Table 2

Sequentially adjusted HRs for diarrhoea, antibiotic use prior to admission, and the diarrhoea:antibiotic interaction term with respect to the primary outcome of all-cause mortality for people admitted with COVID-19

Adjustment	Diarrhoea	Antibiotic use prior to admission	Diarrhoea:antibiotic interaction terms
Adjustment	Diarrhoea	Antibiotic use prior to admission	No diarrhoea:antibiotic*	Diarrhoea:antibiotic*
Unadjusted	0.70 (0.53–0.94), p=0.018	1.42 (1.11–1.81), p=0.005	1.47 (1.14–1.90), p=0.003	0.90 (0.41–2.00), p=0.804
Age	0.88 (0.66–1.18), p=0.397	1.28 (1.00–1.63), p=0.049	1.35 (1.05–1.75), p=0.021	0.78 (0.35–1.73), p=0.542
Age and gender	0.92 (0.69–1.23), p=0.564	1.33 (1.04–1.69), p=0.023	1.41 (1.09–1.82), p=0.010)	0.93 (0.37–1.83), p=0.635
Age, gender, and Index of Multiple Deprivation	0.92 (0.68–1.23), p=0.558	1.34 (1.05–1.71), p=0.020	1.41 (1.09–1.83), p=0.009	0.83 (0.38–1.85), p=0.655
Age, gender, Index of Multiple Deprivation and comorbidities†	0.96 (0.71–1.23), p=0.773	1.33 (1.03–1.70), p=0.026	1.40 (1.08–1.82), p=0.012	0.84 (0.37–1.87), p=0.665
Age, gender, Index of Multiple Deprivation, comorbidities† and severity markers‡	0.95 (0.70–1.29), p=0.761	1.24 (0.96–1.60), p=0.098	1.30 (1.00–1.70), p=0.050	0.79 (0.34–1.80), p=0.571
Age, gender, Index of Multiple Deprivation, comorbidities†, severity markers‡ and ethnicity	0.96 (0.70–1.30), p=0.772	1.22 (0.94–1.57), p=0.135	1.37 (0.97–1.66), p=0.080	0.81 (0.36–1.87), p=0.636
Age, gender, Index of Multiple Deprivation, comorbidities†, severity markers‡ and BMI§	0.96 (0.71–1.31), p=0.808	1.18 (0.92–1.53), p=0.195	1.22 (0.94–1.60), p=0.141	0.86 (0.37–2.00), p=0.719
Full covariate set adjustment	0.96 (0.70–1.32), p=0.813	1.17 (0.91–1.51), p=0.231	1.20 (0.92–1.57), p=0.187	0.92 (0.39–2.14), p=0.839

*The base model for the interaction term consisted of both the diarrhoea primary term and the diarrhoea:antibiotic interaction term; the introduction of the interaction term to the primary diarrhoea term improves the Akaike information criterion (AIC) from 4985.42 to 4981.19, but the Bayesian information criterion (BIC) deteriorates from 4988.23 to 4992.87.
†Comorbidities included: hypertension, ischaemic heart disease, congestive heart failure, cerebrovascular disease, dementia, chronic pulmonary disease, diabetes, chronic renal disease, previous or active malignancy, and moderate-severe chronic liver disease.
‡Severity markers included: C-reactive protein (CRP), urea, creatinine, platelet count, neutrophil count, neutrophil:lymphocyte ratio, lymphocyte count, and initial National Early Warning Score 2 (NEWS 2). All of the severity markers and age were modelled using a 3-knot restricted cubic spline. The Index of Multiple Deprivation was modelled as linear feature. BMI was specified using the categories presented in table 1.
BMI, body mass index.