We present a search for associated production of Higgs and W bosons in pp collisions at a center of mass energy of s√=1.96  TeV in 5.3 fb-1 of integrated luminosity recorded by the D0 experiment. Multivariate analysis techniques are applied to events containing one lepton, an imbalance in transverse energy, and one or two b-tagged jets to discriminate a potential WH signal from standard model backgrounds. We observe good agreement between data and background, and set an upper limit of 4.5(at 95% confidence level and for mH=115 GeV) on the ratio of the WH cross section multiplied by the branching fraction of H→bb to its standard model prediction, which is consistent with an expected limit of 4.8.