Diagnostic Imaging of Infections and Inflammatory Diseases

A Multidiscplinary Approach

Alberto Signore, Ana Maria Quintero, Alberto Signore, Ana Maria Quintero

• Publisher: Wiley-Blackwell
• Year: 2013
• Print ISBN: 9781118484418
• eBook ISBN: 9781118484357
• Edition: 1
• Topic: Medicine
• Subtopic: Radiology, Radiotherapy & Nuclear Medicine

Thoroughly and systematically presents the state-of-the-art in the diagnostic uses of radiologic imaging and nuclear medicine in the diagnosis and management of infectious and inflammatory diseases

Although our understanding of microorganisms has advanced significantly and antimicrobial therapy has become increasingly available, infection remains a major cause of patient morbidity and mortality. Imaging of infection and inflammation provides a classic example of radiology and nuclear medicine's strengths as well as weaknesses in the discovery and diagnosis of disease. Fortunately, the weaknesses are subsiding as new studies and techniques point to better planning and precision in the use of single and combined imaging modalities.

Diagnostic Imaging of Infections and Inflammatory Diseases: A Multidisciplinary Approach deals with the very latest developments in the use of radiologic techniques and modalities in the management of patients with a host of infectious and inflammatory diseases. Tremendously timely and useful, this innovative, multidisciplinary book covers a wide range of topics in three parts:

PART 1: Infections and Host Response

• Epidemiology of Infections in the New Century
• Bacterial Osteomyelitis: the Clinician Point of View

PART 2: Radiological Imaging

• Radiological Imaging of Osteomyelitis
• Radiological Imaging of Spine Infection
• Radiological Imaging of Soft Tissue Infections
• Radiological Imaging of Abdominal Infections and Inflammatory Disease
• Radiological Imaging of Vascular Graft Infection
• Radiological Imaging of TB and HIV

PART 3: Nuclear Medicine Imaging

• Nuclear Medicine Imaging of Infections: Techniques, Acquisition Protocols, and Interpretation Criteria
• Nuclear Medicine Imaging of Osteomyelitis: WBC, Monoclonal Antibody, or Bacterial Imaging?
• Nuclear Medicine Imaging of Spondylodiscitis: The Emerging Role of PET
• Nuclear Medicine Imaging of Soft Tissue Infections
• Nuclear Medicine Imaging of Infections and Inflammatory Diseases of the Abdomen
• Nuclear Medicine Imaging of Vascular Graft Infections: The Added Role of Hybrid Imaging
• Nuclear Medicine Imaging of TB and HIV
• Nuclear Medicine Imaging of Fever of Unknown Origin
• Nuclear Medicine Imaging of Inflammatory Diseases

Along with carefully developed clinical cases describing the management of patients with inflammation and infection, Diagnostic Imaging of Infections and Inflammatory Diseases is an ideal guide for radiologists and nuclear medicine physicians as well as clinical specialists from many other fields.

PART I

Infections and Host Response

CHAPTER 1

Epidemiology of Infections in the New Century

Nicola Petrosillo

National Institute for Infectious Diseases, “L. Spallanzani”, IRCCS, Rome, Italy

Introduction

Over the past few decades, an alarming increase in infections caused by antibiotic-resistant pathogens, including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus spp. (VRE), carbapenem-resistant Pseudomonas aeruginosa, extended-spectrum β-lactamase (ESBL)-producing Escherichia coli and Klebsiella spp., carbapenemase-producing Enterobacteriaceae and multidrug-resistant (MDR) Acinetobacter spp., has been observed in the hospital setting and healthcare-associated facilities [1–4].

The main mechanisms of antimicrobial resistance result from convergence of multiple and different factors, depending on the pathogen: expression of low-affinity penicillin-binding proteins; the alternative pathway for peptidoglycan synthesis; low outer membrane permeability; and presence of genes encoding extended-spectrum, OXA-type (oxacillin-hydrolyzing) or metallo-β-lactamases, carbapenemases, intrinsic or acquired efflux pumps, and aminoglycoside and fluoroquinolone modifying enzymes.

