Edward O. Mason

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.

Prospective comparison of risk factors and demographic and clinical characteristics of community-acquired, methicillin-resistant versus methicillin-susceptible Staphylococcus aureus infection in children.

Context. Community-acquired, methicillin-resistant Staphylococcus aureus (CA-MRSA) infections in children are increasing in frequency for unknown reasons. Objectives. To compare the presence of risk factors for methicillin resistance between patients with CA-MRSA and community-acquired methicillin-susceptible S. aureus (CA-MSSA) infection and to compare the presence of risk factors among household contacts of the patients from both groups. To compare the demographic and clinical characteristics between children with CA-MRSA and CA-MSSA infection. Design. Prospective observational study conducted between February 2, 2000 and November 14, 2000, excluding the month of May and the period between September 2 and October 15. Setting and patients. Texas Children’s Hospital, Houston, TX; inpatients and outpatients with community-acquired S. aureus infection. Main outcome measures. Proportion of MRSA among all community-acquired S. aureus infections. The presence of risk factors associated with methicillin resistance among patients, and their household contacts, with CA-MRSA and CA-MSSA. Results. The monthly rates of methicillin resistance of S. aureus varied between 35 and 51%. CA-MSSA isolates were associated with deep-seated infections significantly more often (30%) than CA-MRSA isolates (11%;P = 0.01). CA-MRSA isolates were generally susceptible to clindamycin and trimethoprim-sulfamethoxazole and resistant to erythromycin. There were no significant differences in the exposure to risk factors between children with CA-MRSA and CA-MSSA infection. No significant risk factors for CA-MRSA were identified among household contacts. Conclusions. MRSA is an established, community-acquired pathogen in our area. This necessitates a change in empiric therapy of infections suspected to be caused by S. aureus.

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.

Clindamycin treatment of invasive infections caused by community-acquired, methicillin-resistant and methicillin-susceptible Staphylococcus aureus in children.

Background. Community-acquired, methicillin-resistant Staphylococcus aureus (CA-MRSA) is an established pathogen in several areas of the United States, but experience with clindamycin for the treatment of invasive MRSA infections is limited. We compared the outcome of therapy for MRSA with that of methicillin-susceptible (MSSA) invasive infections in children treated with clindamycin, vancomycin or beta-lactam antibiotics. Methods. The demographics, hospital course and outcome of children at Texas Children’s Hospital between February and November 2000 and between August 2001 and August 2002 with invasive S. aureus infections were reviewed from medical records in this retrospective study. Results. CA-MRSA and community-acquired methicillin-susceptible S. aureus (MSSA) caused invasive infections in 46 and 53 children, respectively. The median ages (range) of the children were: MRSA, 3.5 years (2 months to 18.6 years); MSSA, 4.8 years (3 months to 19.8 years). The sites of infection for MRSA vs. MSSA isolates, respectively, were: bacteremia, 3 vs. 6; osteomyelitis, 14 vs. 14; septic arthritis, 5 vs. 7; pneumonia, 11 vs. 3; lymphadenitis, 7 vs. 14; other, 5 vs. 8. Among MRSA patients 39 (20 received clindamycin only, 18 had vancomycin initially and 8 were treated with a beta-lactam initially) received clindamycin and 6 received vancomycin as primary therapy. Among MSSA patients, clindamycin, nafcillin or other beta-lactam antibiotics were used in 24, 18 and 9, respectively. The median number of febrile days was 3 (0 to 14) and 2 (0 to 6) for MRSA and MSSA patients, respectively (P = 0.07). The median number of days with positive blood cultures was 2 for the MRSA (n = 16) and 1 for the MSSA (n = 18) patients (P = 0.04). Conclusion. Clindamycin was effective in treating children with invasive infections caused by susceptible CA-MRSA isolates.

