Bacterial Infections of the Central Nervous System in Neurosurgery

Management of infections associated with neurocritical care

The reported incidence of hospital-acquired infections (HAIs) in the neurointensive care unit (NICU) ranges from 20% to 30%. HAIs in US hospitals cost between $28 and $45 billion per year in direct medical costs. These infections are associated with increased length of hospital stay and increased morbidity and mortality. Infection risk is increased in NICU patients due to medication side-effects, catheter and line placement, neurosurgical procedures, and acquired immune suppression secondary to steroid/barbiturate use and brain injury itself. Some of these infections may be preventable but many are not. Their appearance do not always constitute a failure of prevention or physician error. Neurointensivists require indepth knowledge of common nosocomial infections, their diagnosis and treatment, and an approach to evidence-based practices that improve processes of care and reduce HAIs.

Central Nervous System Infections in the Critically Ill

Central nervous system (CNS) infections are frequently encountered in the intensive care unit setting and are a significant source of morbidity and mortality. The constantly changing trends in microbial resistance, as well as the pharmacokinetic difficulties in providing effective concentrations of antimicrobials at the site of infection represent a unique challenge to clinicians. Achievement of a successful outcome in patientswith CNS infections is reliant on eradication of the offending pathogen and management of any neurologic complications. This requires an anatomic and physiologic understanding of the different types of CNS infection, diagnostic strategies, associated complications, causative organisms, and the principles that govern drug distribution into the CNS. This article serves as a review of the epidemiology, pathophysiology, diagnosis, and treatment options for a variety of CNS infections, with a focus on those commonly encountered in an intensive care setting.

Toll-like receptors in health and disease in the brain: mechanisms and therapeutic potential

The discovery of mammalian TLRs (Toll-like receptors), first identified in 1997 based on their homology with Drosophila Toll, greatly altered our understanding of how the innate immune system recognizes and responds to diverse microbial pathogens. TLRs are evolutionarily conserved type I transmembrane proteins expressed in both immune and non-immune cells, and are typified by N-terminal leucine-rich repeats and a highly conserved C-terminal domain termed the TIR [Toll/interleukin (IL)-1 receptor] domain. Upon stimulation with their cognate ligands, TLR signalling elicits the production of cytokines, enzymes and other inflammatory mediators that can have an impact on several aspects of CNS (central nervous system) homoeostasis and pathology. For example, TLR signalling plays a crucial role in initiating host defence responses during CNS microbial infection. Furthermore, TLRs are targets for many adjuvants which help shape pathogen-specific adaptive immune responses in addition to triggering innate immunity. Our knowledge of TLR expression and function in the CNS has greatly expanded over the last decade, with new data revealing that TLRs also have an impact on non-infectious CNS diseases/injury. In particular, TLRs recognize a number of endogenous molecules liberated from damaged tissues and, as such, influence inflammatory responses during tissue injury and autoimmunity. In addition, recent studies have implicated TLR involvement during neurogenesis, and learning and memory in the absence of any underlying infectious aetiology. Owing to their presence and immune-regulatory role within the brain, TLRs represent an attractive therapeutic target for numerous CNS disorders and infectious diseases. However, it is clear that TLRs can exert either beneficial or detrimental effects in the CNS, which probably depend on the context of tissue homoeostasis or pathology. Therefore any potential therapeutic manipulation of TLRs will require an understanding of the signals governing specific CNS disorders to achieve tailored therapy.

