The World Health Organization has formally identified the Severe Acute Respiratory Syndrome virus as a type of corona virus previously unseen in humans. Work is now under way to develop quicker tests to identify infected patients and to design a treatment, or at least a more effective containment regime. As work progresses on combating SARS, international attention is also focusing on the scope and scale of the economic impact of the infection, which has struck more than 3000 people since November 2002, killing about 172 worldwide. But the infection rate and death toll of SARS thus far pales in comparison to other 20th century viral pandemics, and economics will be affected much more by the fear factor and containment efforts than by the number of people actually infected or dying from SARS. The SARS virus is in the family Coronaviridae, a family that includes several viruses that cause upper respiratory infections in humans and animals. Corona virus outbreaks occur primarily in winter months, and are often associated in humans with cold-like symptoms. Corona viruses like SARS are transmitted through aerosols of respiratory secretions ("wet" coughs, sneezes, etc), as well as other transfers of bodily fluids. Basic preventative measures like masks, frequent hand washing and disinfecting surfaces are a relatively effective defense against transmission of the virus. The SARS virus likely is a naturally mutated form of the virus that normally infects animals — something not entirely uncommon in southern China, where trans-species mutation triggered virus scares in Hong Kong in 1997 and 1999. Initial genetic testing of the SARS virus by the National Institute of Allergy and Infectious Diseased shows no evidence of "genetic tampering," meaning the virus most likely is a natural mutation and not an engineered bio-weapon, as some have speculated. The SARS virus appears to have originated around Nov. 16, 2002 in Foshan, Guangdong province, an industrial city just southwest of Guangzhou. Within a month, it had spread to at least six cities in Guangdong, hitting a hospital in Heyuan particularly hard. The next major fulcrum of the spreading disease was Guangzhou, and by mid February there were 305 registered cases of what was then called "atypical pneumonia." From Guangzhou, it spread to Hong Kong and on to Canada, the United States Vietnam and Singapore. Currently, the WHO notes that, despite the global reach of SARS, there are only a small number of areas affected by SARS — including Beijing, Guangdong, Shanxi, Hong Kong, Singapore, Toronto and Hanoi, as well as some isolated pockets in the United States, London and Taiwan. One notable aspect of SARS transmission early on was the preponderance of infected health workers. Of the 305 registered or suspected cases in Guangdong by February 2003, more than 100 were health workers. This accounts for the overall statistics of the disease affecting more young adults than any other age group. And this is one major difference between SARS and some other recent pandemics, which affected primarily the very young or old. But both the transmission rates and the death rates for SARS are low compared to other major 20th century pandemics. The World Health Organization (WHO) estimates the death rate from probable SARS patients at 4 percent, nearly the same as for West Nile Virus. And transmission rates are significantly lower for SARS than for influenza, as the virus is not transmitted by air but through droplets of bodily fluids. Many doctors studying SARS have estimated that, had it been caused by an influenza virus, from the family Orthomyxoviridae, rather than from the Coronaviridae, the infection rate would be 10 times higher or more. And in looking at WHO epidemic curve graphs charting the onset date of probable SARS cases, there is some hope that containment methods for SARS may be stemming the transmission of the disease. The global peak for probable infections occurred in late March, after a smaller spike earlier in the month, with the initial spike in early February. But in breaking down the country of origin, it paints a different picture. The initial February peak primarily represents the epidemic stage in China, before the disease spread to other countries. The rate of new cases of SARS has fallen since mid February in China. The successive peaks in the global chart track SARS as it spread to Hong Kong, Vietnam, Canada, Singapore and the United States. A caveat must be noted here, in that the overall numbers from the WHO are not complete for three main reasons. First, they flat out do not count around 20 percent of the documented probable infection cases, as there is no registered information on date of onset. Second, there remain questions about China's statistical accuracy, as Beijing and local officials initially held reports of "atypical pneumonia" under close wraps and have been slow to readjust their methods of reporting. Finally, there are some anomalies regarding the definitions of "probable" versus "suspected" cases — the United States, for example, has significantly lowered its number of probable SARS infections after removing all the suspected cases from the list while Beijing is about to significantly raise the number of probable SARS cases in the city after altering the definition of probable versus suspected. But the overall picture, despite the anomalies, is that SARS is unlikely to ever reach the pandemic proportions of the 1918 Spanish Flu, which infected 20 to 40 percent of the global population and killed 20 million people. Neither is it likely to match the 1957/58 Asian Flu or the 1968 Hong Kong Flu, both of which also originated in southern China. Again, it is important to remember that SARS is not an influenza virus, but a corona virus, and transmission rates differ significantly. With the death rate likely to remain low by pandemic standards, the biggest economic threat from SARS comes not from the loss of life or the hospitalization of infected patients, but from fear and the containment regime necessary to stem the spread of the virus. Fear has been triggered by misinformation and lack of information, something China, and other Asian nations, are now paying the price for. And the containment of the virus, from improved medical sanitation to closed offices and business to decreased airline travel and increased security will have a lingering impact even after the threat of infection declines.