The SARS epidemic has generated a lot of scientific research and interest into the origin of the virus and the epidemiology of its spread.  One of the more unusual features of this virus that has emerged from the  research  of Asra Ghani of the Department of Infectious Disease Epidemiology at Imperial College, London. She found that most people who get SARS do not infect anyone else, but some individuals appeared to be responsible for transmitting the disease to dozens and sometimes hundreds of others. Such individuals are known as "superspreaders", and these superspreaders have some role in transmission of the disease.

Another disease that exhibits this kind of classic transmission heterogeneity is HIV. In the case of HIV most people have just a few sexual partners and so transmit the virus to one or two other individuals, but a small number of people have a large number of partners, and spread the virus widely. Such a picture is supported by research in countries in Africa that seems to suggest the majority of people have one or two partners. In the case of HIV in Africa individuals who would serve as classic “superspreaders” are long distant truck drivers long suspected of being a factor in the spread of HIV across borders in Africa, or soldiers in times of conflict when a lot of sexual assaults and rape take place such as happened in the genocide in Rwanda.

Further reading:

1. BioMedNet Magazine 21st May - 3rd June 2003 - “SARS: masking the real danger “ (requires free one time registration to access articles)
   
   
2. Donnelly C. A, Ghani A. C et al (2003). “Epidemiological determinants of spread of causal agent of severe acute respiratory syndrome in Hong Kong” The Lancet Volume 361, Number 9370. May  (requires free one time registration to access articles)