Incidence and Predictors of Gram-Negative Bacilli in Hospitalized People Who Inject Drugs with Injection Drug Use-Attributable Infections

The burden of skin and soft tissue, bone and joint infections in an Australian cohort of people who inject drugs

INTRODUCTION

There are currently limited data regarding the clinical and economic significance of skin and soft tissue infections (SSTI) and bone and joint infections in Australian people who inject drugs (PWID).

METHODS

Retrospective cohort study in adult PWID admitted to Monash Health, a large heath care network with six hospitals in Victoria, Australia. Inpatients were identified using administrative datasets and International Classification of Disease (ICD-10) coding for specific infection-related conditions. Cost analysis was based on mean ward, intensive care and hospital-in-the-home (HITH) lengths of stay. Spinal infections and endocarditis were excluded as part of previous studies.

RESULTS

A total of 185 PWID (61 female, 124 male, median age 37) meeting the study criteria were admitted to Monash Health between January 2010 and January 2021. Admitting diagnoses included 78 skin abscesses, 80 cellulitis, 17 septic arthritis, 4 osteomyelitis, 3 thrombophlebitis and 1 each of necrotising fasciitis, vasculitis and myositis. Pain (87.5%) and swelling (75.1%) were the most common presenting complaints. Opioids (67.4%) and methamphetamine (37.5%) were the most common primary drugs injected. Almost half (46.5%) of patients had concurrent active hepatitis C (HCV) infection on admission. Hepatitis B (HBV) and Human Immunodeficiency Virus (HIV) were uncommon. The most significant causative organism was methicillin-susceptible Staphylococcus aureus (24.9%). In 40.0% (74/185) no organism was identified. Patients required a median acute hospital stay of 5 days (2-51 days). There were 15 patients admitted to the intensive care unit (ICU) with median duration 2 days. PICC line insertion for antibiotics was required in 16.8% of patients, while 51.4% required surgical intervention. Median duration of both oral and IV antibiotic therapy was 11 days. Almost half (48.6%) of patients were enrolled in an opioid maintenance program on discharge. Average estimated expenditure was AUD $16, 528 per admission.

CONCLUSION

Skin and soft tissue and joint infections are a major cause of morbidity for PWID. Admission to hospital provides opportunistic involvement of addiction specialty services.

Divergent genetic landscapes drive lower levels of AmpC induction and stable de-repression in Serratia marcescens compared to Enterobacter cloacae

The chromosomally encoded AmpC beta-lactamase is widely distributed throughout the Enterobacterales. When expressed at high levels through transient induction or stable de-repression, resistance to ceftriaxone, a commonly used antibiotic, can develop. Recent clinical guidance suggests, based on limited evidence, that resistance may be less likely to develop in Serratia marcescens compared to the better-studied Enterobacter cloacae and recommends that ceftriaxone may be used if the clinical isolate tests susceptible. We sought to generate additional data relevant to this recommendation. AmpC de-repression occurs predominantly because of mutation in the ampD peptidoglycan amidohydrolase. We find that, in contrast to E. cloacae, where deletion of ampD results in high-level ceftriaxone resistance (with ceftriaxone MIC = 96 µg/mL), in S. marcescens deletion of two amidohydrolases (ampD and amiD2) is necessary for AmpC de-repression, and the resulting ceftriaxone MIC is 1 µg/mL. Two mechanisms for this difference were identified. We find both a higher relative increase in ampC transcript level in E. cloacae ΔampD compared to S. marcescens ΔampDΔamiD2, as well as higher in vivo efficiency of ceftriaxone hydrolysis by the E. cloacae AmpC enzyme compared to the S. marcescens AmpC enzyme. We also observed higher relative levels of transient AmpC induction in E. cloacae vs S. marcescens when exposed to ceftriaxone. In time-kill curves, this difference translates into the survival of E. cloacae but not S. marcescens at clinically relevant ceftriaxone concentrations. In summary, our findings can explain the decreased propensity for on-treatment ceftriaxone resistance development in S. marcescens, thereby supporting recently issued clinical guidance.

