Age, sex, body mass index (BMI), smoking status, ethnicity, previous exposure to relevant viral infections (Epstein-Barr virus (EBV), human cytomegalovirus (CMV), human herpesvirus 6 (HHV-6), human T lymphotropic virus type 1 (HTLV-1), hepatitis C virus (HCV), influenza A virus, and parvovirus B19), and previous prescriptions of selected medications (procainamide, hydralazine, quinidine, and isoniazid) were included as potential confounders. Previous studies found these variables to be associated with at least one of the outcome IMIDs and were thus adjusted for in the analysis [21 (link)–33 (link)].
Age was divided into the following bands: 18 to 29, 30 to 39, 40 to 49, 50 to 59, 60 to 69, and ≥ 70 years. Ethnicity was identified through SNOMED CT codes and was classified into the following groups: white, South Asian, black, mixed ethnicity and other. BMI was divided in accordance with the WHO classification: underweight (body mass index (BMI) < 18.5 kg/m2), normal weight (18.5–24.9 kg/m2), overweight (25–29.9 kg/m2) and obese (≥ 30 kg/m2) [34 ]. Smoking status was categorised as current smoker, ex-smoker and never smoked. A separate ‘data missing’ category was used where data were missing for ethnicity, smoking status, and BMI.
Age was divided into the following bands: 18 to 29, 30 to 39, 40 to 49, 50 to 59, 60 to 69, and ≥ 70 years. Ethnicity was identified through SNOMED CT codes and was classified into the following groups: white, South Asian, black, mixed ethnicity and other. BMI was divided in accordance with the WHO classification: underweight (body mass index (BMI) < 18.5 kg/m2), normal weight (18.5–24.9 kg/m2), overweight (25–29.9 kg/m2) and obese (≥ 30 kg/m2) [34 ]. Smoking status was categorised as current smoker, ex-smoker and never smoked. A separate ‘data missing’ category was used where data were missing for ethnicity, smoking status, and BMI.
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