ProMED-mail |

Published Date: 2003-01-23 23:50:00
Subject: PRO/EDR> Norovirus activity 2002 - USA
Archive Number: 20030123.0206

NOROVIRUS ACTIVITY 2002 - USA
******************************
A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail is a program of the
International Society for Infectious Diseases
<http://www.isid.org>
Date: Thu 23 Jan 2003
From: ProMED-mail <promed@promedmail.org>
Source: Morbidity and Mortality Weekly Report, 52(03): 41-45, Fri 24 Jan
2003 [edited]
<http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5203a1.htm>

Norovirus Activity; United States, 2002
---------------------------------------
During the period June to December 2002, an increased number of outbreaks
of acute gastroenteritis (AGE) were reported on cruise ships sailing into
U.S. ports (1). In addition, since October 2002, several states have noted
an increase in outbreaks of AGE consistent clinically and epidemiologically
with norovirus infection, particularly in institutional settings such as
nursing homes (CDC, unpublished data, 2002). This report describes recent
norovirus activity in 2 states and New York City (NYC) and data from CDC
that indicate the possible emergence of a predominant circulating norovirus
strain.
Washington State:
During the period November to December 2002, the Southwest Washington
Health District, Clark County, Washington, received reports of 10 outbreaks
of AGE affecting 354 patients from 6 long-term care facilities (LTCFs), a
community hospital, an outpatient clinic, and the county jail. Outbreaks in
four LTCFs accounted for 327 (92 percent) of the cases, including 220 (49
percent) among 452 residents and 107 (33 percent) among 326 staff. Onset of
illness for all patients occurred during the period 26 Nov to 13 Dec 2002.
For all 354 patients, illness was characterized by diarrhea (84 percent),
nausea (78 percent), and vomiting (77 percent). The mean duration of
illness was 49 hours (range: 20 to 72 hours); mean duration of outbreak in
the 4 LTCFs was 12 days (range: 9 to 16 days). 8 ill persons were
hospitalized. 3 of the 4 LTCFs included residents receiving various levels
of care (i.e., nursing care). The fourth LTCF provided care exclusively for
persons with Alzheimer's disease and experienced the highest attack rates
(ARs) for residents (AR: 85 percent) and staff (AR: 41 percent), compared
with the other 3 LTCFs (AR among residents: 42 percent; AR among staff: 30
percent). The range of dates of illness onset in each outbreak suggests
person-to-person transmission. The incubation period was 24 to 48 hours. 6
of 7 stool specimens from ill patients in these 4 outbreaks were positive
for norovirus by reverse transcriptase-polymerase chain reaction (RT-PCR)
tests performed at Washington State Public Health Laboratories and included
at least one positive specimen from each of the 4 outbreaks. Public health
nurses visited all affected LTCFs to help implement control measures,
including confining ill residents to their rooms and excluding ill staff
from work until 48 hours after recovery; emphasizing hand hygiene for staff
in accordance with recent CDC recommendations (2); disinfecting
environmental surfaces with 10 percent bleach solution; and postponing
visits from elderly persons, very young children, and persons with
underlying medical conditions. The number of cases declined in all 4 LTCFs
after these interventions.
New Hampshire:
During 2002, the New Hampshire Department of Health and Human Services
(NHDHHS) investigated 35 outbreaks of AGE consistent clinically and
epidemiologically with norovirus infection from LTCFs and assisted-living
facilities (n=29), restaurants (n=2), schools (n=2), and residential summer
camps (n=2). Of the 29 outbreaks in LTCFs and assisted-living facilities,
28 were reported during November to December 2002. In 10 (29 percent)
outbreaks, an etiology of norovirus infection was confirmed by RT-PCR
testing of fecal specimens at NHDHHS or CDC, and 25 (71 percent) outbreaks
were attributed to norovirus based on epidemiologic criteria (3). A total
of 2312 persons had AGE during the 35 norovirus outbreaks, resulting in 13
hospitalizations; 2 ill patients in LTCFs died. Epidemiologic investigation
implicated person-to-person, foodborne, and waterborne transmission in 32,
2, and one outbreak, respectively. Control measures in the LTCFs and
assisted-living facilities included frequent and thorough hand washing,
rapid cleaning of soiled areas, excluding ill staff from work for 48 hours
after resolution of symptoms, ceasing of group activities, and stopping new
admissions into the facilities.
