Altruism is a word that indicates an attitude of love of neighbor or absence of selfishness. In the text shown in the question, Bradford considers caregivers of sick people altruistic, because for him, these people do a painful and bad job without selfishness and showing love and care to those who are going through a difficult situation. Patient caregivers deliver the best they have to do a service that helps and comforts people.
The caretakers unselfishly and willingly did many things for the ill, which, as the speaker says, “dainty and queasy stomachs cannot endure to hear named.” They, who were the only ones in good condition, were concerned more with the needs of their friends than their own's and diligently worked to take care of them. Through this description, then, Bradford wants to convey the selfless nature of the caretakers.