Questionnaire survey
Self-administered questionnaires based on the ‘‘questionnaire for national investigation for SHS and its potential risk factors in Japan’’ (Yamasaki et al., 2006)
were distributed to 297 inhabitants of 91 dwellings at the start of the investigation.
If the participants could not read or write, the householder or partner was requested to answer the questionnaires for them.
‘‘Symptoms that occurred during the last 3 months’’ were given in the questionnaire, including upper respiratory symptoms (rhinitis, blocked nose, sneezing, eye irritation, hoarseness, dry throat), lower respiratory tract symptoms (cough and wheezing), skin symptoms (itching, dryness, redness, eczema), systemic symptoms (headache, fever, excessive fatigue, joint pains, nausea, dizziness, lack of concentration), and psychosocial symptoms (sleeplessness, loneliness, anxiety, hopelessness).
Continuous symptoms were defined as occurring three or more times a week, and sporadic symptoms were defined as occurring once or twice a week.
If subjects reported at least one continuous symptom related to the home environment, they were classified as SBS1; if there was at least one continuous or sporadic symptom related to the home environment, the subject was classified as SBS2.