Spatiotemporal Evolution of SARS-CoV-2 Alpha and Delta Variants during Large Nationwide Outbreak of COVID-19, Vietnam, 2021.

We analyzed 1,303 SARS-CoV-2 whole-genome sequences from Vietnam, and found the Alpha and Delta variants were responsible for a large nationwide outbreak of COVID-19 in 2021. The Delta variant was confined to the AY.57 lineage and caused >1.7 million infections and >32,000 deaths. Viral transmission was strongly affected by nonpharmaceutical interventions.

MYB81, a microspore-specific GAMYB transcription factor, promotes pollen mitosis I and cell lineage formation in Arabidopsis.

Sexual reproduction in flowering plants relies on the production of haploid gametophytes that consist of germline and supporting cells. During male gametophyte development, the asymmetric mitotic division of an undetermined unicellular microspore segregates these two cell lineages. To explore genetic regulation underlying this process, we screened for pollen cell patterning mutants and isolated the heterozygous myb81-1 mutant that sheds ~50% abnormal pollen. Typically, myb81-1 microspores fail to undergo pollen mitosis I (PMI) and arrest at polarized stage with a single central vacuole. Although most myb81-1 microspores degenerate without division, a small fraction divides at later stages and fails to acquire correct cell fates. The myb81-1 allele is transmitted normally through the female, but rarely through pollen. We show that myb81-1 phenotypes result from impaired function of the GAMYB transcription factor MYB81. The MYB81 promoter shows microspore-specific activity and a MYB81-RFP fusion protein is only expressed in a narrow window prior to PMI. Ectopic expression of MYB81 driven by various promoters can severely impair vegetative or reproductive development, reflecting the strict microspore-specific control of MYB81. Our data demonstrate that MYB81 has a key role in the developmental progression of microspores, enabling formation of the two male cell lineages that are essential for sexual reproduction in Arabidopsis.

Determinants of catastrophic health expenditure in Vietnam.

BACKGROUND: The Government of Vietnam has set the goal of achieving universal health coverage (UHC) by 2025. Health insurance (HI) is being considered a tool to achieve this goal. However, out-of-pocket spending and catastrophic health expenditure (CHE) remain high. Research evidence on how to reduce these expenditures to achieve UHC is essential. Therefore, this study examines the determinants of CHE, especially the HI factor. METHOD: To identify HI participation status and other factors associated with CHE, we use logistic regression on a dataset from the 2016 Vietnam Household Living Standards Survey. RESULTS: The study finds that HI is a protective factor against CHE, although this result is not always statistically significant across different subsamples. Moreover, the household head's age and employment status, household size, share of the elderly above 60 years, income, illness status, healthcare utilisation, availability of hospitals, commune health stations with medical doctors and place of residence all correlate with household CHE. CONCLUSION: Although there has been a rise in HI coverage, the financial protection capacity of HI schemes in Vietnam remains inadequate, particularly for households living in rural areas. Further investigations of the causal effect of HI, other health system factors and CHE in rural settings are necessary to reduce the incidence of CHE. Additionally, policies aimed at groups vulnerable to CHE, such as those with higher incidences of severe illness or inpatient admissions, low income, and higher age, should be considered.

Plans for Nationwide Serosurveillance Network in Vietnam.

In recent years, serosurveillance has gained momentum as a way of determining disease transmission and immunity in populations, particularly with respect to vaccine-preventable diseases. At the end of 2017, the Oxford University Clinical Research Unit and the National Institute of Hygiene and Epidemiology held a meeting in Vietnam with national policy makers, researchers, and international experts to discuss current seroepidemiologic projects in Vietnam and future needs and plans for nationwide serosurveillance. This report summarizes the meeting and the plans that were discussed to set up nationwide serosurveillance in Vietnam.

Photoluminescence Properties of Eu-Doped MIL-53(Fe) Obtained by Solvothermal Synthesis.

We report the facial synthesis of Eu-doped MIL-53(Fe) elongated hexagonal dipyramid by solvothermal reaction of Fe(NO3)3, Eu(NO3)3 and terephthalic acid (TPA) in the presence of N,N-dimethylformamide (DMF). The as-synthesized samples were characterized by XRD, Raman, FT-IR, PL, and SEM. From XRD and Raman results, metal replacement (Eu) with the metal ion (Fe) in the crystal lattice may change the high crystallinity of the MIL-53(Fe) structure, and all the metal ions were incorporated into the structures of MIL-53(Fe) as well as replaced Fe ion or located at interstitial site. From PL result, Eu-doped MIL-53(Fe) showed unique Eu fluorescence properties with high emission intensity, thus enabling it to be a promising functional probe for fluorescent imaging.

