Factors that enhance the likelihood of successful stereotactic treatment of brain abscesses

Computed tomography-guided stereotactic surgery in the management of brain lesions: A single-center experience

Background

The present study presents our experience with computed tomography (CT)-guided stereotactic surgery in managing deep-seated brain lesions and provides a background in the expanding fields of morphological stereotactic neurosurgery.

Methods

We conducted this retrospective cohort study on 80 patients managed at the Department of Neurosurgery, Zagazig University Hospitals, Zagazig, Egypt, between January 2019 to January 2021. We targeted patients with morphological stereotactic surgeries performed as the primary management modality of their treatment.

Results

A total of 80 patients, with a mean age of 44.3 years, were included in the study. The stereotactic targets were supratentorial in 71 patients (88.75%), infratentorial in seven patients (8.75%), and both supraand infratentorial in two patients (2.5%). The lesions showed enhancements with IV contrast in 55 patients (68.75%). Stereotactic procedures were performed under local anesthesia in 64 patients and general anesthesia in 16 patients. Of the 80 stereotactic procedures, 52 were biopsies (65%). We observed a significant improvement in the postoperative Karnofsky performance score compared to the postoperative score (63.4 ± 19.8 vs. 56.7 ± 15.4, P = 0.001). The level of agreement between clinical, radiological, and final pathological diagnosis was assessed; it was complete in 47.5% of the patients. The postprocedural CT scan demonstrated intracranial hemorrhage in five patients (6.25%); four (5%) were silent with no neurological complications.

Conclusion

This study provided evidence that the stereotactic procedure is easy to perform, accurate in targeting the lesion, and spares patients from undergoing major surgical procedures. Stereotactic applications of spontaneous intracerebral hemorrhage, deep-seated abscesses, encysted tumors, or medically refractory benign intracranial hypertension can improve the outcome even in medically high-risk patients.

Retrospective Review of the Clinical Outcomes of Surgically Managed Patients with Intracranial Abscesses: A Single-Center Review

OBJECTIVE

This study analyzed patient, radiologic, and clinical factors associated with operative brain abscesses and patients' functional outcomes.

METHODS

A retrospective analysis was conducted of neurosurgical cases of brain abscesses from 2009 to 2019 at a Canadian center. Functional outcome was recorded as Modified Rankin Scale score and Extended Glasgow Outcome Scale score. Multivariate analysis was conducted to identify relevant prognostic factors.

RESULTS

We identified 139 patients managed surgically for brain abscesses. Resection alone was performed in 64% of patients, whereas 26.6% underwent aspiration alone. Most were adults (93.2%) and male (68.3%). Immunocompromise risk factors included diabetes (24.5%), cancer (23.7%), and immunosuppressive therapy (11.5%). Likely sources were postoperative (17.3%), systemic spread (16.5%), and poor dentition (12.9%). Microorganisms cultured from abscess samples were mixed growth (28%), Streptococcus anginosus (24.5%), and Staphylococcus aureus (7.9%). Disposition was home (42.4%) or repatriation to a home hospital (50.4%). By Extended Glasgow Outcome Scale, 25.2% had an unfavorable outcome including a mortality of 11.5%. Factors on multivariate analysis associated with poor outcome included diabetes (odds ratio, 2.8; 95% confidence interval [CI], 1.2-5.0) and ventricular rupture (odds ratio, 5.0; 95% CI, 1.7-13.5; hazard ratio, 12; 95% CI, 3.9-37.0). Supratentorial superficial eloquently located abscess was also associated with poor outcome (hazard ratio, 5.5; 95% CI, 1.8-16.7). Outcomes were similar with surgical excision and aspiration.

CONCLUSIONS

Ventricular rupture and diabetes are significant risk factors for poor outcomes in intraparenchymal brain abscesses. No clear difference in outcomes was found between surgical excision or aspiration in our retrospective cohort.

Predictors of reoperation and noninfectious complications following craniotomy for cerebral abscess

OBJECTIVES

There is a paucity of literature that examines predictors of reoperation and noninfectious complications following treatment of cerebral abscess with craniotomy. The goal of the present study is to identify predictors for each of these outcomes.