New Hampshire's Emergency Department Syndromic Surveillance System also
detected an increase in emergency department (ED) visits for
gastrointestinal illness during December 2002. In response, NHDHHS alerted
all state hospitals, which increased testing for norovirus by the state
laboratory. Since 1 Jan 2003, an additional 11 norovirus outbreaks have
been reported in institutional settings; investigations are ongoing.
New York City:
During the period 6 Nov 2002 to 13 Jan 2003, a total of 66 outbreaks of AGE
consistent epidemiologically with norovirus infection occurred in NYC and
were reported to the NYC Department of Health and Mental Hygiene (DOHMH) or
the New York State Department of Health (NYSDOH). The outbreak settings
included 51 nursing homes, LTCFs, and rehabilitation facilities; 10
hospitals; 3 restaurants; one homeless shelter; and one school.
Approximately 1700 persons were affected. 29 stool specimens were collected
from ill patients during outbreaks in the facilities and were tested for
norovirus by RT-PCR performed either at YSDOH Wadsworth Center or CDC. 19
(66 percent) specimens tested positive for norovirus, one to 10 positive
specimens from each of the 6 outbreak settings. Control measures
implemented throughout all 51 residential facilities included appropriate
hand washing techniques, rapid cleaning of contaminated areas, and
exclusion of ill persons from institutional and congregate settings (e.g.,
schools and child care centers) until 48 hours after symptoms resolved.
On 8 Nov 2002, through its Emergency Department Syndromic Surveillance
System, DOHMH detected a sustained city-wide increase in ED visits from
patients with diarrhea and vomiting. Through broadcast facsimile and
e-mail, DOHMH alerted physicians to collect and send specimens for
diagnostic testing for norovirus in all patients with AGE illness.
Physicians also were encouraged to counsel patients about appropriate
control measures. To identify an etiologic agent, DOHMH field staff were
sent to EDs at 2 hospitals in areas with higher numbers of patients with
AGE. 3 of 4 stool specimens collected from patients reporting to EDs were
positive for norovirus.
CDC Laboratory Surveillance:
During the period May to December 2002, CDC received stool specimens from
48 outbreaks of AGE in the United States. Outbreak settings included
restaurants and catered events (n=12), cruise ships (n=9), schools and
child care centers (n=7), LTCFs and assisted-living facilities (n=5),
residential camps (n=2), sporting events (n=2), and other (n=11). Specimens
from 37 outbreaks were tested for norovirus by RT-PCR; specimens from 11
outbreaks were unsuitable for testing by RT-PCR. Initial RT-PCR testing by
using degenerate primers targeted to a 213-base region of the polymerase
gene (Region B) (4, 5, 6) identified norovirus in specimens from 27 (73
percent) of the 37 outbreaks. Genetic characterization, based on sequencing
of a different 277-base pair region of the capsid gene (Region C) (5,6),
found that 11 (41 percent) of the 27 norovirus-positive outbreaks were
associated with the same strain of norovirus. This lineage within genogroup
II, cluster 4 (GII/4) (4,5) has been provisionally named the Farmington
Hills strain, after Farmington Hills, Michigan, where the first cases with
this norovirus strain were identified. 6 of the 11 outbreaks associated
with the Farmington Hills strain of norovirus occurred on land in 5 states
(Arkansas, Georgia, Kentucky, North Carolina, and Utah). The remaining 5
outbreaks were associated with cruise ships. No epidemiologic link has been
identified between land and cruise ship outbreaks. In addition, specimens
from 2 of the 6 norovirus-positive outbreaks in NYC and the 3
norovirus-positive specimens collected in NYC EDs were sequenced further at
CDC. The Farmington Hills strain was identified in one of the 2 outbreaks
and 2 of the 3 single specimens.
MMWR Editorial Note:
This report highlights increased norovirus circulation in the United
States. Noroviruses are the most common cause of gastroenteritis in the
United States and cause an estimated 23 million cases of AGE annually (1).
Although attention has been drawn recently to outbreaks of norovirus on
cruise ships, an estimated 60 percent to 80 percent of all outbreaks of AGE
occur on land (4). In addition, although many reports have focused on
foodborne transmission of noroviruses (7), this and other recent reports
highlight the potential of norovirus to cause large outbreaks in
institutional settings through non-foodborne modes of transmission (4,5,8).
Anecdotal reports from other state health departments throughout the United
States also are consistent with recent increased activity of norovirus
within institutional and closed settings.
The cause of the increase in norovirus activity is unclear, although it is
probably associated with an increase in community incidence of norovirus
infection, as suggested in NYC and New Hampshire. Outbreaks of norovirus
disease in closed settings have been documented, particularly during the
winter (8,9).
