"I noticed that goitre was painfully prevalent"
by cm

Public DomainGoitre - Credit: Martin Finborud
Goitre is an affliction caused by iodine deficiency, where the thyroid gland in the neck swells up.  Iodine deficiency can also cause mental retardation, so the prevalence of goitre does not bode well for the health of the local population.

Of course, Harker's observation foreshadows a rather different affliction of the neck that we are about to encounter...