Current problems in the diagnosis and treatment of hospital-acquired methicillin-resistant Staphylococcus aureus pneumonia

Is administration of anti-MRSA drugs recommended for patients with pneumonia when MRSA is isolated from respiratory specimens? A systematic review and meta-analysis

It is unclear whether anti-methicillin-resistant Staphylococcus aureus (MRSA) drugs should be uniformly administered to patients with pneumonia when MRSA is isolated from respiratory specimens. A systematic review was conducted to evaluate the efficacy of the uniform administration of anti-MRSA drugs. Two researchers independently searched the literature as of December 2022, extracted relevant papers, and performed a meta-analysis. The outcomes were mortality and adverse events. No applicable randomized controlled trials were found during the study period, but four observational studies were extracted. The relative risk of mortality in the anti-MRSA group was 1.67 [95% confidence interval 0.65-4.30], which did not differ significantly from the non-administered group. Further investigation into the background of patients demonstrated that anti-MRSA drugs were administered to groups in which only MRSA was cultured. However, the pneumonia severity index did not differ from that in the non-treated group. No studies of adverse events were found. Our review did not find a beneficial contribution to mortality from uniform anti-MRSA medication to patients with pneumonia when MRSA was isolated from respiratory specimens. Factors determining risk-based individualized treatment should be validated as the future question.

The monitoring of vancomycin: a systematic review and meta-analyses of area under the concentration-time curve-guided dosing and trough-guided dosing

Background

This systematic review and meta-analysis explored the relationship between vancomycin (VCM) monitoring strategies and VCM effectiveness and safety.

Methods

We conducted our analysis using the MEDLINE, Web of Sciences, and Cochrane Register of Controlled Trials electronic databases searched on August 9, 2020. We calculated odds ratios (ORs) and 95% confidence intervals (CIs).

Results

Adult patients with methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia with VCM trough concentrations ≥15 μg/mL had significantly lower treatment failure rates (OR 0.63, 95% CI 0.47–0.85). The incidence of acute kidney injury (AKI) increased with increased trough concentrations and was significantly higher for trough concentrations ≥20 μg/mL compared to those at 15–20 μg/mL (OR 2.39, 95% CI 1.78–3.20). Analysis of the target area under the curve/minimum inhibitory concentration ratios (AUC/MIC) showed significantly lower treatment failure rates for high AUC/MIC (cut-off 400 ± 15%) (OR 0.28, 95% CI 0.18–0.45). The safety analysis revealed that high AUC value (cut-off 600 ± 15%) significantly increased the risk of AKI (OR 2.10, 95% CI 1.13–3.89). Our meta-analysis of differences in monitoring strategies included four studies. The incidence of AKI tended to be lower in AUC-guided monitoring than in trough-guided monitoring (OR 0.54, 95% CI 0.28–1.01); however, it was not significant in the analysis of mortality.

Conclusions

We identified VCM trough concentrations and AUC values that correlated with effectiveness and safety. Furthermore, compared to trough-guided monitoring, AUC-guided monitoring showed potential for decreasing nephrotoxicity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-05858-6.

Clinical impact of methicillin-resistant staphylococcus aureus on bacterial pneumonia: cultivation and 16S ribosomal RNA gene analysis of bronchoalveolar lavage fluid

Background

Determining whether methicillin-resistant Staphylococcus aureus (MRSA) is a true causative pathogen or reflective of colonization when MRSA is cultured from the respiratory tract remains important in treating patients with pneumonia.

Methods

We evaluated the bacterial microbiota in bronchoalveolar lavage fluid (BALF) using the clone library method with a 16S ribosomal RNA (rRNA) gene analysis in 42 patients from a pneumonia registry who had MRSA cultured from their sputum or BALF samples. Patients were divided into two groups: those treated with (Group A) or without (Group B) anti-MRSA agents, and their clinical features were compared.

Results

Among 248 patients with pneumonia, 42 patients who had MRSA cultured from the respiratory tract were analyzed (Group A: 13 patients, Group B: 29 patients). No clones of S. aureus were detected in the BALF of 20 out of 42 patients. Twenty-eight of 29 patients in Group B showed favorable clinical outcomes, indicating that these patients had non-MRSA pneumonia. Using a microflora analysis of the BALF, the S. aureus phylotype was predominant in 5 of 28 (17.9 %) patients among the detected bacterial phylotypes, but a minor population (the percentage of clones ≤ 10 %) in 19 (67.9 %) of 28 patients. A statistical analysis revealed no positive relationship between the percentage of clones of the S. aureus phylotype and risk factors of MRSA pneumonia.

Conclusions

The molecular method using BALF specimens suggests that conventional cultivation method results may mislead true causative pathogens, especially in patients with MRSA pneumonia. Further studies are necessary to elucidate these clinically important issues.

