Kristina G. Hulten

Three-Year Surveillance of Community-AcquiredStaphylococcus aureus Infections in Children

BACKGROUND Methicillin-resistant Staphylococcus aureus (MRSA) isolates are increasingly frequent causes of skin and soft-tissue infections or invasive infections in many communities. METHODS Prospective surveillance for community-acquired S. aureus infections at Texas Childrens Hospital was initiated on 1 August 2001. Infections meeting the definition of community-acquired were identified. Demographic and clinical data were collected. Antibiotic susceptibilities, including inducible resistance to macrolide, lincosamide, and streptogramin B (MLSB), were determined in the clinical microbiology laboratory with the methodology of the NCCLS. All data were entered into a computer database. Data were analyzed by chi2 tests. RESULTS From 1 August 2001 to 31 July 2004, the percentage of community-acquired S. aureus isolates that were methicillin resistant increased from 71.5% (551 of 771 isolates) in year 1 to 76.4% (1193 of 1562 isolates) in year 3 (P = .008). The number of both community-acquired MRSA (CA-MSRA) isolates and community-acquired methicillin-susceptible S. aureus (CA-MSSA) isolates increased yearly, but the rate of increase was greater for the CA-MRSA isolates. Among the CA-MRSA isolates, 2542 (95.6%) were obtained from children with skin and soft-tissue infections, and 117 (4.4%) were obtained from children with invasive infections. Overall, 62% of children with CA-MRSA isolates and 53% of children with CA-MSSA isolates were admitted to the hospital (P = .0001). The rate of clindamycin resistance increased significantly for both CA-MRSA isolates (P = .003) and CA-MSSA isolates (P = .00003) over the 3 years. MLSB inducible resistance was found in 27 (44%) of 62 clindamycin-resistant CA-MSSA isolates, compared with 6 (4.5%) of 132 clindamycin-resistant CA-MRSA isolates (P < .000001). CONCLUSIONS CA-MRSA isolates account for an increasing percentage and number of infections at Texas Childrens Hospital. Clindamycin resistance increased among community-acquired S. aureus isolates. Community surveillance of community-acquired S. aureus infections is critical to determine the appropriate empiric antibiotic treatment for either local or invasive infections.

Severe Staphylococcal Sepsis in Adolescents in the Era of Community-Acquired Methicillin-Resistant Staphylococcus aureus

Objective. More than 70% of the community-acquired (CA) staphylococcal infections treated at Texas Childrens Hospital are caused by methicillin-resistant Staphylococcus aureus (MRSA). Since September 2002, an increase in the number of severely ill patients with S aureus infections has occurred. This study provides a clinical description of severely ill adolescent patients and an analysis of their isolates using molecular methods. Methods. We identified adolescent patients meeting criteria for severe sepsis requiring admission to the PICU. Patient records were reviewed, and isolates were obtained for susceptibility testing and DNA extraction. Isolates were tested for the presence of virulence genes (cna, tst, lukS-PV, and lukF-PV) and enterotoxin genes (sea, seb, sec, sed, seh, and sej) by polymerase chain reaction. Genomic fingerprints were determined by repetitive-element polymorphism polymerase chain reaction and pulse-field gel electrophoresis. SCCmec cassette type was determined. Results. Fourteen adolescents with severe CA S aureus infections were identified between August 2002 and January 2004. All were admitted to the PICU with sepsis and coagulopathy. Twelve patients had CA-MRSA infections; 2 had CA methicillin-susceptible Staphylococcus aureus (MSSA) infections. The mean age was 12.9 years (range: 10-15 years). Thirteen patients had pulmonary involvement and/or bone and joint infection; 10 patients had ≥2 bones or joints infected (range: 2-10); 4 patients developed vascular complications (deep venous thrombosis); and 3 patients died. All isolates were identical or closely related to the previously reported predominant clone in Houston, Texas (multilocus sequence type 8, USA300), and carried lukS-PV and lukF-PV genes as well as the SCCmec type IVa cassette (12 MRSA isolates) but did not contain cna or tst. Only 1 strain carried enterotoxin genes (sed and sej). Conclusions. Severe staphylococcal infections in previously healthy adolescents without predisposing risk factors have presented more frequently at Texas Childrens Hospital since September 2002. CA MRSA and clonally related CA MSSA characterized as USA300 and sequence type 8 have been isolated from these patients.

