ADC2604 Your comment has just come to my attention.
I mean how come none of the BE passengers have been affected
Because if they are suffering (we can assume some of them may be) they just think they are ill due to something else. To study this subject it is pointless looking at pax unless, for a long period, they flew the same aircraft type for long durations every working day. It would be hard to trace such people and then when you do, you have to stumble on only those who are suffering the symptoms - not an easy data collection exercise for any scientific analysis.
Far easier to study the crew, many of whom who are in the cabin for the entire cycle (for example perhaps at certain problematic times when the pax are not - startup of APU for example was suggested) and therefore crew are better subjects to study.
In summary - how come the pax do not suffer? - they probably have done and put it down to air sickness.
A final thought - both the parents of an ex-girlfriend of mine died of a particular type of cancer - for this type of cancer, such an event to happen to a couple is almost unheard of, the explanation was that they probably had been exposed to something at the same time whilst together. I don't for a minute suggest that their deaths were related to the 146 or 757, but somewhere out there is the toxin - I would like to think that our society is proactive in its approach to such problems.