A sudden or abrupt onset of something really bad is an outbreak. You could experience an outbreak of measles or an outbreak of violence; either way, try to protect yourself.
When you talk about an outbreak of something, it's almost always something terrible, or at least unwanted. You might hear about an outbreak of war in a distant country, or an outbreak of violence in a big city, or an outbreak of disease among farm animals. Outbreak started as a Middle English verb around 1300, becoming a noun meaning "eruption" about three hundred years later.