1202 • CID 2008:47 (1 November) • HEALTHCARE EPIDEMIOLOGY
H E A LT H C A R E E P I D E M I O L O G YI N V I T E D A R T I C L E
Robert A. Weinstein, Section Editor
Gastrointestinal Flu: Norovirus in Health Care
and Long-Term Care Facilities
Maria A. Said, Trish M. Perl, and Cynthia L. Sears
Division of Infectious Diseases, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland
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,cansustainanepidemic.
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
Once given the diminutive name “small, round structured vi-
ruses,” noroviruses have emerged as a growing threat in the
community and in health care facilities. Noroviruses are now
to affect at least 23 million people yearly in the United States
alone  and to contribute to an expanding number of out-
breaks 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 ge-
notype [2, 3]. Characterized by diarrhea, vomiting, abdominal
pain, malaise, and, typically, a low-grade fever, norovirus ill-
nesses quickly resolve, most often on their own. However, viral
shedding may be protracted [4, 5]. Prolonged asymptomatic
Received 16 April 2008; accepted 8 July 2008; electronically published 22 September 2008.
Reprints or correspondence: Dr. Cynthia L. Sears, Divs. of Infectious Diseases and
Gastroenterology, 1550 Orleans St., CRBII, Ste. 1M.05, Baltimore, MD 21231
Clinical Infectious Diseases2008;47:1202–8
? 2008 by the Infectious Diseases Society of America. All rights reserved.
shedding, noroviral persistence in the environment, and a low
infectious dose contributetothesustainedtransmissionofthese
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 . 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% .
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, no-
tably for endemic norovirus disease, is limited, because labo-
ratory diagnosis is currently confined to state and national
public health facilities. In addition, acute attacks of gastroen-
teritis, even when clustered, are frequently not reported to
health officials. Because of the difficulty of diagnosing the dis-
ease and its lack ofperceivedmorbidity,nonationalsurveillance
system for acute gastroenteritis exists in the United States .
Despite these limitations, the growing number of reported no-
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1208 • CID 2008:47 (1 November) • HEALTHCARE EPIDEMIOLOGY
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