SARS: lessons learned thus far

Journal of Family Practice, July, 2003 by Eric Henley

The speed with which public health agencies such as the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) have addressed the outbreak of severe acute respiratory distress syndrome, known as SARS, has been impressive. Working with academic epidemiologists and researchers, they appear to have identified a new virus as the likely causative agent, characterized some of the basic epidemiology and clinical course of the infection, and developed confirmatory lab tests.

Understanding the SARS story is important both for its medical implications and the public health principles it illustrates. This article summarizes key points about SARS, mainly using reference material from the CDC. (1)

* DIAGNOSIS

Infection with the SARS virus produces a range of clinical responses:

* Asymptomatic or mild respiratory illness

* Moderate illness: temperature <100.4[degrees]F (<38[degrees]C) and 1 or more clinical findings such as cough, shortness of breath, or hypoxia

* Severe illness: the above findings plus radiologic evidence or autopsy findings of pneumonia, respiratory distress syndrome, with or without an identifiable cause.

Suspect SARS when patients presenting with any of the above symptoms meet one of these epidemiologic criteria.

* having traveled to areas under CDC travel alerts or advisories

* having had close contact within 10 days of developing symptoms with a person known or suspected to have SARS.

When evaluating such patients, use careful hand hygiene and precautions against airborne transmission (N-95 respirator or standard face mask if this is not available) and direct contact (gloves, gowns).

Probable cases (clinical criteria of severe respiratory illness of unknown cause since February 1, 2003, epidemiological criteria, with or without lab criteria) and suspected cases (same criteria, but with moderate respiratory illness only) should be reported to local or state health departments.

Diagnostic testing

Diagnostic testing should include chest x-ray, pulse oximetry, blood cultures, sputum gram stain and culture, and testing for viral pathogens (influenza and respiratory syncytial virus). Legionella and pneumococcal urine antigen testing can be considered. Acute and convalescent (21 days) serum should be saved for lab testing.

In May, the CDC announced the development of an enzyme-linked immunosorbent assay (ELISA) blood test to identify antibody to the presumed SARS virus. The test is now available to local and state health departments for acute and convalescent testing of patients' serum. A more sensitive polymerase chain reaction test is under development.

Treat with supportive measures

No specific treatment exists for SARS. Treat patients as you would any community-acquired pneumonia of unknown origin and provide supportive therapy as necessary. Hospitalization should be based on the usual indications.

* TRADITIONAL INFECTION CONTROL METHODS CAN WORK

Most importantly, public health departments have demonstrated that traditional infection control measures such as surveillance and isolation/quarantine may be successful in limiting the spread of the infection. Physicians should be aware of these important concepts.

The incubation period for SARS is believed to be up to 10 days. During this time, people are not contagious. Transmission is believed to occur mainly during close face-to-face contact such as happens in households or patient-care settings. Aerosol or airborne transmission is also a possibility, although believed to be much less likely.

Surveillance is the system and process of monitoring for specific conditions. Infectious disease surveillance requires the cooperation of local, state, and federal health departments, private and public laboratories, and clinicians working in private and public settings. A definition of the condition being monitored and a method of identifying and reporting cases are necessary. To maximize surveillance, it helps to have a reporting requirement such as we have for diseases like tuberculosis or measles.

Both isolation of suspected cases and quarantine of contacts have been used to control SARS. In the US, quarantine is usually implemented voluntarily, but, for certain conditions such as SARS, people can be quarantined involuntarily. In the case of a communicable disease such as SARS for which there is no known treatment and which can spread readily under certain circumstances, the strategies of isolation and quarantine are even more important.

A need for better defenses

As of early June, countries most affected were mainland China, Hong Kong, and Taiwan. These countries were subject to a CDC travel advisory, which means people should travel there only if they had essential business. In addition, the CDC issued a travel alert for Singapore, and re-issued one for Toronto after the city failed to contain the initial outbreak. Alerts advise travelers that if they have visited a specific SARS-affected area, they should seek medical attention if they get sick within 10 days.