Spatial clusters of human and livestock anthrax define high-risk areas requiring intervention in Lao Cai Province, Vietnam 1991-2022.

Anthrax, a widespread zoonosis in low and middle-income countries with low disease awareness and insufficient livestock vaccination coverage, has been known in Lao Cai Province in northern Vietnam for years before its apparent absence in 2009, which requires investigation as this infection is frequently reported from neighbouring provinces and countries. We aimed to describe the seasonal patterns of anthrax (1991-2008), compare livestock anthrax vaccine coverage to disease occurrence (1991- 2022), and delineate the high-risk areas to inform local disease surveillance in the province. We illustrated the seasonal pattern of anthrax and provided a comparison between livestock vaccine coverage and disease occurrence by purely spatial SaTScan (Poisson model, 25% population at risk) to detect spatial clusters of human and livestock anthrax using population derived from zonal statistics routines. The number of cases, crude cumulative incidence, and spatial clusters of human and livestock anthrax were mapped in QGIS. Results indicate peak anthrax incidence from May to October. Buffalo, domestic cattle, and horses accounted for 75% of total animal cases. Horse anthrax was more common in Lao Cai than in its neighbours and often occurred in years with human mortality. Vaccination covered less than 30% of the livestock population. We found an apparent pattern where anthrax was controlled from 1998-2003 with higher vaccine coverage (>20%) and identified spatial clusters of human and livestock anthrax in Muong Khuong, Bao Thang, and Bac Ha districts of Lao Cai. The local public health and veterinary agencies are recommended to revisit the high-risk areas and communicate with neighbouring provinces for a regional approach to anthrax surveillance and control.

Metal contamination, their ecological risk, and relationship with other variables in surface sediments of urban rivers in a big city in Asia: case study of Hanoi, Vietnam.

Urban rivers are significantly impacted by anthropogenic pressure. This study presents the updated assessment of the concentrations of 11 metals and other variables (pH, total organic carbon (TOC) and nutrients (total nitrogen, total phosphorus, and total silica)) in the sediments of four urban rivers in inner Hanoi city, Vietnam, during the period 2020-2022. The mean concentrations of Fe, Zn, As, and Cr were higher than the permissible values of the Vietnam National technical regulation on the surface sediment quality. Moreover, Zn and Cr were at the severe effect level of the US EPA guidelines for sediment quality. The calculation of pollution indices (Igeo and EF) demonstrated that Mn, Ni, and Fe were from natural sources whereas other metals were from both anthropogenic and natural sources. The ecological risk index revealed that metals in Hanoi riverine sediments were classified at considerable ecological risk. High values of metals, TOC, and nutrients in the sediments of these urban rivers mostly originate from the accumulation of untreated urban wastewater that is enhanced by low river discharge. Our results may provide scientific base for better management decisions to ensure environmental protection and sustainable development of Hanoi city.

Spatial epidemiology of human anthrax in Son La province, Vietnam, 2003-2022.

AIMS: Anthrax is reported with frequency but poorly understood in Southeast Asian countries including Vietnam. In Vietnam, anthrax surveillance is national. However, case detection, prevention, and control are implemented locally at the provincial level. Here, we describe the epidemiological characteristics, identify spatial clusters of human anthrax, and compare the variation in livestock anthrax vaccine coverage to disease incidence in humans and livestock using historical data in Son La province, Vietnam (2003-2020). METHODS AND RESULTS: Most human cases occurred between April and September. Most of the patients were male, aged 15-54 years old. The human cases were mainly reported by public district hospitals. There was a delay between disease onset and hospitalization of ~5 days. We identified spatial clusters of high-high incidence communes in the northern communes of the province using the local Moran's I statistic. The vaccine coverage sharply decreased across the study period. The province reported sporadic human anthrax outbreaks, while animal cases were only reported in 2005 and 2022. CONCLUSIONS: These results suggest underreporting for human and livestock anthrax in the province. Intersectoral information sharing is needed to aid livestock vaccination planning, which currently relies on reported livestock cases. The spatial clusters identify areas for targeted surveillance and livestock vaccination, while the seasonal case data suggest prioritizing vaccination campaigns for February or early March ahead of the April peak. A regional approach for studying the role of livestock trading between Son La and neighbouring provinces in anthrax occurrence is recommended.

Spatial analysis of human and livestock anthrax in Lai Chau province, Vietnam (2004-2021).

