Isaac P. Thomsen

Relationship Between Maternal and Neonatal Staphylococcus aureus Colonization

OBJECTIVE: The study aimed to assess whether maternal colonization with Staphylococcus aureus during pregnancy or at delivery was associated with infant staphylococcal colonization. METHODS: For this prospective cohort study, women were enrolled at 34 to 37 weeks of gestation between 2007 and 2009. Nasal and vaginal swabs for culture were obtained at enrollment; nasal swabs were obtained from women and their infants at delivery and 2- and 4-month postbirth visits. Logistic regression was used to determine whether maternal colonization affected infant colonization. RESULTS: Overall, 476 and 471 mother-infant dyads had complete data for analysis at enrollment and delivery, respectively. Maternal methicillin-resistant S aureus (MRSA) colonization occurred in 10% to 17% of mothers, with the highest prevalence at enrollment. Infant MRSA colonization peaked at 2 months of age, with 20.9% of infants colonized. Maternal staphylococcal colonization at enrollment increased the odds of infant staphylococcal colonization at birth (odds ratio; 95% confidence interval: 4.8; 2.4–9.5), hospital discharge (2.6; 1.3–5.0), at 2 months of life (2.7; 1.6–4.3), and at 4 months of life (2.0; 1.1–3.5). Similar results were observed for maternal staphylococcal colonization at delivery. Fifty maternal-infant dyads had concurrent MRSA colonization: 76% shared isolates of the same pulsed-field type, and 30% shared USA300 isolates. Only 2 infants developed staphylococcal disease. CONCLUSIONS: S aureus colonization (including MRSA) was extremely common in this cohort of maternal-infant pairs. Infants born to mothers with staphylococcal colonization were more likely to be colonized, and early postnatal acquisition appeared to be the primary mechanism.

Effect of Varying Doses of a Monovalent H7N9 Influenza Vaccine With and Without AS03 and MF59 Adjuvants on Immune Response A Randomized Clinical Trial

IMPORTANCE Human infections with the avian influenza A(H7N9) virus were first reported in China in 2013 and continue to occur. Hemagglutinin H7 administered alone is a poor immunogen necessitating evaluation of adjuvanted H7N9 vaccines. OBJECTIVE To evaluate the immunogenicity and safety of an inactivated H7N9 vaccine with and without AS03 adjuvant, as well as mixed vaccine schedules that included sequential administration of AS03- and MF59-containing formulations and of adjuvanted and unadjuvanted formulations. DESIGN, SETTING, AND PARTICIPANTS Double-blind, phase 2 trial at 5 US sites enrolled 980 adults aged 19 through 64 years from September 2013 through November 2013; safety follow-up was completed in January 2015. INTERVENTIONS The H7N9 vaccine was given on days 0 and 21 at nominal doses of 3.75 µg, 7.5 µg, 15 µg, and 45 µg of hemagglutinin with or without AS03 or MF59 adjuvant mixed on site. MAIN OUTCOMES AND MEASURES Proportions achieving a hemagglutination inhibition antibody (HIA) titer of 40 or higher at 21 days after the second vaccination; vaccine-related serious adverse events through 12 months after the first vaccination; and solicited signs and symptoms after vaccination through day 7. RESULTS Two doses of vaccine were required to induce detectable antibody titers in most participants. After 2 doses of an H7N9 formulation containing 15 µg of hemagglutinin given without adjuvant, with AS03 adjuvant, or with MF59 adjuvant, the proportion achieving an HIA titer of 40 or higher was 2% (95% CI, 0%-7%) without adjuvant (n = 94), 84% (95% CI, 76%-91%) with AS03 adjuvant (n = 96), and 57% (95% CI, 47%-68%) with MF59 adjuvant (n = 92) (P < .001 for comparison of the AS03 and MF59 schedules). The 2 schedules alternating AS03-and MF59-adjuvanted formulations led to lower geometric mean titers (GMTs) of (41.5 [95% CI, 31.7-54.4]; n = 92) and (58.6 [95% CI, 44.3-77.6]; n = 96) than the group induced by 2 AS03-adjuvanted formulations (n = 96) (103.4 [95% CI, 78.7-135.9]; P < .001) but higher GMTs than 2 doses of MF59-adjuvanted formulation (n = 94) (29.0 [95% CI, 22.4-37.6]; P < .001). CONCLUSIONS AND RELEVANCE The AS03 and MF59 adjuvants augmented the immune responses to 2 doses of an inactivated H7N9 influenza vaccine, with AS03-adjuvanted formulations inducing the highest titers. This study of 2 adjuvants used in influenza vaccine formulations with adjuvant mixed on site provides immunogenicity information that may be informative to influenza pandemic preparedness programs. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT01942265.

