Emergence of a predominant clone of community-acquired Staphylococcus aureus among children in Houston, Texas

Modern approaches at the management of children with community-acquired pneumonia

Experts of The Union of Pediatricians of Russia have developed current clinical guidelines for management of children with community-acquired pneumonia, which were approved by the Scientific and Practice Council of Ministry of Public Health of the Russian Federation in January 2022. Particular attention is paid to the etiological structure, modern classification, diagnostic tests and flagship approaches to antibacterial therapy of community-acquired pneumonia in children based on the principles of evidentiary medicine. 

Molecular Epidemiology of Staphylococcus aureus in Skin and Soft Tissue Infections and Bone and Joint Infections in Korean Children

BACKGROUND

Community acquired-methicillin resistant Staphylococcus aureus (MRSA) clones, including ST1, ST8, and ST30 are reported worldwide. However, data among Korean children are limited. Thus, we investigated the molecular characteristics of S. aureus among children in Korea.

METHODS

S. aureus isolated from Korean children diagnosed with skin and soft tissue infection (SSTI) or bone and joint infection due to S. aureus infection at Seoul National University Bundang Hospital, from August 2010 to November 2016, were analyzed for multilocus sequence type (ST) and SCCmec typing. Polymerase chain reaction of Panton-Valentine leukocidin (PVL), qac A/B, smr and mupA genes were also performed. Electronic medical records were reviewed for clinical data and antibiotic susceptibility results. Cases were classified into three groups: health care-associated community-onset (HACO) infections, hospital-onset (HO) infections, and community-acquired (CA) infections.

RESULTS

A total of 67 strains from children with SSTI (41/67, 61.2%) and bone and joint infection (26/67, 38.8%) were included. Among all isolates, 29.9% (20/67) were MRSA, and 70% (14/20) were classified as CA, 20% (4/20) as HACO and 10% (2/20) as HO infections. MRSA rate according to disease was 34.1% (14/41) for SSTI and 23.1% (6/26) for bone and joint infection. MRSA strains included ST72-SCCmec IV (14/20, 70.0%), ST5-SCCmec II (3/20, 15.0%) and ST1-SCCmec IV (2/20, 10.0%). ST30 was the most common cause of SSTI and bone and joint infections and 96.6% (28/29) were methicillin-susceptible Staphylococcus aureus (MSSA). PVL genes were detected in 3 strains (3.8%, ST30-SCCmec IV n = 1, MSSA ST30 n = 2), qac A/B in 3 (MRSA = 3), smr in 3 (MSSA = 1, MRSA = 2) and mupA in 7 (MRSA = 5, MSSA = 2).

CONCLUSION

Molecular epidemiology of S. aureus in Korean children with SSTI and bone and joint infection showed that ST30 was predominant and mostly MSSA. Among MRSA, ST72-SCCmec type IV was the most common strain.

Molecular Characterization of Staphylococcus aureus Isolates From Children With Periorbital or Orbital Cellulitis

BACKGROUND

Periorbital and orbital cellulitis cause significant pediatric morbidity. Here, we define the clinical features of and characterize isolates from children with periorbital or orbital cellulitis caused by Staphylococcus aureus at Texas Children's Hospital in Houston.

METHODS

Patients were identified from a prospective S aureus study database from January 2002 to July 2015. Demographic and clinical data were collected retrospectively. Isolates were genotyped by pulsed-field gel electrophoresis, and Panton-Valentine leukocidin (lukSF-PV [pvl]) genes were detected by quantitative polymerase chain reaction. Data were analyzed with the Fisher exact or Wilcoxon rank-sum test.

RESULTS

Eighty-five patients with periorbital (n = 58) or orbital (n = 27) cellulitis were identified. We found 57 (67%) methicillin-resistant S aureus (MRSA) isolates, 72 (85%) pvl-positive (pvl+) isolates, and 66 (78%) USA300 isolates. No differences in clinical characteristics were found when we compared MRSA to methicillin-susceptible (MSSA) infections or USA300 to non-USA300 infections. Patients with orbital cellulitis were hospitalized a median of 12 days (range, 2-28 days) and received antibiotics for 21 days (range, 10-32 days). Twelve (44%) patients with orbital cellulitis received steroids. Steroid treatment did not affect the length of hospitalization or duration of antibiotic treatment. Six (7%) patients with orbital cellulitis were bacteremic. Patients with periorbital cellulitis were hospitalized for a median of 3 days (range, 0-17 days) and received antibiotics for 11 days (range, 7-32 days). According to computed tomography (CT), 19 (70%) patients with orbital cellulitis and 11 (41%) with periorbital cellulitis had sinusitis.

CONCLUSIONS

The majority of periorbital and orbital S aureus infections at Texas Children's Hospital were caused by MRSA, and no change was observed over time. Empirical antibiotic treatment should include coverage for MRSA. PVL might be an important virulence factor in these presentations. S aureus is associated with sinusitis and its complications.

Analysis of Invasive Community-Acquired Methicillin-Susceptible Staphylococcus aureus Infections During a Period of Declining Community Acquired Methicillin-Resistant Staphylococcus aureus Infections at a Large Children's Hospital

BACKGROUND

The epidemiology of community acquired (CA) Staphylococcus aureus infections is changing in the United States. We investigated the current epidemiology of S. aureus infections at Texas Children's Hospital.

METHODS

Patients with CA-S. aureus skin and soft tissue and invasive infections were retrospectively identified from January 1, 2007 to December 31, 2014. Invasive CA-MSSA isolates were characterized by pulsed field gel electrophoresis, Spa typing, agr type and presence of lukSF-PV (pvl) genes. Medical records were reviewed. Statistical analyses included Fisher exact, χ for trend and Wilcoxon tests.

RESULTS

CA-MRSA infections decreased by 60.4% (1461-578 infections) from 2007 to 2014 (P < 0.0001), while CA-MSSA infections averaged 550 infections annually. Invasive CA-MRSA infections decreased by 67.2% from 61 to 20 infections (P < 0.0001); invasive CA-MSSA averaged 44 infections annually. Among 296 invasive CA-MSSA isolates, 74 (25%) isolates were USA300 and 88 (30%) were pvl+. USA300 declined among invasive CA-MSSA over time (P < 0.008). Musculoskeletal infections were most common (242/296, 82%); 52/242 (21.5%) isolates were USA300 and 62/242 (25.6%) pvl+. All 18 isolates from musculoskeletal infections with deep venous thrombosis and/or septic shock were pvl+ and 16/18 (88.9%) were USA300. Pneumonia isolates were mainly USA300 (8, 66.7%) and pvl+ (11, 91.7%).

