Space-time clustering of glioma cannot be attributed to specific histological subgroups.

We previously showed that infectious exposures may be involved in the aetiology of adult glioma, by analysing for space-time clustering using population-based data from the South of the Netherlands. Here we extended these analyses and describe in detail the space-time clustering patterns in glioma subgroups, gender and age-categories. Knox tests for space-time interactions between cases were applied with fixed thresholds of close in space, <5 km, and close in time, <1 year apart. We used the spatial coordinates of the addresses at diagnosis in the analyses. Tests were repeated replacing geographical distance with distance to the Nth nearest neighbour. N was chosen such that the mean distance was 5 km. Data were also analysed by a second order procedure based on K-functions. There was only statistically significant space-time clustering for oligodendroglioma. Clustering was present for adults aged 30-54 years and was more pronounced among males. Given the low prior probability of an infectious aetiology for this specific subgroup, these results should probably be interpreted as false-positive. We conclude that space-time clustering of glioma cannot be attributed to a specific glioma subgroup. The observed clustering in our previous study is therefore probably an overall effect within and between glioma subgroups.