Results of magnetotelluric survey for studying geothermal system in the Bang area, Quang Binh province

This paper presents the first results from the application of magnetotelluric method (MT) using the new equipment MTU 2000 (Canada) and analysis software to investigate the structure of geothermal area around the Bang hot water source (Quang Binh province). Results of data analysis by MT 1D and 2D models to a depth of 20 km show low resistivity zone in the southwest of Bang hot water (100°C) and allow for interpreting the structural elements of athehydro- geothermal system. This includes a very low resistivity layer at depth of 2 km suggesting a clay cap (heat resistive shield), a relatively low resistivity zone at depth ≥ 2 km reflecting  fractured rocks containing geothermal fluid and hot steam. A lower resistivity body at depth of 12-14 km located about 1.5 km from the hot water source indicates the existence of a heat source or a hot mass of intrusive magma., commonly thought to be sources of typical hydro- geothermal systems potential for energy exploitation. The obtained results not only provide new information for better understanding geothermal resource in the surveyed area, but also point out the methods and technology needed to improve the effectiveness for assessing potential of geothermal resources elsewhere in Vietnam.ReferencesBản đồ Địa chất và khoáng sản Việt Nam tỷ lệ 1:1.000.000. Cục Địa chất và Khoáng sản Việt Nam xuất bản 2004. Lưu trữ Địa chất. Cumming W., 2009: Geothermal resource conceptual models using surface exploration data. In: proceedings, 34th workshop on geothermal reservoir engineering, Stanford University. Data Processing User guide. Phoenix Geophysic Ltd. 2005, 201p. Di Pippo R., 2012: Geothermal Power plant. Principles, applications, case studies. 3rd edition. Elseverdirect, 579p. Doan Van Tuyen, Tran Anh Vu, Nguyen Thi Kim Thuong, 2014: Geochemical Characteristics of Geothermal Hot Water Sources on the Territory of Vietnam. Proceeding, Thirty-Eighth Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, February 24-26, 2014 SGP-TR-202. Duchkov A.D., Nguyen Trong Yem, Dinh Van Toan, and Trinh Viet Bac, 1992: First estimations of heat flow in northern Vietnam. Soviet Geology and Geophysics, Vol. 33, No. 5, pp 92-96. Flynn T., Quy H. H., 1997: Assessment of the geothermal resources of Socialist Republic of Vietnam. Geothermal resources Council Transactions, vol.21, 341-345. IGA report, 2013: Geothermal Exploration best practices: A Guide to resource data collection, analysis, and presentation for Geothermal projects. He Lijuan, 1999: Analysis of heat flow along a transect across the South China Sea. Geothermal Training Programme, Reports 1999, Number 5, 125-140. Hoang Huu Quy, 1998: Overview of the Geothermal potential of Vietnam. Geothermics, Vol.27, n.1, 109-115. Koenig J. et al., 1981: Evaluation of the potential for Geothermal Energy Resources in the SR of Vietnam. Berkeley, CA. Kulinich G.G., Zabolotnikov A.A, Markov Yu., 1989: Cenozoic evalution of the Earth crust and orogeny in South- Eastern Asia (Tiếng Nga). MTU2000: User guide. Phoenix Geophysic Ltd. 2000, 36p. Munoz Gerard, 2014: Exploring for Geothermal Resources with Electromagnetic Methods. Surv Geophys (2014) 35:101-122, Springer, DOI 10.1007/s10712-013-9236-0. Pellerin et al., Johnston M, Hohmann W., 1996: A numerical evaluation of electromagnetic methods in geothermal exploration. Geophysics 61(1996):121-130. Thomas Mathews, et al., 2008: Study on the sozio-economic framework for the use Geothermal energy in Vietnam. Proceedings of the 8th Asian Geothermal Symposium, Hanoi. Trần Huyên, Trương Minh, Nguyễn Tiến Bào, 1999: Về chế độ địa nhiệt ở các bể trầm tích thềm lục địa Việt Nam. Tạp chí Kinh tế Địa chất và Nguyên liệu khoáng. Cục Địa chất và Khoáng sản Việt Nam. Số 18 tháng 2 năm 1999, tr.16-25. Võ Công Nghiệp (chủ biên), 1998: Danh bạ các nguồn nước khoáng và nước nóng Việt Nam. Cục Địa chất và Khoáng sản Việt Nam. Hà Nội, 300tr. Zhdanov M., 2009: Geophysical Electromagnetic Theory and Methods. Methods in Geochemistry and Geophysics, Volume 43. ISSN: 0076-6895 Elsevier, 831pp. WinGLink User guide. Geosystem 200, 182p. www.geosystem.net.

