Peter C. Iwen

Ceftriaxone-Resistant Salmonella Infection Acquired by a Child from Cattle

BACKGROUND The emergence of resistance to antimicrobial agents within the salmonellae is a worldwide problem that has been associated with the use of antibiotics in livestock. Resistance to ceftriaxone and the fluoroquinolones, which are used to treat invasive salmonella infections, is rare in the United States. We analyzed the molecular characteristics of a ceftriaxone-resistant strain of Salmonella enterica serotype typhimurium isolated from a 12-year-old boy with fever, abdominal pain, and diarrhea. METHODS We used pulsed-field gel electrophoresis and analysis of plasmids and beta-lactamases to compare the ceftriaxone-resistant S. enterica serotype typhimurium from the child with four isolates of this strain obtained from cattle during a local outbreak of salmonellosis. RESULTS The ceftriaxone-resistant isolate from the child was indistinguishable from one of the isolates from cattle, which was also resistant to ceftriaxone. Both ceftriaxone-resistant isolates were resistant to 13 antimicrobial agents; all but one of the resistance determinants were on a conjugative plasmid of 160 kb that encoded the functional group 1 beta-lactamase CMY-2. Both ceftriaxone-resistant isolates were closely related to the three other salmonella isolates obtained from cattle, all of which were susceptible to ceftriaxone. CONCLUSIONS This study provides additional evidence that antibiotic-resistant strains of salmonella in the United States evolve primarily in livestock. Resistance to ceftriaxone, the drug of choice for invasive salmonella disease, is a public health concern, especially with respect to children, since fluoroquinolones, which can also be used to treat this disease, are not approved for use in children.

Evaluation of Matrix-Assisted Laser Desorption Ionization-Time-of-Flight Mass Spectrometry in Comparison to 16S rRNA Gene Sequencing for Species Identification of Nonfermenting Bacteria

ABSTRACT Nonfermenting bacteria are ubiquitous environmental opportunists that cause infections in humans, especially compromised patients. Due to their limited biochemical reactivity and different morphotypes, misidentification by classical phenotypic means occurs frequently. Therefore, we evaluated the use of matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) for species identification. By using 248 nonfermenting culture collection strains composed of 37 genera most relevant to human infections, a reference database was established for MALDI-TOF MS-based species identification according to the manufacturers recommendations for microflex measurement and MALDI BioTyper software (Bruker Daltonik GmbH, Leipzig, Germany), i.e., by using a mass range of 2,000 to 20,000 Da and a new pattern-matching algorithm. To evaluate the database, 80 blind-coded clinical nonfermenting bacterial strains were analyzed. As a reference method for species designation, partial 16S rRNA gene sequencing was applied. By 16S rRNA gene sequencing, 57 of the 80 isolates produced a unique species identification (≥99% sequence similarity); 11 further isolates gave ambiguous results at this threshold and were rated as identified to the genus level only. Ten isolates were identified to the genus level (≥97% similarity); and two isolates had similarity values below this threshold, were counted as not identified, and were excluded from further analysis. MALDI-TOF MS identified 67 of the 78 isolates (85.9%) included, in agreement with the results of the reference method; 9 were misidentified and 2 were unidentified. The identities of 10 randomly selected strains were 100% correct when three different mass spectrometers and four different cultivation media were used. Thus, MALDI-TOF MS-based species identification of nonfermenting bacteria provided accurate and reproducible results within 10 min without any substantial costs for consumables.

Invasive Pulmonary Aspergillosis Due to Aspergillus terreus: 12-Year Experience and Review of the Literature

A 12-year retrospective analysis was done to identify and evaluate in detail cases of invasive pulmonary aspergillosis (IPA) caused by Aspergillus terreus. We identified 13 A. terreus infections among 133 total cases of confirmed invasive aspergillosis; 11 were IPA and 2 were primary peritoneal infections. Of the 11 patients with IPA, 7 developed neutropenia during hospitalization, and the remaining four were receiving immunosuppressive agents. Ten patients with IPA died; one liver transplantation patient without neutropenia survived after treatment with amphotericin B, itraconazole, and a pulmonary lobectomy. Six patients developed disseminated disease, with the heart the most common extrapulmonary site identified (four patients). These cases demonstrate that IPA caused by A. terreus rapidly progresses in immunocompromised patients receiving amphotericin B and illustrate the need for sensitive diagnostic tests and more effective antifungal agents.

Inactivation of Phospholipase D Diminishes Acinetobacter baumannii Pathogenesis

ABSTRACT Acinetobacter baumannii is an emerging bacterial pathogen of considerable health care concern. Nonetheless, relatively little is known about the organisms virulence factors or their regulatory networks. Septicemia and ventilator-associated pneumonia are two of the more severe forms of A. baumannii disease. To identify virulence factors that may contribute to these disease processes, genetically diverse A. baumannii clinical isolates were evaluated for the ability to proliferate in human serum. A transposon mutant library was created in a strain background that propagated well in serum and screened for members with decreased serum growth. The results revealed that disruption of A. baumannii phospholipase D (PLD) caused a reduction in the organisms ability to thrive in serum, a deficiency in epithelial cell invasion, and diminished pathogenesis in a murine model of pneumonia. Collectively, these results suggest that PLD is an A. baumannii virulence factor.