CONCLUSIONS

MSSA now cause the majority of invasive CA-S. aureus infections at our institution. Molecular analysis of invasive CA-MSSA isolates suggests strain diversity with USA300 on the decline and that disease presentations are to some extent strain specific. Changes in the CA-S. aureus epidemiology may, in part, be related to changes in immunity to the USA300 clone in the general population.

Prevalence of nasal colonization of methicillin-resistant Staphylococcus aureus among schoolchildren of Barabanki district, Uttar Pradesh, India

Introduction:

The study aimed to determine the prevalence of nasal colonization of methicillin-resistant Staphylococcus aureus (MRSA), the minimum inhibitory concentration (MIC) of oxacillin and vancomycin, inducible clindamycin resistance, and antimicrobial resistance pattern of S. aureus among children of Barabanki district, Uttar Pradesh, India.

Materials and Methods:

School-going children of age group of 5–15 years were identified and selected according to the inclusion and exclusion criteria. Two nasal swabs were collected from each child as per the Centers for Disease Control and Prevention guidelines and transported to laboratory. Swabs were cultured on mannitol salt agar and 5% blood agar and incubated for 18–24 h at 37°C. Identification was done as per routine laboratory protocol. Detection of MRSA was done through cefoxitin 30 μg discs and D-zone test. Antibiotic susceptibility pattern of S. aureus by Kirby–Bauer disc diffusion method along with MIC for oxacillin and vancomycin was performed simultaneously according to Clinical Laboratory Standards Institute guidelines.

Results:

Out of 300 children, 140 (46.67%) were found to be nasal carriage for S. aureus, among which MRSA was found to be 23 (7.67%). All S. aureus and MRSA isolates were sensitive to vancomycin with MIC <2 μg/ml, whereas 23 S. aureus were found resistant to oxacillin with MIC value >4 μg/ml. Resistance to penicillin and co-trimoxazole was highest, whereas all were sensitive to linezolid. MRSA showed 100% susceptibility to linezolid, followed by gentamicin (91.4%) and tetracycline (87%).

Conclusion:

With the risk involved in transmission of infection, steps for identifying the carriers and its eradication should be carried out. Rational use of antibiotics should be given preference too.

Understanding Staphylococcal Nomenclature

Bacteria are often grouped by a variety of properties, including biochemical activity, appearance, and more recently, nucleic acid sequence differences. In the case of human pathogens, significant work goes into "typing" strains to understand relatedness. This is especially true when trying to understand the epidemiology of these organisms. In attempts to group Staphylococci, a variety of methods and nomenclatures have been employed, which can often serve as a point of confusion to those entering the field. Therefore, the intent of this chapter is to give a brief overview of some common methods and associated nomenclature used to type Staphylococci, with S. aureus as an example.

Role of lipase from community-associated methicillin-resistant Staphylococcus aureus strain USA300 in hydrolyzing triglycerides into growth-inhibitory free fatty acids

Part of the human host innate immune response involves the secretion of bactericidal lipids on the skin and delivery of triglycerides into abscesses to control invading pathogens. Two Staphylococcus aureus lipases, named SAL1 and SAL2, were identified in the community-associated methicillin-resistant S. aureus strain USA300, which, presumably, are produced and function to degrade triglycerides to release free fatty acids. We show that the SAL2 lipase is one of the most abundant proteins secreted by USA300 and is proteolytically processed from the 72-kDa proSAL2 to the 44-kDa mature SAL2 by the metalloprotease aureolysin. We show that spent culture supernatants had lipase activity on both short- and long-chain fatty acid substrates and that deletion of gehB, encoding SAL2, resulted in the complete loss of these activities. With the use of gas chromatography-mass spectrometry, we show that SAL2 hydrolyzed trilinolein to linoleic acid, a fatty acid with known antistaphylococcal properties. When added to cultures of USA300, trilinolein and, to a lesser extent, triolein inhibited growth in a SAL2-dependent manner. This effect was shown to be due to the enzymatic activity of SAL2 on these triglycerides, since the catalytically inactive SAL2 Ser412Ala mutant was incapable of hydrolyzing the triglycerides or yielding delayed growth in their presence. Overall, these results reveal that SAL2 hydrolyzes triglycerides of both short- and long-chain fatty acids and that the released free fatty acids have the potential to cause significant delays in growth, depending on the chemical nature of the free fatty acid.

The multifaceted resources and microevolution of the successful human and animal pathogen methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important bacterial pathogens based on its incidence and the severity of its associated infections. In addition, severe MRSA infections can occur in hospitalised patients or healthy individuals from the community. Studies have shown the infiltration of MRSA isolates of community origin into hospitals and variants of hospital-associated MRSA have caused infections in the community. These rapid epidemiological changes represent a challenge for the molecular characterisation of such bacteria as a hospital or community-acquired pathogen. To efficiently control the spread of MRSA, it is important to promptly detect the mecA gene, which is the determinant of methicillin resistance, using a polymerase chain reaction-based test or other rapidly and accurate methods that detect the mecA product penicillin-binding protein (PBP)2a or PBP2'. The recent emergence of MRSA isolates that harbour a mecA allotype, i.e., the mecC gene, infecting animals and humans has raised an additional and significant issue regarding MRSA laboratory detection. Antimicrobial drugs for MRSA therapy are becoming depleted and vancomycin is still the main choice in many cases. In this review, we present an overview of MRSA infections in community and healthcare settings with focus on recent changes in the global epidemiology, with special reference to the MRSA picture in Brazil.

Prevention of surgical site infections

In the current era of pay-for-performance standards, the incidence of surgical site infections is increasingly becoming an institutional marker of quality assurance. Surgical site infections lead to increased morbidity and mortality in the surgical population and contribute to an already rising healthcare cost. As a result, the surgical community goes to great lengths to prevent this costly and occasionally lethal complication. Many practices are evidence based, however, many are not. In this article, the most commonly used preventive strategies in practice today and the evidence behind each are reviewed. In addition, an overview of the epidemiology, pathophysiology and microbiology of surgical site infections will be provided.

