The inability to culture the virus and the lack of an animal model have restricted research. Surveillance, notably for endemic norovirus disease, is limited, because laboratory diagnosis is currently confined to state and national public health facilities. In addition, acute attacks of gastroenteritis, even when clustered, are frequently not reported to health officials. Because of the difficulty of diagnosing the disease and its lack of perceived morbidity, no national surveillance system for acute gastroenteritis exists in the United States [8]. Despite these limitations, the growing number of reported norovirus outbreaks, especially in health care facilities, cannot be ignored.
Evolving Epidemiology of Norovirus Infection
Overall importance of norovirus to enteric disease. Noroviruses are now recognized as, by far, the most common viral cause of gastroenteritis [8], and given the often short-term symptoms and the lack of easy diagnostic techniques, the number of reported norovirus cases is thought to vastly underestimate the true number of cases. Wheeler et al. [9] note that only 1 case is identified for every 1562 cases that likely exist. The ability of noroviruses to persist in the environment for perhaps even 3–4 weeks likely contributes to the high number of outbreaks [10, 11]. An investigation after an unfortunate outbreak associated with the food served at a family reunion in West Virginia revealed that both the chicken brought from New York and the scalloped potatoes brought from West Virginia carried different strains of the virus [12]. In a study of 226 outbreaks in the United States, 24% were associated with multiple strains [13].
Increase in outbreaks and emergence of new viral strains. Although surveillance for norovirus is incomplete, available data suggest that outbreaks of norovirus infection are increasing [8]. Although multiple norovirus strains circulate simultaneously, outbreaks are often dominated by 1 strain, now more easily identified and tracked with the use of PCR [13]. Noroviruses replicate only in the gastrointestinal tract and are highly adaptable, evolving mostly by antigenic drift (and sometimes recombination) that leads to changes in viral capsid protein binding to oligosaccharides on host gut mucosal surfaces [14, 15]. As a result, new norovirus strains, all GII.4 (genogroup II, genotype 4) viruses, were responsible for pandemics in 1995–1996 (US95/96 norovirus strain), 2002 (Farmington Hills strain), 2004 (Hunter strain), and 2006 (2006a/Minerva and 2006b/Laurens strains). Typically, additional local epidemics also occur because of other norovirus genogroups/genotypes [3, 8, 13, 16, 17]. This link between outbreaks and new norovirus variants was elucidated, in part, by data collected in Europe that demonstrated a marked increase in outbreaks of norovirus infection in 2002 that coincided with the emergence of a new variant, first noticed in Germany and The Netherlands and later found to have spread throughout continental Europe and beyond [17]. This pattern represents a recurring theme–new norovirus variant, new epidemic wave–in norovirus epidemiology. Antigenic drift or recombination resulting in the emergence of new norovirus strains suggests that the kindred spirit of noroviruses is the influenza virus, well known for antigenic drift and reassortment that yields epidemic and pandemic disease.
Increasing outbreaks of norovirus disease have fueled international efforts to improve surveillance. The European Foodborne Viruses Network collects epidemiological and molecular data from 13 European countries. As of 2008, the Centers for Disease Control and Prevention is requesting reports of all acute gastroenteritis outbreaks through the National Outbreak Reporting System, whereas previously, only data on food-borne outbreaks were collected [8]. It is expected that this request for voluntary reporting will help provide a national estimate of norovirus disease. The Centers for Disease Control and Prevention has also developed Calicinet, a centralized database of different norovirus sequences, intended to help determine links between outbreaks. Improved surveillance may well impact public health; for example, there is evidence that cruise-ship outbreaks might predict winter norovirus outbreaks and could be used as an early warning system [18].
Increased outbreaks in nursing homes and long-term care facilities. Although norovirus was originally identified as a cause of community-associated gastroenteritis [19], it is now clear that 30%–50% of outbreaks occur in closed facilities, such as hospitals, retirement centers, and nursing homes [8, 13, 20]. Additional analysis of acute gastroenteritis outbreaks reported to the Centers for Disease Control and Prevention during 2000–2004 indicated that an additional 28% of outbreaks occurred in restaurants and catered-meals events, 16% on cruise ships, and 8% in day care centers [13]. The GII.4 strain, in particular, has gained importance in outbreaks in closed institutions, where transmission appears to often occur by person-to-person contact [13, 20]. The reason for the GII.4 predominance is unknown but has been thought to be attributable to enhanced environmental stability of these strains and/or decreased herd immunity that promotes their transmissibility.
