Natal Santos da Silva

Faculdade de Medicina de São José do Rio Preto, Rio Preto, São Paulo, Brazil

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Publications (14)29.01 Total impact

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    ABSTRACT: Background This study aimed to evaluate a different methodology for addressing the evolution of nosocomial bacteremia by vancomycin-resistant enterococci (VRE) in a hospital setting. Methods In this retrospective cohort study, data were collected from the date of first registration up to December 2008 from the electronic medical records of patients with VRE bacteremia in a school hospital. Results Thirty cases of VRE bacteremia and 274 cases of vancomycin-susceptible enterococci (VSE) bacteremia were identified. The average age of the patients was 56 years. The rates of Enterococcus faecium and Enterococcus faecalis in the hospital's intensive care unit (ICU) and wards showed no statistically significant differences. The risk of acquiring VRE bacteremia was at least 3-fold higher in the ICU than in the wards. The risk of death was 2.73-fold higher in patients with VRE bacteremia compared with those with VSE bacteremia. Only one temporal cluster statistically significant of VRE bacteremia was found in the study period. Conclusions The identification of temporal clusters can be an important tool to optimize health actions and thereby reduce the burden of operating costs.
    American journal of infection control 04/2014; 42(4):389–392. · 3.01 Impact Factor
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    ABSTRACT: We describe the epidemiology of malaria in a frontier agricultural settlement in Brazilian Amazonia. We analysed the incidence of slide-confirmed symptomatic infections diagnosed between 2001 and 2006 in a cohort of 531 individuals (2281.53 person-years of follow-up) and parasite prevalence data derived from four cross-sectional surveys. Overall, the incidence rates of Plasmodium vivax and P. falciparum were 20.6/100 and 6.8/100 person-years at risk, respectively, with a marked decline in the incidence of both species (81.4 and 56.8%, respectively) observed between 2001 and 2006. PCR revealed 5.4-fold more infections than conventional microscopy in population-wide cross-sectional surveys carried out between 2004 and 2006 (average prevalence, 11.3 vs. 2.0%). Only 27.2% of PCR-positive (but 73.3% of slide-positive) individuals had symptoms when enrolled, indicating that asymptomatic carriage of low-grade parasitaemias is a common phenomenon in frontier settlements. A circular cluster comprising 22.3% of the households, all situated in the area of most recent occupation, comprised 69.1% of all malaria infections diagnosed during the follow-up, with malaria incidence decreasing exponentially with distance from the cluster centre. By targeting one-quarter of the households, with selective indoor spraying or other house-protection measures, malaria incidence could be reduced by more than two-thirds in this community.
    Transactions of the Royal Society of Tropical Medicine and Hygiene 05/2010; 104(5):343-50. · 1.82 Impact Factor
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    ABSTRACT: The Plasmodium falciparum var gene family encodes large variant antigens, which are important virulence factors, and also targets of the humoral host response. The frequently observed mild outcomes of falciparum malaria in many places of the Amazon area prompted us to ask whether a globally restricted variant (var) gene repertoire is present in currently circulating and older isolates of this area. By exhaustive analysis of var gene tags from 89 isolates and clones taken during many years from all over the Brazilian Amazon, we estimate that there are probably no more than 350-430 distinct sequence types, less than for any similar sized area studied so far. Detailed analysis of the var tags from genetically distinct clones obtained from single isolates revealed restricted and redundant repertoires suggesting either a low incidence of infective bites or restricted variant gene diversity in inoculated parasites. Additionally, we found a structuring of var gene repertoires observed as a higher pairwise typing sharing in isolates from the same microregion compared to isolates from different regions. Fine analysis of translated var tags revealed that certain Distinct Sequence Identifiers (DSIDs) were differently represented in Brazilian/South American isolates when compared to datasets from other continents. By global alignment of worldwide var DBLalpha sequences and sorting in groups with more than 76% identity, 125 clusters were formed and more than half of all genes were found in nine clusters with 50 or more sequences. While Brazilian/South American sequences were represented only in 64 groups, African sequences were found in the majority of clusters. DSID type 1 related sequences accumulated almost completely in one single cluster, indicating that limited recombination occurs in these specific var gene types. These data demonstrate the so far highest pairwise type sharing values for the var gene family in isolates from all over an entire subcontinent. The apparent lack of specific sequences types suggests that the P. falciparum transmission dynamics in the whole Amazon are probably different from any other endemic region studied and possibly interfere with the parasite's ability to efficiently diversify its variant gene repertoires.
