Characteristics of the study population
| Characteristic | CF (n=31) | Healthy (n=32) | |
| Anthropometrics | Sex (m), n (%) | 13 (42) | 13 (41) |
| Gestational age at birth (weeks), mean (SD) | 39.1 (1.4) | 39.8 (1.2) | |
| Length at birth (cm), mean (SD) | 49.2 (1.5) | 49.7 (2.1) | |
| Birth weight (kg), mean (SD) | 3.2 (0.4) | 3.4 (0.5) | |
| Season of birth* | Winter, n (%) | 10 (32) | 8 (25) |
| Spring, n (%) | 12 (39) | 7 (22) | |
| Summer, n (%) | 3 (10) | 9 (28) | |
| Autumn, n (%) | 6 (19) | 8 (25) | |
| Pregnancy | Smoking in pregnancy, n (%) | 7 (23) | 7 (22) |
| Birth | Cesarean section, n(%) | 2 (6) | 3 (9) |
| Nutrition | Breast-feeding, n (%) | 26 (84) | 32 (100) |
| Family history | Maternal atopy, n (%) | 8 (26) | 9 (28) |
| Environment | Siblings, n (%) 0 | 16 (52) | 7 (22) |
| 1 | 10 (32) | 15 (47) | |
| ≥2 | 5 (16) | 10 (33) | |
| Childcare†, n (%) | 0 (0) | 7 (22) | |
| Parental smoking | 12 (39) | 4 (12.5) | |
| Parental education‡ | Low | 6 (19) | 3 (9) |
| Middle | 9 (29) | 13 (41) | |
| High | 16 (52) | 16 (50) | |
| Measurements | No. of weeks with nasal swabs, median(*range) | 19 (5–27) | 23 (15–26) |
| Nasal swabs during antibiotics§, median (*range) | 3 (0–13) | 0 (0–1) | |
| CF genotype¶ | No residual CFTR function (class I and/or II), n (%) | 21 (68) | |
| Residual CFTR function (class I/II and III–VI), n (%) | 6 (19) | ||
| Unknown CFTR function, n (%) | 4 (13) |
*Season of birth is categorised with the calendric definition of season: *Winter 22.12.–20.3.; spring 21.3.–20.6.; summer 21.6–22.9.; fall 23.9.–21.12.)
†Childcare is defined as attending childcare in the first year of life at any time point.
‡Parental education is categorised into low (<4 years of apprenticeship), middle (<4 years of apprenticeship) and high (tertiary education).
§Samples taken during periods with application of any antibiotics.
¶Infants with cystic fibrosis (CF) were grouped in patients with no residual Cystic Fibrosis Transmembrane conductance Regulator (CFTR) function: two known copies of class I and/or II mutations; residual CFTR function: one class I or II mutation plus one other mutation, unknown CFTR function:≥1 mutation not classified or unknown mutation, however, with two copies of disease causing mutations.