Increased illness severity? It is unclear how variable the virulence of noroviruses is. The Farmington Hills strain demonstrated higher attack rates and longer persistence on cruise ships than do other strains, although this difference did not reach statistical significance [16]. The GII.4 variant strain that affected Europe in 2002 was associated with excess deaths; however, this could be attributed to its predominance among hospital and nursing home residents [17], where individuals might have been more vulnerable than the general population. Norovirus gastroenteritis, although generally a mild, self-limited disease, can be less benign when patients are older; recently, confirmed norovirus-associated mortality has been recognized in long-term facilities in the United States [8]. Illnesses among hospital inpatients and even in the community are frequently reported to last 5 days [4, 21]. Additional data suggest that noroviruses may trigger severe outcomes in some hosts, such as older or immunocompromised patients or those with cardiovascular disease. Complications may include acute renal failure or rejection, arrhythmias, hypokalemia, and chronic diarrhea [4, 5, 21, 22].
Why Noroviruses Are Such a Threat in Hospitals and Nursing Homes
Highly transmissible. A little norovirus goes a long way. Less than 10–100 virions can be enough to infect a healthy adult [23]. Data involving outbreaks readily demonstrate the ease of norovirus transmission. A recent lengthy outbreak affecting 27 students and 2 staff members in an elementary school in Washington, D.C., was traced to a contaminated computer mouse and keyboard and was not terminated until this shared resource was successfully disinfected [24]. Investigation into outbreaks associated with a submarine sandwich franchise restaurant identified a sink in which lettuce was cleaned and workers washed their hands as a possible source of cross-contamination that promoted infection [25]. Experiments demonstrate that norovirus can be transmitted sequentially to 7 different surfaces, including door handles and telephone receivers, after volunteers touched 1 surface originally contaminated with only 30 µL of fecal fluid [26].
Multiple modes of transmission. Norovirus transmission occurs by food, water, and airborne routes, as well as incidental hand contact with contaminated surfaces or fomites and through person-to-person contact. It is primarily fecal-oral contamination that drives the spread of norovirus. Estimates suggest that one-half of all outbreaks of food-borne infection in the United States are caused by norovirus [27]. Large outbreaks have implicated oysters, raspberries, and water, among other vehicles [28–30]. As another example, a single ill employee contaminated 76 L of icing distributed on various baked goods, which resulted in ∼3000 outbreak-associated cases of norovirus infection over 4 days [31]. The potential for food-borne spread extends to the global economy of food distribution, as evident by reports of recent norovirus outbreaks in Australia that were traced to oysters imported from Japan [32].
It is now recognized that vomiting with airborne norovirus dispersion is an important route of virus dissemination. An analysis of an outbreak in a large hotel demonstrated that victims' attack rates were inversely related to their distance from a woman who vomited during her meal [33]. An outbreak in an elementary school demonstrated that attack rates were directly related to the number of times pupils were exposed to vomiting episodes, suggesting that spread occurred by the inhalation and swallowing of viral particles [34]. Transmission has even occurred to individuals walking through an emergency department in which a vomiting patient was being evaluated [35].
Although aerosol spread may initiate an outbreak, continued propagation of a norovirus disease outbreak can, in some instances, be attributed to the role of subsequent environmental or fomite contamination [26]. For example, in a concert hall–linked outbreak in Wales involving 300 people, the epidemic investigation suggested a point source outbreak initiated by an attendee who had vomited in the auditorium, with continued case accumulation through environmental contact by people coming to the concert hall over several subsequent days [36]. Health care facilities, in particular, are susceptible to environmental and fomite contamination. Sampling swabs taken from a pediatric intensive care unit demonstrated norovirus to be the most common virus detected, present in 18% of swabs, most frequently from such sites as toilet door handles and toilet taps that are readily soiled with minute amounts of feces [37]. Swabbing of environmental surfaces in a long-term care veterans facility a full 2 weeks after the peak of a norovirus outbreak demonstrated norovirus on toilet seats, a bed rail, a dining table, and an elevator button, even after extensive cleaning of the facility [38].