Invasive Mold Sinusitis: 17 Cases in Immunocompromised Patients and Review of the Literature

A 10-year retrospective analysis of invasive mold infections in hospitalized patients was performed to characterize the epidemiology and clinical features of invasive fungal sinusitis. Seventeen cases of invasive mold sinusitis were identified. Eleven cases were caused by Aspergillus flavus, three were caused by unspecified species, and one each was caused by Aspergillus fumigatus, Rhizopus species, and Alternaria species, respectively. Fifteen patients had hematologic malignancies, and two had end-stage liver disease. The most common presenting symptom was periorbital swelling (seven patients). Sinusitis was diagnosed a median of 19 days after admission. Eight patients (47%) survived; six of these patients were treated with both amphotericin B and surgery. Postmortem examination of six patients showed evidence of disseminated disease; the brain was the most common extrapulmonary site (four patients). To our knowledge, this is the largest currently reported series on invasive mold sinusitis; our report extends the information on invasive mold sinusitis and shows that aggressive therapeutic and surgical interventions are needed to prevent rapid progression of disease in immunocompromised patients.

Histoplasmosis in Solid Organ Transplant Recipients at a Large Midwestern University Transplant Center

Abstract: Histoplasma capsulatum sporadically causes severe infections in solid organ transplant (SOT) patients in the Midwest, but it has been an unusual infection among those patients followed at the University of Nebraska Medical Center (UNMC), located at the western edge of the ‘histo belt.’ Nine SOT patients with histoplasmosis are described (6 renal or renal‐pancreas and 3 liver recipients) who developed severe histoplasmosis over a recent 2.5‐year period at UNMC. Symptoms started a median of 11 months (range, 1.2–90 months) after organ transplant and consisted primarily of fever, cough, shortness of breath, and malaise or fatigue present for approximately 30 days prior to medical evaluation. All patients had an abnormal chest radiograph and/or computed tomographic scan. Tacrolimus was the main immunosuppressant in all 9 patients, along with prednisone or mycophenolate. Dacluzimab or thymoglobulin had been given around the time of transplant in 6 of 9. None was treated for an episode of acute rejection within 2 months before onset of histoplasmosis, although 2 were on high‐dose immunosuppression after recent transplants. Diagnosis was made by culture in 8 of the 9 patients, with positive serum and urine histoplasma antigen tests in all 9 cases. From 1997 to 2001, during a period of relative quiescence of the disease in the general population, the rate of clinical histoplasmosis among SOT patients at UNMC was estimated at 0.11%, whereas during 2002 through the first half of 2004, the rate rose 17‐fold to 1.9%. Histoplasmosis can present as a prolonged febrile illness with subacute pulmonary symptoms in a cohort of SOT patients, despite the absence of a regional outbreak.

Airborne fungal spore monitoring in a protective environment during hospital construction, and correlation with an outbreak of invasive aspergillosis.

OBJECTIVE Evaluate aerobiological monitoring for fungal spores during hospital construction and correlate results with an outbreak of invasive aspergillosis (IA). DESIGN Prospective air sampling for molds was done using the gravity air-settling plate (GASP) method. SETTING A university medical center special care unit consisting of single-patient rooms with high-efficiency particulate air filtration under positive pressure. PATIENTS Five neutropenic patients who subsequently developed IA. RESULTS Four of the five patients with IA were housed in rooms adjacent to a construction staging area. Aerobiological monitoring detected an increase in the number of airborne fungal spores including Aspergillus species in these rooms; however, increased counts preceded IA diagnosis by 1 to 7 days in only three of the five patients. Swab cultures of the exhaust vents within each room confirmed results from air-settling plates. Follow-up monitoring, using the GASP method, demonstrated that control procedures were effective in reducing air mold contamination. CONCLUSION The GASP method, although able to demonstrate that infection control measures reduced mold contamination of the air, was insensitive to detect levels of mold contaminates in time to prevent IA.