Community-acquired, methicillin-resistant and methicillin-susceptible Staphylococcus aureus musculoskeletal infections in children

Background: The clinical characteristics and virulence factors related to musculoskeletal infections caused by community-acquired, methicillin-resistant Staphylococcus aureus (MRSA) in children are not well-defined. Methods: In this retrospective study, the demographics, hospital course and outcome of children with musculoskeletal infections were reviewed from medical records and by contacting patients or their physicians. Antimicrobial susceptibilities were determined by disk diffusion. Polymerase chain reaction was performed to detect genes encoding for virulence factors. Mann-Whitney, χ2 and Kaplan-Meier tests were used for statistical analysis. Results: Community-acquired MRSA and community-acquired methicillin-susceptible S. aureus (MSSA) caused musculoskeletal infections in 31 and 28 children, respectively. The median numbers of febrile days after start of therapy were 4 and 1 for MRSA and MSSA patients, respectively (P = 0.001). The median numbers of hospital days were 13 and 8 for the MRSA and MSSA groups, respectively (P = 0.014). At follow-up, 2 patients in the MRSA and 1 in the MSSA group had developed chronic osteomyelitis. pvl and fnbB genes were found in 87 and 90% versus 24 and 64% in the MRSA versus MSSA groups, respectively. (P = 0.00001 and 0.017). Ten patients with pvl-positive strains had complications versus no patients with pvl-negative isolates (P = 0.002). Conclusions: Febrile days and hospital days were greater in children with musculoskeletal infection caused by MRSA than in those affected by MSSA, but no significant differences were found in the final outcome. pvl and fnbB genes were more frequent in the MRSA than in the MSSA strains. The presence of the pvl gene may be related to an increased likelihood of complications in children with S. aureus musculoskeletal infections.

Panton-valentine leukocidin genes are associated with enhanced inflammatory response and local disease in acute hematogenous Staphylococcus aureus osteomyelitis in children

BACKGROUND. Staphylococcus aureus strains carrying the genes encoding Panton-Valentine leukocidin (pvl-positive [pvl+]) are associated with more febrile days and higher complication rates of osteomyelitis in children than are pvl-negative (pvl−) strains. OBJECTIVES. Selected clinical, laboratory, and radiographic findings in children with osteomyelitis caused by pvl+ and pvl− S aureus strains were compared. METHODS. The demographics, selected clinical features, laboratory values, and radiographic findings of children with community-acquired S aureus osteomyelitis prospectively identified at Texas Childrens Hospital between August 2001 and July 2004 were reviewed. Polymerase chain reaction was performed to detect the genes for pvl (luk-S-PV and luk-F-PV) and fibronectin-binding protein (fnbB) in S aureus isolates. χ2, 2-sample t test, and multiple logistic regression were used for statistical analysis. RESULTS. Methicillin-susceptible and methicillin-resistant S aureus (MSSA and MRSA, respectively) caused osteomyelitis in 33 and 56 children, respectively. Twenty-six isolates were pvl− (26 MSSA), 59 were pvl+ (3 MSSA, 56 MRSA), and 4 were not available for analysis (4 MSSA). On univariate analysis, patients with pvl+ S aureus isolates had significantly higher erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level both at presentation and as a maximum value during hospitalization and were more likely to have a blood culture positive for S aureus during their admission. Patients with pvl+ S aureus isolates were significantly more likely to have concomitant myositis or pyomyositis compared with patients with pvl− S aureus isolates on MRI. In a multivariate analysis pvl remained significantly associated with ESR and CRP levels at presentation and blood culture positive for S aureus. pvl+ status and younger age were associated with myositis on MRI. CONCLUSIONS. Osteomyelitis caused by pvl+ S aureus strains were associated with more severe local disease and a greater systemic inflammatory response compared with osteomyelitis caused by pvl− S aureus.

