Smoking influences the need for surgery in patients with the inflammatory bowel diseases: a systematic review and meta-analysis incorporating disease duration

Table 2 Characteristics of included studies reporting on the association between smoking and colectomy in ulcerative colitis

Study	Country	Source of Patients	Definition of Smoking	Timing of Smoking	Duration of Follow-up	Sample Size	Adjusted Estimates
Beaugerie 2001 [15]	France	Tertiary care	Current: >7 cigarettes/week for ≥6 months after diagnosis Former: Quit for >12 months at time of evaluation	At colectomy or study enrolment	Mean: Current smokers: 10 years Former smokers: 16 years Never smokers: 14 years	96^a	Crude^b
Boyko 1988 [16]	USA	HMO	Current: Smoked >100 cigarettes and continued to smoke or initiated smoking after diagnosis Former: Smoked >100 cigarettes and quit prior to diagnosis and did not restart Never: Smoked <100 cigarettes	At diagnosis	Median (range): 8 years (1, 35)	206	Age; sex
Frolkis 2016 [14]	UK	THIN database	Patient coded in EMR as Current, Former, or Never Smoker within one year of index (diagnosis date)	At diagnosis	Median (Q1, Q3): 5 years (3, 8)	3600	Age at diagnosis; sex; use of immunosuppressants; steroid use within 90 days of diagnosis
Hoie 2007 [17]	Europe^c	Population-based^d	Current: Maintained same smoking behaviour throughout follow-up Former: Dates when patient started and stopped smoking were compared with year of disease onset and colectomy Never: Patients who had never been daily cigarette smokers^e	At diagnosis	Median (range): 10 (9, 12) years	771	Crude

HMO health maintenance organization
^a32 former smokers were matched with 32 current smokers and 32 never smokers
^bCrude hazard ratios were estimated from Kaplan-Meier curves using the method proposed by Guyot et al.[25]
^cGreece, Israel, Italy, Spain, Denmark, the Netherlands, Norway
^dAdditional information on study methodology obtained from Shivananda et al.[32]
^eStudy also reports a hazard ratio for patients with unknown smoking status relative to individuals who never smoked

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