    Gene 03/2010; 453(1-2):37-44. · 2.20 Impact Factor
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    ABSTRACT: The ideal malaria parasite populations for initial mapping of genomic regions contributing to phenotypes such as drug resistance and virulence, through genome-wide association studies, are those with high genetic diversity, allowing for numerous informative markers, and rare meiotic recombination, allowing for strong linkage disequilibrium (LD) between markers and phenotype-determining loci. However, levels of genetic diversity and LD in field populations of the major human malaria parasite P. vivax remain little characterized. We examined single-nucleotide polymorphisms (SNPs) and LD patterns across a 100-kb chromosome segment of P. vivax in 238 field isolates from areas of low to moderate malaria endemicity in South America and Asia, where LD tends to be more extensive than in holoendemic populations, and in two monkey-adapted strains (Salvador-I, from El Salvador, and Belem, from Brazil). We found varying levels of SNP diversity and LD across populations, with the highest diversity and strongest LD in the area of lowest malaria transmission. We found several clusters of contiguous markers with rare meiotic recombination and characterized a relatively conserved haplotype structure among populations, suggesting the existence of recombination hotspots in the genome region analyzed. Both silent and nonsynonymous SNPs revealed substantial between-population differentiation, which accounted for ~40% of the overall genetic diversity observed. Although parasites clustered according to their continental origin, we found evidence for substructure within the Brazilian population of P. vivax. We also explored between-population differentiation patterns revealed by loci putatively affected by natural selection and found marked geographic variation in frequencies of nucleotide substitutions at the pvmdr-1 locus, putatively associated with drug resistance. These findings support the feasibility of genome-wide association studies in carefully selected populations of P. vivax, using relatively low densities of markers, but underscore the risk of false positives caused by population structure at both local and regional levels.
    BMC Genetics 01/2010; 11:65. · 2.81 Impact Factor
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    ABSTRACT: Clinical trials documented alarming post-treatment Plasmodium vivax recurrence rates caused by recrudescence of surviving asexual blood stages, relapse from hypnozoites, or new infections. Here we describe high rates of P. vivax recurrence (26-40% 180 days after treatment) in two cohorts of rural Amazonians exposed to low levels of malaria transmission after a vivax malaria episode treated with chloroquine-primaquine. Microsatellite analysis of 28 paired acute infection and recurrence parasites showed only two pairs of identical haplotypes (consistent with recrudescences or reactivation of homologous hypnozoites) and four pairs of related haplotypes (sharing alleles at 11-13 of 14 microsatellites analyzed). Local isolates of P. vivax were extraordinarily diverse and rarely shared the same haplotype, indicating that frequent recurrences did not favor the persistence or reappearance of clonal lineages of parasites in the population. This fast haplotype replacement rate may represent the typical population dynamics of neutral polymorphisms in parasites from low-endemicity areas.
    The American journal of tropical medicine and hygiene 12/2009; 81(6):961-8. · 2.53 Impact Factor
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    ABSTRACT: IgG antibodies to Toxoplasma gondii were detected in, March-April 2004, in 65.8% (95% confidence interval, 60.8-70.8%) of 342 systematically sampled subjects 5-90 years of age (87.5% of the eligible) living in a rural settlement in Amazonia, with a seroconversion rate of 9% over 1 year of follow-up of 99 seronegative subjects. Multiple logistic regression analysis identified age as the only significant independent predictor of seropositivity at the baseline. Each additional year of age increases the odds of being seropositive by 6%, and 76.8% of the subjects are expected to be seropositive at 30 years of age. A single high-prevalence spatial cluster, comprising 11.9% of the seropositive subjects, was detected in the area; households in the cluster were less likely to have dogs as pets and their heads had a lower education level, when compared with households located outside the cluster. The challenges for preventing human toxoplasmosis in tropical rural settings are discussed.