Pulmonary Manifestations in Children with Invasive Community-Acquired Staphylococcus aureus Infection

BACKGROUND Primary pneumonia and metastatic pulmonary infection have become more common in patients with invasive community-acquired Staphylococcus aureus disease at Texas Childrens Hospital (TCH; Houston). METHODS In this study, we sought to describe pulmonary involvement in children with community-acquired S. aureus invasive infection and to determine whether the presence of genes encoding Panton-Valentine leukocidin (PVL) (luk-S-PV and luk-F-PV) and collagen adhesin (cna) is correlated with pulmonary manifestations. Patients with invasive staphylococcal infections admitted to TCH between 1 August 2001 and 30 June 2004 were studied. Chest imaging and postmortem examination reports were reviewed. Isolates were tested for the presence of genes encoding PVL and collagen adhesin by PCR. RESULTS A total of 47 of 70 patients with community-acquired methicillin-resistant S. aureus (MRSA) infection had abnormal pulmonary imaging findings, compared with 12 of 43 patients with community-acquired methicillin-susceptible S. aureus (MSSA) infection (P < .001). Pneumonia and/or empyema, in addition to septic emboli, were the most common findings. Metastatic pulmonary disease occurred more frequently among patients with osteomyelitis. Severe necrotizing pneumonia was present in 3 children coinfected with influenza and parainfluenza virus. The presence of genes encoding PVL was investigated in 67 MRSA and 36 MSSA isolates. Abnormal chest imaging findings were observed for 51 of 80 patients with PVL-positive isolates, compared with 2 of 23 patients with PVL-negative isolates (P < .001). Only 2 isolates (both of which were MSSA) from patients with abnormal chest radiograph findings carried cna. PVL remained independently associated with abnormal chest imaging findings in patients with secondary pneumonia in a multivariate analysis (P = .03). CONCLUSIONS Pulmonary involvement is commonly observed in patients with invasive community-acquired S. aureus infections. Community-acquired MRSA may cause primary community-acquired pneumonia, as well as metastatic pulmonary disease. The presence of genes encoding PVL is highly associated with pulmonary involvement by S. aureus.

Subtle genetic changes enhance virulence of methicillin resistant and sensitive Staphylococcus aureus

BackgroundCommunity acquired (CA) methicillin-resistant Staphylococcus aureus (MRSA) increasingly causes disease worldwide. USA300 has emerged as the predominant clone causing superficial and invasive infections in children and adults in the USA. Epidemiological studies suggest that USA300 is more virulent than other CA-MRSA. The genetic determinants that render virulence and dominance to USA300 remain unclear.ResultsWe sequenced the genomes of two pediatric USA300 isolates: one CA-MRSA and one CA-methicillin susceptible (MSSA), isolated at Texas Childrens Hospital in Houston. DNA sequencing was performed by Sanger dideoxy whole genome shotgun (WGS) and 454 Life Sciences pyrosequencing strategies. The sequence of the USA300 MRSA strain was rigorously annotated. In USA300-MRSA 2658 chromosomal open reading frames were predicted and 3.1 and 27 kilobase (kb) plasmids were identified. USA300-MSSA contained a 20 kb plasmid with some homology to the 27 kb plasmid found in USA300-MRSA. Two regions found in US300-MRSA were absent in USA300-MSSA. One of these carried the arginine deiminase operon that appears to have been acquired from S. epidermidis. The USA300 sequence was aligned with other sequenced S. aureus genomes and regions unique to USA300 MRSA were identified.ConclusionUSA300-MRSA is highly similar to other MRSA strains based on whole genome alignments and gene content, indicating that the differences in pathogenesis are due to subtle changes rather than to large-scale acquisition of virulence factor genes. The USA300 Houston isolate differs from another sequenced USA300 strain isolate, derived from a patient in San Francisco, in plasmid content and a number of sequence polymorphisms. Such differences will provide new insights into the evolution of pathogens.