Predictors of the pathogenicity of methicillin-resistant Staphylococcus aureus nosocomial pneumonia

BACKGROUND AND OBJECTIVE

The clinical characteristics of patients with nosocomial pneumonia (NP) associated with methicillin-resistant Staphylococcus aureus (MRSA) infection are not well characterized.

METHODS

Three hundred and thirty-seven consecutive patients with MRSA isolation from respiratory specimens who attended our hospital between April 2007 and March 2011 were enrolled. Patients characteristics diagnosed with 'true' MRSA-NP were described with regards to clinical, microbiological features, radiological features and genetic characteristics of the isolates. The diagnosis of 'true' MRSA-NP was confirmed by anti-MRSA treatment effects, Gram-staining or bronchoalveolar lavage fluid culture.

RESULTS

Thirty-six patients were diagnosed with 'true' MRSA-NP, whereas 34 were diagnosed with NP with MRSA colonization. Patients with a MRSA-NP had a Pneumonia Patient Outcomes Research Team score of 5 (58.3% vs 23.5%), single cultivation of MRSA (83.3% vs 38.2%), MRSA quantitative cultivation yielding more than 10(6) CFU/mL (80.6% vs 47.1%), radiological findings other than lobar pneumonia (66.7% vs 26.5%), and a history of head, neck, oesophageal or stomach surgery (30.6% vs 11.8%). These factors were shown to be independent predictors of the pathogenicity of 'true' MRSA-NP by multivariate analysis (P < 0.05).

CONCLUSIONS

'True' MRSA-NP shows distinct clinical and radiological features from NP with MRSA colonization.

[Quantitative Bayesian diagnosis developed for lower respiratory tract infections due to methicillin-resistant Staphylococcus aureus]

Using quantitative Bayesian analysis as a clinical epidemiological approach, we developed a diagnosis for lower respiratory tract infection (LRTI) due to Methicillin-resistant Staphylococcus aureus (MRSA). We retrospectively reviewed the charts of 181 subjects--a derivation cohort-with MRSA retrieved from lower respiratory specimens June 2006 to March 2008. Dividing them into infection or colonization (no infection) groups, we compared them for the presence or absence of clinical parameters, including fever > 38 degrees C, MRSA >106 CFU (colony-forming units)/mL, phagocytosis on Gram staining, serum albumin < 3.0 g/dL, and peripheral WBC count > 15,000/mL. We them determined positive and negative likelihood ratios (LR +, LR -) for these parameters to quantify MRSA-LRTI diagnostic probability based on combined likelihood ratios (Bayesian analysis). We then determined Bayesian MRSA-LRTI diagnostic probabilities (BDPs) in 40 subjects with respiratory MRSA--a validation cohort-from May 2008 to October 2008 clinically judged with either infection (n = 14) or colonization (n = 26) by infection control personnel (ICP) blinded to the test (parameter LR+ and LR -). BDPs (mean +/- SD) quantified by combining the four parameters-fever, MRSA CFU, phagocytosis, and serum albumin-were 62.3 +/- 25.4% for 14 judged with infection, and 40.2% +/- 20.4% for 26 patients judged with colonization (p = 0.005). Using a diagnostic probability of 51% as the cut off, we compared positive and negative predictive Bayesian diagnoses ICP judgment, i.c., 77% vs. 85%. The Bayesian approach proved useful in quantitatively diagnosing infectious disease such as MRSA-LRTI that lack established diagnostic, and may aid physicians in deciding the need for specific antimicrobial therapy.

Pneumonia due to methicillin-resistant Staphylococcus aureus: clinical features, diagnosis and management

PURPOSE OF REVIEW

The review highlights the clinical findings and the management of community-acquired, health-care associated and nosocomial pneumonia due to methicillin-resistant Staphylococcus aureus (MRSA).

RECENT FINDINGS

Although previously considered as a purely nosocomial event, community-acquired MRSA pneumonia is underestimated and is spreading worldwide. A retrospective study showed that almost half of patients with nonnosocomial MRSA pneumonia admitted to a large teaching hospital did not present established criteria for healthcare-associated infections. Recent data show that MRSA ventilator-associated pneumonia is associated with significantly higher mortality than ventilator-associated pneumonia caused by methicillin-susceptible Staphylococcus aureus. Therefore, prompt and appropriate therapy is essential. The optimal therapy for MRSA pneumonia has not been fully elucidated. Although vancomycin has been considered the gold standard for the treatment of MRSA infections, clinical failures have also been reported in the presence of in-vitro susceptibility. Linezolid may provide improved outcomes compared with vancomycin in patients with MRSA pneumonia, but validation in a prospective trial is currently lacking. Recently licensed tigecycline and dalbavancin, a drug in phase III trial, look promising. Animal models showed that immunization against a cytolytic toxin secreted by most Staphylococcus aureus strains protects against lethal pneumonia.

SUMMARY

Rapid recognition of possible staphylococcal infection in patients with severe pneumonia is essential. The treatment of MRSA pneumonia must be prompt and effective in order to allow a fast microbiological clearance and to successfully manage the infection.