Grafting of Poly(poly(ethylene glycol) methacrylate) onto Halloysite Nanotubes via Surface-Initiated Atom Transfer Radical Polymerization.

A synthetic strategy for the functionalization of halloysite nanotubes (HNTs) with poly(poly(ethylene glycol) methacrylate) (PPEGMA) via surface-initiated atom transfer radical polymerization (SIATRP). The covalent immobilization of PPEGMA was confirmed by FT-IR analysis. The preparation of the nanohybrids was further evidenced by the XPS and EDX studies. The morphologies of functionalized HNTs were investigated by FE-SEM analysis. TGA results suggested that the nanohybrids can be used in high temperature applications. Thus, this newly developed surface functionalization protocol offers the tailoring of the HNTs surface with wide functionalities and is potentially useful to the biomedical applications.

Glutathione Capped CdSe Quantum Dots: Synthesis, Characterization, Morphology, and Application as a Sensor for Toxic Metal Ions.

Glutathione (GSH) functionalized CdSe quantum dots (QDs) (GSH-f-CdSe QDs) were prepared via a simple one-pot strategy at low temperature. The as-synthesized CdSe QDs were characterized by FT-IR and XPS analyses. The morphology, physical structure and size distribution of GSH-f-CdSe QDs were investigated by TEM, XRD and DLS analyses, respectively. The GSH-f-CdSe QDs exhibited excellent stability of optical properties as investigated by UV-Vis absorption and photoluminescence (PL) spectroscopy. The high affinity of GSH towards heavy metal ions made the GSH-f-CdSe QDs quite susceptible to Pb2+ ion which poses serious threat to the health and environment. The PL intensity of GSH-f-CdSe QDs was observed to be apparently quenched in the presence of Pb2+ ions in aqueous solution rendering their potentialities as a sensor for detection of toxic heavy metal ions.

Detection of co-infection and recombination cases with Omicron and local Delta variants of SARS-CoV-2 in Vietnam.

The first nationwide outbreak of COVID-19 in Vietnam started in late April 2021 and was caused almost exclusively by a single Delta lineage, AY.57. In early 2022, multiple Omicron variants co-circulated with Delta variants and quickly became dominant. The co-circulation of Delta and Omicron happened leading to possibility of co-infection and recombination events which can be revealed by viral genomic data. From January to October 2022, a total of 1028 viral RNA samples out of 4852 positive samples (Ct < 30) were sequenced by the long pooled amplicons method on Illumina platforms. All sequencing data was analysed by the workflow for SARS-CoV-2 on CLC genomics workbench and Illumina Dragen Covid application. Among those sequenced samples, we detected a case of Delta AY.57/Omicron BA.1 co-infection and two cases of infection with Delta AY.57/Omicron BA.2 recombinants which were nearly identical and had different epidemiological characteristics. Since the AY.57 lineage circulated almost exclusively in Vietnam, these results strongly suggest domestic events of co-infection and recombination. These findings highlight the strengths of genomic surveillance in monitoring the circulating variants in the community enabling rapid identification of viral changes that may affect viral properties and evolutionary events.

Source discrimination of heavy metals in sediment and water of To Lich River in Hanoi City using multivariate statistical approaches.

The concentrations of Mn, Fe, Ni, Cr, Cu, Pb, Zn, As, and Cd were determined to evaluate the level of contamination of To Lich River in Hanoi City. All metal concentrations in 0-10-cm water samples, except Mn, were lower than the maximum permitted concentration for irrigation water standard. Meanwhile, concentrations of As, Cd, and Zn in 0-30-cm sediments were likely to have adverse effects on agriculture and aquatic life. Sediment pollution assessment was undertaken using enrichment factor and geoaccumulation index (I geo). The I geo results indicated that the sediment was not polluted with Cr, Mn, Fe, and Ni, and the pollution level increased in the order of Cu < Pb < Zn < As < Cd. Meanwhile, significant enrichment was shown for Cd, As, Zn, and Pb. Cluster and principal component analyses suggest that As and Mn in sediment were derived from both lithogenic and anthropogenic sources, while Cu, Pb, Zn, Cr, Cd, and Ni originated from anthropogenic sources such as vehicular fumes for Pb and metallic discharge from industrial sources and fertilizer application for other metals.