The CIPAZ study protocol: an open label randomised controlled trial of azithromycin versus ciprofloxacin for the treatment of children hospitalised with dysentery in Ho Chi Minh City, Vietnam

Background: Diarrhoeal disease remains a common cause of illness and death in children <5 years of age. Faecal-oral infection by Shigella spp. causing bacillary dysentery is a leading cause of moderate-to-severe diarrhoea, particularly in low and middle-income countries. In Southeast Asia, S. sonnei predominates and infections are frequently resistant to first-line treatment with the fluoroquinolone, ciprofloxacin. While resistance to all antimicrobials is increasing, there may be theoretical and clinical benefits to prioritizing treatment of bacillary dysentery with the azalide, azithromycin. In this study we aim to measure the efficacy of treatment with azithromycin compared with ciprofloxacin, the current standard of care, for the treatment of children with bacillary dysentery. Methods and analysis: We will perform a multicentre, open-label, randomized controlled trial of two therapeutic options for the antimicrobial treatment of children hospitalised with dysentery. Children (6–60 months of age) presenting with symptoms and signs of dysentery at Children’s Hospital 2 in Ho Chi Minh City will be randomised (1:1) to treatment with either oral ciprofloxacin (15mg/kg/twice daily for 3 days, standard-of-care) or oral azithromycin (10mg/kg/daily for 3 days). The primary endpoint will be the proportion of treatment failure (defined by clinical and microbiological parameters) by day 28 (+3 days) and will be compared between study arms by logistic regression modelling using treatment allocation as the main variable. Ethics and dissemination: The study protocol (version 1.2 dated 27th December 2018) has been approved by the Oxford Tropical Research Ethics Committee (47–18) and the ethical review boards of Children's Hospital 2 (1341/NĐ2-CĐT). The study has also been approved by the Vietnamese Ministry of Health (5044/QĐ-BYT). Trial registration: Clinicaltrials.gov: NCT03854929 (February 26th 2019)

Evaluation of Xpert MTB/RIF and MODS assay for the diagnosis of pediatric tuberculosis

BACKGROUND: Tuberculosis (TB) in children is rarely confirmed due to the lack of effective diagnostic tools; only 10 to 15% of pediatric TB is smear positive due to paucibacillary samples and the difficulty of obtaining high-quality specimens from children. We evaluate here the accuracy of Xpert MTB/RIF in comparison with the Micoroscopic observation drug susceptibility (MODS) assay for diagnosis of TB in children using samples stored during a previously reported evaluation of the MODS assay. METHODS: Ninety-six eligible children presenting with suspected TB were recruited consecutively at Pham Ngoc Thach Hospital in Ho Chi Minh City Viet Nam between May to December 2008 and tested by Ziehl-Neelsen smear, MODS and Mycobacterial growth Indicator (MGIT, Becton Dickinson) culture. All samples sent by the treating clinician for testing were included in the analysis. An aliquot of processed sample deposit was stored at −20°C and tested in the present study by Xpert MTB/RIF test. 183 samples from 73 children were available for analysis by Xpert. Accuracy measures of MODS and Xpert were summarized. RESULTS: The sensitivity (%) in detecting children with a clinical diagnosis of TB for smear, MODS and Xpert were 37.9 [95% CI 25.5; 51.6], 51.7 [38.2; 65.0] and 50.0 [36.6; 63.4], respectively (per patient analysis). Xpert was significantly more sensitive than smear (P=0.046). Testing of additional samples did not increase case detection for MODS while testing of a second sputum sample by Xpert detected only two additional cases. The positive and negative predictive values (%) of Xpert were 100.0 [88.0; 100.0] and 34.1 [20.5; 49.9], respectively, while those of MODS were 96.8 [83.3; 99.9] and 33.3 [19.6; 49.5]. CONCLUSION: MODS culture and Xpert MTB/RIF test have similar sensitivities for the detection of pediatric TB. Xpert MTB RIF is able to detect tuberculosis and rifampicin resistance within two hours. MODS allows isolation of cultures for further drug susceptibility testing but requires approximately one week to become positive. Testing of multiple samples by xpert detected only two additional cases and the benefits must be considered against costs in each setting. Further research is required to evaluate the optimal integration of Xpert into pediatric testing algorithms

