Peggy Mankin

Epidemiology of community-onset staphylococcus aureus infections in pediatric patients: An experience at a children's hospital in central Illinois

BackgroundThe nation-wide concern over methicillin-resistant Staphylococcus aureus (MRSA) has prompted many clinicians to use vancomycin when approaching patients with suspected staphylococcal infections. We sought to characterize the epidemiology of community-onset S. aureus infections in hospitalized children to assist local clinicians in providing appropriate empiric antimicrobial therapy.MethodsFrom January 2005–June 2008, children (0–18 years old) admitted to the Childrens Hospital of Illinois with community-onset S. aureus infections were identified by a computer-assisted laboratory-based surveillance and medical record review.ResultsOf 199 patients, 67 (34%) had invasive infections, and 132 (66%) had skin and soft tissue infections (SSTIs). Among patients with invasive infections, S. aureus isolates were more likely to be susceptible to methicillin (MSSA 63% vs. MRSA 37%), whereas patients with SSTIs, S. aureus isolates were more likely to be resistant to methicillin (MRSA 64% vs. MSSA 36%). Bacteremia and musculoskeletal infections were the most common invasive infections in both groups of S. aureus. Pneumonia with empyema was more likely to be caused by MRSA (P = 0.02). The majority (~90%) of MRSA isolates were non-multidrug resistant, even in the presence of healthcare-associated risk factors.ConclusionEpidemiological data at the local level is important for antimicrobial decision-making. MSSA remains an important pathogen causing invasive community-onset S. aureus infections among hospitalized children. In our hospital, nafcillin in combination with vancomycin is recommended empiric therapy in critically ill patients with suspected invasive staphylococcal infections. Because up to 25% of MSSA circulating in our area are clindamycin-resistant, clindamycin should be used cautiously as empiric monotherapy in patients with suspected invasive staphylococcal infections.

Simultaneous carriage of multiple genotypes of Staphylococcus aureus in children

The co-existence of multiple genotypes in colonization by Staphylococcus aureus has not been fully investigated. The aim of this study was to evaluate the heterogeneity of S. aureus carriage in children. We evaluated 125 nasal and perianal swab samples that were positive for S. aureus from 76 children scheduled for elective surgery. For each sample, at least four colonies with the same or different morphotypes were selected for analysis. Multiple-locus variable-number tandem-repeat fingerprinting was used to determine the genetic relatedness and to characterize the clonality of the S. aureus strains. Of the 125 swabs, 91 (73 %) contained meticillin-sensitive S. aureus (MSSA), 8 (6 %) contained meticillin-resistant S. aureus (MRSA), and 26 (21 %) contained MSSA and MRSA simultaneously. A total of 738 S. aureus strains were evaluated with a mean of 6 colonies (range 4-15) picked from each culture. Of the 125 swabs, 32 (26 %) samples contained two genetically distinct S. aureus strains and 6 (5 %) contained three different genotypes. Multiple S. aureus strains simultaneously carried by individual children were genetically unrelated to each other. We concluded that the co-existence of multiple genotypes of S. aureus was common. The significance of multiple carriage is yet to be determined, but this intraspecies interplay could be important to pathogenicity and virulence in S. aureus.

Differences in adhesion receptor expression between immature and older platelets and red blood cells of neonates and adults

Purpose To examine the hypothesis that reticulated platelets and reticulocytes show elevated adhesion receptor expression compared with mature cells in both adult and neonatal cells. Methods Flow cytometry was used to examine laminin, fibronectin (VLA-6), and thrombospondin (glycoprotein IV [GPIV]) expression in reticulated red cells, reticulated platelets, and older peripherally circulating mature red cells and mature platelets in seven newborn cord blood samples and blood samples from eight adult volunteers. Results The difference in the neonatal reticulated platelet percentage of 9.2 ± 14.8% was not statistically significant from the adult reticulated platelet percentage of 5.0 ± 1.5% in this small population. There was a statistically significant difference between the reticulated cord blood red cell mean of 7.7 ± 1.8% and the adult mean of 3.1 ± 0.43%. Mean expression of VLA-6 was 96% in adult reticulated platelets, 79% in adult mature platelets, 81% in cord reticulated platelets and 65% in cord mature platelets. Mean expression of GPIV was similar, with corresponding values of 90%, 71%, 78%, and 57%. Reticulated red cells in adults averaged 44% VLA-4 and 46% GPIV; cord reticulocytes were 9% and 15%, respectively. Conclusions Reticulated cells newly released from the bone marrow express more adhesive receptors than mature cells in both groups. Cord blood samples showed hypoexpression of both receptor types in red blood cells and platelets.

