Curvature properties of 3-quasi-Sasakian manifolds

We find some curvature properties of 3-quasi-Sasakian manifolds which are similar to some well-known identities holding in the Sasakian case. As an application, we prove that any 3-quasi-Sasakian manifold of constant horizontal sectional curvature is necessarily either 3-\alpha-Sasakian or 3-cosymplectic.