MyD88 expression by CNS-resident cells is pivotal for eliciting protective immunity in brain abscesses

MyD88 KO (knockout) mice are exquisitely sensitive to CNS (central nervous system) infection with Staphylococcus aureus, a common aetiological agent of brain abscess, exhibiting global defects in innate immunity and exacerbated tissue damage. However, since brain abscesses are typified by the involvement of both activated CNS-resident and infiltrating immune cells, in our previous studies it has been impossible to determine the relative contribution of MyD88-dependent signalling in the CNS compared with the peripheral immune cell compartments. In the present study we addressed this by examining the course of S. aureus infection in MyD88 bone marrow chimaera mice. Interestingly, chimaeras where MyD88 was present in the CNS, but not bone marrow-derived cells, mounted pro-inflammatory mediator expression profiles and neutrophil recruitment equivalent to or exceeding that detected in WT (wild-type) mice. These results implicate CNS MyD88 as essential in eliciting the initial wave of inflammation during the acute response to parenchymal infection. Microarray analysis of infected MyD88 KO compared with WT mice revealed a preponderance of differentially regulated genes involved in apoptotic pathways, suggesting that the extensive tissue damage characteristic of brain abscesses from MyD88 KO mice could result from dysregulated apoptosis. Collectively, the findings of the present study highlight a novel mechanism for CNS-resident cells in initiating a protective innate immune response in the infected brain and, in the absence of MyD88 in this compartment, immunity is compromised.

Toll-like receptors in brain abscess

Brain abscesses arise from a localized parenchymal infection, typically elicited by pyogenic bacteria such as Staphylococcus aureus. Despite improvements in detection and treatment strategies, brain abscesses continue to occur, with an increased prevalence in developing countries and immune-compromised patients. Adding to the seriousness of these infections is the recent emergence of antibiotic-resistant strains of bacteria, which are becoming more commonly associated with brain abscesses. Recent studies using a mouse experimental brain abscess model have revealed a complex role for Toll-like receptors (TLRs) in disease pathogenesis. Interestingly, TLR2 has limited impact on the innate immune response during the acute stage of brain abscess formation induced by S. aureus but influences adaptive immunity. In contrast, mice deficient in MyD88, a central adapter molecule for the majority of TLRs in addition to the IL-1R and IL-18R, demonstrate severe defects in innate immunity coupled with exaggerated tissue destruction. It is envisioned that understanding the roles for TLRs in both resident CNS glia as well as infiltrating immune cells will provide insights into how the immune response to bacterial infection can be tailored to achieve effective pathogen destruction without inducing excessive bystander damage of surrounding noninfected brain parenchyma. A discussion of recent findings in this field is presented along with outstanding questions and the concept of a pathogen-necrosis-autoantigen triad for the amplification of TLR signaling is introduced.

Update in the diagnosis and management of central nervous system infections

Central nervous system (CNS) infections presenting to the emergency room include meningitis, encephalitis, brain and spinal epidural abscess, subdural empyema, and ventriculitis. These conditions often require admission to an intensive care unit (ICU) and are complications of ICU patients with neurologic injury, contributing significantly to morbidity and mortality. Reducing morbidity and mortality is critically dependent on rapid diagnosis and, perhaps more importantly, on the timely initiation of appropriate antimicrobial therapy. New insights into the role of inflammation and the immune response in CNS infections have contributed to development of new diagnostic strategies using markers of inflammation, and to the study of agents with focused immunomodulatory activity, which may lead to further adjunctive therapy in human disease.

Nosocomial bacterial meningitis in adults: a prospective series of 50 cases

In order to evaluate characteristics of nosocomial meningitis in adults, we performed a prospective cohort study of 50 episodes of nosocomial bacterial meningitis. These cases were confirmed by culture of cerebrospinal fluid (CSF) in patients aged >16 years. Classic symptoms of bacterial meningitis (headache, neck stiffness and fever) were present in >70% of the episodes, although only a minority (41%) presented with impairment of consciousness. Underlying conditions, such as a history of neurosurgery, recent head injury, CSF leakage or a distant focus of infection, were present in 94% of the episodes. Staphylococcus aureus was the most common pathogen in patients with a history of neurosurgery, causing 10 of 32 episodes (31%). Patients with a distant focus of infection, such as otitis, sinusitis or pneumonia were more likely to have meningitis due to Streptococcus pneumoniae than patients without [six of nine episodes (67%) vs seven of 41 (17%); P=0.01]. Complications occurred in 50% of the episodes and 16% of the patients died. Our study confirms that adults with nosocomial meningitis are a distinct patient group with specific bacterial pathogens, as compared to those with community-acquired bacterial meningitis. Underlying conditions, especially a history of neurosurgery or a distant focus of infection, were present in the large majority of patients, and mortality and morbidity rates were high.

