Demographics of recruited preterm infants from two sites
| All infants | Infants recruited from UHW | Infants recruited from NBT | p-value (UHW versus NBT) | |
| Infants | 55 | 20 (36) | 35 (64) | |
| Samples | ||||
| Nasopharyngeal aspirates | 539 | 145 | 394 | |
| Tracheal aspirate fluid | 276 | 62 | 214 | |
| Bronchoalveolar lavage fluid | 89 | 89 | 0 | |
| Stool | 198 | 64 | 134 | |
| Total | 1102 | 360 | 742 | |
| Male | 36 (65) | 12 (60) | 24 (69) | 0.73 |
| Gestation weeks | 26.0 (24.7–27.5) | 26.8 (25.3–29.4) | 25.9 (24.7–26.6) | 0.07 |
| Birthweight g | 764 (680–918) | 835 (695–1082) | 746 (677–880) | 0.16 |
| Antenatal steroids | 51/55 (93) | 18/20 (90) | 33/35 (94) | 0.18 |
| Vaginal delivery | 29 (53) | 10 (50) | 19 (54) | 0.98 |
| Multiple births | 17 (31) | 6 (30) | 11 (31) | 1 |
| Maternal antibiotics in labour | 14 (25) | 4 (20) | 10 (29) | 0.70 |
| Surfactant administration | 55/55 (100) | 20/20 (100) | 35/35 (100) | 0.27 |
| CLD severity# | ||||
| None | 5 (9) | 4 (20) | 1 (3) | 0.02 |
| Mild | 4 (7) | 3 (15) | 1 (3) | |
| Moderate | 18 (33) | 3 (15) | 15 (43) | |
| Severe/died | 28 (51) | 10 (50) | 18 (51) | |
| Survival to discharge | 47 (85) | 17 (85) | 30 (86) | 1 |
| Ventilation days | 17 (4–32.5) | 25 (3.5–37.8) | 17 (5–28.5) | 0.55 |
| Noninvasive ventilation days | 47 (24.5–64.5) | 38 (19.8–53.5) | 55 (31.5–66) | 0.14 |
| Length of hospital stay days | 93 (69.5–130) | 104.5 (52.8–136.5) | 93 (80–122) | 0.95 |
| Necrotising enterocolitis¶ | ||||
| Grade 1 | 7 (13) | 4 (20) | 3 (9) | 1 |
| Grade 2 | 1 (2) | 0 (0) | 1 (3) | |
| Grade 3 | 6 (11) | 1 (5) | 5 (14) | |
| Patent ductus arteriosus | 40 (73) | 11 (55) | 29 (83) | 0.06 |
| Initial breast milk | 55 (100) | 20 (100) | 35 (100) | 1 |
| Discharge breast milk | 17 (31) | 6 (35) | 11 (37) | 1 |
Data are presented as n, n (%) or median (interquartile range), unless otherwise stated. UHW: University Hospital Wales; NBT: North Bristol Trust; CLD: chronic lung disease of prematurity. #: categorised according to [24] ; ¶: categorised according to Bell's staging criteria.