Novel Risk Factors for Recurrent Clostridium difficile Infection in Children

Objectives: Clostridium difficile, a common cause of antibiotic-associated diarrhea, has been reported to recur in high rates in adults. The rates and risk factors for recurrent C difficile infection (rCDI) in children have not been well established. Methods: We conducted a retrospective cohort study of 186 pediatric patients seen at a tertiary care referral center for a 5-year period diagnosed as having a primary C difficile infection. Children with recurrent disease, defined as return of symptoms of C difficile infection and positive testing ⩽60 days after the completion of therapy, were compared with children who did not experience an episode of recurrence. Results: Of the 186 pediatric patients included in this study, 41 (22%) experienced rCDI. On univariable analysis, factors significantly associated with rCDI included malignancy, recent hospitalization, recent surgery, antibiotic use, number of antibiotic exposures by class, acid blocker use, immunosuppressant use, and hospital-acquired disease. On multivariable analysis, malignancy (odds ratio [OR] 3.39, 95% confidence interval [CI] 1.52–7.85), recent surgery (OR 2.40, 95% CI 1.05–5.52), and the number of antibiotic exposures by class (OR 1.33, 95% CI 1.01–1.75) were significantly associated with recurrent disease in children. Conclusions: The rate of rCDI in children was 22%. Recurrence was significantly associated with the risk factors of malignancy, recent surgery, and the number of antibiotic exposures by class.

Monoclonal Antibodies Against the Staphylococcus aureus Bicomponent Leukotoxin AB Isolated Following Invasive Human Infection Reveal Diverse Binding and Modes of Action

The 2-component leukotoxin LukAB is critical for Staphylococcus aureus targeting and killing of human neutrophils ex vivo and is produced in the setting of human infection. We report 3 LukAB-specific human monoclonal antibodies (mAbs) with distinct mechanisms of toxin neutralization and in vivo efficacy. Three hybridomas secreting mAbs with anti-LukAB activity (designated SA-13, -15, and -17) were generated from B cells obtained from a 12-year-old boy with S. aureus osteomyelitis. Each of the 3 mAbs neutralized LukAB-mediated neutrophil toxicity, exhibited differing levels of potency, recognized different antigenic sites on the toxin, and displayed at least 2 distinct mechanisms for cytotoxic inhibition. SA-15 bound exclusively to the dimeric form of the toxin, suggesting that human B cells recognize epitopes on the dimerized form of LukAB during natural infection. Both SA-13 and SA-17 bound the LukA monomer and the LukAB dimer. Although all 3 mAbs potently neutralized cytotoxicity, only SA-15 and SA-17 significantly inhibited toxin association with the cell surface. Treatment with a 1:1 mixture of mAbs SA-15 and SA-17 resulted in significantly lower bacterial colony counts in heart, liver, and kidneys in a murine model of S. aureus sepsis. These data describe the isolation of diverse and efficacious antitoxin mAbs.

