Cowett 1977.

Methods	Quasi‐randomised controlled trial using group assignment based on date of birth (odd dates vs even dates). Placebo was not used. Allocation concealment: no Blinding of intervention: no Completeness of follow up: yes Blinding of outcome measurement: no
Participants	Single unit study in Rhode Island, United States. Subjects recruited from 15 January 1974 to 15 April 1975. Infants requiring insertion of an umbilical arterial catheter in the first 24 hours of life as part of their management were considered eligible for inclusion. All infants were catheterised for respiratory distress. Catheters were inserted using an aseptic technique. One hundred and thirty‐seven infants were enrolled. Eighty‐three were given antibiotics (58 as prophylaxis; 25 at treating physician request) and 54 were not.
Interventions	Infants born on even days were allocated to Group 1: penicillin 25,000 U/kg intravenously every 12 hours and kanamycin 5 mg/kg intramuscularly every 8 hours. Infants born on odd days were allocated to Group 2 or Group 3, at treating physician discretion. Those who were given antibiotics at the request of the treating physician were in Group 3. The remainder (Group 2) were given no antibiotics. Enrolled infants had blood for culture collected from a peripheral vein just prior to catheter insertion and at the time of catheter removal, and from the catheter at insertion and just prior to removal. The volume of blood collected for culture was 0.5 to 1 mL. At catheter removal, the tip was sent for culture.
Outcomes	Mean (standard deviation) birth weight was 1835 (644) grams in Group 1, 2036 (696) grams in Group 2, and 1686 (819) grams in Group 3. Mean (standard deviation) gestational age was 33 (3) weeks in Group 1, 33 (7) weeks in Group 2, and 32 (4) weeks in Group 3. Mean (standard deviation) duration of catheterisation was 76 (53) hours in Group 1, 76 (48) hours in Group 2, and 94 (63) hours in Group 3. Mortality was 9 of 58 in Group 1 (15.5%), 6 of 54 in Group 2 (11.1%) and 2 of 25 in Group 3 (8.0%). No death was attributed to infection. Peripherally‐collected blood cultures, taken at catheter removal, were obtained from 89 infants (65%); catheter blood cultures, taken just prior to catheter removal, were obtained from 87 infants (64%); catheter tip cultures were obtained from 98 catheters (72%). Rates of positive peripheral blood cultures were 0 of 36 in Group 1, 3 of 35 in Group 2 (two were considered pathogens), and 0 of 18 in Group 3. Catheter blood cultures were positive in 0 of 37 Group 1 infants, 14 of 34 Group 2 infants (four were considered pathogens), and 0 of 16 Group 3 infants. Catheter tip cultures were positive in 8 of 37 in Group 1 (none were considered pathogens), 12 of 36 in Group 2 (one was considered a pathogen), and 1 of 25 in Group 3 (not considered a pathogen). The two pathogens isolated in peripheral blood cultures were Proteus mirabilis and Escherichia coli. In both cases the same organism was isolated from catheter blood cultures but not from the catheter tip. Of the two infants concerned, one (positive for Proteus mirabilis) was clinically unwell, whereas the other was not. Two other infants, also in Group 2, had Escherichia coli isolated in catheter blood cultures but peripheral blood culture was either negative or not taken ‐ both infants were clinically well.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	High risk	Quasi‐randomised controlled trial using group assignment based on date of birth (odd dates vs even dates). Placebo was not used.
Allocation concealment?	High risk	Allocation concealment: no
Blinding? All outcomes	High risk	Blinding of intervention: no Blinding of outcome measurement: no
Incomplete outcome data addressed? All outcomes	Low risk	Completeness of follow up: yes