Early Trends for Invasive Pneumococcal Infections in Children After the Introduction of the 13-valent Pneumococcal Conjugate Vaccine

Background: The 13-valent pneumococcal conjugate vaccine (PCV13) was introduced for routine administration to infants and children in 2010 in the United States. We have monitored clinical and microbiologic features of invasive pneumococcal infections among children before and after PCV13 use. Methods: Infants and children cared for at 8 children hospitals in the United States with culture-proven invasive infections caused by S. pneumoniae were identified in an ongoing prospective surveillance study. Demographic and clinical data were recorded on a standard case report form. Serotype and antimicrobial susceptibilities of isolates were determined. Results: Since routine PCV13 immunization in 2010, invasive pneumococcal infections decreased 42% overall and 53% for children <24 months of age in 2011 compared with the average number of cases for 2007 to 2009. PCV13 serotype isolates decreased 57% during these same time periods; 19A, 7F and 3 decreased by 58%, 54% and 68%, respectively. The number of infections caused by serotypes 1 and 6C also decreased in 2011. The most common non-PCV13 serotypes encountered in 2010 and 2011 combined were 33F, 22F, 12, 15B, 15C, 23A and 11. Bacteremia, pneumonia and mastoiditis cases decreased more than meningitis cases. Conclusions: After the introduction of PCV13, invasive pneumococcal infections decreased among 8 children hospitals compared with the 3 years before PCV13 use. Slight increases in some non-PCV13 serotype isolates were noted in 2011. Continued surveillance is necessary to determine the effectiveness of PCV13 including herd protection as well as any emerging invasive serotypes.

Diffusion of rifampin and vancomycin through a Staphylococcus epidermidis biofilm.

Using an equilibrium dialysis chamber, we evaluated the penetration of vancomycin, rifampin, or both through a staphylococcal biofilm to simulate treatment of an infected biomedical implant. A biofilm of ATCC 35984 (slime-positive Staphylococcus epidermidis; vancomycin MIC and MBC, 1 and 2 micrograms/ml, respectively; rifampin MIC and MBC, 0.00003 and 0.00025 micrograms/ml, respectively) was established on the inner aspect of the dialysis membrane (molecular mass exclusion, 6,000 kDa). Serum containing vancomycin (40 micrograms/ml), rifampin (20 micrograms/ml), or a combination of both was introduced into the inner chamber of the dialysis unit (in direct contact with the biofilm), and serum alone was added to the outer chamber. Rifampin and vancomycin concentrations in both chambers were determined over a 72-h period. In the absence of rifampin, the concentration of vancomycin in the outer chamber exceeded the MBC for the organism after 24 h, and the MBC increased to nearly 8.0 micrograms/ml by 72 h, demonstrating that therapeutic levels of vancomycin can penetrate a staphylococcal biofilm. However, viable bacteria were recovered from the biofilm after 72 h of treatment with no apparent increase in the MIC or MBC of vancomycin. Similarly, concentrations of rifampin exceeding the MBC were detected in the outer chamber after 24 h of treatment, but viable organisms were recovered from the biofilm after 72 h of treatment. In this case, the rifampin MBCs for surviving organisms increased from 0.00025 to > 128 micrograms/ml. The combination of agents prevented the development of resistance to rifampin, improved the perfusion of vancomycin through the biofilm, and decreased the penetration of rifampin but did not sterilize the membrane. These observations provide evidence that bactericidal levels of vancomycin, rifampin, or both can be attained at the surface of an infected implant. Despite this, sterilization of the biofilm was not accomplished after 72 h of treatment. Images

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.

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

Background: Community-acquired (CA), methicillin-resistant Staphylococcus aureus (MRSA) infections among children are increasing in the United States. At Texas Childrens Hospital (TCH), surveillance has been in place since August 2001. The objectives of this study were to describe the distribution of CA S. aureus among patients at TCH and to study genomic relationships of isolates collected between August 2001 and July 2003. Methods: Genomic relationships were determined with repetitive element-polymerase chain reaction (PCR). Multilocus sequence typing was performed for selected strains representing major clones. Molecular characterization of CA-MRSA was performed with PCR, including staphylococcal cassette chromosome (SCCmec), pvl (lukS-PV plus lukF-PV), hla, hlb and selected microbial surface components recognizing adhesive matrix molecule genes, ie, cna, clfA, fnbA and fnbB. Results: A 62% increase was observed in CA S. aureus infections from year 1 (2001–2002) to year 2 (2002–2003), whereas the annual number of hospital admissions was unchanged. CA methicillin-sensitive S. aureus isolates were more likely to be associated with invasive infections than were CA-MRSA isolates (P < 0.01). TCH clone A, sequence type (ST) 8, was responsible for approximately 94% of all CA-MRSA isolated from children in the greater Houston area. Clone A differed from clones B (ST30) and C (ST1) by lacking the cna gene while carrying the fnbB gene. Conclusions: One CA-MRSA clone, TCH clone A, has become the predominant cause of CA S. aureus infections among children in the Houston area. It causes a wide spectrum of diseases, including complicated pneumonia.