Emergence of New Strains of Methicillin-Resistant Staphylococcus aureus in a Neonatal Intensive Care Unit

BACKGROUND Genetically distinct strains of methicillin-resistant Staphylococcus aureus (MRSA) of community rather than hospital origin have emerged in many areas of the United States. We determined if MRSA strains causing bacteremia in infants treated from birth in a neonatal intensive care unit (NICU) demonstrated the genetic traits of community-associated MRSA. METHODS A retrospective cohort study was conducted among NICU infants with bacteremia due to MRSA during 2003 in a large tertiary care center NICU in Houston. MRSA isolates were characterized by antimicrobial susceptibility testing and staphylococcal cassette chromosome mec (SCCmec) typing by polymerase chain reaction. All MRSA cases were reviewed for clinical severity of infection and outcome. RESULTS During 2003, a total of 8 (47%) of 17 infants with bacteremia due to S. aureus had MRSA infection. Isolates from 6 (75%) of these 8 infants carried the SCCmec genes (class B mec and ccr2) that are characteristic of community MRSA; 4 isolates were type IVa. All 6 isolates were resistant to beta-lactam antibiotics and erythromycin; 1 was also resistant to clindamycin. One isolate was nontypeable, and another carried the SCCmec type II gene (typical of hospital-associated strains) and was susceptible only to vancomycin. Seven (88%) of 8 infants presented in septic shock. Despite initial treatment with vancomycin, 3 (38%) died, and 3 survivors had complications requiring prolonged antimicrobial therapy; these 6 infants had MRSA isolates with genetic characteristics of isolates of community origin. CONCLUSIONS Community-associated MRSA strains have emerged as a significant cause of sepsis in neonates hospitalized in NICU since birth and have caused disseminated infection with substantial morbidity and mortality.

Mycobacterium avium subsp. paratuberculosis as one cause of Crohn’s disease

A number of theories regarding the aetiology of Crohn’s disease have been proposed. Diet, infections, other unidentified environmental factors and immune disregulation, all working under the influence of a genetic predisposition, have been viewed with suspicion. Many now believe that Crohn’s disease is a syndrome caused by several aetiologies. The two leading theories are the infectious and autoimmune theories. The leading infectious candidate is Mycobacterium avium subspecies paratuberculosis (Mycobacterium paratuberculosis), the causative agent of Johne’s disease, an inflammatory bowel disease in a variety of mammals including cattle, sheep, deer, bison, monkeys and chimpanzees. The evidence to support M. paratuberculosis infection as a cause of Crohn’s disease is mounting rapidly. Technical advances have allowed the identification and/or isolation of M. paratuberculosis from a significantly higher proportion of Crohn’s disease tissues than from controls. These methodologies include: (i) improved culture techniques; (ii) development of M. paratuberculosis‐specific polymerase chain reaction assays; (iii) development of a novel in situ hybridization method; (iv) efficacy of macrolide and anti‐mycobacterial drug therapies; and (v) discovery of Crohn’s disease‐specific seroreactivity against two specific M. paratuberculosis recombinant antigens. The causal role for M. paratuberculosis in Crohn’s disease and correlation of infection with specific stratification(s) of the disorder need to be investigated. The data implicating Crohn’s as an autoimmune disorder may be viewed in a manner that supports the mycobacterial theory. The mycobacterial theory and the autoimmune theory are complementary; the first deals with the aetiology of the disorder, the second deals with its pathogenesis. Combined therapies directed against a mycobacterial aetiology and inflammation may be the optimal treatment of the disease.

