By Richard R. Watkins, MD, MS, FACP, FIDSA, FISAC

Professor of Internal Medicine, Northeast Ohio Medical University; Division of Infectious Diseases, Cleveland Clinic Akron General, Akron, OH

Dr. Watkins reports no financial relationships relevant to this field of study.

SYNOPSIS: Using a population-based database, investigators found that the rate of readmission within 30 days following hospitalization for S. aureus bacteremia was high (22%) and resulted in high cost to the healthcare system.

SOURCE: Inagaki K, Lucar J, Blackshear C, Hobbs CV. Methicillin-susceptible and methicillin-resistant Staphylococcus aureus bacteremia: Nationwide estimates of 30-day readmission, in-hospital mortality, length of stay, and cost in the United States. Clin Infect Dis 2019;69:2112-2118.

Despite advances in the diagnosis and treatment of Staphylococcus aureus bacteremia, morbidity and mortality remain unacceptably high. Recently, there has been a focus on the rate of readmission for patients with S. aureus bacteremia within 30 days of discharge, which is seen as a quality measure. Therefore, Inagaki and colleagues sought to determine current population-based estimates of important outcome measures, including 30-day readmission rate, associated with S. aureus bacteremia to help optimize patient management.

The study was a retrospective analysis that used information in a nationwide database collected between Jan. 1, 2014, and Nov. 30, 2014. Discharge records were available from 22 states, which accounted for 51% of the U.S. population and 49% of all hospitalizations. Patients included were ≥ 18 years of age and diagnosed with S. aureus bacteremia without prior hospitalization for this diagnosis. The primary outcome was readmission within 30 days of discharge. Secondary outcomes included in-hospital mortality, length of stay, and healthcare costs.

There were 92,089 cases of S. aureus bacteremia identified during the study period. Of these, 48.5% were methicillin-resistant S. aureus (MRSA) and 51.5% were methicillin-sensitive S. aureus (MSSA). The rates of MRSA bacteremia were higher in patients who had Medicare or Medicaid insurance, resided in a low-income neighborhood, were treated in a nonteaching hospital, or had HIV, congestive heart failure (CHF), or chronic lung disease. MRSA bacteremia was more likely to be present with skin and soft tissue infections or pneumonia, while endocarditis, musculoskeletal infection, and central line-associated infection were more likely to be present with MSSA.

Overall in-hospital mortality with S. aureus bacteremia was 13% and it was 14.1% with MRSA bacteremia.

Among the patients who survived their initial episode of S. aureus bacteremia, all-cause 30-day readmission occurred in 22%, which did not differ significantly between MRSA and MSSA. Compared to MSSA, those with MRSA bacteremia were 17% more likely to have a 30-day readmission with bacteremia recurrence (hazard ratio [HR], 1.17; 95% confidence interval [CI], 1.02-1.34). Endocarditis during the index hospitalization was associated with 30-day readmission with bacteremia (HR, 1.44; 95% CI, 1.21-1.72), while skin and soft tissue infection was less so (HR, 0.68; 95% CI, 0.56-0.82).

Patients with CHF, end-stage renal disease, rheumatologic disease, hematologic malignancy, and drug abuse all had an increased risk for 30-day readmission with S. aureus bacteremia, as did those treated at a nonteaching hospital. The odds of in-hospital death were 15% higher (odds ratio [OR], 1.15; 95% CI, 1.07-1.23), and the average length of stay was longer for patients with MRSA bacteremia vs. MSSA. The overall costs were similar. Finally, the mean cost for readmission of a case of recurrent S. aureus bacteremia was $19,186, which was higher than both all-cause readmission and the initial hospitalization for S. aureus bacteremia ($12,425).

COMMENTARY

S. aureus bacteremia is costly in terms of lives lost and healthcare resources consumed. Therefore, investigating ways to improve outcomes with S. aureus bacteremia should be a top priority. Inagaki and colleagues identified several risk factors for readmission within 30 days due to recurrent S. aureus bacteremia. It should not be surprising that patients with significant comorbidities would be at higher risk for readmission. Moreover, the risk for 30-day readmission due to recurrent S. aureus bacteremia (22%) was higher than the 30-day readmission rate for elderly Medicare patients with pneumonia, myocardial infarction, and heart failure (17%). The finding that there was no difference in the readmission rate between MRSA and MSSA might reflect the high readmission rate associated with S. aureus bacteremia overall. Another notable finding was that less than 50% of S. aureus bacteremia cases are due to MRSA. This reflects the changing epidemiology of MRSA, with several studies showing an overall decline in the incidence of MRSA over the last few years.

One interesting finding was that the overall costs of hospitalization were similar between MRSA and MSSA, yet patients with MRSA had longer lengths of stay. The explanation for this is uncertain, although previous studies also have shown no cost differences in hospitalizations between MRSA and MSSA bacteremia.

There are some important caveats with the study that should be considered. First, the quality of pre-discharge and post-discharge care could not be ascertained through the database. For example, it has been shown that infectious disease consultation is associated with improved outcomes in S. aureus bacteremia.1 Second, the database covered 22 states, and it is theoretically possible that some patients diagnosed with S. aureus bacteremia moved out of the state. Third, the investigators did not determine the presence of prosthetic devices, which are important risk factors for recurrent bacteremia. Finally, the study was based on data from more than five years ago, although the latest guidelines on the treatment of MRSA infections (including bacteremia) were published before then.2

Preventing readmission in cases of S. aureus bacteremia is a worthy yet elusive goal. Clinicians should focus on patients with risk factors, especially S. aureus endocarditis, by monitoring them carefully for signs of treatment failure.

REFERENCES

  1. Honda H, Krauss MJ, Jones JC, et al. The value of infectious diseases consultation in Staphylococcus aureus bacteremia. Am J Med 2010;123:631-637.
  2. Liu C, Bayer A, Cosgrove SE, et al. Clinical Practice Guidelines by the Infectious Diseases Society of America for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children. Clin Infect Dis 2011;52:e18-e55.