Swollen-state preparation of chitosan lactate from moulted shrimp shells and its application for harvesting marine microalgae Nannochloropsis sp.

Chitosan lactate (CSS) has been widely used for academic and industrial applications due to its biocompatibility, biodegradability, and high biological activity. Unlike chitosan, which is generally soluble only in acid solution, CSS can be directly used by dissolving in water. In this study, CSS was prepared from moulted shrimp chitosan at room temperature by a solid-state method. Chitosan was first swollen in a mixture of ethanol and water, making it more susceptible to reacting with lactic acid in the next step. As a result, the prepared CSS had a high solubility (over 99 %) and zeta potential (+ 99.3 mV) and was comparable to the commercial product. The preparation method of CSS is facile and efficient for a large-scale process. In addition, the prepared product exhibited a potential flocculant for harvesting Nannochloropsis sp., a marine microalga widely used as a popular food for larvae. In the best condition, the CSS solution (250 ppm) at pH 10 showed the highest recovery capacity (∼ 90 % after 120 min) for harvesting Nannochloropsis sp. Besides, the harvested microalgal biomass showed excellent regeneration after 6 culture days. This paper's findings suggest a circular economy in aquaculture by producing value-added products from solid wastes, which can minimize the environmental impact and move towards sustainable zero-waste.

Catastrophic health expenditure in the Northern midlands and mountainous areas and its determinants, Vietnam from 2014 to 2020: a cross-sectional study.

OBJECTIVES: The study assesses households' catastrophic health expenditure (CHE) by income group, urban versus rural area, and influencing factors in the Northern midlands and mountainous areas of Vietnam. DESIGN/SETTING: A cross-sectional study with the four waves of data from 2014, 2016, 2018 and 2020 Vietnam household living standards surveys was used. PARTICIPANTS: The number of participants in this study were 1658, 1661, 1659 and 1662 households in 2014, 2016, 2018 and 2020, respectively. We included households residing in the Northern midlands and mountain areas of Vietnam. OUTCOMES MEASURE: We examined out-of-pocket health payments and capacity to pay by income groups and place of residence, the incidence of CHE and impoverishment. A logistic regression model was used to examine the influence of demographic and socioeconomic characteristics on CHE. RESULTS: The findings showed a remarkable decrease in CHE between 2014 and 2016, followed by a considerable increase between 2016 and 2018. The CHE rates in the region were between 3.5% and 5%, with the highest value observed in 2014. In addition, the differences in household CHE rates according to income and place of residence were observed. The results also indicated that medical impoverishment ranged between 3.4% and 3.9%. Overall, factors such as the burden of disease, rural settlements, increasing use of healthcare services, visiting private health facilities and having an old-aged person in the household were significantly and positively associated with CHE. By contrast, households that were wealthier, participated in health insurance, had a household head employed and female-headed households, were negatively associated with CHE. CONCLUSIONS: The findings provide useful information that can guide policy-makers to design policies, and interventions necessary to reduce CHE in the region, narrow the gap between the rich and the poor, the rural and urban settlements, and ensure universal health coverage.

Triple therapy with artemether-lumefantrine plus amodiaquine versus artemether-lumefantrine alone for artemisinin-resistant, uncomplicated falciparum malaria: an open-label, randomised, multicentre trial.