    The American journal of tropical medicine and hygiene 08/2009; 81(1):171-6. · 2.53 Impact Factor
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    ABSTRACT: Temporal changes in the prevalence of antigenic variants in Plasmodium falciparum populations have been interpreted as evidence of immune-mediated frequency-dependent selection, but evolutively neutral processes may generate similar patterns of serotype replacement. Over 4 years, we investigated the population dynamics of P. falciparum polymorphisms at the community level by using 11 putatively neutral microsatellite markers. Plasmodium falciparum populations were less diverse than sympatric P. vivax isolates, with less multiple-clone infections, lower number of alleles per locus and lower virtual heterozygosity, but both species showed significant multilocus linkage disequilibrium. Evolutively neutral P. falciparum polymorphisms showed a high turnover rate, with few lineages persisting for several months in the population. Similar results had previously been obtained, in the same community, for sympatric P. vivax isolates. In contrast, the prevalence of the 2 dimorphic types of a major antigen, MSP-2, remained remarkably stable throughout the study period. We suggest that the relatively fast turnover of parasite lineages represents the typical population dynamics of neutral polymorphisms in small populations, with clear implications for the detection of frequency-dependent selection of polymorphisms.
    Parasitology 08/2009; 136(10):1097-105. · 2.36 Impact Factor
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    Natal Santos da Silva, Vitor Dantas Muniz
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    ABSTRACT: This was a descriptive statistical study of 8,516 cases of American tegumentary leishmaniasis in the State of Acre, Brazil, from 2001 to 2006 (second period), comparing the results to a previous publication with data from the same State for 1992 to 1997 (first period). Prevalence in the State more than doubled (55.7/10,000 inhabitants from 1992 to 1997 and 128.5/10,000 inhabitants from 2001 to 2006). Males predominated (68.8%, n = 5,860) in the second period. Mean age in the second period was 26.3 years, slightly lower than in the first. Individuals with low schooling were more affected by the disease. The other variables were area of residence, occupation, diagnostic criterion, clinical form, treatment, relapse, time before seeking treatment, and evolution. In conclusion, American tegumentary leishmaniasis epidemiological indicators worsened in the State between the two periods.
    Cadernos de saúde pública / Ministério da Saúde, Fundação Oswaldo Cruz, Escola Nacional de Saúde Pública 07/2009; 25(6):1325-36. · 0.83 Impact Factor
  • Natal Santos da Silva, Vitor Dantas Muniz
    Cadernos De Saude Publica - CAD SAUDE PUBLICA. 01/2009; 25(6).
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    ABSTRACT: A comparison of dengue virus (DENV) antibody levels in paired serum samples collected from predominantly DENV-naive residents in an agricultural settlement in Brazilian Amazonia (baseline seroprevalence, 18.3%) showed a seroconversion rate of 3.67 episodes/100 person-years at risk during 12 months of follow-up. Multivariate analysis identified male sex, poverty, and migration from extra-Amazonian states as significant predictors of baseline DENV seropositivity, whereas male sex, a history of clinical diagnosis of dengue fever, and travel to an urban area predicted subsequent seroconversion. The laboratory surveillance of acute febrile illnesses implemented at the study site and in a nearby town between 2004 and 2006 confirmed 11 DENV infections among 102 episodes studied with DENV IgM detection, reverse transcriptase-polymerase chain reaction, and virus isolation; DENV-3 was isolated. Because DENV exposure is associated with migration or travel, personal protection measures when visiting high-risk urban areas may reduce the incidence of DENV infection in this rural population.
