9.1. Identification of indicators of epidemic risk

Although a considerable number of determinants may precipitate an epidemic, in any particular situation, most of them are interrelated. Therefore, there is seldom more than one major risk factor or at most only a few with a high predictive value. Nevertheless, in areas of varied and isolated ecological features, such as highland valleys, or of highly concentrated socioeconomic development, there may be large differences in epidemic potential and risk factors between neighbouring areas. The identification of local epidemic-prone areas and risk factors should be based on the retrospective analysis of the malariometric indicators, including the history of past epidemics and the records of potential risk factors suggested by the ecology of the area.

In most antimalarial programmes, the main epidemic risks are known, even if the epidemiological services may not have the recorded information to document that knowledge. For example, in some areas, a major event such as the opening of a road, the beginning of a colonization programme, or the appearance and spread of drug resistance, marks the introduction of new risk factors. These factors may sometimes have been identified several decades previously and their monitoring may have been terminated, as in the case of the Punjab, where a sophisticated epidemic forecasting system was discontinued following the adoption of the national malaria control campaign in the 1950s. In such situations, it is generally possible to obtain the missing records from the relevant services, as well as any information which may indicate an important change in the epidemiological conditions in the area. A simple statistical analysis will then indicate the validity or otherwise of the original epidemiological hypotheses. In areas where there are no reliable epidemiological records but reasonably accurate records of deaths or hospital records, it may be possible to study the correlation between mortality and potential risk factors, as was done in the Punjab in the first quarter of this century (Christophers, 1949).

In other areas, there may be no epidemiological records, but meteorological services may have kept detailed records for many decades, and the ecology of the area may suggest the most probable risk factors. In general, the impact of malaria epidemics is sufficiently serious to remain in people’s memory for some years, so that it may be possible to determine whether the years of remembered epidemics were also years of exceptional meteorological or socioeconomic conditions (graphs 13-15).