Frequency of Disinfectant Resistance Genes in Pediatric Strains of Methicillin-Resistant Staphylococcus aureus

Resistance to chlorhexidine gluconate (CHG) and quaternary ammonium compounds (QACs) is a potential public health threat, given widespread use of these agents for routine hospital cleaning, skin antisepsis, and patient decolonization.1–3 Development of tolerance to CHG and QACs among methicillin-resistant Staphylococcus aureus (MRSA) isolates can be mediated by energy-dependent multidrug efflux proteins, which show increased expression in response to selective pressure from disinfectant use.4 Plasmid-encoded efflux pump genes qac A/B and smr confer tolerance to both CHG and QACs, along with other compounds, including intercalating dyes and cationic biocides.5,6 The efflux pump genes qac A/B and smr have been found in MRSA isolates with varying frequencies globally, mostly in tertiary-care adult and pediatric populations.6 Here we describe an evaluation of pediatric clinical MRSA isolates for the presence of disinfectant resistance genes qac A/B and smr, and for tolerance to CHG. Two hundred eighty-one clinical pediatric MRSA isolates from 2004 through 2009 were selected randomly from the Vanderbilt Children’s Hospital MRSA Repository, a de-identified collection of unique MRSA isolates obtained from emergency room or hospitalized general pediatric patients with MRSA infection. The MRSA Repository is approved by the Vanderbilt Institutional Review Board and maintained as a de-identified dataset with limited clinical information. All isolates were identified by the Vanderbilt University Hospital Laboratory according to Clinical and Laboratory Standards Institute standards prior to repository transfer. Isolates were cultured overnight on blood agar at 37°C, and purified genomic DNA was used as a template for repetitive-element, sequence-based polymerase chain reaction to determine genetic classification of strains (DiversiLab System, Biomerieux). Plasmid-encoded qac A/B and smr genes were evaluated by PCR using previously published primers.7,8 Minimum bactericidal concentrations (MBCs) of a randomly selected subset of 5 qac A/B and 5 smr positive MRSA strains, along with 5 randomly selected negative controls, were determined by broth microdilution methods using 20% w/v chlorhexidine digluconate solution (Sigma-Aldrich Corp., St. Louis, Mo.).1 A Fisher Exact Test was performed to determine statistical significance. Of the 281 isolates identified in the repository, 201 isolates (71.5%) belonged to USA300, the current epidemic clone in the United States. Of the remainder, 31 isolates (11.0%) belonged to USA100, 31 isolates (11.0%) belonged to USA500, and 18 isolates (6.4%) were other pulse types. Genes for qac A/B or smr were detected in 18.5% of isolates (52/281); 13.9% contained smr only, 4.3% harbored qac A/B, and 1 isolate contained both smr and qacA/B. Non-USA300 MRSA isolates were significantly more likely to harbor qac A/B or smr genes than USA300 MRSA isolates (Figure 1; P = 0.0175). MBC testing of 15 MRSA isolates (5 negative controls, 5 qac A/B positive, and 5 smr positive) in serial dilutions of CHG showed that all 15 isolates had MBCs less than 16 μg/mL, well below the recommended in-use concentration of 2000 μg/mL.6 No significant differences in MBC were noted between qac A/B or smr positive isolates and negative controls. Figure 1 Presence of disinfectant resistance genes smr and qac A/B by methicillin-resistant Staphylococcus aureus pulse type. Non-USA300 isolates were more likely than USA300 isolates to harbor smr or qacA/B (P = 0.0175). We found a moderate prevalence of plasmid-encoded disinfectant resistance genes (18.5%) in this random sample of pediatric MRSA isolates, similar to other studies in US pediatric populations.9 In our study, pediatric isolates belonging to USA300, the pulse type associated with the community-associated MRSA epidemic, were less likely than non-USA300 MRSA isolates to possess disinfectant resistance genes. Nearly 15% of the USA300 strains, however, also harbored genes for efflux pumps capable of conferring tolerance to CHG. This was an unexpected finding given the USA300 clone’s predominant association with community-onset MRSA infection, since CHG is considered a healthcare-associated exposure. This study has limited generalizability because it represents a single center study that may not apply to other geographic regions. The de-identified nature of the dataset attached to the MRSA repository did not allow for evaluation of the emergence of disinfectant resistance genes over time, or evaluation of the relationship of disinfectant resistance genes to specific MRSA infections, such as device-associated infection. CHG has gained an increasing role in the infection prevention arsenal for reducing healthcare-associated infections, and CHG resistance threatens current infection prevention efforts directed against multi-drug resistant organisms. CHG is widely used for surgical antisepsis, and daily bathing of critically-ill patients with CHG is commonplace. The Randomized Evaluation of Decolonization vs Universal Clearance to Eliminate (REDUCE) MRSA trial showed that universal decolonization using nasal mupirocin and bathing with CHG significantly reduced rates of bloodstream infections in the community intensive care unit setting.3 The popularity of universal decolonization strategies will further increase the use of CHG in hospital settings. Thus, it is important to consider the mechanisms by which MRSA might survive CHG exposure in the clinical setting. Staphylococcus aureus possesses both chromosomal and plasmid-mediated efflux pumps capable of targeting a wide range of compounds, from antimicrobials to disinfectants. Previous evaluations of CHG bactericidal activity against qac A/B gene-positive MRSA strains have shown evidence of increased tolerance to CHG with elevated MBC in those strains.1, 6 Another study showed increased tolerance and overexpression of S. aureus efflux pumps in association with exposure to disinfectants.4 Our limited evaluation of bactericidal activity showed no evidence of increased MBC in qac A/B or smr positive isolates. Reassuringly, no MRSA isolates harboring phenotypic CHG resistance have been reported to date. In summary, this report demonstrates a moderate prevalence of disinfectant resistance genes in a pediatric population, both in USA300 and non-USA300 MRSA isolates. Non-USA300 isolates were significantly more likely to harbor disinfectant resistance genes. Ongoing evaluation of genotypic and phenotypic CHG resistance will help gauge the effectiveness of future infection prevention efforts utilizing CHG.

