Social and demographic characteristics according to clinical classification are shown in Table 1. The total number of subjects in classes 1 and 2 by clinical classification was 4632. The demographic characteristics according to the clinical class groups were significantly different (p < 0.01). The number of male and female subjects was similar at 2675 and 2547, respectively, and the number of subjects with unknown sex was relatively very low. The number of survived subjects increased from class 1 to class 4. In terms of age at damage, the number of applicants under the age of 10 was 1536, and 452 subjects had unknown age. There were 339 pregnant women and 439 fetuses among those exposed to HDs.
The product names of HDs used according to clinical class are shown in Table 2. The HD products and chemical type according to the clinical classification showed significant differences (p < 0.01). Most of the subjects answered that they used the Oxy Ssakssak New Gaseupgi Dangbun, followed by Cefu Gaseupgi Salgyunje in clinical classes 1 and 2, and by Ekyung Gaseupgi Mate in clinical classes 3 and 4. However, 252 subjects did not remember the name of the HD products used in clinical classes 3 and 4. The main ingredient of the HDs used was PHMG.
A cross-tabulation of the clinical class and exposure rating is shown in Table 3. There was a significant difference between the exposure ratings and clinical classes (p < 0.05). Focusing on the exposure level, 365 subjects with clinical class 1, exposure rating 3 and 4, and clinical class 2, exposure rating 4, were assumed as the overestimation group. However, 344 subjects with clinical classes 3 and 4, exposure rating 1, and clinical class 4, exposure rating 2, were assumed as the underestimation group.
The demographic and exposure characteristics of these groups are shown in Table 4. The sex ratio was similar in the overestimation and underestimation groups. In the overestimation group, 90 subjects (24.7%) were under the age of 10, followed by 52 subjects (14.2%) in their 50s. In the underestimation group, 195 subjects (56.7%) were under the age of 10, followed by 80 subjects (23.3%) in their 30s. There were no current smokers in the underestimation group. The amount sprayed, the distance between the humidifier and the respiratory organ of the subject such as the nose and mouth, and spraying direction were crucial factors affecting exposure. The overestimation group was characterized by more vigorous spray amounts, closer distance to the humidifier, and direct spraying to the breathing zone than the underestimation group.
A comparison of the HD usage characteristics between the overestimation and underestimation groups is shown in Table 5. The overestimation group showed much higher usage characteristics than the underestimation group. The overestimation group showed a significant difference with other groups in the number of months used, one-time use, and daily use time.
Results of regression analysis and curve fitting of the indoor concentration, cumulative exposure time, and exposure level with the clinical classes are shown in Figs. 1, 2, and 3, respectively, after the overestimation and underestimation groups were removed. The regression formula between the exposure level (X) and clinical class (Y) was Y = 0.92 + 3.24E-19*Exp ((X-20.45)/0.88), and the coefficient of determination (R2) value was 0.58 (p < 0.01). As a result of comparing the relationship between exposure ratings and clinical classes, the breakpoint of exposure level between clinical classes 1 (unlikely) and 2 (possible) was 14.73 μg/m3·hr., which was considered to exert adverse health effects, especially lung disease. The exposure level for government compensation of clinical classes 3 and 4 was about 17.57 μg/m3·hr.