PATIENTS AND METHODS

The American College of Surgeons National Surgical Quality Improvement Program (NSQIP) database 2012-2016 file was the data source. Patients were identified using a combination of CPT and ICD-9/10 codes. Exclusions included missing age/gender, secondary surgery, and absent length of stay information. Univariate followed by multivariable analysis using logistic regression was used to identify significant predictors of reoperation and noninfectious postoperative complications (p < 0.05).

RESULTS

166 patients met the above criteria. Median age was 56 (IQR 44-65) and 68.1% of patients were men. The 30-day reoperation rate was 18.1% and increasing white blood cell count (WBC) was identified as a significant risk factor for reoperation (odds ratio [OR] 1.10, 95% CI 1.02-1.19, p = 0.013). Noninfectious complications occurred at a rate of 20.5% at 30 days. Significant predictors were ASA classification ≥4 (OR 4.13, 95% CI 1.74-9.81, p = 0.001), smoking (OR 3.04, 95% CI 1.18-7.78, p = 0.020), and increasing WBC count (OR 1.11, 95% CI 1.03-1.20, p = 0.007). Emergency case status, abscess location (supratentorial versus infratentorial), nor chronic steroid use demonstrated a significant relationship with the studied outcomes.

CONCLUSION

Increasing preoperative WBC count predicts both reoperation and noninfectious complications following craniotomy for cerebral abscess. Less modifiable predictors for noninfectious complications which may help anticipate operative risk are smoking and high ASA classification.

Management of brain abscesses: where are we now?

INTRODUCTION

Brain abscesses affect all age groups and are not peculiar to a particular country, race, or geographical location. It is a disease that, in the past, carried a high morbidity and mortality. With improvements in medical technology and expertise, outcomes have improved tremendously. The causative organisms vary vastly and have evolved with time. Treatment of brain abscesses is primarily with antimicrobial therapy but surgery plays a vital role in achieving better outcomes.

CONTENT

In this article, we review the literature to find out how the epidemiology of this disease has changed through the years and re-visit the basic pathological process of abscess evolution and highlight the new research in the biochemical pathways that initiate and regulate this process. We also highlight how magnetic resonance imaging and its various modalities have improved diagnostic accuracy. Finally, we discuss the pros and cons of traditional open surgery versus newer minimally invasive methods.

Forgotten? Not Yet. Cardiogenic Brain Abscess in Children: A Case Series-Based Review

BACKGROUND

Brain abscess is a significant cause of morbidity in patients with uncorrected or partially palliated congenital cyanotic heart disease (CCHD). Unfortunately, in the developing world, the majority of patients with CCHD remain either uncorrected or only partially palliated. Furthermore, a risk of this feared complication also exists even among those undergoing staged corrective operations in the interval in between operations. There have been no recent articles in the literature on the outcomes of surgical management of cardiogenic brain abscess in children. In this study, we aimed to describe the clinical and demographic profile of patients with cardiogenic cerebral abscess and to highlight the fact that uncorrected or palliated CCHD continue to be at risk for brain abscess.

METHODS

This study was a retrospective analysis of 26 children (age <19 years) being managed for CCHD who were diagnosed with cerebral abscess managed surgically (26 of 39 of cases cerebral abscess in children), at Amrita Institute of Medical Sciences and Research Centre, Kochi, India between December 2000 and January 2014. Data collected retrospectively included demographic information, modes of presentation, diagnosis, location of abscess, details of the underlying heart disease, management of the cerebral abscess, and outcomes of management.

RESULTS

The patient cohort comprised 26 patients (16 males and 10 females), with a mean age of 7.19 years (range, 1.5-19 years). Ten of the 26 patients (38%) required reaspiration after the initial surgery. On follow-up, all the patients had improved symptomatically and demonstrated no signs of cerebral abscess.

CONCLUSIONS

Cardiogenic origin of cerebral abscess is the most common cause of cerebral abscess in children. Unresolved CCHD is a risk factor for the occurrence, persistence, and recurrence of cerebral abscess.

Preoperative C-reactive protein predicts the need for repeated intracerebral brain abscess drainage

BACKGROUND

To determine predicting factors for repeated surgical drainage in patients with intracerebral brain abscesses.

METHODS

Patients operated between 01/2008 and 10/2013 with a single-burr-hole technique to drain an intracerebral brain abscess were included from our prospective database. Clinical and radiological characteristics were analyzed retrospectively and compared between patients requiring a single surgical abscess drainage (S group) vs. patients requiring multiple surgical abscess aspirations (M group).