Assessment of Bacterial Infections and Antibiotic Regimens in Intravenous Drug Users

Bacterial infections in people who inject drugs (PWID) are a significant cause of hospitalizations and increased morbidity in this group. In this review, we evaluated bacterial trends in the most common infections and appropriate empiric antibiotic coverage. Articles from PubMed and Google Scholar were curated in a Google document with shared access. Discussion and development of the paper were achieved over Zoom meetings. The common infections in PWID were skin and soft tissue infections (SSTIs), infective endocarditis, septic arthritis, osteomyelitis, and bloodstream infections (BSIs). The presence of comorbidities increased susceptibility to bacterial infections. Staphylococcus aureus was the predominant species in all the infections and included methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA). The current standard of antibiotic use for Staphylococcus species was found to be sufficient. The gram-negative bacillus Serratia marcescens was prevalent in PWID as a causative agent of septic arthritis, osteomyelitis, and infective endocarditis. Its treatment required a combination of β-lactam and either a fluoroquinolone or an aminoglycoside for a prolonged duration. Streptococci were commonly implicated in SSTIs and BSIs. The appropriate response was seen with β-lactam antibiotics. In PWID, Enterococcus and Pseudomonas were implicated in infective endocarditis of native and prosthetic valves. The former being difficult to treat, a new strategy of using dual β-lactam antibiotics was found to be supported by clinical data. Anti-pseudomonal antibiotics can be avoided in other infections seen in this group, as their prevalence was low. PWID, especially those with comorbidities, have an increased risk of acquiring infections with difficult-to-treat microbes. Therefore, empiric antibiotic treatment should be relevant to the infection, for which bacterial trends and antibiotic susceptibility must be reassessed periodically.

Enterobacter cloacae as sole organism responsible for vertebral osteomyelitis/discitis and vertebral collapse in a patient with intravenous drug abuse

Staphylococcus aureus is the most commonly isolated organism in osteomyelitis, while gram-negative bacteria (GNB) comprises only a minor portion. GNB osteomyelitis is usually seen in patients with bacteraemia, recent genitourinary infection, open fractures or trauma and is rarely seen in the spines. Our case is a man in his 30s with no significant risk factors except an extended history of intravenous drug use (IVDU), who presented with back pain and subsequently developed vertebral collapse. Bone culture grew Enterobacter cloacae, yet blood cultures were negative. To date, there are limited data on the prevalence of GNB osteomyelitis in IVDU and its association. Due to rising rates of IVDU, further research must be done into associated medical complications to provide comprehensive care. Moreover, the emergence of multidrug-resistant GNB strains limits the number of effective antibiotics and is expected to pose more serious public concerns in the future.

Community-acquired skin and soft-tissue infections in people who inject drugs

PURPOSE OF REVIEW

The aim of this review is to discuss the latest evidence of the epidemiology, microbiology, risk factors, diagnosis and management of community-acquired skin and soft tissue infections (SSTIs) in people who inject drug (PWID).

RECENT FINDINGS

SSTIs are common complications in PWID and a major cause of morbidity and mortality. Infections can range from uncomplicated cellulitis, to abscesses, deep tissue necrosis and necrotizing fasciitis. They are predominantly caused by Gram-positive pathogens in particular Staphylococcus aureus and Streptococcus species; however, toxin-producing organisms such as Clostridium botulism or Clostridium tetani should be considered. The pathogenesis of SSTI in the setting of intravenous drug use (IDU) is different from non-IDU related SSTI, and management often requires surgical interventions in addition to adjunctive antibiotics. Harm reduction strategies and education about safe practices should be implemented to prevent morbidity and mortality as well as healthcare burden of SSTI in PWID.

SUMMARY

Prompt diagnosis and proper medical and surgical management of SSTI will improve outcomes in PWID.

