Translation guide
The English word 'flu' refers to influenza, a common viral illness. In Japanese, the most common and natural way to say this is インフルエンザ (influenza), often shortened to インフル in casual speech. There is also a traditional term 流行性感冒, but it is rarely used in everyday conversation.
インフルエンザです。
I have the flu.
Referring to the viral respiratory illness commonly known as the flu.
インフル is perfectly fine in casual conversation with friends and family. In more formal situations or writing, use the full インフルエンザ. For example, when calling in sick to work, it's safer to say インフルエンザです.
すみません、インフルエンザで休みます。
Sorry, I'll be absent due to the flu.
The standard Japanese word for influenza. Used in all contexts, from casual to formal.
今年はインフルエンザが流行している。
The flu is going around this year.
インフルエンザにかかってしまった。
I caught the flu.
A common casual abbreviation of インフルエンザ. Used in everyday conversation, but avoid in formal writing.
昨日からインフルで寝込んでる。
I've been in bed with the flu since yesterday.
The formal medical term for influenza. Rarely used in daily life; mostly seen in medical contexts or older texts.
流行性感冒はインフルエンザウイルスによって引き起こされる。
Influenza is caused by the influenza virus.