I think the disease wasn't well known before this major episode occurred in the 1930s. It was after this that they identified the cause of the decline at that time as being wasting disease. Since then, the plant has recovered partially over most of its range on the Atlantic coast and continues to fluctuate at various levels.
If the plant is tested in the laboratory, they find that the disease is still there, but at very low levels, so the potential for additional declines are there, when the conditions might present themselves again.