Cases of mycoplasma pneumonia, a common infection affecting children that is usually accompanied by prolonged fever and cough, reached a record high during the last week of September, according to the most recent data from the National Institute of Infectious Diseases.

The data published on Tuesday showed an average of 1.64 patients with the disease being reported per medical facility in the week between Sept. 23 and 29. This is the highest number since the institute began recording cases in 1999. The same period in 2023 only had an average of 0.04 patients per hospital.

The institute measures the prevalence of the disease via a weekly average of cases seen by medical facilities across the nation.