Revised US Surveillance case definition for SARS

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Revised U.S. Surveillance Case Definition for Severe Acute Respiratory

Syndrome (SARS) and Update on SARS Cases --- United States and Worldwide,

December

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 " or " 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.

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). Update on SARS Cases

During November 2002--July 2003, a total of 8,098 probable SARS cases were

reported to the World Health Organization (WHO) from 29 countries, including 29

cases from the United States; 774 SARS-related deaths (case-fatality rate:

9.6%) were reported, none of which occurred in the United States (6). Eight U.S.

cases had serologic evidence of SARS-CoV infection; these eight cases have

been described previously (7--10). A total of 156 reported U.S. SARS cases from

the 2003 epidemic remain under investigation, with 137 (88%) cases classified

according to previous surveillance criteria as suspect SARS and 19 (12%)

classified as probable SARS. Because convalescent serum specimens have not been

obtained from the 19 probable and 137 suspect cases that remain under

investigation, whether these persons had SARS-CoV disease is unknown.

Reported by: SARS Team and Executive Committee, Council of State and

Territorial Epidemiologists. SARS Investigative Team, CDC. Editorial Note:

The revised surveillance case definition for SARS reflects an improved

understanding of the clinical and laboratory characteristics of SARS-CoV. The

revision differentiates patients with nonspecific clinical illness or less

definitive epidemiologic associations (i.e., SARS RUIs) from those with

laboratory-confirmed SARS-CoV infection or more definitive epidemiologic links

(i.e., cases

of SARS-CoV disease). Local and state health departments will monitor SARS RUIs

to ensure implementation of prompt public health measures for preventing

disease transmission if SARS-CoV is confirmed subsequently. Numerous SARS RUIs

probably will be excluded as SARS cases as laboratory results become available

during the course of illness. Surveillance data for cases meeting the SARS-CoV

disease case definition will be reported to NNDSS and included in the weekly

statistical summary of notifiable infectious diseases in the United States

published in MMWR (Table 1. Summary of provisional cases of selected notifiable

diseases, United States).

Reporting of cases meeting previous SARS definitions ended in late July 2003.

However, case numbers continue to change as new clinical information or

results of additional laboratory testing on cases reported previously become

available. Updated case counts reflecting these changes are available from CDC

at

http://www.cdc.gov/od/oc/media/sars/cases.htm.

Efforts are under way to prepare for a possible reappearance of SARS-CoV.

CDC, in collaboration with other federal partners, state and local health

officials, professional organizations and societies, and representatives of the

health-care industry, has developed a guidance document to help public health

and

health-care officials detect the reappearance of SARS-CoV in the United States

quickly and implement a decisive and effective public health response. The

document, " Public Health Guidance for Community-Level Preparedness and Response

to Severe Acute Respiratory Syndrome (SARS), " is available at

http://www.cdc.gov/ncidod/sars/sarsprepplan.htm.