Gerardo Martinez-Aguilar

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

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

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

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

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.

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.

Outbreak of nosocomial sepsis and pneumonia in a newborn intensive care unit by multiresistant extended-spectrum β-lactamase-producing Klebsiella pneumoniae: High impact on mortality

We describe a case-control study of a small outbreak of nosocomial sepsis and pneumonia with high mortality due to clonal dissemination of a multiresistant Klebsiella pneumoniae in the neonatal intensive care unit of a Mexican institution. Our study helped to change nosocomial infection control policy in this hospital.

Incidencia de bacteriemia y neumonía nosocomial en una unidad de pediatría

Objetivo. Determinar la incidencia de bacteriemia relacionada con cateter y neumonia asociada a ventilador en ninos hospitalizados. Material y metodos. Estudio prospectivo. En el servicio de Pediatria del Hospital General Regional (HGR) No 1 del Instituto Mexicano del Seguro Social (IMSS), de Durango, Mexico, durante 18 meses, de enero de 1999 a junio del 2000, se implemento un sistema de vigilancia epidemiologica activa para identificar episodios de neumonia y bacteriemia nosocomial de acuerdo a las definiciones operacionales de la Norma Oficial Mexicana (NOM). A los pacientes hospitalizados que por su patologia requirieron de ventilacion mecanica o de cateter intravenoso central se les hizo seguimiento desde el primer dia de exposicion hasta la deteccion del episodio de infeccion o su retiro. Se efectuaron hemocultivos y cultivos de aspirado traqueal. Se calcularon tasas de incidencia para la neumonia asociada a ventilador y de bacteriemia/sepsis por 1 000 dias de exposicion con sus respectivos intervalos de confianza al 95%. Tambien se presenta la tasa mensual de la infeccion por dias de exposicion por medio de graficas de control estadistico. Resultados. Se identificaron 47 episodios de bacteriemia/sepsis relacionada con cateter y 44 de neumonia asociada a ventilador. La tasa de incidencia de neumonia fue de 28 eventos por 1 000 dias de exposicion a ventilador y la de bacteriemia/sepsis fue de 26 eventos por 1 000 dias de exposicion a cateter intravenoso central. Los microrganismos gram positivos (61.11%) predominaron sobre los gram negativos (38.88%). Conclusiones. Este estudio documento tasas de neumonia y bacteriemia en ninos, sustancialmente mas elevadas que en otros informes, lo que hace necesario establecer lineamientos para la prevencion de infecciones en ninos con cateteres intravasculares y sobre los cuidados que requieren los ninos sometidos a ventilacion mecanica. El texto completo en ingles de este articulo esta disponible en: http://www.insp.mx/salud/index.html

Azithromycin compared with β-lactam antibiotic treatment failures in pneumococcal infections of children

Objective: To determine whether treatment failures occurred more commonly with azithromycin than with β-lactam antibiotics in children who developed invasive pneumococcal disease within 30 days of receiving prior antimicrobial therapy. Methods: Retrospective review of medical records of children evaluated at Texas Children’s Hospital between 1996 and 2002 who had received antimicrobials (azithromycin or a β-lactam antibiotic) and developed invasive pneumococcal disease within 30 days. Treatment failure was defined as invasive pneumococcal infection that occurred while taking antimicrobials or within 3 days of stopping azithromycin treatment or 1 day of stopping β-lactam treatment. Penicillin and azithromycin susceptibilities were determined and categorized according to National Committee for Clinical Laboratory Standards guidelines. Results: We identified 21 and 33 children with similar demographic features who had developed invasive pneumococcal disease within 1 month of receiving azithromycin or a β-lactam antibiotic, respectively. Eleven (52%) children in the azithromycin group and 11 (33%) in the β-lactam group met the definition for treatment failures (P = 0.34). Eight treatment failures while receiving azithromycin were caused by pneumococci with the macrolide-resistant (M) phenotype, 2 with the macrolide-, lincosamide- and streptogramin B-resistant (MLSB) phenotype and 1 by a macrolide-susceptible organism. In the β-lactam group 7 had a penicillin-resistant isolate, 3 had an intermediately susceptible isolate and 1 had a susceptible isolate. Conclusions: Our study suggests that treatment failures among patients who developed invasive disease within 30 days of receiving an antimicrobial occur as frequently in patients who receive β-lactam antibiotics as in those who receive azithromycin. Furthermore macrolide resistant organisms are not more likely to be recovered after a macrolide treatment failure than a penicillin-nonsusceptible isolate being recovered after a β-lactam treatment failure (P = 1.0).

