Mortality and Hospital Stay Associated with Resistant Staphylococcus aureus and Escherichia coli Bacteremia: Estimating the Burden of Antibiotic Resistance in Europe

Abstract

The authors calculate excess mortality, excess hospital stay, and related hospital expenditure associated with antibiotic-resistant bacterial bloodstream infections ( Staphylococcus aureus and Escherichia coli) in Europe.

Abstract

Background

The relative importance of human diseases is conventionally assessed by cause-specific mortality, morbidity, and economic impact. Current estimates for infections caused by antibiotic-resistant bacteria are not sufficiently supported by quantitative empirical data. This study determined the excess number of deaths, bed-days, and hospital costs associated with blood stream infections (BSIs) caused by methicillin-resistant Staphylococcus aureus (MRSA) and third-generation cephalosporin-resistant Escherichia coli (G3CREC) in 31 countries that participated in the European Antimicrobial Resistance Surveillance System (EARSS).

Methods and Findings

The number of BSIs caused by MRSA and G3CREC was extrapolated from EARSS prevalence data and national health care statistics. Prospective cohort studies, carried out in hospitals participating in EARSS in 2007, provided the parameters for estimating the excess 30-d mortality and hospital stay associated with BSIs caused by either MRSA or G3CREC. Hospital expenditure was derived from a publicly available cost model. Trends established by EARSS were used to determine the trajectories for MRSA and G3CREC prevalence until 2015. In 2007, 27,711 episodes of MRSA BSIs were associated with 5,503 excess deaths and 255,683 excess hospital days in the participating countries, whereas 15,183 episodes of G3CREC BSIs were associated with 2,712 excess deaths and 120,065 extra hospital days. The total costs attributable to excess hospital stays for MRSA and G3CREC BSIs were 44.0 and 18.1 million Euros (63.1 and 29.7 million international dollars), respectively. Based on prevailing trends, the number of BSIs caused by G3CREC is likely to rapidly increase, outnumbering the number of MRSA BSIs in the near future.

Conclusions

Excess mortality associated with BSIs caused by MRSA and G3CREC is significant, and the prolongation of hospital stay imposes a considerable burden on health care systems. A foreseeable shift in the burden of antibiotic resistance from Gram-positive to Gram-negative infections will exacerbate this situation and is reason for concern.

Please see later in the article for the Editors' Summary

Editors' Summary

Background

Antimicrobial resistance—a consequence of the use and misuse of antimicrobial medicines—occurs when a microorganism becomes resistant (usually by mutation or acquiring a resistance gene) to an antimicrobial drug to which it was previously sensitive. Then standard treatments become ineffective, leading to persistent infections, which may spread to other people. With some notable exceptions such as TB, HIV, malaria, and gonorrhea, most of the disease burden attributable to antimicrobial resistance is caused by hospital-associated infections due to opportunistic bacterial pathogens. These bacteria often cause life-threatening or difficult-to-manage conditions such as deep tissue, wound, or bone infections, or infections of the lower respiratory tract, central nervous system, or blood stream. The two most frequent causes of blood stream infections encountered worldwide are Staphylococcus aureus and Escherichia coli.

Why Was This Study Done?

Although hospital-associated infections have gained much attention over the past decade, the overall effect of this growing phenomenon on human health and medical services has still to be adequately quantified. The researchers proposed to fill this information gap by estimating the impact—morbidity, mortality, and demands on health care services—of antibiotic resistance in Europe for two types of resistant organisms that are typically associated with resistance to multiple classes of antibiotics and can be regarded as surrogate markers for multi-drug resistance—methicillin-resistant S. aureus and third-generation cephalosporin-resistant E. coli.

What Did the Researchers Do and Find?

Recently, the Burden of Resistance and Disease in European Nations project collected representative data on the clinical impact of antimicrobial resistance throughout Europe. Using and combining this information with 2007 prevalence data from the European Antibiotic Resistance Surveillance System, the researchers calculated the burden of disease associated with methicillin-resistant S. aureus and third-generation cephalosporin-resistant E. coli blood stream infections. This burden of disease was expressed as excess number of deaths, excess number of days in hospital, and excess costs. Using statistical models, the researchers predicted trend-based resistance trajectories up to 2015 for the 31 participating countries in the European region.

The researchers included 1,293 hospitals from the 31 countries, typically covering 47% of all available acute care hospital beds in most countries, in their analysis. For S. aureus, the estimated number of blood stream infections totaled 108,434, of which 27,711 (25.6%) were methicillin-resistant. E. coli caused 163,476 blood stream infections, of which 15,183 (9.3%) were resistant to third-generation cephalosporins. An estimated 5,503 excess deaths were associated with blood stream infections caused by methicillin-resistant S. aureus (with the UK and France predicted to experience the highest excess mortality), and 2,712 excess deaths with blood stream infections caused by third-generation cephalosporin-resistant E. coli (predicted to be the highest in Turkey and the UK). The researchers also found that blood stream infections caused by both methicillin-resistant S. aureus and third-generation cephalosporin-resistant E. coli contributed respective excesses of 255,683 and 120,065 extra bed-days, accounting for an estimated extra cost of 62.0 million Euros (92.8 million international dollars). In their trend analysis, the researchers found that 97,000 resistant blood stream infections and 17,000 associated deaths could be expected in 2015, along with increases in the lengths of hospital stays and costs. Importantly, the researchers estimated that in the near future, the burden of disease associated with third-generation cephalosporin-resistant E. coli is likely to surpass that associated with methicillin-resistant S. aureus.

What Do These Findings Mean?

These findings show that even though the blood stream infections studied represent only a fraction of the total burden of disease associated with antibiotic resistance, excess mortality associated with these infections caused by methicillin-resistant S. aureus and third-generation cephalosporin-resistant E. coli is high, and the associated prolonged length of stays in hospital imposes a considerable burden on health care systems in Europe. Importantly, a possible shift in the burden of antibiotic resistance from Gram-positive to Gram-negative infections is concerning. Such forecasts suggest that despite anticipated gains in the control of methicillin-resistant S. aureus, the increasing number of infections caused by third-generation cephalosporin-resistant Gram-negative pathogens, such as E. coli, is likely to outweigh this achievement soon. This increasing burden will have a big impact on already stretched health systems.

Additional Information

Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001104.

• The World Health Organization has a fact sheet on general antimicrobial resistance

• The US Centers for Disease Control and Prevention webpage on antibiotic/antimicrobial resistance includes information on educational campaigns and resources

• The European Centre for Disease Control provides data about the prevalence of resistance in Europe through an interactive database