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Contribution of Infection to Increased Mortality in Women After Cardiac Surgery
Mary A. M. Rogers, PhD;
Kenneth M. Langa, MD, PhD;
Catherine Kim, MD, MPH;
Brahmajee K. Nallamothu, MD, MPH;
Laurence F. McMahon, Jr, MD, MPH;
Preeti N. Malani, MD;
Brant E. Fries, PhD;
Samuel R. Kaufman, MA;
Sanjay Saint, MD, MPH
Arch Intern Med. 2006;166:437-443.
Background: Women have higher mortality rates after coronary artery bypass graft (CABG) surgery compared with men. Explanations for this sex difference are controversial. The objective of this study was to assess whether infection contributes to the increased risk of mortality in women.
Methods: We conducted a cohort study of 9218 Michigan Medicare beneficiaries hospitalized for CABG surgery. The prevalence of infection at any site during hospitalization was determined. Patients were followed up for 100 days after surgery to assess vital status. Analyses were conducted using proportional hazards regression and population attributable risk.
Results: Women hospitalized for CABG surgery were more likely to have an infection than men (16.1% vs 9.8%, P<.001), regardless of age, race, type of admission, hospital volume, or presence of comorbidities. Infections of the respiratory tract, urinary tract, digestive tract, and skin and subcutaneous tissue were more common in women than in men. The risk of death in men increased 3-fold with infection, whereas the risk in women increased 1.8-fold. The interaction between infection and sex on mortality was significant after adjusting for age, type of admission, and presence of comorbidities (P = .008). The unadjusted percentage of deaths attributable to female sex was 13.9%, which decreased to 0.3% when adjusted for infection. Of the excess deaths in women, 96% could be accounted for by the differential distribution of infection between the sexes.
Conclusion: The increased risk of mortality after CABG surgery in women may be explained by underlying differences in the prevalence of infection among men and women.
Author Affiliations: Divisions of General Medicine (Drs Rogers, Langa, Kim, Nallamothu, McMahon, and Saint and Mr Kaufman) and Infectious Diseases and Geriatrics (Dr Malani), Department of Internal Medicine, Department of Obstetrics and Gynecology (Dr Kim), Institute for Social Research, University of Michigan, Ann Arbor; SGIM (Society for General Internal Medicine)–Hartford Foundation Collaborative Centers for Research and Education in the Care of Older Adults, Pittsburgh, Pa (Dr Langa); and Institute of Gerontology (Drs Langa and Fries) and School of Public Health (Dr Fries), University of Michigan; Patient Safety Enhancement Program, University of Michigan Health System (Drs Rogers, Langa, Nallamothu, McMahon, and Saint); and Health Services Research and Development Center of Excellence (Drs Langa, Nallamothu, and Saint) and Geriatric Research, Education, and Clinical Center (Drs Malani and Fries), Veterans Affairs Medical Center; Ann Arbor.
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