    The American journal of tropical medicine and hygiene 11/2008; 79(4):485-94. · 2.53 Impact Factor
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    ABSTRACT: Little follow-up data on malaria transmission in communities originating from frontier settlements in Amazonia are available. Here we describe a cohort study in a frontier settlement in Acre, Brazil, where 509 subjects contributed 489.7 person-years of follow-up. The association between malaria morbidity during the follow-up and individual, household, and spatial covariates was explored with mixed-effects logistic regression models and spatial analysis. Incidence rates for Plasmodium vivax and Plasmodium falciparum malaria were 30.0/100 and 16.3/100 person-years at risk, respectively. Malaria morbidity was strongly associated with land clearing and farming, and decreased after five years of residence in the area, suggesting that clinical immunity develops among subjects exposed to low malaria endemicity. Significant spatial clustering of malaria was observed in the areas of most recent occupation, indicating that the continuous influx of nonimmune settlers to forest-fringe areas perpetuates the cycle of environmental change and colonization that favors malaria transmission in rural Amazonia.
    The American journal of tropical medicine and hygiene 11/2008; 79(4):624-35. · 2.53 Impact Factor
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    ABSTRACT: This paper describes the distribution of cutaneous leishmaniasis (CL) in the city of Acrelandia, state of Acre, and its phlebotomine sandfly population. Epidemiological data were obtained from case reporting forms in 2001-2004, and entomological data resulted from catches performed between 2004 and 2005 using light traps. A total of 82 new cases of CL, aged between 2 and 62 years, 75.6% males, and 83.9% in the rural area, were identified. The prevailing clinical form was cutaneous (92.7%) with a single lesion (78%). Direct microscopic exams of lesions, Montenegro skin reaction tests, and biopsies resulted in 100%, 98% and 79.5% positivity rates, respectively. The therapeutic response was successful in 81.7% of subjects; treatment refractoriness was higher among CL patients with clinical diagnosis only (41.2%) and among those who received inadequate daily doses of antimonial drug (64.3%). Forty specimens of phlebotomine sandfly were collected around houses with CL cases (3 genera, 14 species); three of those species are known as vectors or possible vectors of Leishmania: Nyssomyia antunesi prevailed in the peri-domiciliary environment (59.1%) and forest borders; Nyssomyia whitmani was frequent in peri-domiciliary areas (15%) and was the only female captured in the intra-domiciliary environment; and Trichophoromyia ubiquitalis was found in the peri-domiciliary environment. The information derived from pre-existing epidemiological data, despite limitations, provided an evaluation of diagnosis and treatment efficacy, while the entomological data can be used as a guideline to develop a larger study aimed to identify both vectors and circulating Leishmania species.
    Revista Brasileira de Epidemiologia 06/2008; 11(2):241-251.
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    Revista Brasileira de Epidemiologia 01/2008; 11(2).
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    ABSTRACT: Understanding the genetic structure of malaria parasites is essential to predict how fast some phenotypes of interest originate and spread in populations. In the present study, we used highly polymorphic microsatellite markers to analyze 74 Plasmodium vivax isolates, which we collected in cross-sectional and longitudinal surveys performed in an area of low malaria endemicity in Brazilian Amazonia, and to explore the transmission dynamics of genetically diverse haplotypes or strains. P. vivax populations are more diverse and more frequently comprise multiple-clone infections than do sympatric Plasmodium falciparum isolates, but these features paradoxically coexist with high levels of inbreeding, leading to significant multilocus linkage disequilibrium. Moreover, the high rates of microsatellite haplotype replacement that we found during 15 months of follow-up most likely do not result from strong diversifying selection. We conclude that the small-area genetic diversity in P. vivax populations under low-level transmission is not severely constrained by the low rates of effective meiotic recombination, with clear public health implications.
    The Journal of Infectious Diseases 05/2007; 195(8):1218-26. · 5.85 Impact Factor