Another one today:
Incident: Delta B763 over Greenland on Feb 5th 2018, 5 flight attendants becoming sick in flight
My theory about why we see this more in CC than Pax is that CC are more active, thus higher breathing and heart rate, which may mean more absorbtion of toxins. Also they are standing more often than pax, and if the toxins are lighter than air will be more often with their heads in it....? (CO is less dense than air)