Table 1—

Characteristics of adolescents

CharacteristicsLouvain-la-NeuveBastogneLessinesp-value
Subjects357349141
Males167 (46.8)130 (37.2)72 (51.1)0.006
Age# yrs15.4±0.8115.5±0.8315.5±0.870.54
BMI# kg·m-220.1±2.321.0±3.321.0±3.2<0.001
Number of older siblings#0.93±0.980.98±1.020.85±0.990.43
Parental education278 (77.9)98 (28.1)28 (19.9)<0.0001
Smokers20 (5.6)14 (4.0)16 (11.3)0.007
Maternal smoking during pregnancy25 (7.0)55 (15.8)25 (17.7)0.0002
Parental smoking at home20 (5.6)14 (4.0)16 (11.3)0.007
Breastfed305 (85.4)191 (54.7)76 (53.9)<0.0001
House cleaning with bleach77 (21.6)91 (26.1)60 (42.6)<0.0001
Mould on bedroom walls30 (8.4)19 (5.5)10 (7.1)0.30
Day care attendance241 (67.5)111 (31.8)43 (30.5)<0.0001
Swimming pool attendance
 Indoor copper–silver sanitised pool
  Attendees339 (95.0)4 (1.2)0 (0)<0.0001
  CPA h+225 (108–434)84 (46–210)0 (0–0)<0.0001
 Residential outdoor chlorinated pool
  Attendees76 (21.3 )65 (18.6)14 (9.9)0.01
  CPA h+275 (88–848)154 (48–412)232 (72–336)0.07
 Nonresidential outdoor chlorinated pool
  Attendees244 (68.3 )142 (40.7)53 (37.6)<0.0001
  CPA h+168 (49–336)126 (56–273)306 (108–599)0.0005
 Total outdoor chlorinated pool
  Attendees270 (75.6)183 (52.4)61 (43.3)<0.0001
  CPA h+229 (70–477)147 (57–336)308 (134–599)<0.0001
Public indoor chlorinated pool
  Attendees243 (68.1)348 (99.7)138 (97.9)<0.0001
  CPA h+126 (48–286)400 (255–657)407 (217–724)<0.0001
Asthma
 Parental asthma49 (13.7)39 (11.2)25 (17.7)0.15
 Ever asthma38 (10.6)36 (10.3)14 (9.9)0.97
 Current asthma21 (5.9)21 (6.0)10 (7.1)0.87
Aeroallergen-specific serum IgE
 House dust mite103 (28.9)90 (25.8)32 (22.7)0.34
 Dog15 (4.2)19 (5.4)10 (7.1)0.40
 Cat49 (13.7)44 (12.6)14 (9.9)0.50
 Pollen65 (18.2)92 (26.4)19 (13.5)0.002
 Mould11 (3.1)6 (1.7)7 (5.0)0.14
 At least one aeroallergen136 (38.1)136 (39.0)43 (30.5)0.19
Total serum IgE+ kIU·L−160.0 (22.1–173)42.0 (16.1–127)44.9 (13.8.–147)0.004
Exhaled NO+ ppb13.4 (10.0–21.5)13.0 (9.5–20.6)12 (8.3–17.3)0.03
Exhaled NO >30 ppb61 (17.1)49 (14.0)13 (9.2)0.07
  • Data are expressed as n, n (%), mean±sd or median (interquartile range). BMI: body mass index; CPA: lifetime cumulative pool attendance; Ig: immunoglobulin. #: two-sided unpaired t-test; : two-sided Chi squared test; +: two-sided Mann–Whitney U-test.