Correlated prevalence of hydrocele and microfilaremia in Amazon (Belém, 1951-2005)

For decades, the city of Belém in Brazil's eastern Amazon was the second city in the country with highest prevalence of cases of filariasis due to Wuchereria bancrofti infection. However, this prevalence decreased over time until reaching null records, concomitantly with a decrease in frequency of recorded hydrocele cases. In this context, we analyzed cross-sectional data to evaluate the degree of correlation between prevalence of positive blood microfilariae results during surveillance screening occurred along 54 years (1951-2005) and prevalence of hydrocele cases recorded in the same time period.

The dataset regarding hydrocele cases was obtained from two local hospitals. The Endemic Diseases Control Division of the Health Surveillance Department of the Municipal Health Department of Belém provided dataset regarding positive blood microfilariae cases. Prevalence calculus and linear correlation statistics were performed.

Both positive blood microfilariae and hydrocele cases are well correlated statistically in absolute frequency (r = 0.871, 95%_CI = 0.788 to 0.923, R² = 0.759, p < 0.0001) and in prevalence (r = 0.835, 95%_CI = 0.732 to 0.901, R² = 0.698, p < 0.0001).

We have concluded that blood microfilariae detection and hospitalized hydrocele cases are well correlated in our dataset. In addition, these results support the hypothesis that hydrocele prevalence can be useful to filariasis surveillance and control in endemic areas. However, limitations to hydrocele prevalence as an epidemiological indicator of filariasis are evidenced.