Diabetes Patients at Higher Risk of S aureus Blood Infection

Liam Davenport

March 15, 2016

Diabetes patients are almost three times more likely to contract community-acquired Staphylococcus aureus bacteremia, with the risk escalating with worsening disease, a large population based case-control study indicates.

Among nearly 30,000 individuals followed over 12 years from Danish registries, there was a 2.8-fold increased risk of S aureus blood infection among diabetes patients, and this excess risk was almost doubled again by high HbA1c levels and the presence of microvascular and macrovascular complications.

In their paper, Jesper Smit, MD, department of clinical microbiology, Aalborg University Hospital, Denmark, and colleagues note that S aureus remains a leading cause of bacteremia, associated with a 30-day mortality of 20% to 40%. And although it has long been a common clinical belief that diabetes increases the risk of S aureus infection, until now there has been little evidence to support this.

"To our knowledge, no prior study has investigated diabetes as a risk factor for S aureus bacteremia as the main exposure," they say; their findings are published online March 10 in the European Journal of Endocrinology.

"These results emphasize the importance of improved preventive care for patients with diabetes, including optimized glycemic control and particularly good infection surveillance among patients with long duration of diabetes and complications," they conclude.

Each Case Matched to 10 Controls

The team gathered data from four regional databases of clinical microbiology departments on all patients hospitalized for community-acquired S aureus blood infections in Denmark between 2000 and 2011. Hospital-acquired infections were excluded from the study.

The Danish Civil Registration System was then used to match each case with 10 population controls by age, sex, and residence.

Patients diagnosed with diabetes before the date of S aureus bacteremia admission, either via the recording of an HbA1c level of ≥6.5% or the prescription of an antidiabetic drug, were then identified.

In all, 2638 cases of incident community-acquired S aureus bacteremia were recorded, of which 713 (27.0%) had diabetes prior to the infection. These were compared with 26,379 control individuals, of whom 2495 (9.5%) had diabetes.

Diabetes patients had a substantially increased risk of S aureus bacteremia vs controls, at an adjusted odds ratio (OR) of 2.8, rising to 3.8 among those with a disease duration of ≥10 years.

The risk of S aureus bacteremia also increased as HbA1c levels rose, to an OR of 5.7 among diabetes patients with an HbA1c level of ≥9% compared with controls.

Patients with microvascular complications had a higher OR of infection, of 5.5, compared with controls, while those with macrovascular complications had a 2.7-fold increased risk compared with controls. And those with both microvascular and macrovascular complications were seven times more likely to suffer S aureus infection than control individuals (adjusted OR, 7.0).

"Our results extend the limited existing knowledge on the risk of community-acquired S aureus bacteremia in patients with diabetes," the researchers say.

Interestingly, the presence of type 1 diabetes increased the risk of S aureus bacteremia at an OR of 7.2 compared with controls, vs an OR of just 2.7 among type 2 diabetes patients.

Dr Smit said, however, that these differences should be interpreted with caution, noting that there were only 40 cases and 29 controls with type 1 diabetes.

Diabetic Patients at Increased Risk of Other Infections?

Dr Smit and colleagues have also found evidence of increased risk of other infections among diabetes patients.

"We have done a number of studies, finding there is an increased risk of group B and group G hemolytic streptococcal bacteremia and an increased risk of pneumococcal bacteremia as well," he noted.

"We have started out with the most common pathogens for blood infection, which makes more sense, I think."

And a recent study reported by Medscape Medical News showed that diabetes patients have a 50% increased risk of surgical-site infection compared with those without diabetes.

There are a number of potential explanations for the increased risk of infection among diabetes patients, primarily related to the diabetes itself as opposed to increased contact with healthcare services, Dr Smit said.

Comorbidities associated with diabetes, including foot ulcers, kidney disease, and potentially diabetes-related decreased immunity could be explanations, although there were not enough data to investigate the latter in the current study, he noted.

This opens up the tantalizing possibility that better disease control may reduce the risk of bacteremia in diabetes patients, suggested Dr Smit.

"Based on our study, and taking into account our observations of further increased risk of S aureus with poor glycemic control and with diabetes complications, perhaps improvements in diabetes care would have a positive effect on risk of infection in patients with diabetes."

Dr Smit now seeks to explore the association between S aureus bacteremia and diabetes prognosis.

"We're…planning a very large study assessing the prognostic influence of diabetes….it's very interesting to see whether diabetes matters when you contract S aureus blood infection in terms of prognosis. That's our main focus of interest right now."

This study was supported by research grants from the Heinrich Kopp, Hertha Christensen, and North Denmark Health Sciences Research Foundations. The department of clinical epidemiology is a member of the Danish Center for Strategic Research in Type 2 Diabetes (DD2), supported by the Danish Agency for Science. DD2 is also supported by the Danish Health and Medicines Authority, the Danish Diabetes Association, and an unrestricted donation from Novo Nordisk. Partners in the DD2 project are listed on the project website at http:/www.DD2.nu. The authors report no relevant financial relationships.

Eur J Endocrinol. Published online March 10, 2016. Abstract

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