Epidemiology and treatment of community-associated methicillin-resistantStaphylococcus aureusin children

Similar to the epidemiology of methicillin-sensitive Staphylococcus aureus, community-associated methicillin-resistant S. aureus infections occur in children in different regions of the USA and throughout the world. Although minor skin and soft-tissue infections predominate, life-threatening invasive disease and death can result. The novel genetic elements, staphylococcal cassette chromosome mec IV and V, explain the narrow antibiotic resistance pattern, and suggest the mechanism of spread among staphylococci. Panton-Valentine leukocidin apparently plays a role in its pathogenesis. Clindamycin therapy is often effective for treatment, but inducible resistance can develop if the isolate exhibits macrolide resistance due to the erm mechanism. Other drugs displaying in vitro activity against community-associated methicillin-resistant S. aureus include trimethoprim-sulfamethoxazole, tetracyclines, quinolones, linezolid and vancomycin. While experience in pediatric patients is limited, daptomycin, ketolides, glycylcyclines, newer glycopeptides and beta-lactamase-stable cephalosporins may be useful in the future. Further research could include well-designed studies of mechanisms of virulence, continued surveillance of changes in pathogenicity and susceptibility, as well as treatment effectiveness.

First report in South America of companion animal colonization by the USA1100 clone of community-acquired meticillin-resistant Staphylococcus aureus (ST30) and by the European clone of methicillin-resistant Staphylococcus pseudintermedius (ST71)

Background

Methicillin-resistant staphylococci can colonize and cause diseases in companion animals. Unfortunately, few molecular studies have been carried out in Brazil and other countries with the aim of characterizing these isolates. Consequently, little is known about the potential role of companion animals in transmitting these resistant bacteria to humans. In this work we searched for mecA gene among Staphylococcus isolates obtained from nasal microbiota of 130 healthy dogs and cats attended in a veterinary clinic located in the west region of Rio de Janeiro. The isolates recovered were identified to the species level and characterized using molecular tools.

Results

A community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) isolate related to USA1100 (Southwest Pacific clone) and susceptible to all non-β-lactams was detected in a cat (1.7%, 1/60). Another coagulase-positive isolate harboring mecA was recovered from a dog (1.4%, 1/70) and identified as Staphylococcus pseudintermedius (MRSP) related to the European clone (ST71). The two isolates of Staphylococcus conhii subsp. urealyticus (1.4%, 1/70 dogs and 1.7%, 1/60 cats), similarly to the MRSP isolate, also presented high-level multiresistance. The majority of the methicillin-resistant coagulase-negative staphylococci recovered were Staphylococcus saprophyticus (5.7%, 4/70 dogs and 6.7%, 4/60 cats) and all clustered into the same PFGE type.

Conclusions

This work demonstrates that mecA-harboring Staphylococcus isolates are common members of the nasal microbiota of the healthy companion animals studied (9.2%, 12/130 animals), including some high-level multiresistant isolates of S. pseudintermedius and S. conhii subsp. urealyticus. The detection, for the first time in South America, of USA1100-related CA-MRSA and of ST71 MRSP (European clone), colonizing companion animals, is of concern. Both S. pseudintermedius and S. aureus are important agents of infections for animals. The USA1100 CA-MRSA is a causative of severe and disseminated diseases in healthy children and adults. Additionally, MRSP is a nosocomial pathogen in veterinarian settings. It had already been demonstrated that the virulent ST71 MRSP is geographically spread over Europe and USA, with potential for zoonotic infections.

Molecular identification and antimicrobial susceptibility of Staphylococcus aureus nasal isolates from medical students in Cartagena, Colombia

Staphylococcus aureus (SA) remains a major cause of nosocomial and community-acquired infections worldwide. Nasal carriage of this bacterium among hospital personnel constitutes an important source for nosocomial infections. A cross-sectional study enrolling the whole medical student population (n=387) of the School of Medicine at the Universidad de Cartagena, Colombia, was conducted to evaluate the carriage rates of both methicillin sensitive- and methicillin resistant-SA, the frequency of Panton-Valentine leukocidin genes in the isolates, and risk factors associated with carriage in this selected population. After signing an informed consent, participants completed a survey related to possible risk factors for colonization, and nasal swabs were collected from anterior nares. Staphylococcus aureus strains isolated from carriers were subjected to DNA extraction and PCR assays to determine the presence of MecA and Panton-Valentine leukocidin genes. Typing of the staphylococcal chromosomal cassette was performed for methicillin resistant strains. Molecular analysis was performed for only one strain per carrier. Prevalence of carriage for methicillin sensitive- and methicillin resistant-SA was 25% and 1.6% respectively. Most of the methicillin resistant isolates carried the staphylococcal chromosomal cassette type IV and the genes for Panton-Valentine leukocidin. To determine carrier types among medical students, each participant was subjected to four additional swabs, each taken two weeks apart. 9.8% persistent carriers, 53.1% intermittent carriers, and 37.1% non-carriers of SA were found. There was no association between risk factors analyzed and carriage of the bacterium. The study was conducted from April to September 2009 and found a persistent carriage of methicillin resistant-SA strains bearing the genes for Panton-Valentine leukocidin among medical students, evidencing the potential contribution of this portion of healthcare personnel either to the spread or introduction of these strains into the healthcare environment.

Trends in resource utilization for hospitalized children with skin and soft tissue infections

OBJECTIVE

To describe trends in national resource utilization for pediatric skin and soft tissue infection (SSTI) hospitalizations.

METHODS

This was a cross-sectional analysis of hospital discharges from 1997 to 2009 within the Healthcare Cost and Utilization Project Kids' Inpatient Database for children with isolated SSTIs. Outcomes examined included patient and hospital characteristics, number of hospitalizations, and resource utilization including length of stay (LOS), hospital charges, and performance of incision and drainage (I&D). Trends in resource utilization were assessed by using linear regression in a merged data set with survey year as the primary independent variable. Multivariate logistic regression was conducted for 2009 data to assess factors associated with increased I&D.

RESULTS

The weighted proportion of SSTI hospitalizations among all hospitalizations doubled (0.46% vs 1.01%) from 1997 to 2009. During the same period, patient demographic trends included a shift to increased hospitalizations in infant and preschool-age groups as well as publicly insured children. Mean LOS decreased from 3.11 to 2.71 days. Increased resource utilization included changes in mean charges from $6722 to $11 534 per hospitalization and a twofold increase in I&D (21% to 44%). Factors associated with I&D include young age, African American race, female gender, publicly or uninsured children, and southern region of the United States.

CONCLUSIONS

SSTI is responsible for an emerging increase in health services utilization. Additional study is warranted to identify interventions that may effectively address this public health burden.

Prevalence of USA300 colonization or infection and associated variables during an outbreak of community-associated methicillin-resistant Staphylococcus aureus in a marginalized urban population

BACKGROUND

In 2004, an outbreak of the USA300 strain of methicillin-resistant Staphylococcus aureus (MRSA) was identified in persons with histories of homelessness, illicit drug use or incarceration in the Calgary Health Region (Calgary, Alberta). A prevalence study was conducted to test the hypotheses for factors associated with USA300 colonization or infection.