Anthrax is reported globally with varying disease intensity and seasonality among countries. In Vietnam, anthrax epidemiology and ecology remain understudied. We used historical data of human and livestock anthrax from 2004 to 2021 in Lai Chau province, to identify spatial clusters of human and livestock anthrax, describe epidemiological characteristics, and compare livestock anthrax vaccine coverage to human and livestock disease incidence. Local Moran's I (LISA) using spatial Bayes smoothed commune-level cumulative incidence (per 10,000) for the study period, epidemiological descriptive statistics, livestock vaccine coverage data, and annual incidence rates (per 10,000) at provincial level were used. LISA identified a human anthrax hotspot (high-high) in the southeast which did not overlap spatially with livestock anthrax hotspots in southeastern and northeastern communes. Most human cases were male, aged 15-59 years, handled sick animals, and/or consumed contaminated meat. Almost all cases were reported by grassroot health facilities with a delay of 6.3 days between exposure and case notification to the national surveillance system. 80 % of human cases were reported from June-October. The increase in disease incidence occurred shortly after livestock anthrax vaccine coverage decreased. This study informs vaccination strategy and targeted surveillance and control measures in newly identified high-risk areas and seasons of anthrax.

Spatial and phylogenetic patterns reveal hidden infection sources of Bacillus anthracis in an anthrax outbreak in Son La province, Vietnam.

Bacillus anthracis, the bacterial cause of anthrax, is a zoonosis affecting livestock and wildlife often spilling over into humans. In Vietnam, anthrax has been nationally reportable since 2015 with cases occurring annually, mostly in the northern provinces. In April 2022, an outbreak was reported in Son La province following the butchering of a water buffalo, Bubalus bubalis. A total of 137 humans from three villages were likely exposed to contaminated meat from the animal. Early epidemiological investigations suggested a single animal was involved in all exposures. Five B. anthracis isolates were recovered from human clinical cases along with one from the buffalo hide, another from associated maggots, and one from soil at the carcass site. The isolates were whole genome sequenced, allowing global, regional, and local molecular epidemiological analyses of the outbreak strains. All recovered B. anthracis belong to the A.Br.001/002 lineage based on canonical single nucleotide polymorphism analysis (canSNP). Although not previously identified in Vietnam, this lineage has been identified in the nearby countries of China, India, Indonesia, Thailand, as well as Australia. A twenty-five marker multi-locus variable number tandem repeat analysis (MLVA-25) was used to investigate the relationship between human, soil, and buffalo strains. Locally, four MLVA-25 genotypes were identified from the eight isolates. This level of genetic diversity is unusual for the limited geography and timing of cases and differs from past literature using MLVA-25. The coupled spatial and phylogenetic data suggest this outbreak originated from multiple, likely undetected, animal sources. These findings were further supported by local news reports that identified at least two additional buffalo deaths beyond the initial animal sampled in response to the human cases. Future outbreak response should include intensive surveillance for additional animal cases and additional molecular epidemiological traceback to identify pathogen sources.

Incidence and Spatial distribution of Human and Livestock Anthrax in Cao Bang Province, Vietnam (2004-2020).

Specific knowledge on the distribution of anthrax, a zoonosis caused by Bacillus anthracis, in Southeast Asia, including Vietnam, remains limited. In this study, we describe disease incidence and spatial distribution of human and livestock anthrax using spatially smoothed cumulative incidence from 2004 to 2020 in Cao Bang province, Vietnam. We employed the zonal statistics routine a geographic information system (GIS) using QGIS, and spatial rate smoothing using spatial Bayes smoothing in GeoDa. Results showed higher incidence of livestock anthrax compared with human anthrax. We also identified co-occurrence of anthrax in humans and livestock in northwestern districts and the province center. Livestock anthrax vaccine coverage was <6% and not equally distributed among the districts of Cao Bang province. We provide implications for future studies and recommend improving disease surveillance and response through data sharing between human and animal health sectors.

Microbial contamination in the coastal aquaculture zone of the Ba Lat river mouth, Vietnam.

Contamination of aquaculture products by pathogenic organisms is a major concern in areas where this activity is of high economic importance. The abundances of total coliforms (TC), Escherichia coli (EC) and faecal streptococci (FS) (in CFU.100 mL-1) in seawater in the Red River coastal aquaculture zone were determined. The results showed TC numbers (200 to 9100; average 1822), EC (<100 to 3400; average 469) and FS (<100 to 2100; average 384), of which TC exceeded the allowable threshold of the Vietnam regulation for coastal aquaculture water. TC and EC numbers in 4 wastewater types (domestic, livestock farming sewage, agricultural runoff, and mixed sewage canals) were investigated and revealed the importance of point sources of faecal contamination in seawater. These results underline the need to reduce the release of untreated wastewater and to put into place seawater microbial quality monitoring in areas where the development of sustainable aquaculture is an objective.