Advances in the management of central nervous system infections in the ICU

This chapter focuses on early aggressive management of common infections of the central nervous system that require monitoring in an ICU setting. These include meningitis, encephalitis, brain and epidural abscess, subdural empyema and ventriculitis. It emphasizes priorities in evaluation and management due to increasing morbidity and mortality as a result of failure to appreciate non-specific symptoms or administer timely therapy. The emergence of organisms resistant to penicillin and cephalosporins has also further complicated the early management of bacterial meningitis. Current antimicrobial guidelines are provided along with discussion of new diagnostic and therapeutic strategies and controversial aspects of management.

La méningite post-traumatique : incidence, microbiologie et pronostic

BACKGROUND AND PURPOSE

The aim of our study was to search for the incidence, the responsible organisms and the favoring causes of death of post-traumatic meningitis (PTM).

METHODS

This retrospective study was conducted over a seven-year period (January 1st, 1996 - December 31, 2002) in the ICU and the neurosurgery department of the Habib-Bourguiba University Hospital, Sfax, Tunisia.

RESULTS

Over the study period, 38 patients presented PTM (0.96% of patients hospitalized for head injury), 92% of them had received antibiotic prophylaxis on admission. Mean time between head injury and the diagnosis of PTM was 9+/- 8 days (range: 2-34 days). The most common isolated organisms were multidrug resistant A. baumanii, and K. pneumoniae and reduced susceptibility S. pneumoniae. Factors predictive of prognosis in the 14 days following the diagnosis of meningitis were Glasgow coma score (GCS) on the day of diagnosis of PTM, absence of nuchal rigidity, CSF protein, CSF/blood glucose ratio, and S. pneumoniae as the causal agent of PTM.

CONCLUSIONS

Antibioprophylaxis in patients with head trauma must be avoided to prevent the emergence of multidrug resistant bacteria when PTM occurs. GCS on the day of diagnosis of PTM, CSF protein concentration, CSF/blood glucose ratio, and S. pneumoniae as the causal agent of PTM are predictive factors of mortality of patients with PTM.

Brain abscess: clinical aspects of 100 patients

OBJECTIVE

To verify if, in the last two decades, there have been any changes in epidemiological, clinical, diagnostic, therapeutic and prognostic aspects of patients with brain abscess.

METHOD

We studied retrospectively 100 patients discharged over a 17-year period from Ca' Foncello Regional Hospital, Treviso, Italy with a diagnosis of brain abscess.

RESULTS

Post-surgical abscesses were more frequent than those related to contiguous infections and the spectrum of etiologic agents was very heterogeneous. A cerebral neoplasm was the initial neuroradiological diagnosis in 13 patients; 72 patients underwent a neurosurgical procedure. A comatose state at presentation was associated with an unfavourable outcome.

CONCLUSION

With the exception of some epidemiological aspects, which varied from the literature, in spite of the improvements in diagnostic procedures and treatment, no significant changes occurred in the prognosis of patients with brain abscess.

[Postsurgical meningitis caused by Pseudomonas aeruginosa: study of 15 cases and review of the literature]

OBJECTIVE

Pseudomonas aeruginosa meningitis is a rare condition which is usually associated with pathology in the ORL field, neurosurgery or local neurologic manipulations. The characteristics, epidemiology, and course of this entity were determined.

METHODS

Fifteen episodes of nosocomial postsurgical Pseudomonas aeruginosa meningitis occurred between 1989 and 1996 were retrospectively analyzed.