SHOULD HIGHER VANCOMYCIN TROUGH LEVELS BE TARGETED FOR INVASIVE COMMUNITY-ACQUIRED METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS INFECTIONS IN CHILDREN?

Methicillin-resistant Staphylococcus aureus isolates with vancomycin minimal inhibitory concentrations (MICs) ≥1.5 &mgr;g/mL have been associated with poorer clinical outcomes and treatment failures in adults. We evaluated vancomycin MICs in 71 invasive pediatric community-acquired MRSA isolates from 2004 to 2008, using the E-test micromethod and the E-test macro-method. The modal MIC by micromethod was 1.5 &mgr;g/mL, and median vancomycin MICs did not increase over time.

A Comprehensive Approach to the Management of Children and Adults with Chronic Granulomatous Disease

Chronic granulomatous disease (CGD), a disease characterized by inadequate neutrophil killing of microbial pathogens, affects 4 to 5 per million live births. For many decades following its description, CGD was a fatal disease in childhood. With the development of effective preventive therapies and the early recognition of infectious complications, 90% of children with CGD now survive into adulthood. The management of CGD in adults includes unique challenges and potential disease manifestations. In this article, the authors discuss the current approach to the management of CGD in both children and adults. This includes a focus on the importance of a comprehensive multidisciplinary approach in the care of CGD and its potential complications. In addition, a novel approach to improving education about CGD, and subsequently improving adherence to preventive therapies, is discussed.

Molecular distinctions exist between community-associated methicillin-resistant Staphylococcus aureus colonization and disease-associated isolates in children.