BACKGROUND: Late treatment failures after artemisinin-based combination therapies (ACTs) for falciparum malaria have increased in the Greater Mekong subregion in southeast Asia. Addition of amodiaquine to artemether-lumefantrine could provide an efficacious treatment for multidrug-resistant infections. METHODS: We conducted an open-label, randomised trial at five hospitals or health centres in three locations (western Cambodia, eastern Cambodia, and Vietnam). Eligible participants were male and female patients aged 2-65 years with uncomplicated Plasmodium falciparum malaria. Patients were randomly allocated (1:1 in blocks of eight to 12) to either artemether-lumefantrine alone (dosed according to WHO guidelines) or artemether-lumefantrine plus amodiaquine (10 mg base per kg/day), both given orally as six doses over 3 days. All received a single dose of primaquine (0·25 mg/kg) 24 h after the start of study treatment to limit transmission of the parasite. Parasites were genotyped, identifying artemisinin resistance. The primary outcome was Kaplan-Meier 42-day PCR-corrected efficacy against recrudescence of the original parasite, assessed by intent-to-treat. Safety was a secondary outcome. This completed trial is registered at ClinicalTrials.gov (NCT03355664). FINDINGS: Between March 18, 2018, and Jan 30, 2020, 310 patients received randomly allocated treatment; 154 received artemether-lumefantrine alone and 156 received artemether-lumefantrine plus amodiaquine. Parasites from 305 of these patients were genotyped. 42-day PCR-corrected treatment efficacy was noted in 151 (97%, 95% CI 92-99) of 156 patients with artemether-lumefantrine plus amodiaquine versus 146 (95%, 89-97) of 154 patients with artemether-lumefantrine alone; hazard ratio (HR) for recrudescence 0·6 (95% CI 0·2-1·9, p=0·38). Of the 13 recrudescences, 12 were in 174 (57%) of 305 infections with pfkelch13 mutations indicating artemisinin resistance, for which 42-day efficacy was noted in 89 (96%) of 93 infections with artemether-lumefantrine plus amodiaquine versus 73 (90%) of 81 infections with artemether-lumefantrine alone; HR for recrudescence 0·44 (95% CI 0·14-1·40, p=0·17). Artemether-lumefantrine plus amodiaquine was generally well tolerated, but the number of mild (grade 1-2) adverse events, mainly gastrointestinal, was greater in this group compared with artemether-lumefantrine alone (vomiting, 12 [8%] with artemether-lumefantrine plus amodiaquine vs three [2%] with artemether-lumefantrine alone, p=0·03; and nausea, 11 [7%] with artemether-lumefantrine plus amodiaquine vs three [2%] with artemether-lumefantrine alone, p=0·05). Early vomiting within 1 h of treatment, requiring retreatment, occurred in no patients of 154 with artemether-lumefantrine alone versus five (3%) of 156 with artemether-lumefantrine plus amodiaquine, p=0·06. Bradycardia (≤54 beats/min) of any grade was noted in 59 (38%) of 154 patients with artemether-lumefantrine alone and 95 (61%) of 156 with artemether-lumefantrine plus amodiaquine, p=0·0001. INTERPRETATION: Artemether-lumefantrine plus amodiaquine provides an alternative to artemether-lumefantrine alone as first-line treatment for multidrug-resistant P falciparum malaria in the Greater Mekong subregion, and could prolong the therapeutic lifetime of artemether-lumefantrine in malaria-endemic populations. FUNDING: Bill & Melinda Gates Foundation, Wellcome Trust.

Influenza virus infection history shapes antibody responses to influenza vaccination.

Studies of successive vaccination suggest that immunological memory against past influenza viruses may limit responses to vaccines containing current strains. The impact of memory induced by prior infection is rarely considered and is difficult to ascertain, because infections are often subclinical. This study investigated influenza vaccination among adults from the Ha Nam cohort (Vietnam), who were purposefully selected to include 72 with and 28 without documented influenza A(H3N2) infection during the preceding 9 years (Australian New Zealand Clinical Trials Registry 12621000110886). The primary outcome was the effect of prior influenza A(H3N2) infection on hemagglutinin-inhibiting antibody responses induced by a locally available influenza vaccine administered in November 2016. Baseline and postvaccination sera were titrated against 40 influenza A(H3N2) strains spanning 1968-2018. At each time point (baseline, day 14 and day 280), geometric mean antibody titers against 2008-2018 strains were higher among participants with recent infection (34 (29-40), 187 (154-227) and 86 (72-103)) than among participants without recent infection (19 (17-22), 91 (64-130) and 38 (30-49)). On days 14 and 280, mean titer rises against 2014-2018 strains were 6.1-fold (5.0- to 7.4-fold) and 2.6-fold (2.2- to 3.1-fold) for participants with recent infection versus 4.8-fold (3.5- to 6.7-fold) and 1.9-fold (1.5- to 2.3-fold) for those without. One of 72 vaccinees with recent infection versus 4 of 28 without developed symptomatic A(H3N2) infection in the season after vaccination (P = 0.021). The range of A(H3N2) viruses recognized by vaccine-induced antibodies was associated with the prior infection strain. These results suggest that recall of immunological memory induced by prior infection enhances antibody responses to inactivated influenza vaccine and is important to attain protective antibody titers.

