Severe acute respiratory syndrome (SARS) is a viral illness characterized by a syndrome of fever and respiratory symptoms that can progress to respiratory failure and death. Initial reports of a highly contagious atypical pneumonia originated from Guangdong Province, People's Republic of China, in November 2002. The condition remained isolated to China until February 2003, when an infected physician traveled to Hong Kong. Since then, until 20 April 2003, the disease has spread to affect over 3,500 individuals in 26 countries (WHO 19 April 2003, updates available at http://www.who.int/csr/sars/en). The largest outbreaks have been described in Hong Kong, Toronto, Canada, and Singapore, related to a contact with this infected physician in a Hong Kong hotel. While the Western world has been aware of this condition for only several weeks, considerable progress has been made in the identification of the responsible viral organism. There is less known about the mode of transmission and treatment of this disease, but likely mechanisms include droplet spread, surface contact, and possibly airborne transmission. This review describes the current state of knowledge of SARS, with particular reference to the management of the critically ill patient and the safety and protection of the ICU staff. The recommendations are based on the sparse published data available, collaborations between physicians in many affected centers, recommendations from the World Health Organization and Centers for Disease Control, and local experience.

A novel coronavirus has been isolated from patients meeting the case definition for SARS, using electron microscopy and polymerase chain reaction (PCR) of virus isolated in cell culture [1, 2]. Preliminary serological studies suggest that this virus has not previously infected the population of the United States [1]. The viral genome has been sequenced, and early PCR-based tests are in an evaluation phase.

Case definitions of SARS are currently based on the presence of epidemiological risk factors (close contact with SARS cases or travel to SARS "affected" areas) along with a combination of fever and respiratory symptoms, with or without hypoxia and/or chest radiographic changes [3]. However, as SARS spreads into the general population, our ability to distinguish it from other community-acquired pneumonias based on such epidemiological linkages will become increasingly tenuous. At this time SARS must be considered in the differential diagnosis of any community-acquired or nosocomial pneumonia. A "typical" history (see below), suggestive laboratory values (see below), and failure to respond to conventional antibiotics should raise suspicion. Diagnostic tests will be crucial in the future both to ensure that patients are isolated rapidly, and that treatment is initiated.

The incubation period has been reported as 2–10 days, and early manifestations include influenzalike symptoms such as fever, myalgias, and headache. It is presently not clear at what stage of the disease viral shedding occurs, or whether someone who is infected but asymptomatic can infect others. As our knowledge of SARS and the etiological coronavirus evolves, we will be able to answer these important questions. The viral load may play a role in both the transmission and severity of subsequent disease. The notion of "super spreaders" has been suggested to describe the occasional patient who is associated with spread to large numbers of contacts.

Our current understanding of the illness is that fever occurs in virtually all patients and is often the presenting symptom. Fever may occasionally be absent in the elderly. Some patients have mild respiratory symptoms at the onset, and gastrointestinal manifestations are relatively uncommon. Diarrhea has been reported with increased frequency in recent outbreaks. The respiratory phase starts after 3 – 7 days with dry cough and shortness of breath. In some cases these symptoms are followed by hypoxia and radiological evidence of progressive pulmonary infiltrates. The radiological picture is patchy, of focal infiltrates or consolidation often with a peripheral distribution, which may progress to diffuse infiltration. Pulmonary infiltrates may worsen during the first 10 days, and acute respiratory distress requiring mechanical ventilation has occurred in about 10–20% of patients. The case fatality rate is approximately 3–12% depending on whether the denominator includes both suspect and probable cases (3%) or probable cases alone (12%) [4, 5, 6]. While the mortality rate is higher in older patients particularly those with preexisting comorbidity (e.g., diabetes and immunosuppression), we have also seen young, previously healthy persons succumb to the disease. This may be due to higher viral loads or to their host response.

The disease runs for 7–14 days, and a biphasic course has been described in some patients, with an initial illness, improvement, and subsequent deterioration. This worsening can present as recurrent fever 4–7 days after initial defervescence, new chest infiltrates on radiography, or recurrent respiratory failure. In some patients an initial mild to moderate respiratory illness may initially improve, later to be followed by a progressive deterioration requiring ventilatory support.

Laboratory findings in patients with SARS include thrombocytopenia and leukopenia (in particular lymphopenia). Elevated creatine kinase, lactate dehydrogenase, and transaminases have been noted. There is evidence that the peak lactate dehydrogenase and an initial elevated white cell count may carry a poor prognosis [6]. Epidemiological studies are currently underway to help determine prognostic factors.

Transporting a SARS patient for testing is an infection control challenge. SARS patients should never be transported while being supported by bag-valve-mask ventilation, and should preferably be intubated. The risks and benefit of any procedure should be considered prior to transporting a patient. If bag ventilation is used, a filter should be placed between the bag and the endotracheal tube. Infection control should be also consulted for their advice on proper precautions.

SARS has resulted in significant challenges for critical care medicine and likely will change the ICU environment for some time to come. In affected areas the policies are changing on a daily basis as more information about the virus and the disease is obtained. The ability of this disease to incapacitate staff has resulted in staff safety becoming a priority to maintain adequate critical care services. The concept of "universal precautions" now includes strict respiratory and contact precautions. The guidelines and recommendations will change as our knowledge grows. Information and communication technology have played an important role in allowing collaboration and rapid transfer of information. It is only through such sharing that we can hope to improve the mortality and morbidity of our patients and stay healthy and well ourselves.