Evaluation of heavy metal contamination in the coastal aquaculture zone of the Red River Delta (Vietnam).

Coastal aquaculture contributes significantly to the local economy of many countries however water quality issues in the coastal regions are threatening the sustainability of this economic activity. This paper presents the analysis of seven heavy metals (HM) in surface seawater and wastewater from the Red River coastal aquaculture zone during 2019-2020. HM concentrations (µg.L-1) from 72 seawater samples were: Zn: 60.76 (0.5-188.0); Cu: 26.91 (0.10-96.0); Pb: 7.27 (0.8-31.2); Cr: 6.71 (0.6-28.4); As: 1.38 (0.15-5.78); Cd: 0.44 (0.04-2.41); and Hg: 0.34 (0.02-1.39). All mean values of HM in seawater were lower than the Vietnam regulatory limits for aquaculture seawater although high individual HM concentrations were found in some isolated seawater samples. Concerning wastewater quality, only mean As concentration was higher than the Vietnam regulatory limit for surface water quality, despite the fact that high concentrations of other individual HM were observed. The PCA analysis on the entire dataset of seawater and wastewater samples revealed that HM concentrations in seawater originate from various sources including human activities and natural conditions. The total potential ecological risk index (averaging 18.6; from 7.48 to 39.05) for the Red River coastal zone is in the low range. These results provide a scientific basis for better management of the coastal environment which is important for the sustainable development of the aquaculture industry in this area.

Quantification and Antimicrobial Resistance of Vibrio parahaemolyticus in Retail Seafood in Hanoi, Vietnam.

ABSTRACT: Vibrio parahaemolyticus is a major cause of foodborne diseases and a significant threat to human health worldwide. Most of the infections caused by V. parahaemolyticus are usually associated with the consumption of raw or undercooked seafood. This study was conducted to determine the prevalence, quantitative load, and antimicrobial resistance of V. parahaemolyticus in retail seafood in Hanoi, Vietnam. A total of 120 seafood samples consisting of marine fish (n = 30), oysters (n = 30), shrimp (n = 30), and squid (n = 30) were purchased from different traditional markets in Hanoi between May and October 2020. Isolation of V. parahaemolyticus was based on ISO/TS 21872-1:2017, and the most-probable-number (MPN) method was used for quantification. The disk diffusion method was applied for antimicrobial susceptibility testing. Overall, V. parahaemolyticus was detected in 58.33% of the samples. V. parahaemolyticus was most commonly isolated in shrimp samples, with a prevalence of 86.67%, followed by fish (53.33%), squid (53.33%), and oysters (40%). One V. parahaemolyticus isolate from an oyster carrying the trh gene was detected. Of the positive samples, 27.14% contained V. parahaemolyticus counts of less than 2 log MPN/g, whereas 44.29% ranged from 2 to 4 log MPN/g and 28.57% contained more than 4 log MPN/g. Regarding antimicrobial resistance, 85.71% of V. parahaemolyticus isolates were resistant to at least one antibiotic tested. The highest rate of resistance was observed against ampicillin (81.43%), followed by cefotaxime (11.43%), ceftazidime (11.43%), trimethoprim-sulfamethoxazole (8.57%), and tetracycline (2.86%). The results demonstrate the high prevalence and quantitative load and the antimicrobial resistance of V. parahaemolyticus isolated from seafood sold in the study area.

Unsubstituted and Methylated PAHs in Surface Sediment of Urban Rivers in the Red River Delta (Hanoi, Vietnam): Concentrations, Profiles, Sources, and Ecological Risk Assessment.

Unsubstituted and methylated polycyclic aromatic hydrocarbons (22 PAHs and 17 Me-PAHs) were examined in surface sediments collected from the Red River and four inner-city rivers of Hanoi City, Vietnam. Concentrations of total PAHs and Me-PAHs ranged from 52 to 920 (median 710) and from 70 to 2600 (median 1000) ng/g dry weight in samples of dry and wet seasons, respectively. Significant correlation was observed between total PAHs and organic carbon contents (Spearman's ρ = 0.782; p < 0.05). PAHs were more abundant than Me-PAHs in all samples and dominated by 4-6 ring compounds. The most predominant PAHs were benzo[ghi]perylene, benzo[b/j]fluoranthene, chrysene, pyrene, fluoranthene, and phenanthrene. Methylated derivatives of naphthalene, phenanthrene, anthracene, and benz[a]anthracene were frequently detected. The patterns of PAHs indicated principal pyrogenic sources (notably gasoline exhaust) in this highly urbanized area. The occurrence of several PAHs were occasionally associated with adverse effects on benthic organisms of the inner-city rivers.