RESULTS

Thirty-five patients (mean age 42.6 years, 14 females) including 27 patients in the S group and 8 in the M group were included in this study. Age, gender, causing bacterial agent, surgical technique and abscess volume were comparable for both groups. Preoperative mean C-reactive protein (CRP) (13.9 mg/l vs. 56.1 mg/l, p=0.015) was significantly higher in the M group. Preoperative mean leukocyte count (12.3×10(9)/l vs. 8.9×10(9)/l, p=0.050) was borderline significantly higher in the M group. Although the origin in the overall population was cryptogenic in 43% of the cases, this was never the case in the patient population needing multiple surgeries.

DISCUSSION

Patients with multiple intracerebral brain abscess aspirations showed significantly higher preoperative CRP values than patients who needed surgery only once. Patients with high CRP values at admission and obvious origin of infection might need closer radiographic as well as clinical and laboratory exams after surgery to earlier select patients, which need repeated surgery.

Citrobacter brain abscesses in neonates: early surgical intervention and review of the literature

PURPOSE

Citrobacter koseri, a facultatively anaerobic, lactose-fermenting, gram-negative bacilli, has a strong propensity to form cerebral abscesses. C. koseri brain abscesses can be a devastating disease of infancy and childhood with more than 30% succumbing to the disease and more than 50% suffering severe neurological deficits.

METHODS

This study represents a retrospective review of two cases of C. koseri brain abscesses along with a review of the literature regarding diagnosis and treatment.

RESULTS

Early aggressive surgical and medical treatment resulted in favorable outcomes for two children with C. koseri brain abscesses, one diagnosed at 6 weeks of age and the other at 2 months of age.

CONCLUSION

C. koseri brain abscesses can be devastating and have been associated historically with significant morbidity and mortality. However, favorable outcomes are possible, and aggressive surgical and medical management should be considered for patients with C. koseri abscesses.

Brain abscess: an overview

Intracranial abscess is a formidable entity. Despite the advent of newer antibiotics and surgical strategies, the overall outcome and quality of life issues in brain abscess patients still remain a continuous challenge for the neurosurgical community. It is a direct interplay between the virulence of the offending microorganism and the immune response of the host. An analysis of our experience in the 289 cases of surgically treated pyogenic brain abscess is presented along with an overview of intra-cranial abscess of varied etiology and in different locations. The etiology, pathogenesis, radiological advances and treatment modalities of brain abscess are discussed in light of current literature.

Consensus document on controversial issues for the treatment of infections of the central nervous system: bacterial brain abscesses

BACKGROUND

Bacterial brain abscesses remain a serious central nervous system problem despite advances in neurosurgical, neuroimaging, and microbiological techniques and the availability of new antibiotics. The successful treatment of brain abscesses requires surgery, appropriate antibiotic therapy, and eradication of the primary source; nevertheless many controversial issues on the management of this serious infection remain unresolved.

CONTROVERSIAL ISSUES

The aim of this GISIG (Gruppo Italiano di Studio sulle Infezioni Gravi) working group - a panel of multidisciplinary experts - was to define recommendations for some controversial issues using an evidence-based and analytical approach. The controversial issues were: (1) Which patients with bacterial brain abscesses can be managed safely using medical treatment alone? (1a) What is the efficacy in terms of outcome, tolerability, cost/efficacy, and quality of life of the different antibiotic regimens used to treat bacterial cerebral abscesses? (1b) Which antibiotics have the best pharmacokinetics and/or tissue penetration of brain and/or brain abscess? 2) What is the best surgical approach in terms of outcome in managing bacterial brain abscesses? Results are presented and discussed in detail.

METHODS

A systematic literature search using the MEDLINE database for the period 1988 to 2008 of randomized controlled trials and/or non-randomized studies was performed. A matrix was created to extract evidence from original studies using the CONSORT method to evaluate randomized clinical trials and the Newcastle-Ottawa Quality Assessment Scale for case-control studies, longitudinal cohorts, and retrospective studies. The GRADE method for grading quality of evidence and strength of recommendation was applied.

Transethmoidal drainage of frontal brain abscesses

BACKGROUND

The frontal lobe is the second most common location for brain abscess after the temporal lobe. Since the advent of computed tomography and magnetic resonance imaging scanning, diagnosis has become easier, but the prognosis of brain abscess is still poor. Treatment is based on antimicrobial therapy and neurosurgical evacuation, but controversy still remains as to the merits place of each.

