A statistical analysis of the distribution characteristics of cholera within Ibadan City, Nigeria (1971)

The medical geography of Nigeria in the twentieth century cannot well be written without a full chapter devoted to the cholera epidemics of 1971. Though some medical men had written on the clinical and epidemiological aspects of these epidemics, very little is still known about the prevalence and distribution of the dreadful disease. This paper thus concerns itself with the distribution characteristics of this cholera spread in the largest indigenous city in the country, i.e. Ibadan.

The first stage of the analysis (i.e. the temporal analyses) reveals that the cholera epidemic in Ibadan city in 1971 conformed to the classical epidemic curve of a positively skewed normal distribution with one marked and steep modal peak. The finding is in conformity with that postulated theoretically and empirically discovered in the past. The modal peak is also observed to be asymmetrical thus conforming also to existing theory.

In terms of the cholera distribution characteristics, the epidemic had two waves of diffusion. The first wave covered weeks 1–26 of 1971, while the second wave coincided with the later part of the year. The first cholera epidemic wave had a strongly peaked and very positively skewed curve in both time and the frequency domains; thus the wave could be said to have an abrupt onset and a very rapid decline. The second wave on the other hand was platykurtic and relatively normal in distribution.

During the first epidemic wave, areas of earliest infection (i.e. the traditional core of the city) has a faster rate of diffusion than areas of later diffusion but during that second wave the peripheral areas (areas of later diffusion) were more affected in term of intensity of infection than the core area. The diffusion rate was faster also during the first wave than during the second wave, thus the second wave was of a less severe import than the first.

Though prediction of the second wave from the first wave was not possible, some vestiges of a “time” with “time” relationship of the first and the second wave was noticed.