Photo/Illutration Mycoplasma pneumoniae causes respiratory infections, particularly in children. (Provided by the National Institute of Infectious Diseases)

Health authorities are warning that potentially severe infections caused by Mycoplasma pneumoniae are rising at an alarming rate.

During the seven days leading up to Sept. 22, an average of 1.48 cases of Mycoplasma pneumonia per institution were reported across about 500 medical establishments nationwide, according to the National Institute of Infectious Diseases (NIID).

This marks a rise for four consecutive weeks and the largest number of cases during this period of the year in the past decade.

By prefecture, Fukui has the highest average, with 3.33 cases per medical institution surveyed. Tokyo and Gifu follow with 2.8 cases on average, Ibaraki with 2.69, Osaka with 2.61 and Hiroshima with 2.55.

The respiratory infection spreads through droplets released into the air by sneezing and coughing, and leads to symptoms such as fever, cough, fatigue and headache.

Coughing can persist for several weeks in some cases. Some patients may experience symptoms severe enough to require hospitalization. In rare instances, it can lead to conditions such as encephalitis, a brain inflammation.

While most patients are children aged 14 or younger, cases have also been reported among adults, especially those in their 30s or younger without underlying health conditions, according to Takeshi Saraya, a professor specializing in infectious diseases at Kyorin University in Tokyo.

Saraya advises people to seek medical treatment if they have a severe cough or a prolonged fever, as most Mycoplasma pneumonia patients see improvement in symptoms with antibiotic treatment.

Mycoplasma pneumonia epidemics occur in Japan every four to five years, with a significant increase in cases reported in 2012 and again in 2016.

However, following the COVID-19 pandemic, the number of cases remained low, likely due to improved infection control measures and reduced human interactions.

“Given that infections have been kept in check in recent years, there is a possibility that the momentum of infection is stronger this year,” said Tsuyoshi Kenri from the NIID.

Noting that Mycoplasma pneumonia tends to increase from fall to winter, Kenri reiterated the importance of basic infection prevention measures, such as hand washing and masking.