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Table 2 Sociodemographic characteristics of cases and controls

From: Epidemiological association between multiple chemical sensitivity and birth by caesarean section: a nationwide case-control study

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)  
  1. †Pets include dogs, cats, hamsters, rabbits, guinea pigs, ferrets, and birds but not animals kept for commercial purpose. T-test. §Mann-Whitney U test. Fisher’s exact test. No symbol, chi-squared test. IQR, interquartile range; MCS, multiple chemical sensitivity; NA, not applicable; SD, standard deviation