The conditions present in either of the bores were thoroughly inhospitable during the tunnel's construction, particularly in the bore driven from Airolo, where vapours were persistently present throughout the work. They were also hazardous; in one major accident alone, around 200 workers (the exact number is not known) were killed largely by the compressed air-driven trains that were used to carry excavated material out of the tunnel; other tunnel workers were killed as a result of rock slides, dynamite explosions, and a few drowned due to water inrushes. Of those that survived, several suffered from serious health issues caused by an epidemic of hookworm infection ("Ancylostoma duodenale"). Medical investigations led to "major advances in parasitology, by way of research into the aetiology, epidemiology and treatment of ancylostomiasis". During 1875, the workforce went on strike; this was promptly violently suppressed by local police force (21 men) from Altdorf, resulting in four deaths amongst the workers and the wounding of 13 others. Consequently, 80 workers left the building site afterwards.