Science Homework Help

Help me study for my Microbiology class. I’m stuck and don’t understand.

Your stepbrother John is 5 years old. One day he comes to the breakfast table with a bright red face almost as if he had been slapped. When you look more closely you can see thousands of tiny red bumps on his skin. 

He has a milder rash on his arms and legs and just a few bumps on his trunk. He isn’t acting sick and doesn’t have a fever. He had chickenpox when he was 3 and his immunization schedule is up to date. 

He sticks his tongue out at you while you’re examining his skin and that reminds you to check his throat, which looks normal, no redness. He says his throat hasn’t felt sore. 

Your mom mentions that he had a runny nose for the last few days, but he hasn’t felt ill.

I diagnosed him with human parvovirus B19 (fifth disease). Can you take me through the medical process for reaching this diagnosis (e.g. antaomical diagnosis, differential diagnosis)? Are there any charts or figures or flow charts you can use? Also can you briefly explain why his throat was checked?