Reported cases in Japan of hand, foot and mouth disease, a viral illness commonly found in children, have topped 130,000 since the beginning of the year, the National Institute of Infectious Diseases said Tuesday.

According to the institute, 133,802 people had been sickened as of July 28. In the week from July 22, the number of patients reached 27,773. The disease has been reported across the country but mostly in the greater Tokyo area, the institute said.

The infection usually peaks in the summer, with infants aged 5 or younger accounting for 90 percent of the total, according to the health ministry.

Within a few days of infection, usually through saliva, sufferers develop blisters of about 2 to 3 mm in size on their hands and feet as well as inside their mouths. Fever is not a common symptom of the illness.

The virus can still be found in feces long after recovery. It is therefore important to wash hands well after using the toilet or touching soiled diapers. It is also important not to share towels at nurseries and other facilities for infants.

In rare cases, complications such as meningitis and encephalitis occur as a result of the disease.

If symptoms of complications, such as headaches, vomiting, high fever lasting more than two days, or unfocused vision are detected in the first few days of infection, a doctor should be seen immediately.