Why more women die of bacteraemia

Scientific research is an ongoing process and one conclusion often raises more questions than it answers. Our research, published in the journal of Clinical Microbiology and Infection in June, provides evidence that some types of blood infections are more fatal in women than in men. In a large cohort of patients with bacteraemia caused by Staphylococcus aureus, we found that a higher proportion of women died within 30 days, as compared to men. Now, we have to try and understand why this is so and ask what we can do to improve the prognosis for women with S. aureus bacteraemia.

Staphylococcus aureus is a common bacterium that a third of us carry around with no ill effects. It can cause minor illnesses such as food poisoning, boils and impetigo, and more serious skin and wound infections that usually do not progress to bacteraemia (i.e., when bacteria are found in the blood).

Invasive infections are rare in healthy people, but may develop in patients who are in poor health due to other illnesses that weaken the body and the immune system. Instead of causing a minor infection, the bacteria can enter the bloodstream and cause a generalized infection throughout the body requiring acute medical care and prolonged hospitalization.

Using several validated medical registers, we analysed data on 2,638 patients in Denmark who were diagnosed with S. aureus bacteraemia over a 12-year period.

When mortality was assessed within the first 30 days, we found that 29% of the women died compared to 22% of the men. Women are, therefore, 1.3 times more likely to die within a month of developing Staphylococcus aureus bacteraemia.

We looked thoroughly for factors that might have interfered with or explained the results, including gender-related differences in age and co-morbidities. Nevertheless, based on the available data, we were not able to explain exactly why women experienced increased mortality.

Unfortunately, we didn’t have information on the time interval from initiation of infection to presentation at a doctor’s surgery or hospital. If women tended to seek medical attention at a later point than men it could potentially have influenced their prognosis negatively. However, this does run counter to the fact that women generally present earlier during disease and are more likely to see their doctors regularly than men. Also, it could be that the clinical care differed between men and women, still healthcare in Denmark is unrestricted and free in Denmark, therefore this seems highly unlikely.

Another possibility is that women and men respond exert different immune responses to invasive S. aureus infection, which could subsequently influence outcome. Female and male sex hormones have indeed been shown to influence the immune system in different ways, but unfortunately, the design of our study did not allow for investigation of these potential mechanisms. Finally, we cannot preclude that cultural, behavioural, and environmental differences between men and women over the lifespan may eventually lead to differences in the outcome from S. aureus bacteraemia.

Further studies are needed to answer these questions, but in the meantime, we can take the knowledge we now have to ensure that increased attention is guided towards women with S. aureus bacteremia.