1 table, 1 figure omitted
CDC and the World Health Organization (WHO) are continuing to investigate
the multicountry outbreak of unexplained atypical pneumonia referred to as
severe acute respiratory syndrome (SARS).1 Pending development
of confirmatory laboratory testing capacity, CDC's interim suspected SARS
case definition2 is based on clinical criteria and epidemiologic
linkage to other SARS cases or areas with community transmission of SARS.
This case definition will be updated periodically as new information becomes
available. Epidemiologic and laboratory investigations of SARS are ongoing.
As of April 2, 2003, a total of 2,223 suspected and/or probable SARS cases
have been reported to WHO from 16 countries, including the United States.3,4 The reported SARS cases include 78 deaths (case-fatality proportion:
3.5%). This report summarizes SARS cases among U.S. residents and surveillance
and prevention activities in the United States.
As of April 2, CDC had received 100 reports of suspected SARS cases
from 28 states; 81 (81%) cases occurred among adults. Of these 100 suspected
cases, 94 (94%) persons had traveled within the 10 days before illness onset
to the areas listed in the case definition (revised on March 29 to include
all of mainland China as an area with documented or suspected community transmission),
four had household contact with a person with suspected SARS, and two were
health-care workers (HCWs) who provided medical care to a patient with suspected
SARS. Manifestations of SARS have been relatively less severe among patients
in the United States than among those reported elsewhere. A majority of U.S.
patients had normal chest radiographs, and 23 (23%) were reported to have
pneumonia or respiratory distress syndrome on chest radiograph, thereby meeting
the WHO case definition of a probable case.4 As of April 2, of
the 40 (40%) patients who were hospitalized for ≥24 hours, 13 (33%) remained
hospitalized; one patient had required mechanical ventilatory support, and
no deaths have been reported.
Reports on the clinical status of suspected SARS cases are being received
by state health departments and CDC, and household and HCW contacts are being
monitored for the possibility of secondary transmission. Since SARS investigations
in the United States began, some persons believed initially to have suspected
SARS have been excluded on the basis of more complete clinical histories (e.g.,
no documented fever or respiratory symptoms) or because of testing results
that indicated other etiologies. Alternative diagnoses have included infection
with influenza virus, respiratory syncytial virus, Haemophilus
influenzae, Streptococcus pneumoniae, and Staphylococcus aureus. Community transmission of SARS has
not been identified in the United States; transmission to HCWs has been observed
in one cluster involving two HCWs, compared with numerous reports of possible
transmission to HCWs in other countries.5-7
As a precautionary measure, WHO has recommended that persons traveling
to Hong Kong and Guangdong Province of China consider postponing all but essential
travel. CDC has issued a travel advisory recommending that persons planning
nonessential or elective travel to mainland China, Hong Kong, Hanoi, or Singapore
consider postponing such travel until further notice. To detect possible SARS
cases among travelers returning to the United States from these areas, CDC
and state and local health authorities have implemented enhanced surveillance.
Since March 16, notices (available in English, Chinese, Japanese, Korean,
and Vietnamese) have been provided to approximately 220,000 passengers arriving
in the United States on airline flights originating from China, Vietnam, and
Singapore to inform disembarking passengers and crew about SARS. Persons disembarking
from these countries are urged to monitor their health for 10 days after return,
to seek medical care if they develop fever of ≥100.5°F (39.0°C)
and cough or difficulty breathing within 10 days of travel, and to inform
their health-care providers about recent travel to regions where SARS cases
have been reported.
Efforts are ongoing to characterize further the role of a previously
unrecognized coronavirus in SARS. Polymerase chain reaction–based assays,
isolation studies, electron microscopic studies, and histologic studies are
being developed to detect virus in specimens from patients with suspected
SARS. Indirect immunoflorescence antibody assays and enzyme immunoassays to
anti-coronavirus antibody as an indicator of infection have been developed
and are being applied to specimens from suspected SARS patients. Laboratory
studies at CDC and other laboratories in the WHO-organized SARS Laboratory
Network have detected this new coronavirus in SARS patients, which is consistent
with an etiologic role in this disease. CDC has detected human metapneumovirus
from one SARS patient, and other laboratories also have detected metapneumovirus
from SARS patients.6 The role of these viruses in the pathogenesis
of SARS is unclear.
