According to researchers, infections - including those acquired in hospitals, could explain why women die more frequently than men after heart bypass surgery and the explanations for this sex difference are controversial.

Researchers at the University of Michigan, say why women are more prone to such infections than men is not clear, nor is the reason for the higher death toll, although the body’s systemic inflammatory response to infection has been linked to heart attack and death in other research.

The objective of their study was to assess whether infection contributes to the increased risk of mortality in women.

They based the study on the medical records from 9,218 Michigan residents who had bypass surgery, all of them aged 65 or older.

The researchers found that 16 percent of the women had an infection compared to 9 percent of men, and urinary, digestive, respiratory and skin infections were all more common in women than men.

Lead author Mary Rogers says that overall, they found that women’s increased risk of mortality after coronary artery bypass surgery may be due to differences in infection.

They suspect that there may be a systemic, or body-wide, response to infection, making infection at any site a concern in elderly patients.

Rogers says they were surprised to find that overall, women had the greater mortality, but found on closer examination that there were two underlying relationships.

Whereas women had more infections, men when they had an infection were more likely to die from it.

The study did not ascertain whether the infections were present before surgery or were hospital-acquired, but suggests people with known infections would not be good surgical candidates.

The researchers suggest that older bypass patients in hospital should get up and start moving around soon after surgery to discourage respiratory infections.

They say frequent hand-washing by patients and hospital staff is important as is asking visitors with cods or infections to refrain from visiting.

At present current U.S. national guidelines for bypass surgery advises patients receive antibiotics an hour before their operation begins and continue taking them for at least a day after.

The study is published in the Archives of Internal Medicine.