METHODS

This study describes 2 cases of patients with frontal abscesses treated by endonasal transethmoidal sinus surgery (ESS) and reviews the literature on this topic.

RESULTS

Follow-up revealed no cerebrospinal fluid leak in both patients, complete abscess drainage in one patient, and incomplete drainage in the other.

CONCLUSIONS

ESS drainage of frontal abscesses is feasible in intracerebral and epidural abscesses if they have a thick shell and are in contact with the skull base. The procedure is minimally invasive and relatively simple. It allows for rapid microbial identification and an effective drainage.

Efficacy of stereotactic aspiration in deep-seated and eloquent-region intracranial pyogenic abscesses

Object

Intracranial abscesses located deep in the cerebral parenchyma and in eloquent regions are often difficult to manage surgically. The authors have attempted to analyze the efficacy of stereotactic aspiration in the management of these abscesses.

Methods

Cases involving 22 patients (including 9 children) with deep-seated and/or eloquent-region intracranial abscesses who underwent CT- or MR imaging–guided stereotactic aspiration between January 1995 and July 2001 were analyzed.

Results

A definite source of infection could be identified only in 9 of the cases. In 18 patients, the abscess was deep seated, whereas in the rest it was located in the eloquent cortex. Five patients had abscesses located in multiple sites. In 17 patients only 1 aspiration was required; in 5 others subsequent procedures were required. In the initial postaspiration CT, minor hemorrhage was noted in 3 patients not requiring further intervention. Antibiotics were administered for a period varying from 4 to 8 weeks following aspiration. An early recurrence (within 2 weeks of initial aspiration) was evident in 5 patients. All recurrent abscesses were reaspirated. In 2 patients new abscesses developed while the patients were still receiving antibiotic therapy. There were no late recurrences. In 1 patient ventriculitis developed, with subsequent hydrocephalus requiring a shunt insertion. Follow-up CT scans showed complete resolution of the abscess in all patients. There were no deaths.

Conclusions

Stereotactic aspiration is a useful management option for abscesses located in eloquent or inaccessible regions. Repeated aspiration should be considered in patients in whom the initial aspiration proves ineffective or partially effective. Complete resolution may require repeated stereotactic aspirations and continued antibiotic therapy.

Pyogenic brain abscess

✓ Brain abscesses have been one of the most challenging lesions, both for surgeons and internists. From the beginning of the computed tomography (CT) era, the diagnosis and treatment of these entities have become easier and less invasive. The outcomes have become better with the improvement of diagnostic techniques, neurosurgery, and broad-spectrum antibiotics. Atypical bacterial abscesses are more often due to chemotherapy usage in oncology, long life expectancy in patients with human immunodeficiency virus (HIV) infection, and immunosuppression in conjunction with organ transplantation. Surgical treatment options showed no significant difference with respect to mortality levels, but lower morbidity rates were achieved with stereotactically guided aspiration. Decompression with stereotactically guided aspiration, antibiotic therapy based on results of pus culture, and repeated aspirations if indicated from results of periodic CT follow-up scans seem to be the most appropriate treatment modality for brain abscesses. Immunosuppression and comorbidities, initial neurological status, and intraventricular rupture were significant factors influencing the outcomes of patients. The pitfalls and evolution in the diagnosis and treatment of brain abscesses are discussed in this study.

Management of brain abscess: an overview

✓ Recent advances in neuroimaging have resulted in a marked decrease in morbidity and death due to brain abscesses. The advent of computed tomography–guided stereotaxy has reduced morbidity in patients with deep-seated abscesses. Empirical therapy is best avoided in the present era, particularly given the availability of stereotactic techniques for aspiration and confirmation of diagnosis. Despite these advances, management of abscesses in patients with cyanotic heart disease and in immunosuppressed patients remains a formidable challenge. Unusual as well as more recently recognized pathogens are being isolated from abscesses in immunosuppressed patients. The authors provide an overview of the management of brain abscesses, highlighting their experience in managing these lesions in patients with cyanotic heart disease, stereotactic management of brain abscesses, and management of abscesses in immunosuppressed patients.