The transfer and decay of maternal antibody against Shigella sonnei in a longitudinal cohort of Vietnamese infants.

BACKGROUND: Shigella sonnei is an emergent and major diarrheal pathogen for which there is currently no vaccine. We aimed to quantify duration of maternal antibody against S. sonnei and investigate transplacental IgG transfer in a birth cohort in southern Vietnam. METHODS AND RESULTS: Over 500-paired maternal/infant plasma samples were evaluated for presence of anti-S. sonnei-O IgG and IgM. Longitudinal plasma samples allowed for the estimation of the median half-life of maternal anti-S. sonnei-O IgG, which was 43 days (95% confidence interval: 41-45 days). Additionally, half of infants lacked a detectable titer by 19 weeks of age. Lower cord titers were associated with greater increases in S. sonnei IgG over the first year of life, and the incidence of S. sonnei seroconversion was estimated to be 4/100 infant years. Maternal IgG titer, the ratio of antibody transfer, the season of birth and gestational age were significantly associated with cord titer. CONCLUSIONS: Maternal anti-S. sonnei-O IgG is efficiently transferred across the placenta and anti-S. sonnei-O maternal IgG declines rapidly after birth and is undetectable after 5 months in the majority of children. Preterm neonates and children born to mothers with low IgG titers have lower cord titers and therefore may be at greater risk of seroconversion in infancy

Microscopic Observation Drug Susceptibility Assay (MODS) for Early Diagnosis of Tuberculosis in Children

MODS is a novel liquid culture based technique that has been shown to be effective and rapid for early diagnosis of tuberculosis (TB). We evaluated the MODS assay for diagnosis of TB in children in Viet Nam. 217 consecutive samples including sputum (n = 132), gastric fluid (n = 50), CSF (n = 32) and pleural fluid (n = 3) collected from 96 children with suspected TB, were tested by smear, MODS and MGIT. When test results were aggregated by patient, the sensitivity and specificity of smear, MGIT and MODS against “clinical diagnosis” (confirmed and probable groups) as the gold standard were 28.2% and 100%, 42.3% and 100%, 39.7% and 94.4%, respectively. The sensitivity of MGIT and MODS was not significantly different in this analysis (P = 0.5), but MGIT was more sensitive than MODS when analysed on the sample level using a marginal model (P = 0.03). The median time to detection of MODS and MGIT were 8 days and 13 days, respectively, and the time to detection was significantly shorter for MODS in samples where both tests were positive (P<0.001). An analysis of time-dependent sensitivity showed that the detection rates were significantly higher for MODS than for MGIT by day 7 or day 14 (P<0.001 and P = 0.04), respectively. MODS is a rapid and sensitive alternative method for the isolation of M.tuberculosis from children

Evaluation of Luminex xTAG Gastrointestinal Pathogen Panel Assay for Detection of Multiple Diarrheal Pathogens in Fecal Samples in Vietnam.

Diarrheal disease is a complex syndrome that remains a leading cause of global childhood morbidity and mortality. The diagnosis of enteric pathogens in a timely and precise manner is important for making treatment decisions and informing public health policy, but accurate diagnosis is a major challenge in industrializing countries. Multiplex molecular diagnostic techniques may represent a significant improvement over classical approaches. We evaluated the Luminex xTAG gastrointestinal pathogen panel (GPP) assay for the detection of common enteric bacterial and viral pathogens in Vietnam. Microbiological culture and real-time PCR were used as gold standards. The tests were performed on 479 stool samples collected from people admitted to the hospital for diarrheal disease throughout Vietnam. Sensitivity and specificity were calculated for the xTAG GPP for the seven principal diarrheal etiologies. The sensitivity and specificity for the xTAG GPP were >88% for Shigellaspp.,Campylobacterspp., rotavirus, norovirus genotype 1/2 (GI/GII), and adenovirus compared to those of microbiological culture and/or real-time PCR. However, the specificity was low (∼60%) for Salmonella species. Additionally, a number of important pathogens that are not identified in routine hospital procedures in this setting, such as Cryptosporidiumspp. and Clostridium difficile, were detected with the GPP. The use of the Luminex xTAG GPP for the detection of enteric pathogens in settings, like Vietnam, would dramatically improve the diagnostic accuracy and capacity of hospital laboratories, allowing for timely and appropriate therapy decisions and a wider understanding of the epidemiology of pathogens associated with severe diarrheal disease in low-resource settings

