1) Beginning 2) Bout 3) Breakout 4) Egress 5) Eruption 6) Onset 7) Outburst 8) Plague 9) Rash 10) Recrudescence 11) Spell 1) Epidemic 2) Eruption 3) Explosion 4) Flare-up 5) Happening 6) Irruption 7) Natural event 8) Occurrence 9) Rash 10) Upsurge 11) Wave 
Outbreak is a term used in epidemiology to describe an occurrence of disease greater than would otherwise be expected at a particular time and place. It may affect a small and localized group or impact upon thousands of people across an entire continent. Two linked cases of a rare infectious disease may be sufficient to constitute an outbreak. Out...
• (n.) A bursting forth; eruption; insurrection.
The occurrence of a large number of cases of a disease in a short period of time. ... (09 Oct 1997) ... 
The appearance of several cases of a disease in an area previously experiencing no, or very few, cas
Out'break` noun A bursting forth; eruption; insurrection. 'Mobs and outbreaks .' J. H. Newman. « The flash and outbreak of a fiery mind.» Shak. 
[n] - a sudden violent spontaneous occurrence (usually of some undesirable condition)
A sudden increase of a specific illness in a small area.
The occurrence of cases of disease in excess of what would normally be expected in a defined community, geographical area, and/or season, but in lower than epidemic numbers.
Sudden appearance of a disease in a specific geographic area (e.g. 
eruption 3 irruption noun a sudden violent spontaneous occurrence (usually of some undesirable condition); `the outbreak of hostilities`
a sudden breaking out or occurrence; eruption: the outbreak of war. · a sudden and active manifestation: an outbreak of hives. · an outburst: an outbreak of temper. · an insurrection, revolt, or mutiny. · a public disturbance; riot.
an increase in the number of cases of a specific infectious illness within a setting or population, over a specific timeframe. The number of cases needed to declare an outbreak varies by disease and the size of the setting or population.
Similar to an epidemic, but it usually refers to a group of cases within a smaller area.