MODELING THE EFFECTIVENESS OF ISOLATION STRATEGIES IN PREVENTING STD EPIDEMICS

We formulate and analyze a two-group, selective-mixing, susceptible-in fective-susceptible (SIS), sexually transmitted disease (STD) model wh ere the infection-dependent desirability and acceptability in partners hip formations are zero at high infection levels. We analyze two strat egies to limit the spread of the epidemic by avoiding forming partners hips with people in a highly infected group. In one approach, the peop le in the highly infected group protect themselves by forming partners hips with only people outside their own group. We show that the transm ission dynamics for this approach are similar to the situation where p eople continue to have both intragroup and intergroup partnerships. In the second approach, when one group becomes highly infected, the peop le in the other group adopt an isolation strategy and stop forming any partnerships with people in this highly infected group. We show that the second approach can limit the epidemic to the highly infected grou p. The other group will be infection-free, but as long as the epidemic in the total population exceeds the epidemic threshold, the epidemic will continue to persist. If the group reproductive number of the infe ction-free group is greater than one, and the infection should ever in vade the infection-free group, then it will lead to an epidemic simila r to the one that would have occurred if they had not isolated themsel ves from the other group. In this simple two-group model, although the se isolation strategies may reduce the extent of an STD epidemic, they are ineffective in preventing an epidemic.