Finally, person-to-person transmission occurs. During a collegiate football game in Florida, numerous members of the visiting North Carolina football team became ill, presumably from contaminated turkey sandwiches that they had eaten from box lunches the day before. The day after the football game, despite not having shared any food, members of the Florida team became ill as well [39]. Person-to-person contact is especially important in the health care and long-term care settings, where close living quarters, shared bathrooms, and incontinent patients increase the risk that norovirus can spread from one person to another. Prospective studies of >170 inpatient units in England demonstrated that outbreak rates increased with the number of beds in a unit and shorter lengths of stay and were especially high in geriatric and general medical care units [40].
Highly resistant to disinfectants. Although norovirus is easy to spread, it is much more difficult to remove. Simple detergent cleaning is not sufficient to remove norovirus from fomites or surfaces. Experiments suggest that clean surfaces are obtained only after wiping the surface first with a detergent to remove particulate debris and then applying hypochlorite bleach at 5000 ppm as a disinfectant. Other disinfectants, such as quaternary ammonium compounds or alcohols, are not as effective in removing norovirus [26, 34]. Recent outbreak management provides evidence of the importance of appropriate disinfectant use. When illness continued in a Michigan restaurant in 2006, public health workers discovered that a quaternary ammonium–based sanitizer had been used, and it was not until a bleach solution was used that the restaurant could reopen [11]. New disinfectants, mainly peroxygen compounds, exhibit enhanced activity and appear promising [41]. Proper hand washing–using liquid soap and water for 1 min, rinsing for 20 s, and drying with disposable paper towels–is recommended to eliminate noroviral hand contamination [26]. Data on alcohol-based cleansers suggest that they are insufficient for noroviral disinfection. Feline calicivirus, a surrogate for norovirus, is incompletely decontaminated with alcohol-based cleansers, although a 95% ethanol hand rub was superior to a 70% hand rub in disinfecting calicivirus [42]. Of note, common hospital hand rubs contain an alcohol content of only 60%–62%. No studies address whether increased hospital use of alcohol hand rubs is permissive in the persistence of norovirus outbreaks.
Determinants of host susceptibility to norovirus infection. Despite the impressive transmissibility of noroviruses, not everyone is susceptible to norovirus infection. Overall, symptomatic attack rates in outbreaks infrequently exceed 70% whereas 70%–90% of individuals may exhibit serological evidence of prior norovirus infection [43]. Together, these observations and other data suggest that a small subset of individuals are absolutely resistant to norovirus infection, whereas another subset may acquire only asymptomatic infection. The host determinants of norovirus resistance are complex and incompletely defined. Individuals who are secretor-status positive for histoblood group antigens that are also displayed on mucosal surfaces are susceptible to norovirus infection, because histoblood group antigens serve as receptors for most, but not all, noroviruses [14, 43]. Blood group antigen status (O, A, B, or AB) also affects the host-norovirus interaction, at least for genotype I noroviruses [43–45]. Individuals with an O phenotype more often have symptomatic infection with genotype I noroviruses than do those with a B phenotype, who experience less clinical morbidity. Individuals infected with noroviruses likely develop both humoral and cellular immune responses, but these do not necessarily constitute protective immunity against subsequent norovirus infection [46]. The difficulty of understanding what comprises protective immunity to noroviruses is compounded by the ever-changing diversity of noroviruses, with display of antigen epitopes that may or may not induce cross-protective immunity to other noroviral strains. Short-term immune protection to homologous viral strains has been shown in volunteer studies [43]. Thus, it seems that most individuals can expect to acquire multiple, symptomatic norovirus infections in a lifetime.
What Approaches Will Interrupt Norovirus Spread?
Challenges and costs of norovirus outbreak containment. A nosocomial outbreak of norovirus at Johns Hopkins Hospital involving >500 patients and health care workers illustrated some of the strategies and challenges in containing the virus within the hospital setting [47]. When the outbreak was recognized, disinfection and isolation protocols were instituted, and symptomatic health care workers were instructed to stay home for 72 h after symptoms resolved, consistent with 2005 Federal Food Code and Michigan guidelines for norovirus control (see below) [8, 11, 25]. However, ongoing cases prompted more-stringent measures, including the prohibition of visitors, cohorting of nursing staff, universal use of gowns and gloves in affected units, and cessation of new admissions to the involved hospital unit. Even group therapy sessions in the affected psychiatric unit were halted. Similarly, in several norovirus disease outbreaks in English hospitals, prevention and control measures were rapidly escalated, and units were closed within 3 days, resulting in outbreaks being shortened by a startling 7.5 days, which suggests the need, at times, for seemingly extreme containment measures [48]. Hospital-based norovirus disease outbreaks are expensive. The Johns Hopkins Hospital outbreak cost an estimated $650,000 for the 946-bed hospital [47]. Outbreaks in the United Kingdom have been estimated to cost $1 million per 1000 hospital beds [48].