METHODS

Participants were recruited at sites accessed by this marginalized population. Health care staff administered a questionnaire and collected crack pipes and nasal, axillary and skin infection swabs. Pipes and swabs were cultured according to standard techniques. MRSA isolates were further characterized by polymerase chain reaction (mecA, Panton-Valentine leukocidin and Staphylococcal cassette chromosome mec) and typing methods (pulsed-field gel electrophoresis, staphylococcal protein A typing and multilocus sequence typing). Colonization or infection was determined by having any one of nasal, axillary, skin infection or pipe swabs positive for USA300. Colonized participants had one or more nasal, axillary or pipe swab positive for USA300; infected participants had one or more skin infection swab positive for USA300.

RESULTS

The prevalence of USA300 colonization or infection among 271 participants was 5.5% (range 3.1% to 9.0%). USA300 cases were more likely to report manipulation of skin infections (OR 9.55; 95% CI 2.74 to 33.26); use of crack pipes was not significant despite identification of the USA300 strain on two of four crack pipes tested. USA300 cases were more likely to report drug use between sex trade workers and clients (OR 5.86; 95% CI 1.63 to 21.00), and with casual sex partners (OR 5.40; 95% CI 1.64 to 17.78).

CONCLUSION

Ongoing efforts to promote the appropriate treatment of skin infections in this population are warranted. The association of USA300 colonization or infection and drug use with sexual partners suggest a role for sexual transmission of the USA300 strain of MRSA.

Detection and characterization of an ST97-SCCmec-V community-associated meticillin-resistant Staphylococcus aureus clone in a neonatal intensive care unit and special care baby unit

A total of 29 meticillin-resistant Staphylococcus aureus (MRSA) isolates were obtained from 15 neonates and three healthcare workers (HCWs) in a neonatal intensive care unit (NICU) and special care baby unit (SCBU) and four patients in a medical ward of a Kuwait hospital between 10 and 30 April 2007. The isolates were characterized using antibiogram results, coagulase gene RFLP (coa-RFLP), PFGE, staphylococcal cassette chromosome mec (SCCmec) typing and multilocus sequence typing (MLST). All isolates were assessed for the carriage of Panton-Valentine leukocidin (PVL) and arginine catabolic mobile element (ACME) genes. The isolates belonged to three SCCmec types, six coa-RFLP types, six pulsotypes and six sequence types. One isolate was positive for PVL. None were positive for ACME. All MRSA isolates from the 15 neonates were phenotypically and genetically different from the MRSA isolates obtained from HCWs and those from patients in other wards. They were resistant to gentamicin, kanamycin and fusidic acid, had identical coa-RFLP and PFGE patterns, carried the type V SCCmec element and belonged to MLST sequence type ST97. The results showed the transmission of a rare clone of community-associated MRSA belonging to ST97 with the SCCmec-V genotype among neonates in a NICU and SCBU.

Staphylococcus aureus sinus infections in children

OBJECTIVE

Staphylococcus aureus can cause sinusitis in children. The predominant MRSA clone in the United States, USA300, has been associated with skin and soft tissue as well as invasive diseases. USA300 has increased among CA methicillin-susceptible S. aureus (CA-MSSA) isolates. We describe the clinical characteristics of pediatric patients with S. aureus cultured from sinus specimens, treated at Texas Children's Hospital (TCH), and characterized their isolates by molecular methods.

METHODS

This was a retrospective study of children with endoscopic sinus surgery (ESS) cultures positive for S. aureus between 01/2005 and 12/2008 at TCH. Medical records were reviewed and associated S. aureus isolates were characterized by pulsed field gel electrophoresis (PFGE). Data were analyzed by Mann-Whitney U, Chi-square, Fisher's exact test, and Chi-square for trend.

RESULTS

We identified 56 patients with S. aureus sinus infections; 12 (21%) were MRSA. Seven of 12 (58%) MRSA vs. 5/44 (11%) MSSA were USA300 (p<0.01). All MRSA isolates were non-susceptible to erythromycin compared to 30% of MSSA (p<0.01); 75% of the USA300 strains were non-susceptible to erythromycin compared to 36% of the non-USA300 strains (p<0.04). Co-pathogens were isolated from 77% (43/56) of the patient specimens. Both MRSA and USA300 isolates were associated with Haemophilus influenzae co-isolation (p<0.05). Patients with USA300 strains were significantly younger (p=0.02) and more likely to experience snoring as a symptom associated with their sinusitis (p=0.03) than those infected with non-USA300 strains. Children with MRSA (4/12) tended to have a greater recurrence rate than children with MSSA isolates (5/44) (p=0.09). No significant differences were observed between groups for fever or complications such as neck cellulitis, nasal abscess, meningitis, subdural empyema, and orbital cellulitis.

CONCLUSION

MSSA was more commonly isolated than MRSA from sinus cultures of children who underwent ESS at TCH. The majority of ESS cultures positive for S. aureus, were mixed with other respiratory pathogens, principally H. influenzae. USA300 was the major clone among the MRSA sinusitis isolates, but was not associated with more complications than other S. aureus isolates.

Identification of major clonal complexes and toxin producing strains among Staphylococcus aureus associated with atopic dermatitis

Staphylococcus aureus promotes the onset and severity of atopic dermatitis (AD), which is exacerbated by superantigen toxins SEB and SEC. The genetic identity of these isolates, and their relationship to common hospital- or community-associated methicillin resistant S. aureus (HA-MRSA and CA-MRSA) has not been defined. We conducted spa typing, partial multi-locus sequence typing (MLST), and toxin profiling (seb, sec, lukS-PV) of S. aureus from 119 pediatric and 40 adult AD patients. MLST clonal complexes CC45, CC5, CC15, CC1, CC8 and CC30 accounted for 79% of isolates, representing the same major groups reported for nosocomial S. aureus in hospital intensive care units. The highest disease severity was associated with CC1, which was significantly greater relative to CC15 (p = 0.017) or CC30 (p = 0.040), but with no significant difference relative to CC45, CC5 or CC8. Although there were two few lukS-PV, seb or sec isolates to infer a role in disease severity, CC45 was identified as a source of SEC producing strains, and lukS-PVL was associated with a small number of CC5 pediatric isolates. CC1 harbored the only CA-MRSA that was identified, and was a source of isolates that expressed both seb and sec, and closely resembled the USA400 strain of CA-MRSA.

