Maria Rios

Bacteremia Due to Extended-Spectrum β-Lactamase–Producing Escherichia coli in the CTX-M Era: A New Clinical Challenge

BACKGROUND Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli, particularly those producing CTX-M types of ESBL, are emerging pathogens. Bacteremia caused by these organisms represents a clinical challenge, because the organisms are frequently resistant to the antimicrobials recommended for treatment of patients with suspected E. coli sepsis. METHODS A cohort study was performed that included all episodes of bloodstream infection due to ESBL-producing E. coli during the period from January 2001 through March 2005. Data on predisposing factors, clinical presentation, and outcome were collected. ESBLs were characterized using isoelectric focusing, polymerase chain reaction, and sequencing. RESULTS Forty-three episodes (8.8% of cases of bacteremia due to E. coli) were included; 70% of the isolates produced a CTX-M type of ESBL. The most frequent origins of infection were the urinary (46%) and biliary tracts (21%). Acquisition was nosocomial in 21 cases (49%), health care associated in 14 cases (32%), and strictly community acquired in 8 cases (19%). Thirty-eight percent and 25% of patients had obstructive diseases of the urinary and biliary tracts, respectively, and 38% had recently received antimicrobials. Nine patients (21%) died. Compared with beta-lactam/beta-lactamase-inhibitor and carbapenem-based regimens, empirical therapy with cephalosporins or fluoroquinolones was associated with a higher mortality rate (9% vs. 35%; P=.05) and needed to be changed more frequently (24% vs. 78%; P=.001). CONCLUSIONS ESBL-producing E. coli is a significant cause of bloodstream infection in hospitalized and nonhospitalized patients in the context of the emergence of CTX-M enzymes. Empirical treatment of sepsis potentially caused by E. coli may need to be reconsidered in areas where such ESBL-producing isolates are present.

The Global Ecology and Epidemiology of West Nile Virus

Since its initial isolation in Uganda in 1937 through the present, West Nile virus (WNV) has become an important cause of human and animal disease worldwide. WNV, an enveloped virus of the genus Flavivirus, is naturally maintained in an enzootic cycle between birds and mosquitoes, with occasional epizootic spillover causing disease in humans and horses. The mosquito vectors for WNV are widely distributed worldwide, and the known geographic range of WNV transmission and disease has continued to increase over the past 77 years. While most human infections with WNV are asymptomatic, severe neurological disease may develop resulting in long-term sequelae or death. Surveillance and preventive measures are an ongoing need to reduce the public health impact of WNV in areas with the potential for transmission.

Monocytes-macrophages are a potential target in human infection with West Nile virus through blood transfusion

BACKGROUND:  West Nile virus (WNV) transmission by transfusion was documented in 2002. Approximately 80 percent of WNV infections are asymptomatic and 1 percent develop severe neurological illness. In animals, Langerhans‐dendritic cells support initial viral replication, followed by replication in lymphoid tissues and dissemination to organs and possibly to the CNS. The cellular tropism of WNV infection after transfusion and the particular human blood cells that sustain viral replication remain largely unknown. Whether primary monocyte‐derived macrophages (MDMs) support WNV infection‐replication and produce infectious virions, with an in vitro system, was investigated.

Circulation of Different Lineages of Dengue Virus Type 2 in Central America, Their Evolutionary Time-Scale and Selection Pressure Analysis

Dengue is caused by any of the four serotypes of dengue virus (DENV-1 to 4). Each serotype is genetically distant from the others, and each has been subdivided into different genotypes based on phylogenetic analysis. The study of dengue evolution in endemic regions is important since the diagnosis is often made by nucleic acid amplification tests, which depends upon recognition of the viral genome target, and natural occurring mutations can affect the performance of these assays. Here we report for the first time a detailed study of the phylogenetic relationships of DENV-2 from Central America, and report the first fully sequenced DENV-2 strain from Guatemala. Our analysis of the envelope (E) protein and of the open reading frame of strains from Central American countries, between 1999 and 2009, revealed that at least two lineages of the American/Asian genotype of DENV-2 have recently circulated in that region. In occasions the co-circulation of these lineages may have occurred and that has been suggested to play a role in the observed increased severity of clinical cases. Our time-scale analysis indicated that the most recent common ancestor for Central American DENV-2 of the American/Asian genotype existed about 19 years ago. Finally, we report positive selection in DENV-2 from Central America in codons of the genes encoding for C, E, NS2A, NS3, and NS5 proteins. Some of these identified codons are novel findings, described for the first time for any of the DENV-2 genotypes.

