Seasonal variation in the incidence rate of tuberculous meningitis is associated with sunshine hours

Abstract

Tuberculous meningitis (TBM) is a severe complication of tuberculosis and occurs mainly during early childhood. The incidence rate of TBM varies with season, and serum vitamin D levels, which are dependent on sunlight, might play a role. We studied the association between TBM incidence rate and hours of sunshine in Cape Town, South Africa and found a significant association between the incidence rate of TBM and hours of sunshine 3 months earlier (incidence rate ratio per 100 sunshine hours 0·69, 95% confidence interval 0·54-0·88, P = 0·002). The association supports the hypothesis that vitamin D might play a role in the pathophysiology of TBM. Further prospective studies in which vitamin D status is measured are necessary to determine causality.

Fig. 1

[colour online]. Incidence rate of tuberculous meningitis (TBM) (dashed curve; right y-axis) and sunshine hours (SH; dotted curve; left y-axis) are shown per quarter (=3 months). The solid curve (postponed sunshine hours) illustrates the inverse association with the incidence rate of TBM. Low amounts of sunshine during winter months lead to an increase in TBM incidence (black arrows). For reasons of clarity only part of the graph is shown.