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.
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.
新型コロナウイルスの発生が報告された。
An outbreak of the novel coronavirus was reported.
感染症の発生を防ぐ。
Prevent the outbreak of infectious diseases.
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.
エボラ出血熱のアウトブレイクが発生した。
An Ebola outbreak occurred.
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.
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).
インフルエンザの流行が始まった。
An influenza outbreak has begun.
Outbreak (of war, conflict). A formal, written term. Commonly used in historical or news contexts.
Literally 'war begins'. A more neutral, everyday expression.
突然、戦争が始まった。
Suddenly, war broke out.
Also used for fires. Often in official reports.
火災が発生した。
A fire broke out.
Common, everyday expression for a fire occurring.
昨夜、近所で火事が起きた。
A fire broke out in the neighborhood last night.
Used for sudden outbreaks of violence, riots, etc. Formal.
暴動が勃発した。
A riot broke out.
More general: 'violent incidents occur/break out'.
市内で暴力事件が発生した。
Violent incidents broke out in the city.
General term for occurrence, including pests, tornadoes, etc.
害虫が大量発生した。
There was an outbreak of pests.
Frequent occurrence, outbreak of many cases. Often used for accidents or incidents.
竜巻が多発している。
Tornadoes are breaking out frequently.