Treatment of infections caused by antimicrobial-resistant gram-positive bacteria

An increasing proportion of Staphylococcus aureus infections are caused by methicillin-resistant S aureus. Treatment of infections caused by this organism is challenging, especially because therapy with vancomycin, the traditional antibiotic of choice for methicillin-resistant S aureus infections, is associated with an increasing frequency of treatment failure, and vancomycin insensitive and vancomycin-resistant strains have emerged. In addition, Enterococcus sp. isolated from human infections are increasingly resistant to multiple antimicrobial agents. Newer drugs available for treatment of resistant Gram-positive bacterial infections in the United States include linezolid, daptomycin, tigecycline and telavancin. The precise role for these newer agents is still evolving. Organisms resistant to each of these antimicrobials have emerged. New drugs in development include cephalosporins and carbapenems with MRSA activity.

Diagnosis and management of community-associated MRSA infections in children

The history of antibiotic resistance in Staphylococcus aureus spans more than half a century. Methicillin-resistant S. aureus (MRSA) has emerged as an almost ubiquitous pathogen in both the community and hospital settings. The predominant clone responsible for community-associated MRSA, USA300, is a highly successful pathogen, as demonstrated by its rapid global spread and associated morbidity and mortality. The management of MRSA infections in pediatric patients is complicated by the limited number of effective antibiotics that have been well-studied in children. The gold standard antimicrobial, vancomycin, has several shortcomings that have prompted the development of newer agents for the treatment of MRSA disease. Moreover, the emergence of vancomycin-intermediate or -resistant S. aureus, while uncommon, portends a potential new era of resistance that will require research and development of the next generation of antibiotics that act by novel mechanisms.

Clinical and molecular epidemiology of Staphylococcus aureus catheter-related bacteremia in children

BACKGROUND

Staphylococcus aureus (SA) is an important cause of catheter-related bacteremia (CRB). The USA300 clone increasingly causes healthcare associated infections. We compared children with SA-CRB due to USA300 versus non-USA300 isolates and identified risk factors for complications.

METHODS

Children at Texas Children's Hospital (TCH) with SA-CRB were identified from a prospective S. aureus surveillance study. S. aureus isolates were characterized by methicillin susceptibility and pulsed field gel electrophoresis.

RESULTS

From August 2001 to October 2007, 112 children with a first episode of SA-CRB and corresponding isolates were identified. USA300 accounted for 21 isolates. Metastatic infection complicated 10.7% of cases and was associated with methicillin resistance. Other complications were recurrence (n = 16), death (n = 13), thrombosis (n = 9), and intravascular "cast" (n = 6). Four patients with non-USA300 SA-CRB had endocarditis. Prolonged bacteremia was more common in methicillin-resistant SA (12/29) than in methicillin-susceptible SA SA-CRB (14/83) (P = 0.007). Complications were more common in patients with bacteremia > or =4 days (16/26 [61.5%]) versus patients with bacteremia <4 days (25/86 [29%]) (P = 0.003). The complication rate was lower in patients who had the catheter removed <4 days (22.5%) versus patients whose catheter was removed > or =4 days after infection or not removed (44.4%) (P = 0.02). Children with USA300 versus non-USA300 isolates did not differ with respect to frequency or type of complications.

CONCLUSIONS

At Texas Children's Hospital, the USA300 clone caused 19% of initial SA-CRB episodes and was associated with methicillin resistance. Complications occurred in 36.6% of the patients and were associated with prolonged bacteremia and catheter removal > or =4 days after infection or failure to remove the catheter.

Hospital-acquired Staphylococcus aureus infections at Texas Children's Hospital, 2001-2007

OBJECTIVE

To document the introduction of the methicillin-resistant Staphylococcus aureus (MRSA) USA300 clone into a children's hospital. Current molecular epidemiology of infections due to the USA300 strain of MRSA in the pediatric healthcare setting remains obscure.

DESIGN

Retrospective study of patients with hospital-acquired S. aureus infection during the period from August 1, 2001, through July 31, 2007, at Texas Children's Hospital in Houston.

METHODS

Patients with hospital-acquired S. aureus infection from whom an isolate was available for molecular analysis were included. Clinical information was obtained from patient medical records and the electronic hospital information system. S. aureus isolates underwent antimicrobial susceptibility testing, pulsed-field gel electrophoresis, and polymerase chain reaction testing for staphylococcal cassette chromosome (SCC) mec, agr, the diamine N-acetyltransferase gene, and the Panton-Valentine leukocidin genes (pvl).

RESULTS

Of 242 patients with hospital-acquired S. aureus infection, 147 (61%) had methicillin-susceptible S. aureus infection. Of the 95 MRSA isolates causing hospital-acquired infection, 69 (73%) were USA300 isolates, and that rate did not increase over time. Skin and soft tissue infection (P < .001), onset of infection less than 10 days after admission (P = .007), and lack of comorbidities (P < .001) were associated with hospital-acquired MRSA infection caused by the USA300 strain, compared with other isolates (hereafter referred to as non-USA300 isolates). Nine of 10 patients with a S. aureus infection at the time of death were infected with a non-USA300 strain. USA300 carried SCCmec IV, agr I, the diamine N-acetyl transferase gene, and pvl. USA300 isolates were more susceptible to clindamycin, gentamicin, and trimethoprim-sulfamethoxazole than were other non-USA300 isolates (P < .01).

CONCLUSIONS

In our patient population, the annual numbers of observed cases of hospital-acquired S. aureus infection have remained constant. USA300 was the most common clone and, compared with other non-USA300 MRSA isolates, was associated with skin and soft tissue infection, early onset of infection after admission, and greater susceptibility to antimicrobial agents.

Mapping the distribution of invasive Staphylococcus aureus across Europe

Franklin Lowy discusses a new study in PLoS Medicine in which the investigators developed an interactive tool for analyzing the spatial distribution of invasive Staphylococcus aureus.

USA300 is the predominant genotype causing Staphylococcus aureus septic arthritis in children

BACKGROUND

Staphylococcus aureus is the most common cause of septic arthritis (SA) in children. USA300 is the predominant community methicillin-resistant (MRSA) clone. Panton-Valentine leukocidin genes (pvl) have been associated with severe disease.

METHODS

Patients with S. aureus SA were identified from the Texas Children's Hospital surveillance study. Pulsed field gel electrophoresis and pvl polymerase chain reaction were performed on isolates.