Antibiotic and antiparasitic residues in surface water of urban rivers in the Red River Delta (Hanoi, Vietnam): concentrations, profiles, source estimation, and risk assessment.

Antibiotic residues and antimicrobial resistance in surface water are issues of global concern, especially in developing countries. In this study, the occurrence of seven antibiotics and one antiparasitic agent was determined in surface water samples collected from four rivers running through Hanoi urban area in the Red River Delta, northern Vietnam. The pharmaceuticals in water samples were analyzed by solid-phase extraction combined with liquid chromatography-tandem mass spectrometry method. The concentrations of pharmaceuticals in our samples ranged from 3050 to 16,700 (median 7800) ng/L, which were generally higher than levels found in river water from many other locations in the world. Amoxicillin, oxfendazole, and lincomycin were the most dominant and frequently detected compounds (detection rate 100%), which together accounted for 76 ± 14% of total concentrations. Sulfacetamide and sulfamethoxazole were detected at moderate concentrations in more than two-thirds of the analyzed samples. The remaining antibiotics (i.e., azithromycin, ciprofloxacin, and ofloxacin) were found at lower detection frequency and concentrations. Antibiotic concentrations in the water samples were not significantly different between the investigated rivers. Meanwhile, levels of pharmaceuticals in the samples collected in February 2020 were higher than those found in the remaining samples, largely due to the sharp decrease in sulfamethoxazole and azithromycin concentrations of the samples collected in March and April. Considerable ecological risks of antibiotics in surface water were estimated for some compounds such as amoxicillin, ciprofloxacin, and ofloxacin.

TaqMan Assays for Simultaneous Detection of Bacillus anthracis and Bacillus cereus biovar anthracis.

Anthrax is a worldwide zoonotic disease caused by the spore-forming bacterium Bacillus anthracis. Primarily a disease of herbivores, human infections often result from direct contact with contaminated animal products (cutaneous and inhalational anthrax) or through consumption of infected meat (gastrointestinal anthrax). The genetic near neighbor, Bacillus cereus biovar anthracis (Bcbva), causes an anthrax-like illness in the wildlife and livestock of west and central Africa due to the presence and expression of B. anthracis-specific virulence factors in this background. While Bcbva infections have not been reported in humans, a recent seroprevalence study detected Bcbva antibodies in the rural population around Taï National Park. This work describes the development of new TaqMan multiplex PCRs for the simultaneous detection of B. anthracis and Bcbva. The assays are designed to amplify Ba-1, capB, and lef markers in B. anthracis and genomic island IV (GI4), capB, and lef in Bcbva. Our assays allow for the rapid discrimination of B. anthracis and Bcbva and will provide insights into the molecular epidemiology of these two important pathogens that share an overlapping geographical range in west and central Africa.

Epidemiological and comparative genomic analysis of Bacillus anthracis isolated from northern Vietnam.

To understand the epidemiological and genetic background of anthrax cases occurring in Vietnam from 2011 to 2015, we surveilled and genetically analyzed Bacillus anthracis isolated in the north of the country. Epidemiological surveillance showed that most human cutaneous anthrax cases occurred in association with animal dissection. Whole-genome sequences were obtained from six B. anthracis strains from human patients with cutaneous anthrax in the endemic area. Comparative genomic analysis showed that the genetic homogeneity among Vietnamese B. anthracis strains was very high. All Vietnamese B. anthracis strains belonged to the canSNP lineage of A.Br.011/009, which mostly consists of strains of the trans-Eurasian (TEA) group, including the most closely related strain, Carbosap. To clarify the genetic diversity of Vietnamese strains and strains belonging to A.Br.011/009 and A.Br.008/011 canSNP lineages, we applied a reference genome-based single-nucleotide polymorphism (SNP) and gene-by-gene genomic analysis (whole-genome MLST) strategy. The phylogeny from core genome SNPs revealed that the Vietnamese strains were positioned close to each other; moreover, several SNPs specific to Vietnamese B. anthracis were identified. Whole-genome MLST analysis revealed the differences in the number of SNPs between Vietnamese strains, which could enable discrimination at the strain level.

