Ramya Srinivasan

A Prospective Study of Ventilator-Associated Pneumonia in Children

OBJECTIVE. We conducted a prospective, observational study in a tertiary care pediatric center to determine risk factors for the development of and outcomes from ventilator-associated pneumonia. METHODS. From November 2004 to June 2005, all NICU and PICU patients mechanically ventilated for >24 hours were eligible for enrollment after parental consent. The primary outcome measure was the development of ventilator-associated pneumonia, which was defined by both Centers for Disease Control and Prevention/National Nosocomial Infections Surveillance criteria and clinician diagnosis. Secondary outcome measures were length of mechanical ventilation, hospital and ICU length of stay, hospital cost, and death. RESULTS. Fifty-eight patients were enrolled. The median age was 6 months, and 57% were boys. The most common ventilator-associated pneumonia organisms identified were Gram-negative bacteria (42%), Staphylococcus aureus (22%), and Haemophilus influenzae (11%). On multivariate analysis, female gender, postsurgical admission diagnosis, presence of enteral feeds, and use of narcotic medications were associated with ventilator-associated pneumonia. Patients with ventilator-associated pneumonia had greater need for mechanical ventilation (12 vs 22 median ventilator-free days), longer ICU length of stay (6 vs 13 median ICU-free days), higher total median hospital costs (

Iodine quantification with dual-energy CT: phantom study and preliminary experience with renal masses.

308534 vs

Use of 16S rRNA gene for identification of a broad range of clinically relevant bacterial pathogens

252652), and increased absolute hospital mortality (10.5% vs 2.4%) than those without ventilator-associated pneumonia. CONCLUSIONS. In mechanically ventilated, critically ill children, those with ventilator-associated pneumonia had a prolonged need for mechanical ventilation, a longer ICU stay, and a higher mortality rate. Female gender, postsurgical diagnosis, the use of narcotics, and the use of enteral feeds were associated with an increased risk of developing ventilator-associated pneumonia in these patients.

Ultrasound for differentiation between perforated and nonperforated appendicitis in pediatric patients.

OBJECTIVE The purpose of this study was to validate the utility of dual-source dual-energy MDCT in quantifying iodine concentration in a phantom and in renal masses. MATERIALS AND METHODS A series of tubes containing solutions of varying iodine concentration were imaged with dual-source dual-energy MDCT. Iodine concentration was calculated and compared with known iodine concentration. Single-phase contrast-enhanced dual-source dual-energy MDCT data on 15 patients with renal lesions then were assessed independently by two readers. Dual-energy postprocessing was used to generate iodine-only images. Regions of interest were placed on the iodine image over the lesion and, as a reference, over the aorta, for recording of iodine concentration in the lesion and in the aorta. Another radiologist determined lesion enhancement by comparing truly unenhanced with contrast-enhanced images. Mixed-model analysis of variance based on ranks was used to compare lesion types (simple cyst, hemorrhagic cyst, enhancing mass) in terms of lesion iodine concentration and lesion-to-aorta iodine ratio. RESULTS In the phantom study, there was excellent correlation between calculated and true iodine concentration (R(2) = 0.998, p < 0.0001). In the patient study, 13 nonenhancing (10 simple and three hyperdense cysts) and eight enhancing renal masses were evaluated in 15 patients. The lesion iodine concentration and lesion-to-aorta iodine ratio in enhancing masses were significantly higher than in hyperdense and simple cysts (p < 0.0001). CONCLUSION Iodine quantification with dual-source dual-energy MDCT is accurate in a phantom and can be used to determine the presence and concentration of iodine in a renal lesion. Characterization of renal masses may be possible with a single dual-source dual-energy MDCT acquisition without unenhanced images or reliance on a change in attenuation measurements.

