Translation guide
How to express 'outbreak' in Japanese depends on what is breaking out: a disease, war, fire, or something else. The most common and versatile word is 発生 (hassei), but specific contexts call for different terms.
disease outbreak
outbreak of war
fire broke out
To refer to the sudden occurrence of a disease affecting many people.
General term for outbreak, occurrence, or incidence. Used for diseases, but also for other events. Often combined with the disease name.
An outbreak of the novel coronavirus was reported.
Epidemic, prevalence, spread. Emphasizes the widespread nature of a disease. Often used for seasonal influenza.
Loanword from English, used in technical or news contexts, especially for sudden, severe outbreaks.
To refer to the start of a war, battle, or hostilities.
To refer to the sudden start of a fire.
To refer to the sudden start of violent events or social unrest.
To refer to the sudden appearance or increase of something like insects, storms, etc.
発生 (hassei) is a general term for 'occurrence' and can be used for diseases, fires, accidents, etc. 勃発 (boppatsu) is specifically for sudden, violent outbreaks like war or riots. Using 勃発 for a disease outbreak would sound odd.
War broke out.
感染症の発生を防ぐ。
Prevent the outbreak of infectious diseases.
インフルエンザの流行が始まった。
An influenza outbreak has begun.
An Ebola outbreak occurred.
Outbreak (of war, conflict). A formal, written term. Commonly used in historical or news contexts.
War broke out.
the outbreak of the Pacific War
Literally 'war begins'. A more neutral, everyday expression.
Suddenly, war broke out.
Also used for fires. Often in official reports.
A fire broke out.
Common, everyday expression for a fire occurring.
A fire broke out in the neighborhood last night.
Used for sudden outbreaks of violence, riots, etc. Formal.
A riot broke out.
More general: 'violent incidents occur/break out'.
Violent incidents broke out in the city.
General term for occurrence, including pests, tornadoes, etc.
There was an outbreak of pests.
Frequent occurrence, outbreak of many cases. Often used for accidents or incidents.
Tornadoes are breaking out frequently.
感染症が発生した。
An infectious disease outbreak occurred.
In many cases, Japanese uses a verb like 発生する (hassei suru) or 起きる (okiru) instead of a noun. For example, 'There was an outbreak' is often '発生した' (hassei shita).