title: Seasonal variation in short-term mortality after surgery for colorectal cancer?
abstract: OBJECTIVE
  Comorbidity has a major impact on short-term and long-term survival of colorectal cancer (CRC) and many CRC patients suffer from comorbidities. Mortality rates for comorbidities like cardio-respiratory diseases exhibit distinct seasonal variations with highest rates in the winter. Therefore, we hypothesized some seasonal variation in 30-day mortality after surgery for CRC as well.
  
  
  METHODS
  In a nationwide study, we examined the seasonal pattern in 30-day mortality after surgery for CRC from 1996 to 2006. We identified 33 556 CRC patients in the Danish hospital discharge registries. Monthly 30-day mortality rates were calculated and we constructed a fitted curve of the monthly mortality rates using a periodic regression model. We stratified the analyses for tumour site, urgency of surgery for colon cancer and the level of comorbidity based on American Society of Anaesthesiologists (ASA) score.
  
  
  RESULTS
  The overall 30-day mortality was 8.7% [95% confidence interval 8.4-9.0%). Significant seasonal variation in monthly 30-day mortality could not be identified. For colon cancer, a nonsignificant increase was seen in July. An even higher increase in July was observed for CRC patients with moderate or severe comorbidity (ASA score >or= III), but was also nonsignificant.
  
  
  CONCLUSIONS
  Although comorbidity is a well-known negative predictor of short-term survival of CRC, monthly 30-day mortality after surgery for CRC did not exhibit seasonal variation like that observed for comorbid conditions such as cardio-respiratory diseases.
authors.affiliation: Department of Surgery P, Aarhus University Hospital, Aarhus, Denmark. lene.h.iversen@dadlnet.dk
authors.forename: L H
authors.initials: LH
authors.lastname: Iversen
authors.forename: H
authors.initials: H
authors.lastname: Nielsen
authors.forename: L
authors.initials: L
authors.lastname: Pedersen
authors.forename: H
authors.initials: H
authors.lastname: Harling
authors.forename: S
authors.initials: S
authors.lastname: Laurberg
mesh_terms: D003082:Colectomy; D015179:Colorectal Neoplasms / Q000401:mortality* / Q000601:surgery; D016001:Confidence Intervals; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D011184:Postoperative Period; D011379:Prognosis; D012042:Registries; D012189:Retrospective Studies; D012621:Seasons; D015996:Survival Rate / Q000639:trends; D013997:Time Factors