Table 2. ORs for a pooled sample (in the first cycle) and an individual animal (in the second cycle) to be MRSA-positive in an intervention study performed in 51 veal calf farms to reduce MRSA carriage, the Netherlands 2010–2012.
1st production cycle: ORs for a pooled sample to be MRSA-positive | 2nd production cycle: ORs for an individual animal sample to be MRSA-positive | |||||||
---|---|---|---|---|---|---|---|---|
Sampling moment-Arm of study | MRSA-positive/N total a | OR | 95% CI | Wald P-value b | MRSA-positive/N total c | OR | 95% CI | Wald P-value b |
Week 12—Control | 95/170 | 9.70 | 3.62–26.03 | <0.01 | 183/478 | 13.69 | 4.07–46.00 | <0.01 |
Week 12—RAB-CD | 79/170 | 5.97 | 2.24–15.87 | <0.01 | 171/465 | 14.72 | 4.69–49.31 | <0.01 |
Week 12—RAB | 57/170 | 3.08 | 1.76–5.39 | <0.01 | 111/488 | 6.35 | 3.95–10.20 | <0.01 |
Week 0—Control | 33/170 | 1.17 | 0.42–3.25 | 0.77 | 26/482 | 0.56 | 0.15–2.02 | 0.37 |
Week 0—RAB-CD | 32/170 | 1.31 | 0.48–3.62 | 0.60 | 37/465 | 1.44 | 0.41–5.03 | 0.57 |
Week 0—RAB | 27/170 | Ref. | - | - | 26/488 | Ref. | - | - |
Results from generalized linear mixed models accounting for clustering at farm level in which study arm and sampling moment were grouped in a single determinant to evaluate interaction effects (i.e. differential effects by arm of intervention and time). MRSA, methicillin resistant Staphylococcus aureus; RAB, farms reducing antimicrobials by protocol; RAB-CD, farms reducing antimicrobials by protocol and applying a cleaning and disinfection program; Control, farms without interventions; Ref., reference category of the variable.
a 17 farms per arm of intervention, 2 sampling moments and 10 pooled samples per farm.
b Overall p<0.01.
c 17 farms per arm of intervention, 2 sampling moments and a mean of 28 animals sampled per farm.