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°F (<38°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.
History of SARS
On February 11, 2003, the World Health Organization (WHO) was first informed by Chinese health authorities of 305 cases of acute respiratory syndrome in Guangdong province in southern China. As it turned out, these cases had started in November 2002, and the disease was characterized by transmission to health-care workers and household contacts.
People who visited China in this period and were exposed to SARS became unwitting carriers. Disease outbreaks occurred subsequently in Vietnam, Hong Kong, Singapore, Toronto, and Taiwan. In April, as international pressure increased, Chinese authorities began acknowledging the wider extent of the SARS outbreak, including hundreds of cases in Beijing and smaller numbers in other parts of the country.
As of June 16, 2003, the WHO had reported 8460 cases of SARS worldwide with a death rate of 9%.2 At that time, the CDC had reported 72 probable and 329 suspected cases in the US, almost all travel-related.1
Theoretical source: civet cats
In April, scientific teams from several countries identified a new coronavirus as the likely cause of SARS. This family of viruses had previously been identified as a cause of mild upper respiratory illnesses. In mid-April, CDC and others announced they had sequenced the genome of the specific coronavirus thought to cause SARS. In late May, researchers from Hong Kong and China announced they had discovered a virtually identical virus in a species of tree-dwelling cat, the civet, that is eaten as wild game in southern China, where SARS is believed to have started. One theory is that the virus may have lived in animals and passed to humans through a mutation or other mechanism.3