  In this paper, sufficient conditions for contact $(+1)$-surgeries along
Legendrian knots in contact rational homology 3-spheres to have vanishing
contact invariants or to be overtwisted are given. They can be applied to study
contact $(\pm1)$-surgeries along Legendrian links in the standard contact
3-sphere. We also obtain a sufficient condition for contact $(+1)$-surgeries
along Legendrian two-component links in the standard contact 3-sphere to be
overtwisted via their front projections.
