Table 1

Demographic, occupational and clinical characteristics of the participants

Positive SIC (n=17)Negative SIC (n=27)p Value
Gender (female)13 (76)23 (85)0.466
Age, years*47 (39–49)47 (35–53)0.942
Referral by WCB13 (76)20 (74)0.858
Job/industry
 Professional cleaners915
  Healthcare facilities25
  Various industries34
  Private houses13
  Public buildings22
  Kitchens11
 Healthcare workers79
 Food workers12
 Pharmaceutical workers01
Exposure to respiratory sensitisers16 (94)16 (59)0.033
 QAC106
 QAC and glutaraldehyde13
 Glutaraldehyde37
 Ethanolamines20
 No identified sensitiser111
Current and ex-smokers6 (35)8 (30)0.694
Atopy†7 (41)13 (48)0.651
Asthma pre-existing to exposure2 (12)2 (7)0.624
Duration of exposure before the onset of asthma, months*12 (5–153)53 (31–165)0.114
Duration of asthma before SIC, months*25 (7–59)25 (10–55)0.980
Delay since last work exposure, months*10 (0.3–16)8 (0.1–24)0.808
Work-related respiratory symptoms
 Wheezing14 (82)14 (52)0.056
 Breathlessness14 (82)20 (74)0.716
 Cough11 (65)21 (78)0.343
 Chest tightness11 (65)18 (67)0.893
 Sputum4 (24)8 (30)0.740
Work-related rhinitis8 (47)16 (59)0.429
Work-related dermatitis5 (29)5 (19)0.401
Inhaled corticosteroid
 Number with inhaled corticosteroid13 (76)15 (56)0.160
 Low dose‡3 (18)5 (19)
 Medium dose‡5 (29)5 (19)0.494
 High dose‡5 (29)5 (19)
Short-acting β2-agonist≥once a day7 (41)1 (4)0.002
Baseline FEV1,% predicted*92 (73–101)100 (88–109)0.049
Baseline FEV1/FVC, %*71 (63–77)80 (73–83)0.002
Baseline airway obstruction§5 (29)1 (4)0.016
  • Data are presented as n (% of available data) unless otherwise specified.

  • *Median value with 25th–75th IQR in parentheses.

  • †Atopy defined by a positive skin-prick test to at least one common inhalant allergen.

  • ‡Low dose: equal or less than 500 µg beclomethasone dipropionate equivalent/day; medium dose: more than 500 µg but equal or less than 1000 µg/day; and high dose: more than 1000 µg/day.

  • §Airway obstruction defined by an FEV1 <80% predicted value and an FEV1/FVC ratio <70%.

  • FEV1, forced expiratory volume in one-second; FVC, forced vital capacity; PC20, provocative concentration of histamine causing a 20% fall in FEV1; QAC, quaternary ammonium compound; SIC, specific inhalation challenge; WCB, workers' compensation board.