Fevers, toxicity, severe pain and dysphagia; marked asymmetry of retropharynx on exam. CT makes the diagnosis.
NSAIDs are a risk as well (Pubmed).
Group A streptococci and other mouth organisms.
Drain it then penicillin or any other beta-lactam will nuke a group A strep.
Initially overtreat until cultures back as could be a mixed infection: (third generation cephalosporins PLUS metronidazole ) OR penicillin/beta-lactamase inhibitors OR (quinolone PLUS metronidazole OR clindamycin) OR carbapenems.
Dexamthasone 10 mg iv single dose led to a more rapid symptomatic improvement without complications (PubMed).