Methicillin-Resistant Staphylococcus aureus Pneumonia in Diabetics: A Single-Center, Retrospective Analysis
Introduction
Pneumonia caused by methicillin-resistant Staphylococcus aureus (MRSA) represents a significant clinical challenge due to its high morbidity and mortality, particularly in vulnerable populations such as individuals with diabetes mellitus (DM). Diabetes is associated with hyperglycemia, impaired immunity, and chronic complications like pulmonary microangiopathy, all of which increase susceptibility to infections. Despite the growing prevalence of MRSA globally—especially in Asia, where detection rates exceed 50% in some regions—there is limited research on the clinical characteristics, antimicrobial resistance patterns, and outcomes of MRSA pneumonia specifically in diabetic populations. This study aimed to compare diabetic and non-diabetic patients with S. aureus pneumonia, focusing on risk factors, disease severity, co-infections, and the impact of glycemic control on outcomes.
Methods
A retrospective cohort study was conducted at Ruijin Hospital, a tertiary care center in Shanghai, China, from 2014 to 2017. Patients diagnosed with S. aureus pneumonia were categorized into diabetic (DM, n = 144) and non-diabetic (non-DM, n = 221) groups. Inclusion criteria required a positive sputum culture for S. aureus, with pneumonia confirmed by clinical and radiological findings. Data collected included demographics, comorbidities, mechanical ventilation use, HbA1c levels, CURB-65 scores (an index assessing pneumonia severity based on confusion, urea levels, respiratory rate, blood pressure, and age ≥65), length of hospital stay, mortality, and antimicrobial susceptibility profiles.
Antimicrobial susceptibility testing followed Clinical and Laboratory Standards Institute guidelines, using E-tests for agents such as penicillins, cephalosporins, quinolones, aminoglycosides, macrolides, and others. Co-infection rates with additional pathogens were analyzed. Logistic regression models identified independent risk factors for mortality.
Results
Clinical Characteristics
The diabetic cohort was older (mean age 70.6 vs. 64.0 years, P < 0.01) and had a higher body mass index (23.7 vs. 21.9 kg/m², P < 0.01). DM patients exhibited more comorbidities (e.g., cardiovascular disease, renal insufficiency) and required invasive mechanical ventilation more frequently (46.5% vs. 28.1%, P < 0.01). Although MRSA prevalence was numerically higher in diabetics (65.3% vs. 56.1%, P > 0.05), this difference did not reach statistical significance. Diabetic patients also had higher CURB-65 scores (34.1% scoring 3–5 vs. 22.2% in non-DM, P < 0.05), longer hospital stays (191.4 vs. 171.1 days, P < 0.05), and a non-significant trend toward elevated mortality (30.6% vs. 23.1%, P = 0.112).
Antimicrobial Resistance
Both groups showed complete susceptibility to vancomycin, teicoplanin, and linezolid. However, DM patients demonstrated higher resistance rates to most antibiotics compared to non-DM individuals:
- β-lactams: Resistance to cefazolin (60% vs. 62.6%, P = 0.751) and ampicillin/sulbactam (60.4% vs. 57.3%, P = 0.715).
- Quinolones: Resistance to ciprofloxacin (62.2% vs. 45.7%, P = 0.034) and levofloxacin (63.8% vs. 53.9%, P = 0.075).
- Aminoglycosides: Gentamicin resistance was 53.4% in DM vs. 42.8% in non-DM (P = 0.059).
- Macrolides and lincosamides: Erythromycin resistance (74.6% vs. 70.5%, P = 0.415) and clindamycin resistance (65.4% vs. 60.9%, P = 0.421).
Co-Infections
Co-infections were common in both groups (47.2% in DM vs. 45.7% in non-DM, P > 0.05). Acinetobacter baumannii was the predominant co-pathogen in diabetics (22.2%), whereas Klebsiella pneumoniae was most frequent in non-diabetics (19.9%). Notably, co-infection with K. pneumoniae in DM patients correlated with higher mortality (44%), while Pseudomonas aeruginosa co-infection was linked to increased mortality in non-DM (59.3%).
Risk Factors for Mortality
Univariate analysis identified age (OR = 1.031, 95% CI 1.023–1.046, P < 0.001), comorbidities (OR = 1.489, 95% CI 1.250–1.773, P < 0.001), co-infection (OR = 1.620, 95% CI 1.293–2.031, P < 0.001), and CURB-65 score (OR = 2.072, 95% CI 1.727–2.485, P < 0.001) as significant predictors of mortality. In multivariate analysis, only MRSA infection (OR = 2.080, 95% CI 1.037–4.173, P = 0.039) and CURB-65 score (OR = 2.470, 95% CI 1.968–3.101, P < 0.001) emerged as independent risk factors.
Impact of Glycemic Control
HbA1c levels were stratified into three categories: 4–7%, 7–8%, and >8%. Higher HbA1c correlated with increased MRSA infection rates (50.0% in 4–7%, 55.6% in 7–8%, 60.0% in >8%), co-infection rates (36.4% in 4–7% vs. 60.0% in >8%), and CURB-65 scores (1.68 vs. 3.20). Mortality escalated with poorer glycemic control: 22.7% in the 4–7% group, 33.3% in 7–8%, and 60.0% in >8%.
Discussion
This study highlights the heightened vulnerability of diabetic patients to severe MRSA pneumonia. The increased prevalence of MRSA in DM patients aligns with prior evidence suggesting that hyperglycemia facilitates microbial colonization and biofilm formation. Elevated CURB-65 scores in diabetics reflect greater disease severity, likely due to systemic inflammation, impaired neutrophil function, and microvascular complications.
The higher antimicrobial resistance observed in DM patients may stem from frequent antibiotic exposure and immune dysfunction, complicating treatment regimens. Despite resistance to multiple agents, vancomycin, teicoplanin, and linezolid remain universally effective, underscoring their role as first-line therapies.
Co-infections with A. baumannii in diabetics and K. pneumoniae in non-diabetics suggest distinct pathogen dynamics influenced by host factors. The association of K. pneumoniae with higher mortality in DM patients may relate to hypervirulent strains or synergistic interactions with MRSA.
The identification of MRSA and CURB-65 as independent mortality predictors emphasizes the need for early recognition and aggressive management of high-risk patients. Poor glycemic control (HbA1c >8%) exacerbates infection risk and severity, reinforcing the importance of glucose management in diabetic care.
Limitations
This study’s retrospective design and single-center data limit generalizability. The small sample size in HbA1c subgroups may underpower statistical comparisons. Additionally, sputum cultures alone cannot reliably distinguish colonization from active infection, potentially leading to misclassification.
Conclusion
Diabetic patients, particularly those with poor glycemic control, face elevated risks of MRSA pneumonia, antimicrobial resistance, co-infections, and mortality. MRSA infection and CURB-65 scores are critical prognostic indicators. Clinicians must prioritize glycemic control, early microbiological diagnosis, and tailored antibiotic therapy to improve outcomes in this high-risk population.
doi.org/10.1097/CM9.0000000000000270
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