Since July 2002, a total of 41 percent of outbreaks in which strains were
characterized genetically at CDC were associated with a single, newly
identified strain of norovirus. The strain was found in various settings
and over a wide geographic distribution, and no common source of these
outbreaks has been identified. The finding of a predominant strain is
unusual and contrasts with surveillance data from 1997 to 2000, which
rarely detected identical strains from distinct outbreaks (4). However,
data from 1995 to 1997 suggested the emergence of a globally common strain
that accounted for 55 percent of all norovirus outbreaks investigated by
CDC during that period (5).
Like the Farmington Hills strain, the "common strain" of 1995 to 1997 was
classified as a GII/4 strain. These strains have been associated previously
with outbreaks in closed settings, and it is possible that this GII/4
predominant strain of norovirus has characteristics of infection that
increase person-to-person transmissibility, such as an increased prevalence
of vomiting (4). Characteristics of norovirus include a low infectious
dose, relative stability in the environment, and spread through multiple
modes of transmission, which make norovirus outbreaks difficult to control
(8,9). Measures to prevent spread should include emphasizing basic food and
water sanitation measures and encouraging good hygiene, particularly
appropriate hand washing techniques, disposal of waste and soiled
materials, and disinfection.
Development of more sensitive and specific RT-PCR detection methods and the
increased use of nucleotide sequencing of detected strains (4,6) has
enabled the identification of a common strain of norovirus and the
possibility of linking outbreaks of norovirus disease throughout the United
States and the world. However, no surveillance of non-foodborne outbreaks
of AGE exists in the United States (10). Development of improved
surveillance systems to monitor endemic and epidemic norovirus disease is
needed to understand modes of transmission and identify more specific
control measures.
CaliciNet is a database system under development that collects molecular
and epidemiologic data from outbreaks of norovirus throughout the United
States (CDC, unpublished data, 2002). Efforts to incorporate web-based
reporting of non-foodborne outbreaks of AGE by states are under way.
CDC encourages local and state health departments to test for noroviruses
when investigating outbreaks of suspected viral AGE. For assistance in
testing for noroviruses and for strain characterization, local and state
health departments should contact CDC's Viral Gastroenteritis Section at
<CaliciNet@cdc.gov>.
References:
(1) CDC. Outbreaks of gastroenteritis associated with noroviruses on cruise
ships---United States, 2002. MMWR 2002;51:1112--5.
(2) CDC. Guideline for hand hygiene in health-care settings:
recommendations of the Healthcare Infection Control Practices Advisory
Committee and the HICPAC/SHEA/APIC/IDSA Hand Hygiene Task Force. MMWR
2002;51(No. RR-16).
(3) Owen CE. Viral gastroenteritis: small round structured viruses,
caliciviruses and astroviruses. Part II. The epidemiological perspective. J
Clinical Pathology 1996;49:959--64.
(4) Fankhauser RL, Noel JS, Monroe SS, Ando T, Glass RI. Molecular
epidemiology of "Norwalk-like viruses" in outbreaks of gastroenteritis in
the United States. J Infect Dis 1998;178:1571--8.
(5) Noel JS, Fankhauser RL, Ando T, Monroe SS, Glass RI. Identification of
a distinct common strain of "Norwalk-like viruses" having a global
distribution. J Infect Dis 1999;179:1334--44.
(6) Ando T, Gentsch JR, Jin Q, Lewis DC, Glass RI. Detection and
differentiation of antigenically distinct small round-structured viruses
(Norwalk-like viruses) by reverse transcription-PCR and southern
hybridization. J Clin Microbiol 1995;33:64--71.
(7) Bresee JS, Widdowson MA, Monroe SS, Glass RI. Foodborne viral
gastroenteritis. Clin Infect Dis 2002;35:748--53.
(8) Green KY, Belliot G, Taylor JL, et al. A predominant role for
Norwalk-like viruses as agents of epidemic gastroenteritis in Maryland
nursing homes for the elderly. J Infect Dis 2002;185:133--46.
(9) Mounts AW, Ando T, Koopmans M, Bresee JS, Noel JS, Glass RI. Cold
weather seasonality of gastroenteritis associated with Norwalk-like
viruses. J Infect Dis 2000;181:284--7.
10) Mead PS, Slutsker L, Dietz V, et al. Food-related illness and death in
the United States. Emerg Infect Dis 1999;5:607--25.
--
ProMED-mail
<promed@promedmail.org>

See Also