Table 2. Between-Group Differences for Infection-Related Outcome Measures^a.

Analysis	Probiotic (n = 155)	Placebo (n = 155)	Absolute difference (95% CI)	Adjusted incidence rate ratio (95% CI)	P value
Primary outcome, No. (%) with data	152 (98.1)	153 (98.7)
Cumulative antibiotic administration, mean (SD), days	12.9 (18.4)	12.0 (18.6)	0.9 (–3.25 to 5.05)	1.13 (0.79 to 1.63)	.50
Secondary outcome, No. (%) with dataa	152 (98.1)	153 (98.7)
Cumulative systemic antibiotic administration, mean (SD), days
For urinary tract infectionb	7.1 (15.0)	6.7 (13.6)	0.4 (–2.81 to 3.61)	1.17 (0.75 to 1.84)	.48
For upper respiratory tract infectionsb	3.3 (9.4)	3.4 (10.1)	0.1 (–2.09 to 2.29)	1.13 (0.71 to 1.78)	.61
For lower respiratory tract infectionsb	6.2 (14.6)	4.0 (7.6)	2.2 (–0.4 to 4.8)	1.4 (1.1 to 1.9)	.02
For skin infectionsb	3.4 (8.7)	3.7 (13.1)	0.3 (–2.20 to 2.80)	0.92 (0.54 to 1.57)	.76
Incidence of infection, mean (SD), No. per person
Of any infection	2.5 (2.5)	2.4 (2.7)	0.1 (–1.3 to 1.5)	1.0 (0.8 to 1.2)	.92
Of urinary tract infections	0.8 (1.4)	0.8 (1.4)	0 (–0.3 to 0.3)	1.1 (0.6 to 2.1)	.68
Of gastrointestinal infections	0.03 (0.2)	0.04 (0.2)	0 (0 to 0.1)	0.8 (0.2 to 2.6)	.68
Of upper respiratory tract infections	0.4 (0.8)	0.5 (0.9)	0.1 (–0.1 to 0.3)	0.8 (0.5 to 1.2)	.31
Of lower respiratory tract infections	0.6 (1.0)	0.5 (0.9)	0.1 (–0.1 to 0.3)	1.2 (0.8 to 1.7)	.41
Of skin infections	0.6 (1.2)	0.5 (1.1)	0.1 (–0.2 to 0.4)	1.2 (0.7 to 2.0)	.49
≥1 Infection, No. (%)	111 (73.0)	102 (66.7)	0.1 (0 to 0.2)	1.4 (0.8 to 2.4)c	.20
Duration of infection for those with ≥1 infection, mean (SD)d	6.8 (4.7)	6.0 (4.9)	0.9 (–0.4 to 2.2)	0.1 (0 to 0.2)e	.05
Cumulative number of infection days per person-year, mean (SD)f	22 (30.8)	21 (40.7)	1 (–7.1 to 9.1)	1.1 (0.8 to 1.5)	.67

Abbreviation: IQR, interquartile range.

^aCumulative systemic antibiotic administration days for gastrointestinal infection was not reported due to a small number of participants having gastrointestinal infection (2 participants in the probiotic group and 0 in the placebo group).

^bCumulative infection-site–specific antibiotic administration days were rate variables expressed per person-year. The mean rates were calculated by dividing the number of days that an antibiotic was administered for a specific infection (as indicated in the care home medical records) by the period of exposure days.

^cIndicates adjusted odds ratio (95% CI).

^dDuration of infection was calculated by dividing the number of infection days by the total number of infections. Values in this category are based on a count of 111 in the probiotic group and 102 in the placebo group. See eFigure 2 in Supplement 2 for the distribution.

^eIndicates adjusted mean difference (95% CI).

^fCumulative number of infection days was a rate variable expressed as infection days per person-year, with the number of suspected infection days as the numerator over the period of exposure days. During weekly visits, research nurses would record whether care home residents displayed signs of infection (and if so, record which infection[s]) following discussions with care home staff. This was asked and recorded separately from whether a care home resident received an antibiotic on a given day.