RESULTS

A previous cranioencephalic trauma was recorded in 46.6% of patients. The portals of entry included: intraventricular catheter (IC) (12 cases), CSF fistula (2 cases), and craniotomy (1 case). In five occasions (41.6%) the microorganism was also recovered from the intraventricular catheter. Once culture results were available, therapy with active drugs against Pseudomonas was instituted and in 7 occasions was accompanied by the removal of IC. Eight patients eventually cured and two patients relapsed. The absence of cure was significantly associated with non-removal of the IC (p < 0.01). The infection resulted in death in 26.6% of patients.

CONCLUSIONS

Postsurgical Pseudomonas aeruginosa meningitis is an entity of growing relevance. It is associated with relevant morbi-mortality. Catheter removal is essential to obtain a favorable outcome.

Postoperative intracranial abscess--clinical aspects in the differential diagnosis to early recurrence of malignant glioma

Out of 2941 patients who received a clean, major craniotomy, 39 patients (1.3%) developed the complication of an intracranial deep infection, i.e. abscess or empyema. A total of 14 patients with a postoperative abscess were initially operated upon intracerebral malignant glioma (WHO III or IV) and could be compared to a matched group of patients with recurrent malignancy concerning clinical and radiological aspects. A statistically significant elevation of median values was seen for erythrocyte sedimentation rate (ESR), fibrinogen and body temperature in the study group. C-reactive protein (CRP) was not investigated in the control group and could not be compared, but it was elevated in all abscess patients when measured. CT-scan did not allow a safe differentiation between infection and recurrent glioma. Local signs like suppuration of the wound could be observed in 71% of patients with intracranial infection. Postoperative abscesses had been diagnosed in all cases within 3 months, whereas none of the early recurrences of intracerebral malignoma became symptomatic before 12 weeks after initial operation. Therefore, the course of time seems to be another important factor in this differential diagnosis.

Ceftizoxime versus vancomycin and gentamicin in neurosurgical prophylaxis: a randomized, prospective, blinded clinical study

In a prospective, randomized, blinded study, 826 patients undergoing clean neurosurgical procedures received single intravenous doses of ceftizoxime (2 g) (n = 422) or a combination of vancomycin (1 g) and gentamicin (80 mg) (n = 404) 1 hour before an incision was made. Patients with infected or contaminated wounds and those receiving shunts or other implants were excluded. Primary wound infections occurred within 30 days in five patients in each group and were most common after spinal surgery and procedures through previous incisions. Secondary infections (pneumonias, urinary tract infections, and intravenous line-related bacteremia) occurred in 24 patients in the ceftizoxime group and 25 in the vancomycin/gentamicin group. The infection rates after transsphenoidal procedures (n = 129) were remarkably low in both groups. Ceftizoxime caused no adverse drug reactions, but six patients in the vancomycin/gentamicin group had clinically significant infusion-related hypotension or flushing. Placement of a temporary external drain, use of an operating microscope, preoperative steroids, and diabetes were not associated with increased infection rates. Analysis of routinely encountered ventricular cerebrospinal fluid and simultaneously obtained peripheral blood showed low but detectable levels of all three antibiotics within 2 hours; only ceftizoxime, however, achieved cerebrospinal fluid levels sufficient to inhibit the staphylococcus and Gram-negative bacilli most often associated with postneurosurgical infections. We conclude that ceftizoxime is as effective as vancomycin and gentamicin in neurosurgical prophylaxis but is less toxic and penetrates cerebrospinal fluid better.

CSF pharmacokinetics of ceftazidime in neurosurgical patients with an external ventriculostomy

In 11 neurosurgical patients (seven women, four men, aged 22-73 years) undergoing external ventriculostomy, serum and cerebrospinal fluid (CSF) pharmacokinetics of ceftazidime (CAZ) administered as a chemoprophylactic agent were evaluated. Concentrations of CAZ in CSF correlated significantly (p less than 0.05) with serum concentrations and with leucocyte counts in CSF. Peak concentrations in CSF (range 0-25.5 mg/l) exceeded the MIC90 of Staphylococcus species in two and of Pseudomonas and Enterobacter species in five of 11 patients. The MIC90 values of the other relevant bacteria causing CNS infections in these patients were surpassed in nine of 11 patients.