Demographics, Epidemiology, Mortality, and Difficult-To-Treat Resistance Patterns of Bacterial Bloodstream Infections in the Global United States Military Health System from 2010-2019: A Retrospective Cohort Study

Objective

To describe demographics, causative pathogens, hospitalization, mortality, and antimicrobial resistance of bacterial bloodstream infections (BSIs) among beneficiaries in the global U.S. Military Health System (MHS), a single-provider healthcare system with 10-year longitudinal follow-up.

Design

Retrospective cohort study

Setting

Clinical and demographic data collected from the MHS Data Repository and collated with microbiological data obtained from the Defense Centers for Public Health-Portsmouth.

Participants

12,748 MHS beneficiaries diagnosed with 15,357 bacterial BSIs (2010-2019).

Main Outcome(s) and Measure(s)

Demographic data and diagnosis codes preceding BSI episodes and during hospitalizations were collected. Inpatient admission data identified acute clinical diagnoses, intensive care unit (ICU) admission, and mortality. BSI pathogens were evaluated for antimicrobial resistance, including difficult-to-treat resistance (DTR). Crude mortality trends were assessed.

Results

The decade analyzed included 15,357 BSI episodes in 12,748 patients; 6,216 patients (48.8%) were ≥65 years and 83.7% of episodes had ≥1 comorbidity (12,856 of 15,357). Approximately 29% of episodes with hospitalization required ICU admission and ∼34% had concurrent urinary tract infections. Pathogen distribution was 53% and 47% for Gram-positive bacteria and Gram-negative bacilli (GNB), respectively. Inpatient mortality was 4.4%, and at one year was 23.4%; 0.5% (16 of 2,977) of deaths were associated with DTR GNB. Among an average 8,145,778 individuals receiving care annually in the MHS, annual rates of overall BSI, methicillin-resistant Staphylococcus aureus , vancomycin-resistant Enterococcus spp., and DTR GNB BSI were 18.9, 1.30, 0.25, and 0.05 per 100,000 beneficiaries, respectively. Over the decade, annual mortality did not significantly increase for any pathogen and decreased by ∼3% for lactose-fermenting GNB BSI (p=0.048).

Conclusions

In the global U.S. MHS, mortality burden associated with BSI was substantial (approximately 1 in 4 dying at 1 year), relatively unchanged over a decade, and associated with older age and comorbidities. First-line treatment options remained available for 99.7% of BSIs. Population-level improvements in BSI survival might be maximally influenced by focusing on prevention, early detection, prompt antibiotics, and other novel therapies not contingent on in vitro activity.

Summary Box

What is already known on this topic:

• Bloodstream infections (BSIs) are associated with high healthcare burden and poor patient outcomes, including high mortality.

• Modeling data based on assumptions suggest that mortality associated with antimicrobial-resistant pathogens is increasing.

What this study adds:

• Among Military Health System (MHS) beneficiaries, overall and difficult-to-treat antimicrobial-resistant BSIs averaged an annual rate of 18.9 and 0.05 per 100,000 beneficiaries, respectively.

• Over a decade, mortality did not increase annually for any BSI group, while lactose-fermenting Gram-negative BSI mortality decreased (∼3%) and 50% of BSIs associated with deaths at 1-year occurred >42 days after BSI diagnosis.

• Bacterial BSI deaths in MHS are often associated with advanced age (74% ≥65 years) and comorbidities (97% with ≥1 comorbidity), rather than absence of first-line antimicrobial treatment options.