Revised U.S. surveillance case definition for Severe Acute Respiratory Syndrome and update on SARS cases—United States and worldwide, December 2003

Morbidity and Mortality Weekly Report, Dec 12, 2003

During the 2003 epidemic of" severe acute respiratory syndrome (SARS), CDC and the Council of State and Territorial Epidemiologists (CSTE) developed surveillance criteria to identify persons with SARS. The surveillance case definition changed throughout the epidemic as understanding of the clinical, laboratory, and transmission characteristics of SARS-associated coronavirus (SARS-CoV) increased (1-5). On June 26, CSTE adopted a position statement to add SARS-CoV disease to the National Notifiable Disease Surveillance System (NNDSS). The position statement included

criteria for defining a SARS case for national reporting. On November 3, CSTE issued a new interim position statement * with a revised SARS case definition. This report summarizes the new U.S. surveillance case definition for SARS and updates reported cases of SARS worldwide and in the United States.

Summary of Changes to Case Definition

The revised SARS case definition (Box) modifies the clinical, epidemiologic, laboratory, and case-exclusion criteria in the U.S. surveillance case definition used during the 2003 epidemic. In the clinical criteria, "early" illness replaces "asymptomatic" of "mild" illness. The epidemiologic criteria include the following new categories: 1) possible exposure to SARS-CoV and 2) likely exposure to SARS-CoV. Laboratory criteria for evidence of SARS-CoV infection reflect advances in testing technology. The case-exclusion criteria have been changed to allow for exclusion when a serum sample collected >28 days after onset of symptoms is negative for antibody to SARS-CoV.

BOX. Revised Council of State and Territorial Epidemiologists
surveillance case definition for severe acute respiratory syndrome
(SARS), December 2003

Clinical Criteria
Early illness

* Presence of two or more of the following features: fever (might be
subjective), chills, rigors, myalgia, headache, diarrhea, sore throat,
or rhinorrhea

Mild-to-moderate respiratory illness

* Temperature of >100.4[degrees]F (>38[degrees]C) * and

* One or more clinical findings of lower respiratory illness (e.g.,
cough, shortness of breath, of difficulty breathing)

Severe respiratory illness

* Meets clinical criteria of mild-to-moderate respiratory illness and

* One or more of the following findings:

--Radiographic evidence of pneumonia, or

--Acute respiratory distress syndrome, of

--Autopsy findings consistent with pneumonia or acute respiratory
distress syndrome without an identifiable cause

Epidemiologic Criteria

Possible exposure to SARS-associated coronavirus (SARS-CoV)

One or more of the following exposures in the 10 days before onset of
symptoms:

* Travel to a foreign of domestic location with documented or suspected
recent transmission of SARS-CoV [dagger] of

* Close contact [section] with a person with mild-to-moderate or severe
respiratory illness and history of travel in the 10 days before onset
of symptoms to a foreign or domestic location with documented or
suspected recent transmission of SARS-CoV [dagger]

Likely exposure to SARS-CoV

One or more of the following exposures in the 10 days before onset of
symptoms:

* Close contact [section] with a person with confirmed SARS-CoV disease
or

* Close contact [section] with a person with mild-to-moderate or severe
respiratory illness for whom a chain of transmission can be linked to a
confirmed case of SARS-CoV disease in the 10 days before onset of
symptoms

Laboratory Criteria

Tests to detect SARS-CoV are being refined and their performance
characteristics assessed [paragraph]; therefore, criteria for
laboratory diagnosis of SARS-CoV are changing. The following are
general criteria for laboratory confirmation of SARS-CoV:

* Detection of serum antibody to SARS-CoV by a test validated by CDC
(e.g., enzyme immunoassay), or

* Isolation in cell culture of SARS-CoV from a clinical specimen, of

* Detection of SARS-CoV RNA by a reverse transcription polymerase chain
reaction test validated by CDC and with subsequent confirmation in a
reference laboratory (e.g., CDC).

Information about the current criteria for laboratory diagnosis of
SARS-CoV is available at
http://www.cdc.gov/ncidod/sars/labdiagnosis.
htm.

Exclusion Criteria

A case may be excluded as a SARS report under investigation (SARS RUI),
including as a CDC-defined probable SARS-CoV case, if any of the
following apply:

* An alternative diagnosis can explain the illness fully **, or

* Antibody to SARS-CoV is undetectable in a serum specimen obtained >28
days after onset of illness [double dagger], or

* The case was reported on the basis of contact with a person who was
excluded subsequently as a case of SARS-CoV disease; then the reported
case also is excluded, provided other epidemiologic of laboratory
criteria are not present.

Case Classification
SARS RUI

Reports in persons from areas where SARS is not known to be active

* SARS RUI-1: Cases compatible with SARS in groups likely to be first
affected by SARS-CoV [subsection] if SARS-CoV is introduced from a
person without clear epidemiologic links to known cases of SARS-CoV
disease or places with known ongoing transmission of SARS-CoV

Reports in persons from areas where SARS activity is occurring

* SARS RUI-2: Cases meeting the clinical criteria for mild-to-moderate
illness and the epidemiologic criteria for possible exposure (spring
2003 CDC definition for suspect cases [paragraphs])

* SARS RUI-3: Cases meeting the clinical criteria for severe illness
and the epidemiologic criteria for possible exposure (spring 2003 CDC
definition for probable cases)

* SARS RUI-4: Cases meeting the clinical criteria for early or
mild-to-moderate illness and the epidemiologic criteria for likely
exposure to SARS-CoV

SARS-Co V disease

* Probable case of SARS-CoV disease: meets the clinical criteria for
severe respiratory illness and the epidemiologic criteria for likely
exposure to SARS-CoV

* Confirmed case of SARS-CoV disease: clinically compatible illness
(i.e., early, mild-to-moderate, or severe) that is laboratory confirmed

* A measured documented temperature of >100.4[degrees]F
(>38[degrees]C) is expected. However, clinic judgment may allow a
small proportion of patients without a documented fever to meet this
criterion. Factors that might be considered include patient's
self-report of fever, use of antipyretics, presence of
immunocompromising conditions or therapies, lack of access to health
care, of inability to obtain a measured temperature. Initial case
classification based on reported information might change, and
reclassification might be required.