Multinational study of pneumococcal serotypes causing acute otitis media in children

Background. Streptococcus pneumoniae is a major cause of acute otitis media (AOM) in young children. More than 90 immunologically distinct pneumococcal serotypes have been identified, but limited information is available regarding their relative importance in AOM. Methods. We analyzed nine existing datasets comprising pneumococcal isolates from middle ear fluid samples collected from 1994 through 2000 from 3232 children with AOM from Finland, France, Greece, Israel, several East European countries, the US and Argentina. We examined the distribution of pneumococcal serotypes in relation to several demographic and epidemiologic variables, including gender, age, antibiotic resistance and source of culture material. Results. The major serotypes identified included 19F and 23F, each comprising 13 to 25% of pneumococcal middle ear fluid isolates in most datasets; 14 and 6B, comprising 6 to 18%; whereas 6A, 19A and 9V each comprised 5 to 10%. Despite differences in location, study design and antibiotic susceptibility, each major serotype was prominent in most age groups of each dataset. Serotypes represented in the 7-valent pneumococcal conjugate vaccine (PCV-7, 4, 6B, 9V, 14, 18C, 19F, 23F) accounted for 60 to 70% of all pneumococcal isolates in the 6- to 59-month age range, but only 40 to 50% of isolates in children <6 or ≥60 months old. Serotype 3 and, in certain datasets, serotypes 1 and 5, were more important in the <6- and ≥60-month age groups. In each age group vaccine-related serotypes (mainly 6A and 19A) comprised an additional 10 to 15% of all pneumococcal isolates. Four serotypes (23F, 19F, 14 and 6B) accounted for 83% of all penicillin-resistant observations. Conclusions. This analysis of several geographically diverse datasets indicates that a limited number of serotypes, largely represented in PCV-7, accounted for the majority of episodes of pneumococcal AOM in children between 6 and 59 months of age. Certain serotypes appeared to be relatively more significant in children <6 months or >59 months of age.

Activity of oral antibiotics in middle ear and sinus infections caused by penicillin-resistant Streptococcus pneumoniae : implications for treatment

The increasing prevalence of intermediately and highly penicillin-resistant strains of Streptococcus pneumoniae is a problem worldwide. However, optimal management of patients with middle ear and sinus infections caused by resistant pneumococci has not been established. We performed agar dilution susceptibility studies on 71 strains of penicillin-resistant pneumococci (minimum inhibitory concentration (MIC), > or = 0.1 microgram/ml) recovered from middle ear and sinus cultures of Houston children against 13 oral antibiotics with the use of both established and newly proposed National Committee for Clinical Laboratory Standards susceptibility criteria. Of the 62 middle ear isolates 35 (56%) were intermediately resistant and 27 (44%) were highly resistant to penicillin. Of the 9 sinus isolates tested, 5 (56%) were intermediately resistant (MIC between 0.1 and 1 micrograms/ml) and 4 (44%) were highly resistant (MIC > or = 2 micrograms/ml) to penicillin. The MIC90 increased with increasing penicillin resistance for the antibiotics tested except for rifampin, ciprofloxacin, loracarbef, clindamycin and trimethoprim-sulfamethoxazole. None of the highly penicillin-resistant isolates was susceptible to loracarbef or trimethoprim-sulfamethoxazole. The MIC90 values for clindamycin and rifampin were similar for the intermediately and highly penicillin-resistant groups, and the number of susceptible isolates in each group remained greater than 90% for both antibiotics. Thirty-five isolates were resistant to erythromycin but susceptible to clindamycin, a susceptibility pattern distinctly different from that seen in South Africa and Europe, where clindamycin resistance parallels erythromycin resistance.(ABSTRACT TRUNCATED AT 250 WORDS)