Erratum
After publication of the original article [1], it came to the authors’ attention that a few values in Table 2 were added incorrectly. The correct values are as follows: for total cases ‘disk shape balloon’ and ‘ball type balloon’ the incidence observed was 0.037 % (14/38348) and 0.060 % (28/46640), respectively. All other values within Table 2 are correct.
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