Sphagneticola Trilobata (L.) Pruski (Asteraceae) Methanol Extract Induces Apoptosis in Leukemia Cells through Suppression of BCR/ABL.

We will study the effects of the methanol extract of Sphagneticola trilobata (L.) Pruski (Asteraceae) (MeST) on the growth of leukemia cells that may contain the BCR/ABL gene. This study also clarifies the mechanism of this effect on these cells. For this purpose, the cells harboring wild-type BCR/ABL, imatinib-resistant BCR/ABL (K562 and TCCYT315I), or Ba/F3 cells transfected with wild-type or mutant BCR/ABL genes were used. The results showed that MeST effectively inhibited the viability of leukemia cells in both a dose- and time-dependent manner. The effect of MeST seems to be more sensitive in the cells that carry imatinib-resistant BCR/ABL (especially the T315I BCR/ABL mutation) than those with wild-type BCR/ABL. Furthermore, we have demonstrated that the death caused by MeST is apoptosis and the treatment with MeST could suppress the expression of BCR/ABL, subsequently altering the downstream cascade of BCR/ABL such as AKT and MAPK signaling. In conclusion, MeST has been able to suppress the growth of leukemia cells harboring BCR/ABL. The mechanism of the anti-leukemic effect of MeST on cells harboring imatinib-resistant BCR/ABL mutations could be due to the disruption of the BCR/ABL oncoprotein signaling cascade.

Impact of health insurance on healthcare utilisation patterns in Vietnam: a survey-based analysis with propensity score matching method.

OBJECTIVES: The study aims to evaluate the impact of the Revised Health Insurance Law 2014 on the utilisation of outpatient and inpatient care services, healthcare services utilisation at different levels of providers, types of providers and types of visits across different entitlement groups. DESIGN/SETTING: Secondary data from two waves of the Vietnam Household Living Standard Survey (VHLSS) 2016, VHLSS 2014 were used. A cross-sectional study applying propensity score matching was conducted. PARTICIPANTS: A total of 4900 individuals who reported using healthcare services are analysed. OUTCOMES MEASURE: Numbers of outpatient and inpatient visits, frequency of healthcare service utilisation at commune health stations, district hospitals, provincial hospitals, public and private health facilities, number of visits at health facility for medical treatment and health checks per year. RESULTS: The result indicates that health insurance (HI) policy increased the number of outpatient visits for the enrolled between 0.87 and 1.29. The greatest impact was found on participants of heavily subsidised health insurance (HSHI) programmes with 1.29 visits per person per year. Similarly, an increase between 0.08 and 0.16 in the number of inpatient admissions was because of participation in HI. With regard to type of healthcare providers, the study found that participation in HI has the most effect on the use of healthcare services at district hospitals. However, the study demonstrated that the impacts of HI on the increase in the frequency of visiting commune health stations, number of visits at the provincial hospital for HSHI groups, and number of visits at health facilities for health check and consultation were sensitive to unobserved characteristics. CONCLUSION: Our findings imply that policy-makers in Vietnam could continue expanding health insurance coverage to increase access to healthcare services for citizens, especially vulnerable groups. In addition, the government should draw more attention to primary healthcare level.

Impact of Health Insurance on Health Care Utilisation and Out-of-Pocket Health Expenditure in Vietnam.

BACKGROUND: In recent years, health insurance (HI) has been chosen by many low- and middle-income countries to obtain an important health policy target-universal health coverage. Vietnam has recently introduced the Revised Health Insurance Law, and the effects of the voluntary health insurance (VHI) and heavily subsidised health insurance (HSHI) programmes have not yet been analysed. Therefore, this study is aimed at examining the impact of these HI programmes on the utilisation of health care services and out-of-pocket health expenditure (OOP) in general and across different health care providers in particular. METHODS: Using the two waves of Vietnam Household Living Standard Surveys 2014 and 2016 and the difference-in-difference method, the impacts of VHI and HSHI on health care utilisation and OOP in Vietnam were estimated. RESULTS: For both the VHI and HSHI groups, we found that HI increased the probability of seeking outpatient care, the mean number of outpatient visits, the total number of visits, and the mean number of visits at the district level of health care providers in the last 12 months. However, there was no evidence that the HSHI programmes increased the mean number of inpatient visits and the number of visits at the provincial hospital. We also found that while the VHI programme reduced OOP for both outpatient and inpatient care, the HSHI scheme did not result in a reduction in OOP for hospitalisation, although HI lowered the total OOP. Similarly, we found that for both groups, HI reduced OOP when the insured visited district and provincial hospitals. However, the statistically significant impact was not demonstrated when the enrolees of HSHI programmes visited provincial hospitals. CONCLUSION: The study offers evidence that the Vietnamese HI scheme increased health care service utilisation and decreased OOP for the participants of the VHI and HSHI programmes. Therefore, the government should continue to consider improving the HI system as a strategy to achieve universal health coverage.

