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We present a study of the Oosterhoff (Oo) dichotomy in the Galactic bulgeusing 8\,141 fundamental mode RR~Lyrae stars. We used public photometric datafrom the Optical Gravitational Lensing Experiment (OGLE) and the VistaVariables in the V\'ia L\'actea survey (VVV). We carefully selected fundamentalmode stars without modulation and without association with any globular clusterlocated toward the Galactic bulge. Subsequently, we identified and separatedthe Oosterhoff groups I and II on the basis of their period-amplitudedistribution and using a relation fitted to the Oosterhoff I locus. BothOosterhoff groups were then compared to observations of two bulge globularclusters and with models of stellar pulsation and evolution. We found that someof the variables classified as Oo\,II belong to a third Oo group. TheOosterhoff II variables are more metal-poor on average, more massive, andcooler than their Oosterhoff I counterparts. The analysis of their spatialdistribution shows a systematic difference between \textit{foreground}, centraland \textit{background} regions in the occurrence of the Oosterhoff II group.The difference between the Oo\,I and II groups is also seen in their distancedistributions with respect to the Galactic bar, but neither group is associatedwith the bar.

On the Oosterhoff dichotomy in the Galactic bulge: I. spatial distribution