my $delete = join('|', map quotemeta, sort @element_to_delete);
my $re = qr/(?:^|,)(?:$delete)(?=,|$)/;

for (@key_to_search) {
  if (defined $new_reports{$_}) {
    $new_reports{$_} =~ s/$re//g;
    delete $new_reports{$_} unless length $new_reports{$_}
  }
}