(Caution, Bodily fluid imagery)

Subject - Health
Extra points!

A 19 year old female has been experiencing for the last 2 days, a soar throat, pain when she talks, and a mild fever (99.5 - 100.5) that is on and off. She also lacks an appetite. She thinks she has symptoms of sinusitis. She has bloody yellow mucus when she blows her nose.

Question: What is bloody yellow mucus usually a sign of?

Answer needs to be at least one sentence long.