Outbreaks of norovirus gastroenteritis on cruise ships prove equally difficult to control and may continue on consecutive cruises, despite cleaning measures [10, 16]. This has been attributed to inadequate disinfection, shedding of virus by asymptomatic crew members, and repeated introduction of noroviruses as new passengers and crew members board the ships. This flow of people might be compared to an emergency department; therefore, hospitals, like these ships, are at high risk of acquiring new viruses.
A multistrain outbreak of norovirus gastroenteritis in a Houston, Texas, shelter during the aftermath of Hurricane Katrina (2005) proved extremely difficult to control because of the close quarters among evacuees, insufficient toilet and hand hygiene facilities, and an inability to cohort symptomatic patients and to separate exposed from unexposed individuals, as well as delayed cleaning. Together, these factors resulted in ongoing transmission until the shelter was closed [49]. Although public health measures require separation and isolation of sick people, the reality of separating family members after such a traumatic experience made this intervention untenable.
Recommendations for prevention and control of norovirus. Prevention and control efforts should focus on the potential transmission modes suggested by the epidemiologic investigation. For example, the recognition of increasing food-borne outbreaks in Michigan with enhanced severity prompted officials to amend their Food Laws, adopting and strengthening the recommendations contained in the 2005 Federal Food Code for norovirus control [8, 11, 25]. Included in the Michigan rules are instructions for employees to wash their hands with warm running water and soap, exclusion from work until asymptomatic for 48–72 h, and, on return to work, further restriction from handling kitchenware and ready-to-eat foods for an additional 72 h. Vomiting incidents in food establishments are to be treated as emergencies that require discarding anything potentially contaminated by vomitus and cleaning with diluted bleach (1/10–1/50 dilution) the area (a 7–8-m radius) of the vomiting incident. Depending on where vomiting occurred, restaurant or bathroom closure is to be considered to be a public health containment measure. The recommendations to exclude infected employees from work for at least 48–72 h is based on older data that suggest that viral shedding ceases within 100 h after symptom resolution [50]. Recent data, in contrast, suggest that protracted norovirus excretion may occur after illnesses, lasting a median of 28 days, with ∼104 viral copies/g of stool [5]. The precise contributions of person-to-person spread, environmental contamination, and/or other factors to ongoing transmission in outbreak situations are unclear.
On the basis of prior efforts to prevent and control norovirus epidemics, we make recommendations for containment of outbreaks in health care and long-term care facilities, as specified in table 1. The proposed interventions target the various means by which the virus spreads and aim to prevent the introduction, dissemination, and continuation of norovirus transmission. As learned at our institution [47], aggressive interventions at the onset of an outbreak are likely necessary to reduce both morbidity and cost. Norovirus will continue to evolve and likely evade the host immune response. Therefore, combating this common infection requires marked diligence to public health education and infection-control measures. Vigilance in surveillance, isolation, and disinfection is required to keep our health care and long-term care facilities free of noroviruses and to protect those who are most vulnerable.
Table 1
Prevention and control of norovirus in health care facilities.
Acknowledgments
Potential conflicts of interest. All authors: no conflicts.
- Received April 16, 2008.
- Accepted July 8, 2008.
- © 2008 by the Infectious Diseases Society of America
References
This Article
- AbstractFree
- » Full Text (HTML)Free
- Full Text (PDF)Free
Classifications
-
- Invited Articles
Services
Citing Articles
Google Scholar
PubMed
Related Content
Share
- Email this article
-
CiteULike
Connotea
Delicious
Facebook
Google+
Mendeley
Twitter
Published on behalf of
IDSA Members: For your free access to this journal, log in via the IDSA members area.
The Journal
Impact Factor: 8.186
5-Yr impact factor: 7.898
For The Media
For Authors
- Services for authors
- Self-archiving Policy
- IDSA Conflict of Interest policy
- Instructions for Authors
- ICMJE Form
- Submit Now!
Open access options for authors visit Oxford Open
This journal enables compliance with the NIH Public Access Policy
Corporate Services
Alerting Services
Related IDSA Publications