These resistance determinants, depending on their origin, can be chromosomally encoded or acquired from mobile genetic elements, and easily transferred among microbial strains, thus conferring extended drug resistance upon them [5–7].

Numerous factors are associated with high rates of antimicrobial resistance in the healthcare setting, including pressure on antibiotic use, severity of illness, numerosity of invasive devices, length of hospital stay, immunosuppression, malnutrition and ease of cross-transmission of antimicrobial-resistant pathogens [8,9].

Staphylococcal infections: healthcare-acquired MRSA and beyond

In 2003, 59.5% of S. aureus isolates in the US National Nosocomial Infection Surveillance (NNIS) intensive care units (ICUs) were MRSA [10]. Similarly, in some European countries, according to European Antimicrobial Resistance Surveillance System (EARSS) data, greater than 60% of isolates in 2007, mostly in critical care areas, were MRSA [11]. However, during recent years, although MRSA rates in most European countries are high, a significant downward trend has been reported in many ICUs [12–14].

MRSA is one of the main pathogens in hospital settings, including surgery and intensive care, and is becoming an alarming problem also in nursing home and other healthcare facilities. Patients colonized with MRSA can easily develop an infection when they undergo invasive procedures. Indeed, the role of S. aureus nasopharyngeal carriage as a risk factor for infection in the hospital setting has been widely documented [15]. Approximately 30% of colonized patients may develop an MRSA infection [16] and in nearly 20%, this is a bacteremia. In recent reports, carbapenem use has been related to MRSA colonization, with eight new cases of MRSA colonization per 1000 days of carbapenem therapy [17].

Despite the worldwide use of vancomycin, S. aureus resistance to this glycopeptide remains rare. Only nine cases of vancomycin-resistant S. aureus [VRSA; defined by a vancomycin minimum inhibitory concentration (MIC) of ≥1.6 mg/dL] have been identified to date and, as of 2007, approximately 100 vancomycin-intermediate S. aureus (VISA) isolates (defined by a vancomycin MIC of 0.4–0.8 mg/dL) have been reported worldwide [18].

Currently, the main concern is the shift in susceptibility to vancomycin, the so-called MIC “creep”. This phenomenon is represented by small incremental increases in vancomycin MIC within the susceptibility range. One of the most controversial issues in the treatment of MRSA is the evidence for reduced vancomycin treatment efficacy in the management of bacteremia and pneumonia by MICs at the upper limit of susceptibility (i.e. MICs of 0.2 mg/dL compared with ≤0.1 mg/dL, which are still considered to be susceptible) [19–25]. The increase in treatment failure might be the result of higher frequencies of hetero-resistance to van­comycin among isolates with vancomycin MICs of 0.2 mg/dL [26]. Indeed, VISA isolates are those with a MIC between 0.4 and 0.8 mg/dL, whereas heterogeneous VISA (hVISA) strains appear to be sensitive to vancomycin with a susceptibility range of 0.1–0.2 mg/dL, even though they contain a subpopulation of vancomycin-intermediate daughter cells (MIC ≥0.4 mg/dL) [27].

Finally, although MRSA infections were traditionally limited to hospitals, reports of community-associated cases of MRSA (CA-MRSA) infections began to emerge in the late 1990s in the USA [28]. CA-MRSA are genetically and phenotypically distinct from the typical multidrug-resistant healthcare-associated MRSA. These strains are resistant to β-lactam antibiotics and typically susceptible to other antistaphylococcal agents; they often encode for Panton–Valentine leukocidin (PVL) and other exotoxins and virulence factors [29].

The vast majority of CA-MRSA carry one of two smaller SCCmec types, IV and V, without the additional resistance genes. In general, they are more susceptible to non-β-lactam antibiotics and appear to be associated with increased transmission and hospitalization, skin and soft tissue infection and, rarely, severe diseases including necrotizing pneumonia [30].

