Thu, Apr 30, 2009 - Page 8 News List

Controlling hubs is key to battling infections

By Lai Shih-kung 賴世剛

More than 100 people have died in swine flu outbreaks in the US and Mexico, causing another global panic like that created by the outbreak of SARS. But Taiwan’s government has been tardy in laying out a disease prevention strategy, while the immediate response has not been comprehensive.

If swine flu — like SARS — is transmitted through close human contact, it is easy to see that more human interaction will lead to a higher infection risk. Therefore in urban areas, especially larger cities, infection rates will be higher. When creating a prevention strategy, the big challenge is to increase the efficiency of how prevention resources are distributed.

We first need to discuss the pattern of disease spread. If we can grasp how this takes place, prevention work can be carried out in potential infection zones. Since it is difficult to predict individual behavior, let alone wider social interaction, it is also difficult to understand how a disease spreads between individuals and groups.

If, however, we widen our perspective to the level of the city, we can assume or perhaps show through experimental data that the number of infections is proportional to a city’s population. If this assumption holds, we might be able to identify principles for distribution of prevention resources based on my recent study on rural-urban scale distribution.

Complex systems in natural and human environments share similarities, as seen in the collapse of the Soviet Union, stock markets, earthquake frequency and urban space distribution. Complexity science aims to explore the characteristics of complex systems. In the context of larger spaces, swine flu must spread via carriers to each city and county through the transportation network.

My study of population distribution scales in Taiwan’s urban and rural areas using computer simulations shows that the distribution of urban systems displays characteristics of scale-free networks. In other words, once a logarithm has been established for population size and number of cities, the distribution displays a clear relationship.

The number of big cities is lower than that of small towns, and there should be a statistical relationship between population size and node number in individual interaction networks. This may be able to serve as an index to the number of nodes for a network. So if we want to prevent swine flu from being transmitted through urban-rural networks, we need to find the most crucial points on the networks, or hubs.

According to one academic analysis of scale-free networks, we should concentrate prevention resources in such hubs to eliminate their distributive function and thus control the spread of the disease.

In other words, we should make every effort to control the disease in larger urban areas such as Taipei and Kaohsiung, and then assess the situation in smaller towns according to size, so that transmission networks for a disease can be disrupted.

Prevention work within a city can also follow this rule. By identifying the hubs of interpersonal interaction networks — such as public places with frequent human activity — we might be better able to block channels for disease transmission and protect the city as a whole.

Technical issues of prevention depend on the collective effort of professional medical workers. It is better for the government to launch cross-disciplinary teams with medical workers and professionals from all fields so that all necessary precautions can be taken before the situation arises. The battle can then be won together.

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