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1.  Invasive Methicillin-Resistant Staphylococcus aureus Infections Among Patients on Chronic Dialysis in the United States, 2005–2011 
Incidence of invasive methicillin-resistant Staphylococcus aureus (MRSA) infections decreased substantially among dialysis patients during 2005–2011 based on surveillance data from 9 metropolitan areas. Despite decreases, an estimated 15 169 invasive MRSA infections occurred in US dialysis patients in 2011.
Background. Approximately 15 700 invasive methicillin-resistant Staphylococcus aureus (MRSA) infections occurred in US dialysis patients in 2010. Frequent hospital visits and prolonged bloodstream access, especially via central venous catheters (CVCs), are risk factors among hemodialysis patients. We describe the epidemiology of and recent trends in invasive MRSA infections among dialysis patients.
Methods. We analyzed population-based data from 9 US metropolitan areas from 2005 to 2011. Cases were defined as MRSA isolated from a normally sterile body site in a surveillance area resident who received dialysis, and were classified as hospital-onset (HO; culture collected >3 days after hospital admission) or healthcare-associated community-onset (HACO; all others). Incidence was calculated using denominators from the US Renal Data System. Temporal trends in incidence and national estimates were calculated controlling for age, sex, and race.
Results. From 2005 to 2011, 7489 cases were identified; 85.7% were HACO infections, and 93.2% were bloodstream infections. Incidence of invasive MRSA infections decreased from 6.5 to 4.2 per 100 dialysis patients (annual decrease, 7.3%) with annual decreases of 6.7% for HACO and 10.5% for HO cases. Among cases identified during 2009–2011, 70% of patients were hospitalized in the year prior to infection. Among hemodialysis cases, 60.4% of patients were dialyzed through a CVC. The 2011 national estimated number of MRSA infections was 15 169.
Conclusions. There has been a substantial decrease in invasive MRSA infection incidence among dialysis patients. Most cases had previous hospitalizations, suggesting that efforts to control MRSA in hospitals might have contributed to the declines. Infection prevention measures should include improved vascular access and CVC care.
PMCID: PMC3805174  PMID: 23964088
invasive MRSA; dialysis; methicillin-resistant S. aureus
3.  Molecular Characterization of Ambiguous Mutations in HIV-1 Polymerase Gene: Implications for Monitoring HIV Infection Status and Drug Resistance 
PLoS ONE  2013;8(10):e77649.
Detection of recent HIV infections is a prerequisite for reliable estimations of transmitted HIV drug resistance (t-HIVDR) and incidence. However, accurately identifying recent HIV infection is challenging due partially to the limitations of current serological tests. Ambiguous nucleotides are newly emerged mutations in quasispecies, and accumulate by time of viral infection. We utilized ambiguous mutations to establish a measurement for detecting recent HIV infection and monitoring early HIVDR development. Ambiguous nucleotides were extracted from HIV-1 pol-gene sequences in the datasets of recent (HIVDR threshold surveys [HIVDR-TS] in 7 countries; n=416) and established infections (1 HIVDR monitoring survey at baseline; n=271). An ambiguous mutation index of 2.04×10-3 nts/site was detected in HIV-1 recent infections which is equivalent to the HIV-1 substitution rate (2×10-3 nts/site/year) reported before. However, significantly higher index (14.41×10-3 nts/site) was revealed with established infections. Using this substitution rate, 75.2% subjects in HIVDR-TS with the exception of the Vietnam dataset and 3.3% those in HIVDR-baseline were classified as recent infection within one year. We also calculated mutation scores at amino acid level at HIVDR sites based on ambiguous or fitted mutations. The overall mutation scores caused by ambiguous mutations increased (0.54×10-23.48×10-2/DR-site) whereas those caused by fitted mutations remained stable (7.50-7.89×10-2/DR-site) in both recent and established infections, indicating that t-HIVDR exists in drug-naïve populations regardless of infection status in which new HIVDR continues to emerge. Our findings suggest that characterization of ambiguous mutations in HIV may serve as an additional tool to differentiate recent from established infections and to monitor HIVDR emergence.
PMCID: PMC3798419  PMID: 24147046
4.  Optimization of a Low Cost and Broadly Sensitive Genotyping Assay for HIV-1 Drug Resistance Surveillance and Monitoring in Resource-Limited Settings 
PLoS ONE  2011;6(11):e28184.
Commercially available HIV-1 drug resistance (HIVDR) genotyping assays are expensive and have limitations in detecting non-B subtypes and circulating recombinant forms that are co-circulating in resource-limited settings (RLS). This study aimed to optimize a low cost and broadly sensitive in-house assay in detecting HIVDR mutations in the protease (PR) and reverse transcriptase (RT) regions of pol gene. The overall plasma genotyping sensitivity was 95.8% (N = 96). Compared to the original in-house assay and two commercially available genotyping systems, TRUGENE® and ViroSeq®, the optimized in-house assay showed a nucleotide sequence concordance of 99.3%, 99.6% and 99.1%, respectively. The optimized in-house assay was more sensitive in detecting mixture bases than the original in-house (N = 87, P<0.001) and TRUGENE® and ViroSeq® assays. When the optimized in-house assay was applied to genotype samples collected for HIVDR surveys (N = 230), all 72 (100%) plasma and 69 (95.8%) of the matched dried blood spots (DBS) in the Vietnam transmitted HIVDR survey were genotyped and nucleotide sequence concordance was 98.8%; Testing of treatment-experienced patient plasmas with viral load (VL) ≥ and <3 log10 copies/ml from the Nigeria and Malawi surveys yielded 100% (N = 46) and 78.6% (N = 14) genotyping rates, respectively. Furthermore, all 18 matched DBS stored at room temperature from the Nigeria survey were genotyped. Phylogenetic analysis of the 236 sequences revealed that 43.6% were CRF01_AE, 25.9% subtype C, 13.1% CRF02_AG, 5.1% subtype G, 4.2% subtype B, 2.5% subtype A, 2.1% each subtype F and unclassifiable, 0.4% each CRF06_CPX, CRF07_BC and CRF09_CPX.
The optimized in-house assay is broadly sensitive in genotyping HIV-1 group M viral strains and more sensitive than the original in-house, TRUGENE® and ViroSeq® in detecting mixed viral populations. The broad sensitivity and substantial reagent cost saving make this assay more accessible for RLS where HIVDR surveillance is recommended to minimize the development and transmission of HIVDR.
PMCID: PMC3223235  PMID: 22132237

Results 1-4 (4)