Strategies for the management of bacterial brain abscess

We reviewed the medical and surgical management of brain abscess and compared the results of different methods of treatment. Treatment of brain abscess requires a combination of antimicrobial agents, surgical intervention, and eradication of the primary foci of infection. We believe that pathologic confirmation and/or microbiologic studies are needed to ensure proper management, with the selection of antibiotics based on the available culture and susceptibility results. A 6- to 8-week course of parenteral antibiotics, plus regular follow-up computed tomography scans for at least 3 months to evaluate the therapeutic response is also recommended. The method of surgical treatment is of lesser importance than adherence to the basic principles of abscess management, and which surgical treatment is chosen depends on the patient's clinical status, the neuroradiographic characteristics of the abscess, and the experience of the surgeons who will be carrying out the procedure.

Gemella morbillorum deep brain abscess successfully treated with combined stereotactic, medical, and imaging approach

A rare case of brain abscess due to Gemella morbillorum, a normal inhabitant of the oral cavity, is presented. The aim of this report is to draw the attention of radiology literature readers to this little known pathogen, which caused a potentially life-threatening condition in an immunocompetent young man, and to emphasise the usefulness of a combined stereotactic, medical, and imaging approach to deep-located brain abscesses.

[Intracranial purulent collections. Review of 34 surgically treated cases in 12 years (1989-2000)]

We made a revision of 34 cases of intracerebral supurations (31 brain abscesses and 3 subdural empyemas) treated at our department of neurosurgery of "Mutua de Terrassa" during the period of 1989-2000. Treatment used was tapping of the abscess and aspiration in 28 cases and craneotomy and resection in only two cases. Three subdural empyemas were treated with burr-holes and aspiration. Results were evaluated using the Glasgow Outcome Scale at 6 months after discharge, resulting in 7 deaths (20.6%), 17 fully recovered patients (50%) and 10 with minor deficits (29.4%). Glasgow Coma Score at admission and the age were the unique variables significantly correlated with the final outcome. After analyzing the cost of treatment in our patients we suggest using antibiotic ambulatory treatment when the disease shows an adequate clinical and radiological response, thus permitting to shorten the usually long period of hospitalization of patients with intracerebral supurative diseases.

Interactive magnetic resonance imaging-guided management of intracranial cystic lesions by using an open magnetic resonance imaging system

OBJECT

The authors present their experience with neurosurgical procedures requiring real-time imaging feedback such as aspiration of a cystic structure or abscess cavity, decompression of hydrocephalic ventricles, management of arachnoid cysts, and installation of permanent or temporary drainage conduits, in which interactive magnetic resonance (MR) imaging guidance was used to monitor structural alterations associated with the procedure.

METHODS

Drainage of eight intraparenchymal brain abscesses in seven patients, decompression of space-occupying cystic or necrotic brain tumors in four patients, and endoscopic management of hydrocephalus associated with arachnoid cysts in three patients were performed using MR imaging-guided frameless stereotaxy in an open-configuration 0.5-tesla superconducting MR imaging system. Intraoperative MR imaging guidance provided accurate information on the course of the surgical procedure and associated intraoperative changes in tissue position, such as the degree of cyst aspiration, the presence or absence of hemorrhage or induced swelling, and changes associated with decompression of adjacent brain parenchyma and the ventricular system. No clinically significant complications were encountered in any patient. There were no targeting errors, and procedural objectives were accomplished in all cases.

CONCLUSIONS

Drainage of brain abscesses, punctures of cystic or necrotic intracranial lesions with subsequent aspiration, and management of hydrocephalus can be performed safely and accurately by monitoring the procedure using real-time MR imaging to obtain immediate feedback on associated dynamic tissue changes.

Ultrasound-based navigation during intracranial burr hole procedures: experience in a series of 100 cases

BACKGROUND

To establish a rational basis for intraoperative ultrasound guidance in neurosurgical procedures via a single burr hole approach based on the experience of one hundred cases.

METHODS

The single burr hole approach is carried out using a bayonet-shaped ultrasound transducer with a tip dimension of 8 x 8 mm. The ultrasound probe with a mounted puncture adapter fits a standard burr hole and allows real-time imaging of the ongoing surgical steps.