Infective Pyomyositis and Myositis in Children in the Era of Community-Acquired, Methicillin-Resistant Staphylococcus aureus Infection

BACKGROUND Cases of pyomyositis and myositis have been increasing in frequency at Texas Childrens Hospital (Houston) since 2000. The increase appears to correlate with the emergence of community-acquired methicillin-resistant Staphylococcus aureus (MRSA). METHODS The medical records of patients with pyomyositis and myositis hospitalized at Texas Childrens Hospital during the period from January 2000 through December 2005 were reviewed. Available S. aureus isolates were obtained for susceptibility testing, to determine the presence of pvl (lukS-PV and lukF-PV), and for pulsed-field gel electrophoresis analysis. RESULTS Forty-five previously healthy children with bacterial pyomyositis or myositis were analyzed. The causes were S. aureus (in 57.8% of children) and Streptococcus pyogenes (in 2.2%); 40.0% of children had negative culture results. The number of cases increased between 2000 and 2005, primarily as a result of an increase in the prevalence of community-acquired MRSA. The mean patient age was 5.5 years (range, 0.06-15 years). The thigh (40.0% of children) and pelvis (28.9%) were the most commonly affected sites. The mean abscess diameter was 3.5 cm. Eighteen children required at least 1 muscle drainage procedure. Of the 24 available S. aureus isolates (15 community-acquired MRSA isolates and 9 community-acquired, methicillin-susceptible S. aureus [MSSA] isolates), 16 were found to be USA300 by pulsed-field gel electrophoresis, and 17 carried pvl. Patients with community-acquired MRSA, USA300, and/or pvl-positive strains required more drainage procedures than did those with community-acquired MSSA, non-USA300, and/or pvl-negative strains (81% vs. 40% [P=.05], 82% vs. 29% [P=.02], and 81% vs. 38% [P=.07], respectively). CONCLUSIONS Community-acquired MRSA is an increasing cause of pyomyositis and myositis in children. Community-acquired MRSA, USA300, pvl-positive S. aureus isolates caused more severe disease than did community-acquired MSSA, non-USA300, and pvl-negative isolates, respectively.

Venous thrombosis associated with staphylococcal osteomyelitis in children

BACKGROUND. Venous thrombosis (VT) in children with Staphylococcus aureus osteomyelitis occurs rarely. We describe clinical features of infections and molecular characterization of isolates of children at Texas Childrens Hospital with S aureus osteomyelitis and VT. METHODS. We reviewed records and imaging studies (chest radiographs, ultrasound, computed tomography, and MRI) of 9 patients at Texas Childrens Hospital with acute S aureus osteomyelitis and new onset VT between August 1999 and December 2004. Isolates were fingerprinted by pulsed-field gel electrophoresis and tested for the presence of genes encoding selective virulence factors. RESULTS. The mean age of the patients was 10.6 years. All 9 of the patients had osteomyelitis with sites of infection adjacent to the VT. The femoral and popliteal veins were most commonly affected. Two patients had VTs develop on the same side in which a central line had been in place. Four patients had chest radiographs consistent with septic emboli; inferior vena cava filters were placed in 3. Evaluation for hypercoagulable state revealed 3 patients with lupus anticoagulant, 1 with anticardiolipin IgG antibody, and 5 with no defect. Most laboratory abnormalities had resolved at follow-up. Seven patients had infections caused by methicillin-resistant S aureus belonging to the same clonal group (USA300); all were community acquired. Seven isolates carried the Panton-Valentine leukocidin (luk-S-PV and luk-F-PV) genes. CONCLUSIONS. The predominant community-acquired, methicillin-resistant S aureus clone in Houston, Texas, (USA300) may have a unique propensity to cause VT in association with osteomyelitis. Management of the venous thrombosis in this setting may be complicated by the rapid evolution of septic emboli.