RESULTS

Forty-five patients with S. aureus SA were identified between August 2001 and October 2008. Median age was 5.5 years (0.3-17.9 years); 69% were previously healthy. The most common joints affected were hip (40%) followed by knee (36%). Associated infection sites were osteomyelitis (n = 14), pyomyositis/myositis (n = 13), and cellulitis (n = 9). Bacteremia for 1 to 5 days occurred in 31% of the patients. Patients with associated osteomyelitis were more likely to be bacteremic (P = 0.001), have fever >2 days (P = 0.03), and to have C-reactive protein (CRP) > or = 10 mg/dL (P = 0.01). Of 44 available isolates, 16 were MRSA; 13 of 16 were USA300 and 14 of 16 were pvl+. Twenty-eight isolates were MSSA; 8 of 28 were USA300 and 13 of 28 were pvl+. Infections caused by USA300 isolates were associated with longer duration of fever than non-USA300 isolates (median, [range]: 4 [0-15] days vs 1 [0-8] days) (P = 0.03). Overall, 61% of the isolates were pvl+. CRP > or = 10 mg/dL was more likely in pvl+ infections than in pvl- infections (P = 0.05).

CONCLUSIONS

S. aureus SA caused by USA300 isolates is associated with longer duration of fever. Empirical treatment of SA should include MRSA. CRP levels > or = 10 mg/dL, fever >2 days, and bacteremia should raise suspicion for associated osteomyelitis.

Pediatric musculoskeletal infection: trends and antibiotic recommendations

In the past decade, the incidence of methicillin-resistant Staphylococcus aureus infections in children has increased. This phenomenon has led to a rise in complex, deep infections involving the musculoskeletal system for which a comprehensive approach of evaluation and treatment has become necessary. Whenever possible, cultures should be obtained to guide specific antibiotic selection. The potential for infections involving multiple tissue locations within the same patient and the risk for complications such as deep vein thrombosis necessitate a thorough, often multidisciplinary, approach in the care of these children. MRI is valuable in defining the anatomic and spatial extent of infection as well as in guiding the decision and approach for surgery. Most patients have favorable outcomes with sequential parenteral to oral antibiotic therapy after adequate surgical débridement of the infection. Close outpatient follow-up is essential to ensure antibiotic compliance and to identify late consequences of the infection.

Pediatric and neonatal Staphylococcus aureus bacteremia: epidemiology, risk factors, and outcome

OBJECTIVE

To evaluate the impact of methicillin-resistant Staphylococcus aureus on the prevalence of S. aureus bloodstream infection among children.

METHODS

Retrospective analysis of demographic data, risk factors for infection, and clinical outcomes for children (age, less than 18 years) with S. aureus bacteremia hospitalized at a children's hospital during 2001-2006.

RESULTS

We identified 164 episodes of S. aureus bacteremia among 151 children. The prevalence of bacteremia due to methicillin-susceptible S. aureus during 2001-2003 was approximately the same as that during 2004-2006 (29 and 30 cases, respectively, per 10,000 hospitalized children [hereafter, "per 10,000 hospitalizations"]), but the prevalence of bacteremia due to methicillin-resistant S. aureus increased from 4 to 11 cases, respectively, per 10,000 hospitalizations (P=.015). A total of 48% of infections involved children who had S. aureus-positive blood cultures less than 3 days after hospital admission. Seventy-four percent of these children had a preexisting comorbidity. When the prevalence of S. aureus bacteremia was stratified by race, sex, or age, neonates hospitalized at birth and Hispanic children had significantly reduced risks of infection. Children younger than 1 year of age (excluding neonates hospitalized at birth) had an increased prevalence of hospital-onset S. aureus bacteremia. There was a disproportionate increase in the risk of S. aureus bacteremia for each additional week of hospitalization among children with hospital-onset S. aureus bacteremia. Children with methicillin-resistant S. aureus bacteremia had a longer hospital stay, were transferred to another facility at a greater rate than they were discharged home, and had a greater mortality rate, compared with children with methicillin-susceptible S. aureus bacteremia.

CONCLUSION

This study documents the prevalence of S. aureus bacteremia among children with a high risk for acquiring this infection, and it describes populations of children who are at higher risk for bacteremia due to either methicillin-susceptible or methicillin-resistant S. aureus. Methods to improve prevention of S. aureus bacteremia are needed for children with healthcare-associated risk factors for S. aureus bacteremia.

Spread of methicillin-resistant Staphylococcus aureus USA300 in a neonatal intensive care unit

BACKGROUND

Reports of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in neonatal intensive care units (NICU) and in otherwise healthy patients without obvious risk factors have been increasing in frequency. Described herein is a cluster of cases of CA-MRSA USA300 strains in an NICU affecting infants, health-care workers and the health-care workers' families.

METHODS

Infants and health-care workers with infection and colonization due to MRSA between 1 January 2004 and 30 June 2005 in a tertiary care center NICU in San Antonio, TX were studied. Antimicrobial susceptibility testing and polymerase chain reaction detection of the mecA gene characterized the MRSA isolates. All MRSA cases were reviewed for clinical severity of infection and outcome.

RESULTS

During the 18 months studied, a total of four (0.6%) of 676 infants had CA-MRSA bacteremia or colonization. One infant with necrotizing pneumonia died and three health-care workers who directly cared for the infected infants developed soft-tissue infections caused by CA-MRSA. Four family members of two health-care workers subsequently developed soft-tissue infections. All of the analyzed isolates (eight of nine) belonged to pulsed-field type USA300 and possessed Panton-Valentine leukocidin genes, which have been associated with severe skin and soft-tissue infections, and necrotizing pneumonia.

CONCLUSIONS

It is likely that the CA-MRSA USA300 strain can be transmitted between NICU patients to health-care workers and their family members. The CA-MRSA cases reported here reinforce the virulence of CA-MRSA USA300 strains and emphasize the need to embrace infection control practices designed to protect hospitalized patients, health-care workers and their family members.

Pediatric antibody response to community-acquired Staphylococcus aureus infection is directed to Panton-Valentine leukocidin

We examined the antibody responses of pediatric patients infected with community-associated Staphylococcus aureus isolates. The data show that patients infected with Panton-Valentine leukocidin (PVL)-positive strains developed a dominant immunoglobulin G anti-PVL antibody response that correlates with markers of inflammation.