Objective: To define the molecular epidemiology of colonization and disease-associated isolates of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA). Design: Laboratory-based comparative study of clinical staphylococcal isolates. Methods: We analyzed 255 pediatric CA-MRSA isolates for molecular characteristics associated with colonization and disease. We used polymerase chain reaction to determine the presence of Panton-Valentine Leukocidin and the lantibiotic element, bsaB, and to characterize the staphylococcal cassette chromosome mec type and accessory gene regulator locus. Pulsed-field gel electrophoresis was used to determine genetic relatedness between strains. Results: A total of 150 isolates were obtained from patients with clinical disease (37 invasive infections, 113 noninvasive infections) and 105 from subjects with nasal colonization alone. Of 150 disease-associated isolates, 123 (82%) belonged to pulsed-field gel electrophoresis group USA300, whereas only 19 (18%) of 105 colonization isolates were of the USA300 lineage. Colonization isolates were less likely to possess staphylococcal cassette chromosome mec type IV, Panton-Valentine Leukocidin, or agr type 1 (P < 0.001). Conclusions: Colonization strains of CA-MRSA in children differ significantly from those strains recovered from patients with staphylococcal infections. This suggests that only colonization with specific strain types, rather than methicillin-resistant Staphylococcus aureus colonization in general, increases the risk for CA-MRSA disease.

Longitudinal Assessment of Colonization With Staphylococcus aureus in Healthy Collegiate Athletes

BACKGROUND Staphylococcus aureus is the leading cause of skin and soft tissue infections in the United States, and S. aureus colonization increases the risk of infection. Although athletes have a higher risk of infection with S. aureus than the general population, most studies in athletes have not assessed colonization. METHODS We conducted a prospective cohort study of Vanderbilt University varsity athletes from August 2008 to April 2010. We assessed nasal and oropharyngeal colonization with methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains by obtaining swabs at enrollment and monthly thereafter until the end of the study. The athletes were also monitored for skin and soft tissue infections. RESULTS We enrolled 377 athletes and trainers (224 in contact sports and 153 in noncontact sports). The total S. aureus colonization prevalence ranged from 34% to 62%, and for MRSA it ranged from 8% to 29%. The colonization rate in the summer was significantly higher than that in the winter (odds ratio for MRSA [ORMRSA], 1.70 [95% confidence interval (CI), 1.23-2.35]; ORMSSA, 1.38 [95% CI, 1.05-1.82]). Of 603 MRSA isolates, 75% carried the staphylococcal cassette chromosome mec (SCCmec) type IV, and 5% carried the genes encoding Panton-Valentine leukocidin. Nine symptomatic S. aureus infections occurred, 7 of which were between July and September. CONCLUSIONS The S. aureus colonization rate is higher than previously reported and fluctuated over time in this prospective cohort of athletes. The higher colonization prevalence during summer might explain the infectious outbreak during the summer months and may represent a key intervention time for preventing S. aureus disease in athletes.

Host response to Staphylococcus aureus cytotoxins in children with cystic fibrosis

BACKGROUND Staphylococcus aureus is one of the earliest bacterial pathogens to colonize the lungs of children with cystic fibrosis and is an important contributor to pulmonary exacerbations. The adaptive host response to S. aureus in cystic fibrosis remains inadequately defined and has important implications for pathogenesis and potential interventions. The objectives of this study were to determine the functional antibody response to select staphylococcal exotoxins (LukAB, alpha-hemolysin, and PVL) in children with cystic fibrosis and to evaluate the relationship of this response with pulmonary exacerbations. METHODS Fifty children with cystic fibrosis were enrolled and followed prospectively for 12months. Clinical characteristics and serologic profiles were assessed at routine visits and during pulmonary exacerbations, and functional antibody assessments were performed to measure neutralization of LukAB-mediated cytotoxicity. RESULTS For each antigen, geometric mean titers were significantly higher if S. aureus was detected at the time of exacerbation. For LukAB, geometric mean titers were significantly higher at exacerbation follow-up compared to titers during the exacerbation, consistent with expression during human disease, and the humoral response capably neutralized LukAB-mediated cytotoxicity. Moreover, the presence of a positive S. aureus culture during a pulmonary exacerbation was associated with 31-fold higher odds of having a LukA titer ≥1:160, suggesting potential diagnostic capability of this assay. CONCLUSIONS The leukotoxin LukAB is expressed by S. aureus and recognized by the human adaptive immune response in the setting of pulmonary infection in cystic fibrosis. Anti-LukAB antibodies were not only predictive of positive staphylococcal culture during exacerbation, but also functional in the neutralization of this toxin.