CDC SARS Investigative Team; LM Fox, MD, EIS Officer, CDC.
The number of SARS cases, and the number of countries reporting such
cases, continues to increase worldwide. Transmission within hospitals and
households continues in some areas, and transmission within communities (e.g.,
Hong Kong) continues to be reported. In the absence of a complete understanding
of how SARS is transmitted, efforts to limit transmission in the United States
have focused on early identification of potential cases through surveillance
and implementation of infection-control measures in health-care settings and
CDC has developed interim infection-control guidelines for use in U.S.
health-care and household settings.8 These recommendations are
based on experience in the United States to date and will be revised as more
information becomes available. Infection-control practitioners and clinicians
providing medical care for patients with suspected SARS should consult these
guidelines frequently to keep current with recommendations.
Transmission in health-care settings has been documented in several
countries. Transmission to HCWs appears to have occurred primarily after close
contact with symptomatic persons before recommended infection-control precautions
for SARS were implemented. Because a primary strategy to reduce transmission
in health-care settings is early recognition and isolation of patients who
might have SARS, triage practices in hospitals and ambulatory-care settings
might require reevaluation. CDC guidelines for triage of potential SARS cases
are available at http://www.cdc.gov/ncidod/sars/triage_interim_guidance.htm.
In the United States, decisions to admit persons with suspected SARS
to health-care facilities should be based on clinical criteria. Patients with
suspected SARS who are discharged should limit interactions outside the home
and not go to work, school, out-of-home child care, or other public areas
until 10 days after resolution of fever and respiratory symptoms. Additional
guidance for these patients is available at http://www.cdc.gov/ncidod/sars/ic-closecontacts.htm.
The majority of U.S. residents with SARS have recovered or stabilized
clinically without specific antiviral therapy. The U.S. case-fatality proportion
is lower than that reported in some other countries.3 Possible
explanations for this include differing case definitions among countries or
differences in the sensitivity of surveillance, leading to identification
in the United States of patients with less severe or early manifestations
of infection or of a larger proportion of patients with other respiratory
illnesses. Until confirmatory laboratory testing is available, the case definition
will include clinical criteria more likely to identify potentially infectious
persons. Various therapies, including antiviral agents (e.g., oseltamivir
or ribavirin) and corticosteroids, have been administered to SARS patients,
but the efficacy of these therapies has not been determined.
Health-care providers of patients whose illness is consistent with the
case definition for SARS should continue diagnostic evaluation for other causes
of respiratory illness and, when appropriate, empiric therapy that includes
activity against organisms associated with community-acquired pneumonia of
uncertain etiology, including both typical and atypical respiratory pathogens.9 Health-care providers who report suspected SARS cases should notify
their state health departments if these patients receive confirmatory testing
that indicates a diagnosis other than SARS. Information on suggested diagnostic
testing and evaluation for persons with possible SARS is available at http://www.cdc.gov/ncidod/sars/diagnosis.htm.
The potential for transmission of SARS during airline travel is unknown.
Transmission of other infectious agents (e.g., Mycobacterium
tuberculosis) during air travel has been demonstrated.10 When
an airline flight crew reports a passenger with respiratory illness, quarantine
officials might board the aircraft on arrival in the United States to assess
whether the passenger's symptoms match the case definition of SARS and give
the passenger information about following up. If a passenger with suspected
SARS is identified after passengers have disembarked, public health authorities
will work with the airline to contact passengers and crew for information
about the development of an illness suggestive of SARS. Although ill travelers
have spread SARS rapidly across international borders, the proportion, if
any, of persons who acquired SARS during international travel as a result
of in-flight transmission is unknown.
Despite vigorous efforts to identify and isolate suspected cases, reducing
transmission of the etiologic agents of SARS might be difficult. Understanding
the epidemiology of respiratory pathogens such as those that cause SARS is
challenging; approximately 40%-60% of persons with pneumonia do not have a
defined etiology, even when extensive testing for known respiratory pathogens
is attempted.9 Minimizing transmission will require sustained attention
to infection-control interventions within health-care settings and the community.
The development of laboratory testing techniques to identify infected persons
rapidly will be an important step toward understanding and reducing transmission
References: 10 available
Update: Outbreak of Severe Acute Respiratory Syndrome—Worldwide,
2003. JAMA. 2003;289(16):2059-2060. doi:10.1001/jama.289.16.2059