The role of molecular methods in the prevention of nosocomial methicillin-resistant Staphylococcus aureus clusters in cancer patients

In 2002, an increased incidence of nosocomial methicillin-resistant Staphylococcus aureus (MRSA) in our institution triggered a conventional investigation that failed to identify a common source. Molecular typing of the 70 nosocomial MRSA isolates obtained identified a predominant health care-associated clone A in the first trimester. Aggressive infection control measures led to a significant decrease in the number of isolates per 10,000 hospital days between the first trimester and the last 2 trimesters of 2003 (6.4 vs 3.8; P = .04). This was attributed to a decrease in clone A: SCCmec II, USA100, PVL gene-negative (2.3 per 10.000 patient-days vs 0.1 per 10,000 patient-days; P = .004). However, in 2003, 23% of the nosocomial isolates were SCCmec IV, USA300, PVL gene-positive. At that time, molecular methods allowed the detection and prevention of a nosocomial MRSA outbreak caused by a health care-associated clone; however, the community strains (SCCmec IV) have become a frequent cause of nosocomial infection in our institution.

Community-acquired methicillin-resistant Staphylococcus aureus pneumonia: radiographic and computed tomography findings

OBJECTIVE

The aim of our study was to review the radiologic findings of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) pneumonia.

MATERIALS AND METHODS

The hospital infection control computer database was used to identify patients who had a CA-MRSA infection with organisms isolated from blood, bronchoalveolar lavage fluid, or pleural fluid samples. Criteria for CA-MRSA pneumonia were consolidation seen on chest radiography or computed tomography (CT), growth of MRSA from sputum and/or sterile pulmonary site, clinical complaints of cough and/or shortness of breath. Chest radiographs and CT scans for 9 patients (5 men, mean age 45 y, range 35 to 71 y) were retrospectively reviewed by 2 chest radiologists.

RESULTS

The most common chest radiographic finding was consolidation, which was bilateral in 7 patients and unilateral in 2 patients. The consolidation was patchy and nonsegmental in 5 and segmental in 4 patients. Two patients had cavitation evident on the chest radiograph. The most common CT scan findings were bilateral (n=8), often symmetric (n=5) consolidation, bilateral septal lines (n=7), and multiple nodules (n=5). Cavitation was present in 5 patients, either in regions of consolidation (n=5) or in large nodules (n=3). Five patients with CA-MRSA pneumonia had rapid clinical deterioration requiring ventilatory support. Two patients died.

CONCLUSIONS

CA-MRSA pneumonia is characterized by extensive bilateral consolidation and frequent cavitation and is commonly associated with rapid progression and clinical deterioration. CT is superior to radiography in demonstrating the presence of cavitation.

Prevalence of and risk factors for community-acquired methicillin-resistant and methicillin-sensitive staphylococcus aureus colonization in children seen in a practice-based research network

OBJECTIVE

We sought to define the prevalence of and risk factors for methicillin-resistant Staphylococcus aureus nasal colonization in the St Louis pediatric population.

METHODS

Children from birth to 18 years of age presenting for sick and well visits were recruited from pediatric practices affiliated with a practice-based research network. Nasal swabs were obtained, and a questionnaire was administered.

RESULTS

We enrolled 1300 participants from 11 practices. The prevalence of methicillin-resistant S aureus nasal colonization varied according to practice, from 0% to 9% (mean: 2.6%). The estimated population prevalence of methicillin-resistant S aureus nasal colonization for the 2 main counties of the St Louis metropolitan area was 2.4%. Of the 32 methicillin-resistant S aureus isolates, 9 (28%) were health care-associated types and 21 (66%) were community-acquired types. A significantly greater number of children with community-acquired methicillin-resistant S aureus were black and were enrolled in Medicaid, in comparison with children colonized with health care-associated methicillin-resistant S aureus. Children with both types of methicillin-resistant S aureus colonization had increased contact with health care, compared with children without colonization. Methicillin-sensitive S aureus nasal colonization ranged from 9% to 31% among practices (mean: 24%). The estimated population prevalence of methicillin-sensitive S aureus was 24.6%. Risk factors associated with methicillin-sensitive S aureus colonization included pet ownership, fingernail biting, and sports participation.

CONCLUSIONS

Methicillin-resistant S aureus colonization is widespread among children in our community and includes strains associated with health care-associated and community-acquired infections.

Update on bacterial pathogens: virulence and resistance

The present article is an update of the literature on bacterial pathogens. Recognizing the interest and scientific and public health importance of infections produced by bacterial pathogens with new virulence mechanisms and/or new mechanisms of resistance to antimicrobial agents, a multidisciplinary group of Spanish physicians and microbiologists organized a joint session and revised the most important papers produced in the field during 2006. Each article was analyzed and discussed by one of the members of the panel. This paper focus on a variety of diseases that pose major clinical and public health challenges today; and include infections produced by community-acquired methicillin-resistant Staphylococcus aureus and S. aureus small colony variants, infections produced by multiply resistant coagulase-negative staphylococci, pneumococcal infections, human listeriosis, meningococcal disease, Haemophilus influenzae, pertussis, Escherichia coli, ESBL-producing organisms, and infections due to non-fermenters. After a review of the state of the art, papers selected in this field are discussed.

Hospital-acquired infections in the NICU: epidemiology for the new millennium

Nosocomial infections are an important cause of morbidity and mortality in the preterm neonate. Extrinsic and intrinsic risk factors make the preterm neonate particularly susceptible to infection. This review focuses on two major pathogens that cause nosocomial infection, Candida and methicillin-resistant Staphylococcus aureus. The difficult diagnosis of meningitis in the neonate also is discussed.

Molecular epidemiology of clinically significant antibiotic resistance genes

Antimicrobials were first introduced into medical practice a little over 60 years ago and since that time resistant strains of bacteria have arisen in response to the selective pressure of their use. This review uses the paradigm of the evolution and spread of beta-lactamases and in particular beta-lactamases active against antimicrobials used to treat Gram-negative infections. The emergence and evolution particularly of CTX-M extended-spectrum beta-lactamases (ESBLs) is described together with the molecular mechanisms responsible for both primary mutation and horizontal gene transfer. Reference is also made to other significant antibiotic resistance genes, resistance mechanisms in Gram-negative bacteria, such as carbepenamases, and plasmid-mediated fluoroquinolone resistance. The pathogen Staphylococcus aureus is reviewed in detail as an example of a highly successful Gram-positive bacterial pathogen that has acquired and developed resistance to a wide range of antimicrobials. The role of selective pressures in the environment as well as the medical use of antimicrobials together with the interplay of various genetic mechanisms for horizontal gene transfer are considered in the concluding part of this review.

