PSI above 400 is life threatening

‘PSI levels above 400 may be life-threatening to ill and elderly persons. Healthy people may experience adverse symptoms that affect normal activity.’

The quality of our air hit 371 on the PSI scale on Thursday. This is 29 points short of 400. According to the PSI definition, above 400 is life threatening. How threatening is this? Is it more serious than the dengue situation at the moment? Is