Severe acute respiratory syndrome is a respiratory disease in humans which is caused by the SARS coronavirus (SARS-CoV). There has been one near pandemic to date, between the months of November 2002 and July 2003, with 8,096 known infected cases and 774 confirmed human deaths (a case-fatality rate of 9.6%) worldwide being listed in the World Health Organization's (WHO) 21 April 2004 concluding report. Within a matter of weeks in early 2003, SARS spread from the Guangdong province of China to rapidly infect individuals in some 37 countries around the world.
Mortality by age group as of 8 May 2003 is below 1% for people aged 24 or younger, 6% for those 25 to 44, 15% in those 45 to 64 and more than 50% for those over 65. For comparison, the case fatality rate for influenza is usually around 0.6% (primarily among the elderly) but can rise as high as 33% in locally severe epidemics of new strains. The mortality rate of the primary viral pneumonia form is about 70%.
As of May 2006, the spread of SARS has been fully contained, with the last infected human case seen in June 2003 (disregarding a laboratory induced infection case in 2004). However, SARS is not claimed to have been eradicated (unlike smallpox), as it may still be present in its natural host reservoirs (animal populations) and may potentially return into the human population in the future.
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.
WHO has today revised its initial estimates of the case fatality ratio of SARS. The revision is based on an analysis of the latest data from Canada, China, Hong Kong SAR, Singapore, and Viet Nam.
On the basis of more detailed and complete data, and more reliable methods, WHO now estimates that the case fatality ratio of SARS ranges from 0% to 50% depending on the age group affected, with an overall estimate of case fatality of 14% to 15%.
The likelihood of dying from SARS in a given area has been shown to depend on the profile of the cases, including the age group most affected and the presence of underlying disease. Based on data received by WHO to date, the case fatality ratio is estimated to be less than 1% in persons aged 24 years or younger, 6% in persons aged 25 to 44 years, 15% in persons aged 45 to 64 years, and greater than 50% in persons aged 65 years and older.