Epidemic diseases and host clustering: an optimum cluster size ensures maximum survival.

The risk of infection is generally believed to increase with gregariousness. Using a discrete time spatial simulation model we tested the effect of host clustering on transmission of infection within a population. Over a large parameter range, an optimum cluster size was observed to ensure maximum probability of escaping infection. Although the within cluster transmission increased with cluster size, the between cluster distance increased thereby decreasing the probability of transmission across clusters. The probability of stochastic extinction of the pathogen also increased with increasing cluster size. Thus contrary to the popular belief, clustering can be an effective strategy to minimize the risk of infections.