Antibacterial and Antivirulence Activities of Acetate, Zinc Oxide Nanoparticles, and Vitamin C Against E. coli O157:H7 and P. aeruginosa

Infectious diseases remain one of the major health challenges worldwide due to the problem of antimicrobial resistance. Conventional antimicrobials have the disadvantage that bacteria rapidly acquire resistance to them, so alternatives must be developed to combat antibiotic resistance. Nanotechnology and the repurposing of existing drugs with known biological profiles are new approaches to replacing conventional antimicrobials. In this paper, we have tested the antibacterial activity of sodium acetate (NaA), vitamin C (VC), and zinc oxide nanoparticles (ZnO NPs) against Escherichia coli O157:H7 ATCC 51659 and Pseudomonas aeruginosa ATCC 27853. MIC values for tested compounds ranged from 0.08 to 6.5 mg ml^-1, and the effect of combinations and safety profiles against HepG2 cell line of these compounds were also evaluated. At sub-MIC values, tested compounds had a potential antivirulence effect by inhibiting motility and reducing biofilm formation and maturation. Collectively, ZnO NPs and VC are considered safe alternatives to traditional antibiotics that are capable of reducing the development of antibiotic resistance in microbes. Graphical abstract representing the main aim and the final findings of our work. Spread of multidrug-resistant (MDR) bacterial strains created an urge for alternative safe antimicrobial agents. In this work, we found that ZnO NPs and vitamin C are potential candidates that could be used against MDR E.coli and P. aeruginosa.

Tackling Extended Hospital Stays in Patients with Acute Bacterial Skin and Skin Structure Infections

Hospitalisation rates for acute bacterial skin and skin structure infection (ABSSSI) are rising and represent a large pharmacoeconomic burden as treatment may involve an extended number of days of antibiotic therapy. This article first aims to provide a review of treatment challenges associated with ABSSSIs in both hospital and outpatient settings, and shows that while more traditionally treatment has been conducted in a hospital setting, for a number of patients, a variety of considerations, including pharmacoeconomics, infection control, and patient preference, has led to the development of recommendations to assess the eligibility of patients for early discharge from hospital to complete their antibiotic regimen in the outpatient setting. However, such patients require monitoring for drug adherence to oral regimens or complications associated with daily intravenous administration, such as injection site reactions and infection. This review also focuses on one of a number of new antibiotics for ABSSSI, dalbavancin, as the long-acting glycopeptide with the most clinical experience to date. This antibiotic has been shown to be as effective as a daily/twice daily regimen with similar safety profiles. Health economic analysis of dalbavancin is also presented. It has shown that in some, though not all, clinical settings a reduction in the overall treatment cost is evident as, despite a higher medication cost, the lower hospitalisation time can lead to greater cost savings. In conclusion, while the burden of ABSSSI is rising, new treatment options provide additional therapeutic choice, although pharmacoeconomic considerations might limit use in some cases.

Clinical factors predictive of Gram-negative bloodstream infection at the Emergency Department

Introduction

Bloodstream infection is a common condition at the Emergency Department (ED). Appropriate antibiotic therapy is also crucial for patients with bloodstream infection particularly at the ED. This study therefore aimed to find clinical factors predictive of types of bacterial pathogens in bloodstream infection patients presenting at the ED focused on Gram-negative bacterial infections.

Methods

This was a retrospective study. The inclusion criteria were adult patients who were suspected for bloodstream infection defined by blood culture collection presenting at the ED and intravenous antibiotics were initiated during the ED visits. The study period was between January 1^st, 2016 and December 31^st, 2018. Clinical data of the eligible patients were retrieved from the ED database. Factors associated with Gram-negative infection were calculated by logistic regression analysis.

Results

There were 727 patients at the ED who had positive blood culture for bacteria. Of those, 504 patients (69.33%) had positive blood culture for Gram-negative bacteria. There were three independent factors for Gram-negative infection including sex, solid organ malignancy, and body temperature. The highest adjusted odds ratio (95% confidence interval) was 2.004 (1.330, 3.020) for solid organ malignancy.

Conclusions

Gram-negative bacterial infection was more prominent than Gram-positive bacterial infection in patients presenting at the ED (69.33%). Solid organ malignancy, being female, and a high body temperature were independent factors of Gram-negative bacterial infection.