Excerpt from Severe Acute Respiratory Syndrome (SARS)

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Background

Severe acute respiratory syndrome (SARS) is a serious, potentially life-threatening viral infection caused by a previously unrecognized virus from the Coronaviridae family. This virus has been named the SARS-associated coronavirus (SARS-CoV). Previously, Coronaviridae were best known as the second most common cause of the common cold.

SARS initially manifests as a flulike syndrome that may progress to pneumonia, respiratory failure, and, in some cases, death. The mortality rate associated with SARS is significantly higher than that of influenza or other common respiratory tract infections.

The SARS coronavirus strain is believed to have originated in Guangdong province in southern China prior to its spread to Hong Kong, neighboring countries in Asia, and Canada and the United States during the 2002-2003 outbreak. In early 2004, several new cases of SARS were investigated in Beijing and in the Anhui province of China. All of these cases were epidemiologically linked to the National Institute of Virology in Beijing, where the outbreak is thought to have originated. The most recent outbreak was believed to have been successfully contained without spread into the general population. Despite concerns that new cases of SARS would emerge in the region, no new cases had been reported as of July 1, 2007. The world's attention has instead focused on the potential for a global avian influenza pandemic due to the H5N1 influenza strain. 

The World Health Organization (WHO) and the US Centers for Disease Control and Prevention (CDC) have posted guidelines and medical information (in both online and traditional forms) for health care professionals to help decrease the transmission of the SARS virus, to ensure appropriate isolation or quarantine of individuals suspected or confirmed to have SARS-CoV infection, and to guide the evaluation and treatment of the disease.^{1, 2}

For more information on this and other emerging infectious diseases, see Medscape's Emerging and Reemerging Infectious Diseases Resource Center.

Pathophysiology

Coronaviruses cause diseases in pigs, birds, and other animals. Preliminary research indicates that SARS-CoV may have originated in livestock (eg, chickens, ducks) or small mammals. Chinese horseshoe bats, which carry SARS-like viruses with genetic homology to SARS-CoV, may have also had a role. From its reservoir, the virus may have mutated, allowing transmission to and infection of humans, perhaps facilitated by the proximity in which humans and livestock live in rural southern China.

As shown in Image 19, the 3 existing coronaviruses include mammalian and avian viruses. These contribute to numerous veterinary diseases (eg, feline infectious peritonitis, avian infectious bronchitis). The coronaviruses can also cause both upper and, more commonly, lower respiratory tract illness in humans (group 1 [human coronavirus 229E] and group 2 [human coronavirus OC43]).

The 1997 avian flu epidemic in Hong Kong, which originated in poultry and spread to humans (resulting in the slaughter of 1.5 million chickens and ducks), is a prime example of this type of zoonotic transmission. Another theory holds that the SARS-CoV originated in small weasel-like animals called civet cats (see Image 18). Closely related to mongooses, these mammals were sold in Guangdong province wet markets as a delicacy. Close contact with the animals themselves, or with their saliva or feces, could have transmitted a mutated form of the virus to humans.

The 2002-2003 SARS outbreak predominantly affected mainland China, Hong Kong, Singapore, and Taiwan. In Canada, a significant outbreak occurred in the area around Toronto, Ontario. In the United States, 8 individuals contracted laboratory-confirmed SARS. All patients had traveled to areas where active SARS-CoV transmission had been documented.

SARS is thought to be primarily transmitted via close person-to-person contact. Most cases have involved persons who lived with or cared for a person with SARS or who had exposure to contaminated secretions from a patient with SARS. Some affected patients may have acquired SARS-CoV infection after their skin, respiratory system, or mucous membranes came into contact with infectious droplets propelled into the air by a coughing or sneezing patient with SARS. SARS may also be spread when a person touches infectious secretions or a contaminated surface or object and then directly contacts his or her own eyes, nose, or mouth. 

The WHO reported that leaky, backed-up sewage pipes, fans, and a faulty ventilation system were likely responsible for a severe outbreak of SARS in the Amoy Gardens residential complex in Hong Kong. However, an analysis by the WHO, entitled "Status of the outbreak and lessons for the immediate future," on the distribution of cases at this development has suggested that transmission may have occurred within the complex via airborne, virus-laden aerosols.³

In May 2003, the WHO reported that only 16 of the more than 7800 people infected with SARS-CoV had contracted the virus on airplanes. All of these cases had occurred before airlines began screening passengers for symptoms (including fever). The strict screening of passengers appeared to be effective in preventing transmission of SARS-CoV in the months following the original outbreak.

Frequency

United States

As of July 1, 2007, only 8 laboratory-confirmed cases of SARS had been reported in the United States—all related to the original outbreak. No SARS-related deaths have been reported in the United States. Current statistics can be reviewed at the Centers for Disease Control and Prevention Web site.²

International

Worldwide numbers of SARS cases from the original outbreak (November 2002 through July 31, 2003) included 8096 cases, 774 deaths, and 7295 recoveries. Individual country statistics are as follows:

• Mainland China - 5327 cases, 349 deaths
• Hong Kong - 1755 cases, 299 deaths
• Taiwan - 346 cases, 37 deaths
• Canada (primarily around Toronto, Ontario) - 251 cases, 43 deaths
• France - 7 cases, 1 death
• Malaysia - 5 cases, 2 deaths
• Philippines - 14 cases, 2 deaths
• Singapore - 238 cases, 14 deaths
• South Africa - 1 case, 1 death
• Thailand - 9 cases, 2 deaths
• Vietnam - 63 cases, 5 deaths

Current statistics can be accessed from the WHO Web site.¹ See Image 13 for a map showing the worldwide distribution of SARS cases during the 2002-2003 outbreak.

Mortality/Morbidity

SARS can result in significant illness and medical complications that require hospitalization, intensive care treatment, and mechanical ventilation.

• The mortality rate of SARS is higher than that of non-H5N1 influenza strains or other common respiratory tract infections.
• The overall mortality rate of SARS has been approximately 10%. According to the CDC and the WHO, the death rate among individuals older than 65 years exceeds 50%.
• The WHO has set the SARS containment period at 20 days. If no new cases of SARS are reported in a given area over a 20-day period, given the relatively short incubation period of the disease, the WHO considers SARS infections in that area to be contained.

Race

All races are equally affected.

Sex

Both sexes are equally affected.

Age

SARS-CoV infection has no predilection for any age group; however, as stated above, morbidity and mortality rates are greater in elderly patients.

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