The Effect of Maternal Pertussis Immunization on Infant Vaccine Responses to a Booster Pertussis-Containing Vaccine in Vietnam.

BACKGROUND: Maternal vaccination with an acellular pertussis (aP)-containing vaccine is a recommended strategy in a growing number of industrialized countries, to protect young infants from disease. Little is known on the effect of this strategy in low- and middle-income countries. Following a previous report on the effect of adding a pertussis and diphtheria component to the tetanus vaccination program in pregnant women in Vietnam, we report on infant immune responses to a booster aP vaccine dose in this randomized controlled clinical trial. METHODS: Thirty infants of Tdap (tetanus, diphtheria, and acellular pertussis)-vaccinated pregnant women and 37 infants of women vaccinated with a tetanus-only vaccine received a fourth aP-containing vaccine dose in the second year of life. Blood was taken 1 month after the fourth infant dose. Immunoglobulin G (IgG) antibodies against pertussis toxin (PT), filamentous hemagglutinin (FHA), pertactin (Prn), tetanus toxoid (TT), and diphtheria toxoid (DT) were measured using commercially available enzyme-linked immunosorbent assays (ELISA). RESULTS: One month after the booster dose, significantly lower antibody titers were measured in the Tdap group for anti-TT IgG (P < .001) only. Anti-DT IgG, anti-PT IgG, anti-Prn IgG, and anti-FHA IgG antibody titers were comparable for both groups. A rise in antibody concentrations was elicited for all (except DT) antigens after boosting. CONCLUSIONS: The present results indicate that the blunting of infant pertussis responses induced by maternal immunization, measured after a primary series of aP vaccines, was resolved with the booster aP vaccine dose. These results add to the evidence for national and international decision makers on maternal immunization as a vaccination strategy for protection of young infants against infectious diseases.

Age as risk factor for Helicobacter pylori recurrence in children in Vietnam.

BACKGROUND: The determinants for acquisition of Helicobacter pylori infection remain incompletely understood. The study aim was to investigate risk factors for recurrence in children in Vietnam during 1 year immediately following successful H. pylori eradication. MATERIALS AND METHODS: In a prospective longitudinal study, 136 children, 3-15 years of age, were seen every 3 months for a total of four visits. Helicobacter pylori infection status was determined by an antigen-in-stool test (Premier Platinum HpSA PLUS) on samples obtained at each visit. A questionnaire was filled out at the start of the study. RESULTS: After 1 year, 30 children had become H. pylori positive, while 17 were lost to follow-up. Low age was the most prominent independent risk factor for recurrence: adjusted hazard ratio (HR) among children aged 3-4, 5-6, and 7-8 years, relative to those aged 9-15 years, were, respectively, 14.3 [95% CI 3.8-53.7], 5.4 [1.8-16.3] and 2.6 [0.7-10.4]. Surprisingly, female sex tended to be associated with increased risk (adjusted HR among girls relative to boys 2.5 [95% CI 1.1-5.9]). No other factors such as sibship size, birth order, bed sharing, sanitary standards, or factual antibiotic dose per kilo bodyweight in the eradication trial were found to be significant risk factors for re-infection. CONCLUSIONS: The main risk factor for recurrence with H. pylori was found to be age, with the youngest children running the greatest risk. The finding lends support to the observation that early childhood may be the main age of acquisition of H. pylori infection and for postponing attempts of eradication in high-prevalence areas unless motivated for medical reasons.

Eradication of Helicobacter pylori in children in Vietnam in relation to antibiotic resistance.

BACKGROUND: Low Helicobacter pylori eradication rates are common in pediatric trials especially in developing countries. The aim of the study was to investigate the role of antibiotic resistance, drug dosage, and administration frequency on treatment outcome for children in Vietnam. MATERIALS AND METHODS: Antibiotics resistance of H. pylori was analyzed by the Etest in 222 pretreatment isolates from children 3-15 years of age who were originally recruited in a randomized trial with two treatment regiments: lansoprazole with amoxicillin and either clarithromycin (LAC) or metronidazole (LAM) in two weight groups with once- or twice-daily administration. The study design was an observational study embedded in a randomized trial. RESULTS: The overall resistance to clarithromycin, metronidazole, and amoxicillin was 50.9%, 65.3%, and 0.5%, respectively. In LAC, eradication was linked to the strains being susceptible to clarithromycin (78.2% vs 29.3%, p = .0001). Twice-daily dosage of proton-pump inhibitor (PPI) and clarithromycin was more effective for eradication than once-daily dosage for resistant strains (50.0% vs 14.7%, p = .004) and tended to be so also for sensitive strains (87.5% vs 65.2%, p = .051). Exact antibiotic dose per body weight resulted in more eradication for resistant strains (45.3% vs 8.0%, p = .006). These differences were less pronounced for the LAM regimen, with twice-daily PPI versus once daily for resistant strains resulting in 69.2% and 50.0% eradication (p = .096), respectively. CONCLUSIONS: Helicobacter pylori clarithromycin resistance was unexpectedly high in young children in Vietnam. Clarithromycin resistance was an important cause for eradication treatment failure. Twice-daily administration and exact antibiotic dosing resulted in more eradicated infections when the strains were antibiotic resistant, which has implications for the study design in pediatric H. pylori eradication trials.