Is There Still Room for Novel Viral Pathogens in Pediatric Respiratory Tract Infections

Viruses are the most frequent cause of respiratory disease in children. However, despite the advanced diagnostic methods currently in use, in 20 to 50% of respiratory samples a specific pathogen cannot be detected. In this work, we used a metagenomic approach and deep sequencing to examine respiratory samples from children with lower and upper respiratory tract infections that had been previously found negative for 6 bacteria and 15 respiratory viruses by PCR. Nasal washings from 25 children (out of 250) hospitalized with a diagnosis of pneumonia and nasopharyngeal swabs from 46 outpatient children (out of 526) were studied. DNA reads for at least one virus commonly associated to respiratory infections was found in 20 of 25 hospitalized patients, while reads for pathogenic respiratory bacteria were detected in the remaining 5 children. For outpatients, all the samples were pooled into 25 DNA libraries for sequencing. In this case, in 22 of the 25 sequenced libraries at least one respiratory virus was identified, while in all other, but one, pathogenic bacteria were detected. In both patient groups reads for respiratory syncytial virus, coronavirus-OC43, and rhinovirus were identified. In addition, viruses less frequently associated to respiratory infections were also found. Saffold virus was detected in outpatient but not in hospitalized children. Anellovirus, rotavirus, and astrovirus, as well as several animal and plant viruses were detected in both groups. No novel viruses were identified. Adding up the deep sequencing results to the PCR data, 79.2% of 250 hospitalized and 76.6% of 526 ambulatory patients were positive for viruses, and all other children, but one, had pathogenic respiratory bacteria identified. These results suggest that at least in the type of populations studied and with the sampling methods used the odds of finding novel, clinically relevant viruses, in pediatric respiratory infections are low.

Rhinovirus is an important pathogen in upper and lower respiratory tract infections in Mexican children

BackgroundMost of the studies characterizing the incidence of rhinovirus (RV) have been carried out in hospitalized children and in developed countries. In those studies, RV-C has been associated with more severe respiratory tract infections than RV species A and B. In this study we determined the frequency and diversity of RV strains associated with upper and lower respiratory tract infections (URTI, LRTI) in Mexico, and describe the clinical characteristics of the illness associated with different RV species.MethodsA prospective surveillance of 526 and 250 children with URTI and LRTI was carried out. Respiratory samples were analyzed by RT-PCR for viruses. The 5′ untranslated region of the RV genome was amplified and sequenced.ResultsIn the case of URTI, 17.5% were positive for RV, while this virus was found in 24.8% of LRTI. The RV species was determined in 73 children with URTI: 61.6% were RV-A, 37% RV-C and, 1.4% RV-B; and in 43 children with LRTI: 51.2% were RV-A, 41.8% RV-C, and 7% RV-B. No significant differences in clinical characteristics were found in patients with RV-A or RV-C infections. A high genetic diversity of RV strains was found in both URTI and LRTI.ConclusionsBoth RV-A and RV-C species were frequently found in hospitalized as well as in outpatient children. This study underlines the high prevalence and genetic diversity of RV strains in Mexico and the potential severity of disease associated with RV-A and RV-C infections.

Serotypes and susceptibility of Streptococcus pneumoniae strains isolated from children in Mexico

OBJECTIVE To identify serotypes and susceptibility of S. pneumoniae strains from 48 children with invasive infections and 50 carriers. MATERIAL AND METHODS Typing was performed by the Quellung reaction and susceptibility by Kirby-Bauer and Etest according to CLSI standards. RESULTS Of 31 meningeal strains, serotypes 19F, 3, 6B, 14 and 23F were predominant. Resistance to penicillin and STX was 16 and 58%, respectively; of 17 invasive non-meningeal strains, serotypes 19F and 3 were predominant and resistance to penicillin and SXT was 0 and 82%, respectively; of carrier strains, serotypes 6A, 6B, 19F and 23F were predominant. CONCLUSIONS A 10-valent conjugate vaccine could offer a better coverage for meningeal strains.