The fight against malaria has been declared a Millennium Development Goal by the World Health Organization, and as such receives significant worldwide funding. Despite this fact, the public health agencies that manage this program lack the means to assess whether campaigns are effectively able to reduce or eliminate malaria within individual countries. For example, when there are a high number of imported cases within a country, each case has the potential to generate small local chains of transmission, which inflate the figures for the number of people infected locally and could falsely give the impression that control measures are ineffective. Over time, this may discourage funding bodies from investing in such projects. In collaboration with Tom Churcher (Imperial College) and colleagues, we proposed a simple method for assessing elimination campaigns. This method is based on an analysis of the proportion of imported cases among the cases detected within a given country (Figure 1 below). If the majority of cases are imported, this means that local chains of transmission remain negligible and that the epidemic would come to an end if importation of further cases were prevented. Conversely, if most cases occur as a result of local infection, the epidemic could persist even without imported cases. The method is based on sophisticated mathematical models and statistics for determining the threshold above which it may be assumed that a local epidemic is under control. This method has been used to assess an elimination campaign in Swaziland (Southern Africa). It is simple and intuitive, and may also be applied to studies of other epidemics.
Figure 1: Proportion of imported cases required to conclude local transmission is not self-sustaining (green area). Such work is essential to ensure long term political and financial support towards efficient programs is maintained.
- Churcher TS, Cohen JM, Novotny J, Ntshalintshali N, Kunene S, Cauchemez S. Measuring the path toward malaria elimination. Science 2014; 1230: 1230-1232.