CA-MRSA strains have rapidly emerged worldwide and are now endemic in the USA where they are amongst the most commonly isolated pathogens in emergency departments. Furthermore, nosocomial transmission of CA-MRSA and hospital outbreaks have recently been observed in several countries [31].

Enterococcus spp.

Another emerging concern in surgery and intensive care areas is VRE diffusion [32]. Although the vast majority of clinical enterococcal infections are caused by Enterococcus faecalis, Enterococcus faecium has emerged in recent years as a major multiresistant nosocomial pathogen, with a great capacity for acquiring multiple antibiotic-resistance determinants, especially those encoding glycopeptide resistance (e.g. vanA- and vanB-resistance genotypes). Almost 100% of E. faecium isolates are now resistant to ampicillin, but high-level aminoglycoside resistance is also a major problem, as it is common in both E. faecalis and E. faecium, ranging from 25% to 50% in European countries.

Various risk factors for acquisition of VRE have been proposed, including environmental risk factors (extensive use of broad-spectrum antimicrobial agents; patient overcrowding in facilities; admission to an ICU, transplant ward or unit with high colonization pressure; contaminated surfaces and fomites where enterococci can survive for a long period even in dry conditions); patient risk factors (severity of illness; prolonged hospitalization; presence of indwelling catheters or invasive devices; prolonged mechanical ventilation; age; non-ambulatory status; immunosuppression as post-transplantation status; diarrhea; renal failure/chronic hemodialysis; and proximity to patients who are colonized by VRE); clinical risk factors (poor adherence to infection-control practices; unrecognized antimicrobial resistance in the facility; inappropriate treatment; and use of contaminated equipment) [33].

Multidrug-resistant Enterobacteriaceae: are we facing a new era?

Among Gram-negative agents, ESBL-producing Enterobacteriaceae are a great concern. The epidemiology of ESBLs has changed dramatically: until recently, most infections caused by ESBL-producing bacteria were described as being acquired nosocomially, often appearing in specialized units, but are now increasingly found in non-hospitalized patients, and the mode of transmission or source of this pathogen is still unknown [34,35].

More recently, the worldwide epidemic of Enterobacteriaceae resistant to carbapenems is also a major concern. Carbapenems have been widely used as the treatment of choice for serious infections caused by ESBL producers, exerting selection pressure for carbapenem resistance. Klebsiella pneumoniae carbapenemases (KPC)-type enzymes are emerging resistance determinants, especially for K. pneumoniae [36–38]. During the last decade, a rapidly evolving spread of KPC and β-lactamases has been documented worldwide, creating an endemic situation in many countries. KPC-associated infections are predominantly nosocomial and systemic infections, affecting patients with multiple risk factors [38,39]. Therapeutic failures and adverse impact on patient outcome, with high mortality rates ranging from 22% to 57%, have been reported [36].

Non-fermentative Gram-negative infections: a threat for critical patients

Multidrug-resistant non-fermentative organisms are a major concern in healthcare facilities worldwide. In more than 300 US hospitals surveyed by the Centers for Disease Control (CDC), rates of carbapenem resistance in Actinobacter baumannii isolates increased from 9% in 1995 to 40% in 2004 [40]. A. baumannii infections, mainly ventilator-associated pneumonia (VAP) and bloodstream infections, frequently affect critically ill patients in ICUs with major risk factors, including older age, presence of severe underlying diseases, immunosuppression, major trauma or burn injuries, a scheduled invasive procedure, as well as the presence of indwelling catheters, invasive mechanical ventilation, ...

Table of contents

• Cover
• Title page
• Copyright page
• List of Contributors
• Foreword
• Preface
• PART I: Infections and Host Response
• PART II: Radiological Imaging
• PART III: Nuclear Medicine Imaging
• Index