Publications by authors named "Darunee Buddhari"

17 Publications

  • Page 1 of 1

Correlation between reported dengue illness history and seropositivity in rural Thailand.

PLoS Negl Trop Dis 2021 Jun 15;15(6):e0009459. Epub 2021 Jun 15.

State University of New York Upstate Medical University, Syracuse, New York, United States of America.

In the latest World Health Organization (WHO) recommendation for Dengvaxia implementation, either serological testing or a person's history of prior dengue illness may be used as supporting evidence to identify dengue virus (DENV)-immune individuals eligible for vaccination, in areas with limited capacity for laboratory confirmation. This analysis aimed to estimate the concordance between self-reported dengue illness histories and seropositivity in a prospective cohort study for dengue virus infection in Kamphaeng Phet province, a dengue-endemic area in northern Thailand. The study enrolled 2,076 subjects from 516 multigenerational families, with a median age of 30.6 years (range 0-90 years). Individual and family member dengue illness histories were obtained by questionnaire. Seropositivity was defined based on hemagglutination inhibition (HAI) assays. Overall seropositivity for DENV was 86.5% among those aged 9-45 years, which increased with age. 18.5% of participants reported a history of dengue illness prior to enrollment; 30.1% reported a previous DENV infection in the family, and 40.1% reported DENV infection in either themselves or a family member. Relative to seropositivity by HAI in the vaccine candidate group, the sensitivity and specificity of individual prior dengue illness history were 18.5% and 81.6%, respectively; sensitivity and specificity of reported dengue illness in a family member were 29.8% and 68.0%, and of either the individual or a family member were 40.1% and 60.5%. Notably, 13.4% of individuals reporting prior dengue illness were seronegative. Given the high occurrence of asymptomatic and mild DENV infection, self-reported dengue illness history is poorly sensitive for prior exposure and may misclassify individuals as 'exposed' when they were not. This analysis highlights that a simple, highly sensitive, and highly specific test for determining serostatus prior to Dengvaxia vaccination is urgently needed.
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http://dx.doi.org/10.1371/journal.pntd.0009459DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8232416PMC
June 2021

Precision Tracing of Household Dengue Spread Using Inter- and Intra-Host Viral Variation Data, Kamphaeng Phet, Thailand.

Emerg Infect Dis 2021 06;27(6):1637-1644

Dengue control approaches are best informed by granular spatial epidemiology of these viruses, yet reconstruction of inter- and intra-household transmissions is limited when analyzing case count, serologic, or genomic consensus sequence data. To determine viral spread on a finer spatial scale, we extended phylogenomic discrete trait analyses to reconstructions of house-to-house transmissions within a prospective cluster study in Kamphaeng Phet, Thailand. For additional resolution and transmission confirmation, we mapped dengue intra-host single nucleotide variants on the taxa of these time-scaled phylogenies. This approach confirmed 19 household transmissions and revealed that dengue disperses an average of 70 m per day between households in these communities. We describe an evolutionary biology framework for the resolution of dengue transmissions that cannot be differentiated based on epidemiologic and consensus genome data alone. This framework can be used as a public health tool to inform control approaches and enable precise tracing of dengue transmissions.
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http://dx.doi.org/10.3201/eid2706.204323DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8153871PMC
June 2021

Comparative Analyses of Historical Trends in Confirmed Dengue Illnesses Detected at Public Hospitals in Bangkok and Northern Thailand, 2002-2018.

Am J Trop Med Hyg 2020 Dec 14. Epub 2020 Dec 14.

Department of Virology, Armed Forces Research Institute of Medical Sciences (AFRIMS), Bangkok, Thailand.

Dengue is a re-emerging global public health problem, the most common arbovirus causing human disease in the world, and a major cause of hospitalization in endemic countries causing significant economic burden. Data were analyzed from passive surveillance of hospital-attended dengue cases from 2002 to 2018 at Phramongkutklao Hospital (PMKH) located in Bangkok, Thailand, and Kamphaeng Phet Provincial Hospital (KPPH) located in the lower northern region of Thailand. At PMKH, serotype 1 proved to be the most common strain of the virus, whereas at KPPH, serotypes 1, 2, and 3 were the most common strains from 2006 to 2008, 2009 to 2012, and 2013 to 2015, respectively. The 11-17 years age-group made up the largest proportion of patients impacted by dengue illnesses during the study period at both sites. At KPPH, dengue virus (DENV)-3 was responsible for most cases of dengue fever (DF), whereas it was DENV-1 at PMKH. In cases where dengue hemorrhagic fever was the clinical diagnosis, DENV-2 was the predominant serotype at KPPH, whereas at PMKH, it was DENV-1. The overall disease prevalence remained consistent across the two study sites with DF being the predominant clinical diagnosis as the result of an acute secondary dengue infection, representing 40.7% of overall cases at KPPH and 56.8% at PMKH. The differences seen between these sites could be a result of climate change increasing the length of dengue season and shifts in migration patterns of these populations from rural to urban areas and vice versa.
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http://dx.doi.org/10.4269/ajtmh.20-0396DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7941814PMC
December 2020

Complete Coding Sequences of 22 East/Central/South African Genotype Chikungunya Virus Isolates from Thailand (2018 to 2019).