Evaluation of two triple-therapy regimens with metronidazole or clarithromycin for the eradication of H. pylori infection in Vietnamese children: a randomized, double-blind clinical trial.

BACKGROUND: Eradication of Helicobacter pylori infection in children in developing countries needs further investigations upon which to base treatment recommendations. The aim of the study was to compare two 2-week triple therapies in a randomized double-blind trial. MATERIALS AND METHODS: In order not to exceed recommended dosages, the 238 H. pylori-infected children, aged 3 to 15 years (mean 8.6), were divided in two weight categories receiving at weights 13-22 kg: lansoprazole 15 mg once-daily and amoxicillin 500 mg twice-daily with metronidazole 250 mg twice-daily or clarithromycin 250 mg once-daily; at weights 23-45 kg: lansoprazole 15 mg and amoxicillin 750 mg with metronidazole 500 mg or clarithromycin 250 mg, all administered twice daily. H. pylori status was assessed by culture and a monoclonal-based antigen-in-stool test (Premier Platinum HpSA PLUS) and side effects by structured questionnaires. RESULTS: The overall per-protocol eradication (n = 233) was similar in the two treatment regimens, 62.1% for the metronidazole and 54.7% for the clarithromycin-containing therapy. Eradication rate was higher in children >or= 23 kg (70.9%) than in children < 23 kg (45.7%). In children >or= 23 kg (n = 117) that received twice-daily administration of all drugs, efficacy of the metronidazole and clarithromycin-containing treatments were 69.5% and 72.4%, respectively. CONCLUSIONS: The two treatments gave similar eradication rates. Significant differences for both treatments were found by weight, which could be the result of the once-daily proton pump inhibitor and clarithromycin and/or more antibiotic resistant strains in younger children.

Seroprevalence of Helicobacter pylori infection in urban and rural Vietnam.

Helicobacter pylori-associated diseases, such as peptic ulcer and gastric cancer, are common in Vietnam, but the prevalence of the infection is largely unknown. A validated enzyme-linked immunosorbent assay was used for seroepidemiology with 971 samples from the general population, ages 0 to 88 years, with 546 samples from an urban population (Hanoi), and with 425 samples from a poor, rural province (Hatay). The overall seroprevalence of the infection was 746 per 1,000, with a prevalence of 788 per 1,000 in Hanoi and 692 per 1,000 in Hatay (P=0.0007). The risk for infection in the rural area of Hatay was 40% lower than in the urban population of Hanoi, with the odds ratio being 0.59 (95% confidence interval, 0.43 to 0.81). The study shows that the prevalence of H. pylori infection is high in Vietnam and especially high in a large urban area, such as the city of Hanoi.

Enzyme-linked immunosorbent assay for Helicobacter pylori needs adjustment for the population investigated.

Helicobacter pylori infection and peptic ulcer disease are common in developing countries, e.g., Vietnam. An enzyme-linked immunosorbent assay (ELISA) for screening of patients and for seroepidemiology is a useful tool but needs to be validated in the population studied. We used in-house ELISA with sonicated Swedish and Vietnamese strains as antigens to measure immunoglobulin G antibodies after absorption with sonicated Campylobacter jejuni in sera from 270 H. pylori culture-confirmed peptic ulcer patients, 128 Swedish urea-breath test and immunoblot-positive healthy controls, and 432 Vietnamese immunoblot-positive population controls. Sonicated whole-cell antigen based on the local strains showed a significantly better performance. Immunoblot-positive peptic ulcer patients had significantly higher antibody concentrations than immunoblot-positive population controls, necessitating a lower cutoff level if serology is used for screening or epidemiological purposes. The study shows that the parameters of ELISA for H. pylori need to be adjusted for the population being investigated.