Secretion of Pseudomonas aeruginosa Type III Cytotoxins is Dependent on Pseudomonas Quinolone Signal Concentration

According to World Health Organization statistics of 2011, infectious diseases remain in the top five causes of mortality worldwide. However, despite sophisticated research tools for microbial detection, rapid and accurate molecular diagnostics for identification of infection in humans have not been extensively adopted. Time-consuming culture-based methods remain to the forefront of clinical microbial detection. The 16S rRNA gene, a molecular marker for identification of bacterial species, is ubiquitous to members of this domain and, thanks to ever-expanding databases of sequence information, a useful tool for bacterial identification. In this study, we assembled an extensive repository of clinical isolates (n = 617), representing 30 medically important pathogenic species and originally identified using traditional culture-based or non-16S molecular methods. This strain repository was used to systematically evaluate the ability of 16S rRNA for species level identification. To enable the most accurate species level classification based on the paucity of sequence data accumulated in public databases, we built a Naïve Bayes classifier representing a diverse set of high-quality sequences from medically important bacterial organisms. We show that for species identification, a model-based approach is superior to an alignment based method. Overall, between 16S gene based and clinical identities, our study shows a genus-level concordance rate of 96% and a species-level concordance rate of 87.5%. We point to multiple cases of probable clinical misidentification with traditional culture based identification across a wide range of gram-negative rods and gram-positive cocci as well as common gram-negative cocci.

Plasminogen activation inhibitor concentrations in bronchoalveolar lavage fluid distinguishes ventilator-associated pneumonia from colonization in mechanically ventilated pediatric patients.

OBJECTIVE Acute appendicitis is the most common condition requiring emergency surgery in children. Differentiation of perforated from nonperforated appendicitis is important because perforated appendicitis may initially be managed conservatively whereas nonperforated appendicitis requires immediate surgical intervention. CT has been proved effective in identifying appendiceal perforation. The purpose of this study was to determine whether perforated and nonperforated appendicitis in children can be similarly differentiated with ultrasound. MATERIALS AND METHODS This retrospective study included 161 consecutively registered children from two centers who had acute appendicitis and had undergone ultra-sound and appendectomy. Ultrasound images were reviewed for appendiceal size, appearance of the appendiceal wall, changes in periappendiceal fat, and presence of free fluid, abscess, or appendicolith. The surgical report served as the reference standard for determining whether perforation was present. The specificity and sensitivity of each ultrasound finding were determined, and binary models were generated. RESULTS The patients included were 94 boys and 67 girls (age range, 1-20 years; mean, 11 ± 4.4 [SD] years) The appendiceal perforation rate was significantly higher in children younger than 8 years (62.5%) compared with older children (29.5%). Sonographic findings associated with perforation included abscess (sensitivity, 36.2%; specificity, 99%), loss of the echogenic submucosal layer of the appendix in a child younger than 8 years (sensitivity, 100%; specificity, 72.7%), and presence of an appendicolith in a child younger than 8 years (sensitivity, 68.4%; specificity, 91.7%). CONCLUSION Ultrasound is effective for differentiation of perforated from nonperforated appendicitis in children.

Rearrangement of a Large Novel Pseudomonas aeruginosa Gene Island in Strains Isolated from a Patient Developing Ventilator-Associated Pneumonia

Pseudomonas aeruginosa is an opportunistic pathogen that can, like other bacterial species, exist in antimicrobial resistant sessile biofilms and as free-swimming, planktonic cells. Specific virulence factors are typically associated with each lifestyle and several two component response regulators have been shown to reciprocally regulate transition between biofilm-associated chronic, and free-swimming acute infections. Quorum sensing (QS) signal molecules belonging to the las and rhl systems are known to regulate virulence gene expression by P. aeruginosa. However the impact of a recently described family of novel quorum sensing signals produced by the Pseudomonas Quinolone Signal (PQS) biosynthetic pathway, on the transition between these modes of infection is less clear. Using clonal isolates from a patient developing ventilator-associated pneumonia, we demonstrated that clinical observations were mirrored by an in vitro temporal shift in isolate phenotype from a non-secreting, to a Type III cytotoxin secreting (TTSS) phenotype and further, that this phenotypic change was PQS-dependent. While intracellular type III cytotoxin levels were unaffected by PQS concentration, cytotoxin secretion was dependent on this signal molecule. Elevated PQS concentrations were associated with inhibition of cytotoxin secretion coincident with expression of virulence factors such as elastase and pyoverdin. In contrast, low concentrations or the inability to biosynthesize PQS resulted in a reversal of this phenotype. These data suggest that expression of specific P. aeruginosa virulence factors appears to be reciprocally regulated and that an additional level of PQS-dependent post-translational control, specifically governing type III cytotoxin secretion, exists in this species.