RESULTS

One hundred cases with five indications have been operated on so far: tapping of the ventricular system (46 patients), tapping of intracranial cysts (23 patients), biopsy of intracranial tumors (15 patients), evacuation of intracranial abscesses (9 patients), and evacuation of intracerebral hematomas (7 patients). Depending on their size, the ventricles could be clearly visualized in 34 of 46 patients. In the remaining patients the free margin of the falx served as orientation. Two ventricles could neither be visualized nor entered. Visualization and puncture of intracranial cysts were easy to achieve throughout, as was the case with abscesses. Tumor biopsy was unsuccessful in two patients harboring lymphomas at distances of more than 50 mm from probe to target. Intracerebral hematomas were easily visualized but, due to the presence of clots, aspiration was impossible in two patients. One patient with a giant glioblastoma died the day after the uneventful biopsy due to increased cerebral edema. No other complications occurred.

CONCLUSIONS

The presented method of ultrasound-based neuronavigation is an easy-to-use, fast, and safe technique of real-time imaging for free-hand single burr hole procedures.

Stereotactic surgery in the management of brain abscess

BACKGROUND

Bacterial brain abscesses can be diagnosed and treated with stereotactic aspiration.

METHODS

From 1991 to 1997 we have used computed tomography-guided stereotactic aspiration to diagnose and treat 21 patients with a total of 58 bacterial brain abscesses. The ages of the patients ranged from 4 to 72 years (median 25 years); 11 of these 21 patients had multiple abscesses. The number of abscesses per patient with multiple abscesses ranged from 2 to 9, all located deep in subcortical white matter.

RESULTS

All patients underwent stereotactic surgical drainage and an 8-week intravenous antibiotic medical treatment. Of the 58 abscesses, 23 were aspirated. Of these 23 abscesses, 19 were radiologically stage III or IV and four were stage I or II. Pathological examination confirmed radiological staging in 19 patients (83%). Except for the three patients who have mild residual hemiparesis and one patient recovering from ataxia, all patients had complete neurological recovery.

CONCLUSIONS

Computed tomography-guided stereotaxy achieved all the objectives of management; namely, ascertaining the diagnosis, draining the content of the mass, and obtaining pus for accurate bacteriological diagnosis without morbidity. Stereotactic aspiration combined with an 8-week intravenous antibiotic regimen has yielded an effective therapeutic result in all of our abscesses, small or large, solitary or multiple, superficial or deep-seated. A high radiological-pathological correlation was also deduced from this study.

[Intracranial abscess and empyema: neurosurgical management]

Brain abscesses and empyemas are severe infections with lethal outcomes in the case of inappropriate treatment. The files of 34 patients with brain abscesses, and nine with intracranial empyemas treated over eight years (1990-1997) were analyzed retrospectively. Cases were evaluated for treatment and compared with data from the literature. Patients with brain abscess underwent either aspiration of the lesion through a burr hole (79.5% of the cases), or craniotomy and excision (8.8% of the cases); 11.7% were treated only with antibiotics. The operative mortality was 2.9% and the outcome was satisfactory in 85% of patients. These results are in agreement with data from the literature. Prognosis is strongly related to the initial clinical status. Current methods of treatment include surgical aspiration of large abscesses with a mass effect, and are usually associated with a poor clinical status. Excision is suggested whenever aspiration procedures have failed, or in the presence of foreign material or fungal abscess. Medical treatment is indicated for small and deeply located abscesses in patients with satisfactory clinical states. Empyemas in our series were treated with burr hole and pus aspiration. The mortality rate was 11%, and 62.5% of the patients made a good recovery. In agreement with other reported studies, the method of treating subdural empyema is much less significant than an aggressive early drainage of the infection. Although brain abscesses and empyema remain a significant neurosurgical concern, aggressive treatment can result in an excellent outcome in the majority of patients.

Infections of the nervous system

Epidemiologic trends causing infections of the nervous system remain a significant source of morbidity and mortality one half-century after the introduction of penicillin. This article outlines common causes of bacterial meningitis, aseptic meningitis syndrome, encephalitis, abscess, spinal cord syndromes, and cranial and peripheral nerve problems. Recommendations for diagnostic evaluation and both empiric and definitive antimicrobial therapy are offered; controversial management issues are also discussed. The protean manifestations of varicella-zoster virus and Lyme diseases are outlined. In addition, special considerations in the immunocompromised host, including organ transplant recipients, cancer patients, and HIV-positive persons are explained, and antimicrobial therapy is discussed.