The SARS Network

The Severe acute respiratory syndrome (SARS) Network refers to the system by which the SARS virus managed to have initial seedings in many different geographical locations, with intense but tightly circumscribed activity, without breaking out into an epidemic.

An overview of networks

An undirected network of 6 nodes and 7 edges.

In the context of network theory a network is graph (network) that uses encodes the components of a system and their interactions. Each component in a system is represented with a node, and their connections between each other are represented with corresponding edges. Networks can be either random or non-random, they may depict complex or simple structures, and their edges may be directed or undirected. Networks are particularly useful in depicting and analyzing complex systems.

Networks examples:

• The social network of all professional, friendship, and family ties.
• The network describing the interactions between genes, proteins, and metabolites integrate the processes behind living cells.
• The network describing which communication devices interact with each other, capturing internet connections or wireless links, is the heart of the modern communication system.
• The power grid, a network of generators and transmission lines, supplies with energy virtually all modern technology.

Spreading processes

Content in a complex network can spread via two major methods: conserved spread and non-conserved spread. In conserved spread, the total amount of content that enters a complex network remains constant as it passes through. In non-conserved spread, the amount of content changes as it enters and passes through a complex network. The non-conserved model is the most suitable for explaining the transmission of most infectious diseases, neural excitation, information and rumors, etc.

SARS overview

Severe acute respiratory syndrome (SARS) is a viral respiratory disease originating in southern China eventually infecting 8,273 and killing 775 people worldwide, between November 2002 and July 2003. On 16 November 2002, the first official case of SARS was recorded in Guangdong Province, China. The People's Republic of China (PRC) notified the World Health Organization (WHO) about the outbreak four months later, on February 10, after 305 recorded cases and 5 deaths; In those four months, severe acute respiratory syndrome (SARS) was thought to be the first new, easily transmissible infectious disease of the twenty-first century.

SARS as a network

The severity of the symptoms and the infection of hospital staff alarmed global health authorities, fearful of another emergent epidemic. On 12 March 2003, the WHO issued a global alert, followed by a health alert by the United States Centers for Disease Control and Prevention (CDC). SARS spread from China to 25 countries and Taiwan, seeding itself in localities in Toronto, Ottawa, San Francisco, Ulan Bator, Manila, Singapore, Taiwan, Hanoi and Hong Kong whereas within China it spread to Guangdong, Jilin, Hebei, Hubei, Shaanxi, Jiangsu, Shanxi, Tianjin, and Inner Mongolia. Panic was evident, as there was great uncertainty about its causes, cure, and most important its level of contagion.

Panic was not only concentrated among the public. Mathematical epidemiologists originally estimated the virus would between infect between 30,000 and 10 million persons, within the first 120 days. Despite this estimate SARS has not emerged as a global pandemic. Instead, initial seeding of the virus was followed by intense but tightly circumscribed activity in some locales with only scant activity in others. It turned out that only 782 cases were reported during those initial three months. There were some crucial features of SARS that greatly facilitated the global containment of the disease. Firstly, patients are infectious only after they exhibit symptoms. As a result, some researchers feel ‘SARS might almost be classified as “easy” to manage’. Another feature of SARS favourable to its containment is its transmission via large droplets (as opposed to small droplets or aerosols), requiring close contact.

Many infectious diseases spread through populations via the networks formed by physical contacts among individuals. SARS is no different. One of the striking features of the SARS epidemic was the manner in which airline networks acted as corridors for the spread of the disease. From its onset it became clear that the role of air transport in the diffusion of the disease was key. This is why, despite its relatively low level of contagion, the SARS Network still managed to become a large diameter network. It is true that the origin of the virus being connected with such an important node, like Hong Kong, made it especially prone to diffusion by air travel. Moreover, had a similar disease originated in a less connected node, like Central Africa, one would not expect the virus to infect such an extended part of the network. Nevertheless, it is apparent that the world was ill-prepared to mitigate the diffusion of SARS via international air transport, and should another virus both come to infect an important node in the global transportation network, and be relatively contagious, epidemic or even pandemic may ensue.

See also

• Network Science
• Complex network
• Scale-free network
• Random network
• Small-world network
• Erdős–Rényi model

Further reading

• "Network Science Center," http://www.dodccrp.org/files/Network_Science_Center.asf
• Linked: The New Science of Networks, A.-L. Barabási (Perseus Publishing, Cambridge)
• A course on complex network analysis by Albert-László Barabási

Notes

This article "The SARS Network" is from Wikipedia. The list of its authors can be seen in its historical and/or the page Edithistory:The SARS Network. Articles copied from Draft Namespace on Wikipedia could be seen on the Draft Namespace of Wikipedia and not main one.

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