[Osteoarticular infections with staphylococcus aureus secreting Panton-Valentine leucocidin]

Panton-Valentine Leucocidin (PVL) is associated in the USA with community-acquired meticillin resistant strains of Staphylococcus aureus (CA-MRSA). Bone and joint infection due to such strains appears to be more severe, necessiting longer antibiotic course and various surgical procedure. Our study of 14 PVL positive bone and joint infection, performed in France where PVL is rarely (2/14) associated with meticillin resistance, demonstrates that severity is linked with PVL secretion more than with resistance. Considering PVL associated bone and joint infections as a toxin-mediated disease, prompt diagnosis is needed in order to start specific therapeutic procedures. PVL mediated infection could be evoked in front of severe acute osteomyelitis or arthritis, with radiological abnormalities present in the first days of evolution and with pejorative evolution despite antibiotic treatment. Evolution toward multifocal osteomyelitis and/or multiple abscesses seems to be a major characteristic of such infection. Therapeutic approach should use an association of parenteral antibiotics with at least one molecule active against protein synthesis like Clindamycin, associated with betalactams or Vancomycin in area of high incidence of CA-MRSA. Surgical procedure should be considered whenever focal abscesses of bones or adjacent tissue is detected and should be repeated in most cases.

Antimicrobial-resistant pathogens: an emerging pediatric threat

The clinical impact of these three bacterial threats is readily apparent to any who practice pediatrics. The potential virulence of CA-MRSA and MDR pneumococci and the threat of failed antimicrobial options for MDRGN pose enormous challenges now and in the near future. With careful attention to antimicrobial stewardship, however, and knowledge of the clinical and epidemiologic factors of these organisms, one can hope to mitigate the impact on patient care and outcomes while awaiting ongoing discovery of new antimicrobial options. Most important, however, will be careful and thoughtful management of any new antimicrobial products to protect their efficacy for the future.

A review of community-associated methicillin-resistant Staphylococcus aureus skin and soft tissue infections

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a cause of infection among otherwise healthy children and adults in the community. Skin and soft tissue infections are most common, but invasive manifestations also occur. A limited number of strains that may possess unique virulence or transmissibility factors have accounted for the majority of these infections. These strains emerged in the community but now are being transmitted in both community and healthcare settings. Incision and drainage remains the primary treatment for skin abscesses. Strains of MRSA circulating in the community generally are susceptible to a number of nonbeta-lactam antimicrobial agents, although resistance patterns may vary temporally and geographically. Educating patients on strategies to prevent further transmission is a critical component of case management. More data are needed to determine optimal strategies for management and prevention of MRSA skin infections in the community.

Increase of the USA300 clone among community-acquired methicillin-susceptible Staphylococcus aureus causing invasive infections

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) USA300 is a predominant cause of community-acquired (CA) infection in the United States. We compared clinical characteristics of children with USA300 versus non-USA300 CA-methicillin-susceptible S. aureus (CA-MSSA) invasive infections at Texas Children's Hospital (TCH).

METHODS

Medical records were reviewed from children with invasive CA-MSSA infections at TCH between August 1, 2001 and September 30, 2006. Isolates were characterized by pulsed-field gel electrophoresis and polymerase chain reaction for Panton-Valentine leukocidin genes (pvl).

RESULTS

Invasive CA-MSSA infections increased from 14 in year 1 to 36 in year 5 (5-year total = 122 patients). Among the CA-MSSA isolates available for typing in the 5-year period, USA300 MSSA strains increased from 14% (2 of 14) to 35% (11 of 31) (P = 0.03). USA300 MSSA strains were more likely than non-USA300 MSSA strains to be nonsusceptible to erythromycin [66% (19 of 29) versus 28% (25 of 88); P < 0.01]. Osteomyelitis cases increased from 43% (6 of 14) in year 1 to 67% (24 of 36) in year 5. The majority of pvl(+) MSSA isolates were USA300 (71% (25 of 35); only 5% (4 of 82) of pvl(-) MSSA isolates were USA300. Patients with osteomyelitis caused by pvl isolates had significantly higher mean values for erythrocyte sedimentation rate at admission (P = 0.005) and erythrocyte sedimentation rate maximum value (P = 0.002), maximum C-reactive protein (P = 0.04), and absolute neutrophil count at presentation (P = 0.04) compared with patients whose isolates were pvl(-).

CONCLUSIONS

USA300 accounted for a growing proportion of CA-MSSA isolates among children and was associated with increased numbers of invasive CA-MSSA infections at TCH, especially osteomyelitis. Associations were found in CA-MSSA osteomyelitis between pvl and increased concentrations of systemic inflammatory markers in patients.

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

Background

Community 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.

Results

We sequenced the genomes of two pediatric USA300 isolates: one CA-MRSA and one CA-methicillin susceptible (MSSA), isolated at Texas Children's 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.

Conclusion

USA300-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.

Evaluation and treatment of community-acquired Staphylococcus aureus infections in term and late-preterm previously healthy neonates

OBJECTIVE

We describe the evaluation and treatment of neonatal community-acquired Staphylococcus aureus disease in the era of community-acquired methicillin-resistant S. aureus.

METHODS

We retrospectively reviewed the evaluation and treatment of 126 community-acquired S. aureus infections of term and late-preterm previously healthy neonates who were < or = 30 days of age between August 2001 and July 2006 at Texas Children's Hospital.

RESULTS

S. aureus infections included 43 pustulosis, 68 cellulitis/abscess, and 15 invasive infections. We found 84 methicillin-resistant and 42 methicillin-susceptible S. aureus isolates. Twenty-one patients received outpatient antibiotics before hospital presentation. Systemic infection evaluation included urine, blood, and cerebrospinal fluid cultures in 79, 102, and 84 neonates, respectively. Culture revealed S. aureus urinary tract infections in 1, S. aureus bacteremias in 6, and aseptic cerebrospinal fluid pleocytosis of unclear cause in 11 neonates. Physicians admitted 106, transferred 5 to other hospitals, and discharged 15 afebrile patients with topical or oral antibiotics. Clindamycin was the predominant antistaphylococcal intravenous and oral antibiotic for pustulosis and cellulitis/abscess infections. One patient with systemic S. aureus and herpes simplex virus infection died. At discharge after inpatient treatment, physicians prescribed no antibiotics for 43 patients and oral or topical antibiotics for 62 patients. Outpatient treatment failed for 1 patient who was discharged after intravenous therapy and was readmitted. Eighty percent (16 of 20) of patients with mastitis alone completed treatment with outpatient oral antibiotics.

CONCLUSIONS

Evaluation and treatment strategies for neonatal community-acquired S. aureus disease are varied at our hospital. Prospective studies are needed to determine optimal management strategies.