The actual answer.. by one measure, is a speck under 7.7%. Within a very insignificant significant digit of the lowest percentage since.. well, I can't quite say ever in the same sense of ever ever. Pre-columbian paleoeconomic employment taxonomies are not quite my field. Lowest for an October though... Maybe ever is fair in that context though since I am pretty sure October was not a pre-Columbian concept. Not all because of the loss of existing manufacturing jobs of course. Remember October employment for the Pittsburgh region is at at all time high, so even stable employment counts in any one industry would be declining in percentage within the region.
The less flippant point is that there is a myth out there that the local manufacturing decline is all ancient history. As trend the last 5 years have not been kind; the last decade has not been kind. There was a bit of stability in the mid to latter 1990's, but what that was masking was continuing decline in most of the legacy manufacturing sectors in the region while there was a decent chunk of new manufacturing jobs being created at the Sony Plant in Westmoreland County. Take that one establishment out of the mix, and the trend has been mostly unabated.
How long has the trend been going on in some form? Pittsburgh, the region, employed the largest percentange of the US manufacturing workforce in 1909. So a bit more than a century ago.
Looking forward there are some announced hits coming that have not shown up in the data yet. You might have worried more when you saw the headlines that Heinz is soon to be closing 5 plants, but that actually does not matter in this context since Heinz actually does not have any manufacturing plants in the MSA any longer.