Usage of thus

Migraine, the most debilitating common form of headache, afflicts perhaps 18 million Americans, who collectively lose 64 million workdays a year and thus cost the nation $50 billion in medical expenses and lost.

Is the usage of thus correct in the above sentance? Especially, I am suspicious of "and thus"!

Meriam defines "thus' as follows:

1 : in this or that manner or way
2 : to this degree or extent : SO
3 : because of this or that : HENCE, CONSEQUENTLY
4 : as an example

--Thanks for your help!

[Casiopea]

Migraine, the most debilitating common form of headache, afflicts perhaps 18 million Americans, who collectively lose 64 million workdays a year, and thus (i.e., and so) [they] cost the nation $50 billion in medical expenses and loss.