outbreak vs upsurge

outbreak

noun
  • A sudden increase. 

  • An eruption; the sudden appearance of a rash, disease, etc. 

  • Synonym of breakout (“escape from prison”) 

  • An outburst or sudden eruption, especially of violence and mischief. 

verb
  • To burst out or break forth. 

upsurge

noun
  • A sudden strong rise or flow. 

verb
  • to surge up, or to become stronger or greater 

How often have the words outbreak and upsurge occurred in a corpus of books? (source: Google Ngram Viewer )