The Hallucal-Sesamoid Complex: Normal Anatomy, Imaging, and Pathology.

Objective: To compare the ability of four biomarkers to distinguish between those with ventilator-associated pneumonia (VAP) vs. lower respiratory tract bacterial colonization in mechanically ventilated intensive care unit (ICU) pediatric patients. Design: Prospective, pilot cohort study. Setting: Tertiary care childrens hospital, pediatric ICU. Patients: All pediatric ICU patients mechanically ventilated >48 hrs were eligible for enrollment between April 2006 to May 2007. Thirty-three patients were consecutively screened and enrolled after institutional consent process. Interventions: None. Measurements and Main Results: VAP was defined by both Centers for Disease and Prevention/National Nosocomial Infections Surveillance criteria and clinician diagnosis; those not meeting the criteria were considered to be colonized. Plasminogen activation inhibitor (PAI-1), soluble triggering receptor expressed on myeloid cells, receptor for advanced glycation end-products, and surfactant protein D levels were measured in bronchoalveolar lavage samples on average within 24 hrs of suspicion for VAP, i.e., a positive screening endotracheal Gram stain. Sixteen patients were diagnosed with VAP and 17 met the criteria for colonization. PAI-1 was associated with VAP independent of age, sex, race, acute lung injury/acute respiratory distress syndrome, Pediatric Risk of Mortality 3 score, pediatric logistic organ dysfunction score, and duration of intubation. The receiver operating characteristics for PAI-1 showed good discrimination with an area under the curve of 0.82. PAI-1 levels of ≥2.8 ng/mL had a sensitivity of 81.3%, specificity of 76.5%, and positive likelihood ratio of 3.5. Levels of soluble triggering receptor expressed on myeloid cells, receptor for advanced glycation end-products, and surfactant protein D were not significantly associated with VAP. Conclusions: In mechanically ventilated pediatric ICU patients, PAI-1 is independently associated with the diagnosis of VAP. Real-time measurement of PAI-1 levels in bronchoalveolar lavage fluid may be of benefit in the early diagnosis and subsequent treatment of VAP in ICU patients.

Knee Imaging Following Anterior Cruciate Ligament Reconstruction: The Surgeon's and Radiologist's Perspectives

ABSTRACT Bacterial gene islands add to the genetic repertoire of opportunistic pathogens. Here, we perform comparative analyses of three Pseudomonas aeruginosa strains isolated sequentially over a 3-week period from a patient with ventilator-associated pneumonia (VAP) who received clindamycin and piperacillin-tazobactam as part of their treatment regime. While all three strains appeared to be clonal by standard pulsed-field gel electrophoresis, whole-genome sequencing revealed subtle alterations in the chromosomal organization of the last two strains; specifically, an inversion event within a novel 124-kb gene island (PAGI 12) composed of 137 open reading frames [ORFs]. Predicted ORFs in the island included metabolism and virulence genes. Overexpression of a gene island-borne putative β-lactamase gene was observed following piperacillin-tazobactam exposure and only in those strains that had undergone the inversion event, indicating altered gene regulation following genomic remodeling. Examination of a separate cohort of 76 patients with VAP for integration at this tRNAlys recombination site demonstrated that patients exhibiting evidence of integration at this site had significantly higher 28-day mortality. These findings provide evidence that P. aeruginosa can integrate, rapidly remodel, and express exogenous genes, which likely contributes to its fitness in a clinical setting.

Noninvasive measurements of oxygenation defect in children: beyond research toward clinical prevention and therapeutics.

The first metatarsophalangeal joint and hallucal-sesamoid complex are critical structures in weightbearing and susceptible to several pathologies including turf toe, sesamoiditis, degenerative or inflammatory arthritides, infection, and avascular necrosis. This review article summarizes the complex anatomy of the region, covers common pathologies while clarifying terms such as turf toe and sesamoiditis, reviews imaging techniques, and discusses management.