Callicarpa Species from Central Vietnam: Essential Oil Compositions and Mosquito Larvicidal Activities.

There are around 140 species in the genus Callicarpa, with 23 species occurring in Vietnam. The Vietnamese Callicarpa species have been poorly studied. In this work, the leaf essential oils of C. bodinieri, C. candicans, C. formosana, C. longifolia, C. nudiflora, C. petelotii, C. rubella, and C. sinuata, have been obtained from plants growing in central Vietnam. The chemical compositions of the essential oils were determined using gas chromatography - mass spectrometry. Mosquito larvicidal activities of the essential oils were carried out against Aedes aegypti. All of the Callicarpa leaf essential oils showed larvicidal activity, but two samples of C. candicans were particularly active with 48-h LC50 values of 2.1 and 3.8 µg/mL. Callicarpa candicans essential oil should be considered as a potential alternative mosquito control agent.

Source profiling of arsenic and heavy metals in the Selangor River basin and their maternal and cord blood levels in Selangor State, Malaysia.

Arsenic and 5 heavy metals (nickel, copper, zinc, cadmium and lead) were quantitated in surface water (n = 18) and soil/ore samples (n = 45) collected from 5 land uses (oil palm converted from forest, oil palm in peat swamp, bare land, quarry and forest) in the Selangor River basin by inductively coupled plasma mass spectrometry (ICP-MS). Geographic information system (GIS) was used as a spatial analytical tool to classify 4 land uses (forest, agriculture/peat, urban and bare land) from a satellite image taken by Landsat 8. Source profiling of the 6 elements was conducted to identify their occurrence, their distribution and the pollution source associated with the land use. The concentrations of arsenic, cadmium and lead were also analyzed in maternal blood (n = 99) and cord blood (n = 87) specimens from 136 pregnant women collected at the University of Malaya Medical Center for elucidating maternal exposure as well as maternal-to-fetal transfer. The source profiling identified that nickel and zinc were discharged from sewage and/or industrial effluents, and that lead was discharged from mining sites. Arsenic showed a site-specific pollution in tin-tungsten deposit areas, and the pollution source could be associated with arsenopyrite. The maternal blood levels of arsenic (0.82 ± 0.61 µg/dL), cadmium (0.15 ± 0.2 µg/dL) and lead (2.6 ± 2.1 µg/dL) were not significantly high compared to their acute toxicity levels, but could have attributable risks of chronic toxicity. Those in cord blood were significantly decreased in cadmium (0.06 ± 0.07 µg/dL) and lead (0.99 ± 1.2 µg/dL) but were equivalent in arsenic (0.82 ± 1.1 µg/dL) because of the different kinetics of maternal-to-fetal transfer.

Seroprevalence of Scrub Typhus, Typhus, and Spotted Fever Among Rural and Urban Populations of Northern Vietnam.

AbstractRickettsial infections are recognized as important causes of fever throughout southeast Asia. Herein, we determined the seroprevalence to rickettsioses within rural and urban populations of northern Vietnam. Prevalence of individuals with evidence of prior rickettsial infections (IgG positive) was surprisingly low, with 9.14% (83/908) testing positive to the three major rickettsial serogroups thought to circulate in the region. Prevalence of typhus group rickettsiae (TG)-specific antibodies (6.5%, 58/908) was significantly greater than scrub typhus group orientiae (STG)- or spotted fever group rickettsiae (SFG)-specific antibodies (P < 0.05). The majority of TG seropositives were observed among urban rather than rural residents (P < 0.05). In contrast, overall antibody prevalence to STG and SFG were both very low (1.1%, 10/908 for STG; 1.7%, 15/908 for SFG), with no significant differences between rural and urban residents. These results provide data on baseline population characteristics that may help inform development of Rickettsia serological testing criteria in future clinical studies.