The Role of Maternally Acquired Antibody in Providing Protective Immunity Against Nontyphoidal Salmonella in Urban Vietnamese Infants: A Birth Cohort Study.

BACKGROUND: Nontyphoidal Salmonella (NTS) organisms are a major cause of gastroenteritis and bacteremia, but little is known about maternally acquired immunity and natural exposure in infant populations residing in areas where NTS disease is highly endemic. METHODS: We recruited 503 pregnant mothers and their infants (following delivery) from urban areas in Vietnam and followed infants until they were 1 year old. Exposure to the dominant NTS serovars, Salmonella enterica serovars Typhimurium and Enteritidis, were assessed using lipopolysaccharide (LPS) O antigen-specific antibodies. Antibody dynamics, the role of maternally acquired antibodies, and NTS seroincidence rates were modeled using multivariate linear risk factor models and generalized additive mixed-effect models. RESULTS: Transplacental transfer of NTS LPS-specific maternal antibodies to infants was highly efficient. Waning of transplacentally acquired NTS LPS-specific antibodies at 4 months of age left infants susceptible to Salmonella organisms, after which they began to seroconvert. High seroincidences of S. Typhimurium and S. Enteritidis LPS were observed, and infants born with higher anti-LPS titers had greater plasma bactericidal activity and longer protection from seroconversion. CONCLUSIONS: Although Vietnamese infants have extensive exposure to NTS, maternally acquired antibodies appear to play a protective role against NTS infections during early infancy. These findings suggest that prenatal immunization may be an appropriate strategy to protect vulnerable infants from NTS disease

No Clinical Benefit of Empirical Antimicrobial Therapy for Pediatric Diarrhea in a High-Usage, High-Resistance Setting.

BACKGROUND: Pediatric diarrheal disease presents a major public health burden in low- to middle-income countries. The clinical benefits of empirical antimicrobial treatment for diarrhea are unclear in settings that lack reliable diagnostics and have high antimicrobial resistance (AMR). METHODS: We conducted a prospective multicenter cross-sectional study of pediatric patients hospitalized with diarrhea containing blood and/or mucus in Ho Chi Minh City, Vietnam. Clinical parameters, including disease outcome and treatment, were measured. Shigella, nontyphoidal Salmonella (NTS), and Campylobacter were isolated from fecal samples, and their antimicrobial susceptibility profiles were determined. Statistical analyses, comprising log-rank tests and accelerated failure time models, were performed to assess the effect of antimicrobials on disease outcome. RESULTS: Among 3166 recruited participants (median age 10 months; interquartile range, 6.5-16.7 months), one-third (1096 of 3166) had bloody diarrhea, and 25% (793 of 3166) were culture positive for Shigella, NTS, or Campylobacter. More than 85% of patients (2697 of 3166) were treated with antimicrobials; fluoroquinolones were the most commonly administered antimicrobials. AMR was highly prevalent among the isolated bacteria, including resistance against fluoroquinolones and third-generation cephalosporins. Antimicrobial treatment and multidrug resistance status of the infecting pathogens were found to have no significant effect on outcome. Antimicrobial treatment was significantly associated with an increase in the duration of hospitalization with particular groups of diarrheal diseases. CONCLUSIONS: In a setting with high antimicrobial usage and high AMR, our results imply a lack of clinical benefit for treating diarrhea with antimicrobials; adequately powered randomized controlled trials are required to assess the role of antimicrobials for diarrhea