Outbreak of Bloodstream Infection Temporally Associated with the Use of an Intravascular Needleless Valve

BACKGROUND Needleless intravascular catheter connector valves have been introduced into clinical practice to minimize the risk of needlestick injury. However, infection-control risks associated with these valves may be underappreciated. In March 2005, a dramatic increase in bloodstream infections was noted in multiple patient care units of a hospital in temporal association with the introduction of a needleless valve into use. METHODS Surveillance for primary bloodstream infection was conducted using standard methods throughout the hospital. Blood culture contamination rates were monitored. Cultures were performed using samples obtained from intravascular catheter connector valves. RESULTS The relative risk of bloodstream infection for the time period in which the suspect connector valve was in use, compared with baseline, was 2.79 (95% confidence interval, 2.27-3.43). In critical care units, the rate of primary bloodstream infection increased with the introduction of the valve from 3.87 infections per 1000 catheter-days to 10.64 infections per 1000 catheter-days (P<.001), and it decreased to 5.59 infections per 1000 catheter-days (P=.02) in the 6 months following removal of the device from use. Similarly, in inpatient nursing units, the rate of bloodstream infection increased from 3.47 infections per 1000 catheter-days to 7.3 infections per 1000 catheter-days (P=.02) following introduction of the device, and it decreased to 2.88 infections per 1000 catheter-days (P=.57) following removal of the device from use. Similar events occurred in the cooperative care units. The rate of blood culture contamination did not substantially change over the course of the study. Of 37 valves that were subjected to microbiological sample testing, 24.3% yielded microbes, predominantly coagulase-negative staphylococci. CONCLUSION A significant association between primary bloodstream infection and a needleless connector valve was observed. Evaluation of needleless connector valves should include a thorough assessment of infection risks in prospective randomized trials prior to their introduction to the market.

NOSOCOMIAL INVASIVE ASPERGILLOSIS IN LYMPHOMA PATIENTS TREATED WITH BONE MARROW OR PERIPHERAL STEM CELL TRANSPLANTS

OBJECTIVES To determine the prevalence of aspergillosis in lymphoma patients housed in a protective environment while undergoing a bone marrow transplant or peripheral stem cell transplant and its relation to lymphoma type, type of transplant, period of neutropenia, method of diagnosis, species of Aspergillus, and the use of empiric amphotericin B. DESIGN Clinical, autopsy, and microbiology records were reviewed retrospectively to determine the presence or absence of invasive aspergillosis. All positive specimens underwent further review to determine parameters outlined above. SETTING The review took place at the University of Nebraska Medical Center with lymphoma patients housed in the oncology/hematology special care unit, which consists of 30 single-patient rooms under positive pressure with high-efficiency particulate air filtration. PATIENTS 417 lymphoma patients admitted to the oncology/hematology special care unit who underwent 427 courses of high-dose chemotherapy with or without total body irradiation followed by a stem cell rescue. RESULTS Twenty-two cases (5.2%) of nosocomial invasive aspergillosis (14 caused by Aspergillus flavus, 2 by Aspergillus terreus, 2 by Aspergillus fumigatus, and 4 by characteristic histology) were diagnosed. The prevalence of disease according to transplant was 8.7% for allogeneic bone marrow transplant (2/23 treatments), 5.6% for autologous peripheral stem cell transplant (9/161), and 4.5% for autologous bone marrow transplant (11/243). Fifteen patients were presumptively diagnosed prior to death (68.2%) most commonly by histologic examination of skin biopsies. All 22 patients received amphotericin B therapy, 17 prior to aspergillosis diagnosis, and 7 (31.8%) survived. No patient with disseminated disease survived. CONCLUSIONS Even when housing lymphoma patients undergoing myeloablative therapy in a protective environment containing high-efficiency particulate air filtration, there was a risk of developing aspergillosis. These data also showed that antemortem diagnosis with aggressive amphotericin B therapy was most effective in the management of infected lymphoma patients when engraftment occurred and the disease did not become disseminated.

Impact of the More-Potent Antibiotics Quinupristin-Dalfopristin and Linezolid on Outcome Measure of Patients with Vancomycin-Resistant Enterococcus Bacteremia

BACKGROUND The impact of antibiotic resistance on the clinical outcome of patients with vancomycin-resistant Enterococcus (VRE) bacteremia remains unclear. There are limited data comparing patient outcomes during the early era of vancomycin resistance with the period of more-potent antibiotic availability. METHODS A retrospective review was conducted of 113 patients with VRE bacteremia at a single institution from August 1993 to September 2005. Patients were assigned to a group on the basis of initial antibiotic choice for treatment of VRE (linezolid, quinupristin-dalfopristin, or combinations of other agents, before newer options were available). Outcome measurements were examined for the initial episode of VRE bacteremia, and multiple logistic regression analysis was performed to compare group outcomes. RESULTS Overall mortality was 37.2% (42 of 113 patients). VRE bacteremia caused or significantly contributed to death in 29 (69%) of 42 patients. Seventy-one patients were initially treated with linezolid, 20 with quinupristin-dalfopristin, and 22 with combinations of other agents. Univariate analysis indicated significantly more deaths in the quinupristin-dalfopristin group (odds ratio, 5.45; 95% confidence interval, 1.89-15.9) and in the other-agents group (odds ratio, 2.94; 95% confidence interval, 1.09-7.94) than in the linezolid group. However, after adjustment for severity of illness, treatment group was not a significant independent factor. CONCLUSION Despite the development of antimicrobial agents with greater potency against VRE, a significant change in clinical outcome was not observed. This suggests that vancomycin resistance does not significantly influence mortality and points to the continued need for prospective, randomized clinical trials.