Table 2 Sociodemographic characteristics of cases and controls
Variable | Cases (MCS) n = 183 | Controls (non-MCS) n = 345 | P value |
|---|---|---|---|
Age (years), mean ± SD | 39.8 ± 10.6 | 40.2 ± 10.9 | 0.853‡ |
Age at MCS onset (years), mean ± SD | 23.6 ± 12.1 | NA |  |
Female sex, n (%) | 109 (59.6) | 200 (58.0) | 0.724 |
Body mass index, median (IQR) | 21.1 (19.0–23.0) | 21.3 (19.5–23.9) | 0.104§ |
History of smoking, n (%) | 103 (56.3) | 127 (36.8) | < 0.001 |
Age at start of smoking (years), mean ± SD | 21.0 ± 6.12 | 19.2 ± 3.20 | 0.008‡ |
Passive smoking, n (%) | 106 (57.9) | 125 (36.2) | < 0.001 |
Birth by caesarean section, n (%) | 73 (39.9) | 24 (7.0) | < 0.001 |
History of MCS | |||
 Patient’s mother, n (%) | 31 (16.9) | 1 (0.3) | < 0.001 |
 Patient’s father, n (%) | 20 (10.9) | 0(0) | < 0.001 |
 Patient’s sibling(s), n (%) | 35 (19.1) | 3 (0.9) | < 0.001 |
Comorbidity, n (%) | |||
 Bronchial asthma | 48 (26.2) | 9 (2.6) | < 0.001 |
 Allergic rhinitis | 119 (65.0) | 78 (22.6) | < 0.001 |
 Metal allergy | 76 (41.5) | 9 (2.6) | < 0.001 |
 Fibromyalgia | 22 (12.0) | 0 (0) | < 0.001 |
 Chronic fatigue syndrome | 25 (13.7) | 0 (0) | < 0.001 |
 Electromagnetic hypersensitivity | 25 (13.7) | 0 (0) | < 0.001 |
 Migraine | 62 (33.9) | 46 (13.3) | < 0.001 |
Occupational history, n (%) | |||
 Worker in the manufacturing industry | 43 (23.5) | 57 (16.5) | 0.052 |
 Construction worker | 14 (7.7) | 13 (3.8) | 0.054 |
 Agricultural worker | 19 (10.4) | 5 (1.4) | < 0.001 |
 Chemical researcher | 6 (3.3) | 4 (1.2) | 0.089¶ |
 Cosmetics salesperson | 10 (5.5) | 3 (0.9) | 0.001¶ |
 Shoe store clerk | 10 (5.5) | 2 (0.6) | < 0.001¶ |
 Healthcare worker | 22 (12) | 23 (6.7) | 0.036 |
 Drugstore clerk | 10 (5.5) | 5 (1.4) | 0.008 |
Pet ownership before MCS onset†| 146 (79.8) | 203 (58.8) | < 0.001 |
Mouth breathing | 126 (68.9) | 140 (40.6) | < 0.001 |
Number of vaccinations in the past 10 years, n (%) | < 0.001 | ||
 0 | 48 (26.2) | 162 (47.0) |  |
 1–5 | 49 (26.8) | 111 (32.2) |  |
 6–10 | 32 (17.5) | 56 (16.2) |  |
  ≥ 11 | 54 (29.5) | 16 (4.6) |  |
Number of times living in a house < 1 year-old, n (%) | < 0.001 | ||
 0 | 40 (21.9) | 138 (40.0) |  |
 1–2 | 114 (62.3) | 198 (57.4) |  |
  ≥ 3 | 29 (15.8) | 9 (2.6) |  |