Severe Acute Respiratory Syndrome

Mapping the genetic code of viruses linked to SARS

On April 12, 2003, scientists working around the clock at the Michael Smith Genome Sciences Centre in Vancouver, British Columbia finished mapping the genetic sequence of a coronavirus believed to be linked to SARS. The team was led by Dr. Marco Marra and worked in collaboration with the British Columbia Centre for Disease Control and the National Microbiology Laboratory in Winnipeg, Manitoba, using samples from infected patients in Toronto. The map, hailed by WHO as an important step forward in fighting SARS, is being shared with scientists worldwide via the GSC website. See the SARS virus article for more details.

Related Topics:
April 12 - 2003 - Vancouver, British Columbia - Genetic sequence - Marco Marra - British Columbia - National Microbiology Laboratory - Winnipeg, Manitoba - SARS virus

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Dr. Donald Low of Mount Sinai Hospital in Toronto described the discovery as having been made with "unprecedented speed." http://www.cbc.ca/stories/2003/04/12/sars_code030412 A team slaved over the problem 24 hours a day for a mere six days.

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As at April 17, 2003 an increase over the previous week in the death rate and especially the increase in deaths in young previously healthy patients has reinforced concerns about the severity of the illness and increased anxiety in cities such as Hong Kong. The reasons for this mortality increase cannot yet be stated with certainty. The following factors may be involved:

Related Topics:
April 17 - 2003 - Hong Kong

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• Statistical clustering: It may be in part coincidence that a group of younger deaths have occurred over a short period of time. This can only be adequately assessed by detailed statistical analysis of different cohorts (groups) of patients.
• Late presentations: Patients presenting late in the disease would be expected to have a worse outcome. This has been given as an explanation in a number of cases.
• Drug resistance: This has been proposed as a possible explanation by a Professor of virology from Chinese University. There has been a significant debate in the medical community about the effectiveness of ribavirin. It seems unlikely that the effectiveness would change so dramatically in a short time in young patients.
• Variation in the severity of the disease: This is an important possibility. There have been a number of anecdotal reports that the disease is more severe in the cluster of patients from Amoy Gardens. The W.H.O. considers this as a potentially important factor (16 April Press briefing). One possible explanation for this is that the environmental process involved led to exposure to large amounts of virus. Another suggestion is that a slight change in the coronavirus led to more severe disease in this cluster. Exposure to a larger amount of virus, or a more severe disease could be sufficient to impact even on the young and previously healthy. These hypotheses can be tested by assessing the outcome in this cohort in addition to RNA typing of the virus in order to determine if slight variation is associated with different disease patterns.
• Variation in the level of medical care: This is a possible factor. The first cohort of 138 patients had a mortality rate of 3.6%. This data has been published in The New England Journal of Medicine (http://content.nejm.org/cgi/content/abstract/NEJMoa030685v2 )

This graphic represents the evolution of the people probably infected, by main countries (Moving Average of 7 days) and the mortality rate for the last 2 weeks.

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People probably infected = Cumulative case − Number of deaths − Number of people discharged.

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Mortality rate = Deaths / (Deaths + Discharged)

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(Source : WHO WEB SITE)

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