Acquisition of High-Level Mupirocin Resistance and Its Fitness Cost among Methicillin-Resistant Staphylococcus aureus Strains with Low-Level Mupirocin Resistance

ABSTRACT We investigated whether methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) isolates with low-level mupirocin resistance can serve as recipients of a pSK41-like plasmid conferring high-level mupirocin resistance without substantial fitness cost. Our results suggest that acquisition of the plasmid conferring high-level mupirocin resistance was not necessarily associated with fitness cost in some MRSA recipients with low-level mupirocin resistance.

Association of whole blood aggregation response with immunogold-labeled glycoproteins in adult and neonatal platelets

A growing body of recent data has provided specifics about the hemostatic system in infants, emphasizing differences from adults. Although platelet structure in newborns and adults appears to be quite similar, precise information about platelets in the first week of life indicates functional hyporeactiveness. This study was designed with a twofold purpose: one was to determine if aggregation results corresponded to immunogold-labeled activation markers; the second was to use immunogold labeling to determine if infant platelets circulate in an activated state. The results showed significant differences in ristocetin (P = .03) and collagen (P = .003) impedance, and whole blood aggregation lag times in infants when compared to adults. Treatment of neonatal platelets with collagen yielded decreased ATP release compared with adults. Immunogold labeling of specific activation markers CD62 (P-selectin) and CD63 (GP53) revealed that neonatal platelets were not circulating in an activated state. Significant (P = .04) anti-CD41 (GPIIb) immunogold labeling differences were observed after thrombin stimulation, with adults binding more particles. These data suggest that hyporeactivity of neonatal platelets is not due to a circulating preactivated state, but instead may be a consequence of impaired intracellular signaling that affects both aggregation and membrane activation labeling. Whether this signaling is secondary to an intrinsic neonatal alteration or a maternal (in utero) environmental effect is yet to be determined.

Molecular surveillance of Staphylococcus aureus colonization in a neonatal intensive care unit

In a survey of staphylococcal colonization, Staphylococcus aureus was detected in 7 of 67 infants (10%). Two of the infants (3%) carried methicillin-resistant S aureus (MRSA), revealing an unsuspected transmission of MRSA within the neonatal intensive care unit. Molecular surveillance of S aureus provided useful information to improve infection control practices.

A prospective study of methicillin-resistant Staphylococcus aureus colonization in children scheduled for elective surgery

BACKGROUND Staphylococcus aureus is a major cause of surgical wound infections. To obtain contemporary data on S aureus, we performed a prospective study of colonization and infection in children scheduled for elective surgical procedures. METHODS A nasal swab and clinical information were obtained at the presurgical outpatient visit. At operation, nasal and perianal swabs were obtained. S aureus were isolated and characterized. RESULTS We enrolled 499 patients from June 2005 to April 2007. Wound classes were 1 (73%), 2 (22%), 3 (5%), and 4 (0.2%). Prophylactic antibiotics were administered for 153 (31%). Postoperative length of stay ranged from 0 (77%) to 6 days, with 19 (4%) staying 4 days or more. Screening cultures grew S aureus for 186 procedures (36.6%); of these, 141 were methicillin-resistant S aureus (MRSA) (76% of all staphylococcal cultures or 28% of all procedures). Most MRSA had Staphylococcal Chromosomal Cassette mec type II and resistance to clindamycin-typical for hospital-associated strains. There were 10 (2%) surgical site infections, including 4 methicillin-sensitive S aureus, 1 MRSA, 2 with no growth, and 2 with no cultures. CONCLUSION Methicillin-resistant S aureus colonization was common in asymptomatic children. Most strains appeared to be health care-associated and resistant to clindamycin. Wound infection rate remained low despite the high prevalence of staphylococcal colonization.

CD62 expression during thrombus formation.

A large right atrial mass was discovered in a 16-year-old female patient receiving chemotherapy treatment for Hodgkin disease. The patient was participating in a platelet function research study. During laboratory examination of platelet activation, increasing CD62 and CD63 expression were found to mirror the clot formation. Further investigation of platelet expression of CD62 and CD63 by flow cytometry might reveal it to be a valuable tool in predicting impending thrombus formation.