I had to read it in Eng 113 a couple years ago. From what i remember it was about disease. I guess when he wrote it, his family had been going through (I want to say TB but Im not sure) some stuff with disease. It is saying that its like youre something as disgusting as a cockroach when you have a disease. People scream and shout because theyre afraid of you etc... Its a metaphore of how hard life is for someone who isn't "normal" like the rest of functioning society.