I am guessing the authors made it purposefully vague how many members an expedition consists of, but I was curious as to what answer other DMs have given their players to this question who is bound to come up.
I am not just talking about battle-experienced guards and mercenaries such as those statted up in City of Seven Spears, but sages, cooks, etc.
The number that I've seen most people throwing around (and that I used myself) is each deep jungle expedition is about 100 people. 20-30 guards/warriors, another 20-30 sage/researchers and the rest porters, pack animal handlers and supply folks.