West Nile Virus Adheres to Human Red Blood Cells in Whole Blood

Background. West Nile virus (WNV) is endemic in the United States. It is transmissible by blood transfusion, and the nations blood supply is currently screened for WNV. Documented transmission of WNV infection through red blood cell (RBC) units in which the plasma co-component had a low viral load could be explained, in at least 1 instance, by cell-association of WNV; in this case, the RBC unit was released as negative by minipool nucleic acid testing (NAT) performed on plasma but was intermittently NAT-positive when subsequently tested as an individual sample. We hypothesized that a proportion of WNV bound to blood cells and was not measured by NAT performed on plasma samples. We have investigated whether WNV binds to RBCs, leading to reduction of WNV RNA detection by NAT performed on plasma samples.Methods. Equal volumes of leukoreduced RBCs and their corresponding plasma components from 20 blood donors with NAT results that were positive for WNV were tested in 5 replicates by reverse-transcriptase polymerase chain reaction TaqMan for WNV. In addition, aliquots from 8 of the RBC units were tested by infectivity assays using Vero cells.Results. The reverse-transcriptase polymerase chain reaction TaqMan assay showed that the viral load in the RBC components exceeded that in the corresponding plasma units by 1 order of magnitude. In addition, viruses associated with the RBCs were infectious in Vero cell cultures.Conclusions. These observations reinforce the notion that extraction of viral RNA from whole blood could improve assay sensitivity for blood donor screening and further reduce the residual risk of WNV transmission through transfusion.

Dengue in the United States of America: A Worsening Scenario?

Dengue is a febrile illness caused by any of the four dengue virus types (DENV-1 to -4, genus Flavivirus, family Flaviviridae) mainly transmitted by the mosquito Aedes aegypti. DENV can be transmitted by blood transfusion. Dengue has been historically present in the continental United States (US), in the state of Hawaii, and in the US insular territories in the Caribbean and the Pacific. During the second half of the 20th century, most of the cases reported in the US were imported cases brought to the country by travelers. Since 2009, cases of autochthonous dengue have been recognized in the state of Florida after 75 years of absence, followed by intensification of transmission in endemic places including the US territories of US Virgin Islands and Puerto Rico, which experienced a large dengue epidemic in 2010. The widespread distribution of dengue mosquito vectors, deficient mosquito control measures and increased frequency of DENV-infected visitors to the US coming from dengue-endemic locations or places experiencing epidemics appear to be jointly responsible for the emergence and reemergence of dengue in the US and its territories.

Evolutionary dynamics of West Nile virus in the United States, 1999-2011: phylogeny, selection pressure and evolutionary time-scale analysis.

West Nile virus (WNV), an arbovirus maintained in a bird-mosquito enzootic cycle, can infect other vertebrates including humans. WNV was first reported in the US in 1999 where, to date, three genotypes belonging to WNV lineage I have been described (NY99, WN02, SW/WN03). We report here the WNV sequences obtained from two birds, one mosquito, and 29 selected human samples acquired during the US epidemics from 2006–2011 and our examination of the evolutionary dynamics in the open-reading frame of WNV isolates reported from 1999–2011. Maximum-likelihood and Bayesian methods were used to perform the phylogenetic analyses and selection pressure analyses were conducted with the HyPhy package. Phylogenetic analysis identified human WNV isolates within the main WNV genotypes that have circulated in the US. Within genotype SW/WN03, we have identified a cluster with strains derived from blood donors and birds from Idaho and North Dakota collected during 2006–2007, termed here MW/WN06. Using different codon-based and branch-site selection models, we detected a number of codons subjected to positive pressure in WNV genes. The mean nucleotide substitution rate for WNV isolates obtained from humans was calculated to be 5.06×10−4 substitutions/site/year (s/s/y). The Bayesian skyline plot shows that after a period of high genetic variability following the introduction of WNV into the US, the WNV population appears to have reached genetic stability. The establishment of WNV in the US represents a unique opportunity to understand how an arbovirus adapts and evolves in a naïve environment. We describe a novel, well-supported cluster of WNV formed by strains collected from humans and birds from Idaho and North Dakota. Adequate genetic surveillance is essential to public health since new mutants could potentially affect viral pathogenesis, decrease performance of diagnostic assays, and negatively impact the efficacy of vaccines and the development of specific therapies.

Genetic Variability of West Nile Virus in US Blood Donors, 2002–2005

This virus is diverging from precursor isolates as its geographic distribution expands.

DNA analysis for the Dombrock polymorphism

BACKGROUND: RBC typing for Doa and Dob is notoriously difficult, and inaccurate typing can predispose patients to hemolytic transfusion reactions. The DO1/DO2 polymorphism is associated with three nucleotide changes: 378 C>T, 624 T>C and 793 A>G. While the 378 C>T‐ and 624 T>C‐containing codons are silent mutations, the 793 A>G polymorphism in codon 265 encodes asparagine for Doa and aspartic acid for Dob.

Epidemiological Scenario of Dengue in Brazil.

Dengue is the most important reemerging mosquito-borne viral disease worldwide. It is caused by any of four Dengue virus types or serotypes (DENV-1 to DENV-4) and is transmitted by mosquitoes from the genus Aedes. Ecological changes have favored the geographic expansion of the vector and, since the dengue pandemic in the Asian and Pacific regions, the infection became widely distributed worldwide, reaching Brazil in 1845. The incidence of dengue in Brazil has been frequently high, and the number of cases in the country has at some point in time represented up to 60% of the dengue reported cases worldwide. This review addresses vector distribution, dengue outbreaks, circulating serotypes and genotypes, and prevention approaches being utilized in Brazil.