[dagger] Types of locations specified will vary (e.g., country,
airport, city, building, of floor of building). The last date a
location may be a criterion for exposure is 10 days (one incubation
period) after removal of that location from CDC travel alert status.
The patient's travel should have occurred on or before the last date
the travel alert was in place. Transit through a foreign airport meets
the epidemiologic criteria for possible exposure in a location for
which a CDC travel advisory is in effect. Information about CDC travel
alerts and advisories and assistance in determining appropriate dates
are available at
http://www.cdc.gov/ncidod/sars/travel.htm.

[section] Close contact is defined as having cared for of lived with a
person with SARS or having a high likelihood of direct contact with
respiratory secretions and/or body fluids of a person with SARS (during
encounters with the patient of through contact with materials
contaminated by the patient) either during the period the person was
clinically ill of within 10 days of resolution of symptoms. Examples of
close contact include kissing of embracing, sharing eating or drinking
utensils, close (i.e., <3 feet) conversation, physical examination, and
any other direct physical contact between persons. Close contact does
not include activities such as walking by a person of sitting across a
waiting room or office for a brief time.

[paragraph] The identification of the etiologic agent of SARS (i.e.,
SARS-CoV) led to the rapid development of enzyme immunoassays and
immunofluorescence assays for serologic diagnosis and reverse
transcription polymerase chain reaction assays for detection of
SARS-CoV RNA in clinical samples. These assays can be very sensitive
and specific for detecting antibody and RNA, respectively, in the later
stages of SARS-CoV disease. However, both are less sensitive for
detecting infection early in illness. The majority of patients in the
early stages of SARS-CoV disease have a low titer of virus in
respiratory and other secretions and require time to mount an antibody
response. SARS-CoV antibody tests might be positive as early as 8-10
days after onset of-illness and often by 14 days after onset of
illness, but sometimes not until 28 days after onset of illness.
Information about the current criteria for laboratory diagnosis of
SARS-CoV is available at
http://www.cdc.gov/ncidod/sars/labdiagnosis.
htm.

** Factors that may be considered in assigning alternate diagnoses
include the strength of the epidemiologic exposure criteria for
SARS-CoV disease, the specificity of the alternate diagnostic test, and
the compatibility of the clinical presentation and course of illness
with the alternative diagnosis.

[double dagger] Current data indicate that > 95% of patients with
SARS-CoV disease mount an antibody response to SARS-CoV. However,
health officials mar choose not to exclude a case on the basis of lack
of a serologic response if reasonable concern exists that an antibody
response could not be mounted.

[subsection] Consensus guidance is in development between CDC and CSTE
on which groups are most likely to be affected first by SARS-CoV if it
reemerges. SARS-CoV disease should be considered at a minimum in the
differential diagnoses for persons requiring hospitalization for
pneumonia confirmed radiographically or acute respiratory distress
syndrome without identifiable etiology and who have one of the
following risk factors in the 10 days before the onset of illness:

* Travel to mainland China, Hong Kong, or Taiwan, of close contact with
an ill person with a history of recent travel to one of these areas, or

* Employment in an occupation associated with a risk for SARS-CoV
exposure (e.g., health-care worker with direct patient contact or
worker in a laboratory that contains live SARS CoV), or

* Part of a cluster of cases of atypical pneumonia without an
alternative diagnosis.

Guidelines for the identification, evaluation, and management of these
patients are available at
http://www.cdc.gov/ncidod/sars/absenceofsars.
htm.

[paragraphs] During the 2003 SARS epidemic, CDC case definitions were
the following: Suspect case

* Meets the clinical criteria for mild-to-moderate respiratory illness
and the epidemiologic criteria for possible exposure to SARS-CoV but
does not meet any of the laboratory criteria and exclusion criteria or

* Unexplained acute respiratory illness that results in death of a
person on whom an autopsy was not performed and that meets the
epidemiologic criteria for possible exposure to SARS-CoV but does not
meet any of the laboratory criteria and exclusion criteria

Probable case

* Meets the clinical criteria for severe respiratory illness and the
epidemiologic criteria for possible exposure to SARS-CoV but does not
meet any of the laboratory criteria and exclusion criteria.

The revised case definition also classifies each SARS case as either a SARS report under investigation (SARS RUI) or SARS-CoV disease. SARS RUI is a sensitive, nonspecific case classification based solely on clinical or epidemiologic criteria and includes cases classified previously as probable or suspect. SARS-CoV disease is a more specific case classification based on selected clinical and epidemiologic criteria or laboratory confirmation. SARS RUIs might subsequently meet the definition for SARS-CoV disease based on results from laboratory testing (Tables 1 and 2).