The number of influenza patients is rapidly increasing, particularly among adolescents, marking the largest outbreak since 2016.

According to the Korea Disease Control and Prevention Agency, the influenza-like illness, or ILI, rate — a measure of suspected flu patients among 1,000 outpatients at 300 sample monitoring medical institutions nationwide — surged to 73.9 between Dec. 22 and 28 last year.

The figure reflects a dramatic 136 percent rise from the previous week’s rate of 31.3 per 1,000 people.

The current ILI rate is the highest since 2016, when it peaked at 86.2. In comparison, recent years saw peaks of 73.9 in 2023, 61.3 in 2022, and 60.7 in 2021. During 2020 and 2021, when flu outbreaks were largely suppressed due to COVID-19 precautions, the highest ILI rates were significantly lower, at 3.3 and 4.8, respectively.