Microbiol Resour Announc 2020 Oct 15;9(42). Epub 2020 Oct 15.

Department of Virology, U.S. Army Medical Directorate-Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.

The coding-complete genome sequences of 22 chikungunya virus strains collected from the 2018-2019 outbreak in Thailand are reported. All sequences belong to the East/Central/South African (ECSA) genotype and contain two mutations, E1:K211E and E2:V264A, which were previously shown to be associated with increased viral infectivity, dissemination, and transmission in .
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http://dx.doi.org/10.1128/MRA.00438-20DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7561681PMC
October 2020

Key Findings and Comparisons From Analogous Case-Cluster Studies for Dengue Virus Infection Conducted in Machala, Ecuador, and Kamphaeng Phet, Thailand.

Front Public Health 2020 12;8. Epub 2020 Feb 12.

Department of Medicine, SUNY Upstate Medical University, Syracuse, NY, United States.

Dengue viruses (DENV) pose a significant and increasing threat to human health across broad regions of the globe. Currently, prevention, control, and treatment strategies are limited. Promising interventions are on the horizon, including multiple vaccine candidates under development and a renewed and innovative focus on controlling the vector, . However, significant gaps persist in our understanding of the similarities and differences in DENV epidemiology across regions of potential implementation and evaluation. In this manuscript, we highlight and compare findings from two analogous cluster-based studies for DENV transmission and pathogenesis conducted in Thailand and Ecuador to identify key features and questions for further pursuit. Despite a remarkably similar incidence of DENV infection among enrolled neighborhood contacts at the two sites, we note a higher occurrence of secondary infection and severe illness in Thailand compared to Ecuador. A higher force of infection in Thailand, defined as the incidence of infection among susceptible individuals, is suggested by the higher number of captured mosquitoes per household, the increasing proportion of asymptomatic infections with advancing age, and the high proportion of infections identified as secondary-type infections by serology. These observations should be confirmed in long-term, parallel prospective cohort studies conducted across regions, which would advantageously permit characterization of baseline immune status (susceptibility) and contemporaneous assessment of risks and risk factors for dengue illness.
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http://dx.doi.org/10.3389/fpubh.2020.00002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7028768PMC
May 2021

An Innovative, Prospective, Hybrid Cohort-Cluster Study Design to Characterize Dengue Virus Transmission in Multigenerational Households in Kamphaeng Phet, Thailand.

Am J Epidemiol 2020 07;189(7):648-659

Difficulties inherent in the identification of immune correlates of protection or severe disease have challenged the development and evaluation of dengue vaccines. There persist substantial gaps in knowledge about the complex effects of age and sequential dengue virus (DENV) exposures on these correlations. To address these gaps, we were conducting a novel family-based cohort-cluster study for DENV transmission in Kamphaeng Phet, Thailand. The study began in 2015 and is funded until at least 2023. As of May 2019, 2,870 individuals in 485 families were actively enrolled. The families comprise at least 1 child born into the study as a newborn, 1 other child, a parent, and a grandparent. The median age of enrolled participants is 21 years (range 0-93 years). Active surveillance is performed to detect acute dengue illnesses, and annual blood testing identifies subclinical seroconversions. Extended follow-up of this cohort will detect sequential infections and correlate antibody kinetics and sequence of infections with disease outcomes. The central goal of this prospective study is to characterize how different DENV exposure histories within multigenerational family units, from DENV-naive infants to grandparents with multiple prior DENV exposures, affect transmission, disease, and protection at the level of the individual, household, and community.
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http://dx.doi.org/10.1093/aje/kwaa008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7393304PMC
July 2020

Retrospective use of next-generation sequencing reveals the presence of Enteroviruses in acute influenza-like illness respiratory samples collected in South/South-East Asia during 2010-2013.

J Clin Virol 2017 09 14;94:91-99. Epub 2017 Jul 14.

Department of Virology, Armed Forces Research Institute of Medical Sciences, 315/6, Rajavithi Road, Rajathewi, Bangkok, Thailand. Electronic address:

Background: Emerging and re-emerging respiratory pathogens represent an increasing threat to public health. Etiological determination during outbreaks generally relies on clinical information, occasionally accompanied by traditional laboratory molecular or serological testing. Often, this limited testing leads to inconclusive findings. The Armed Forces Research Institute of Medical Sciences (AFRIMS) collected 12,865 nasopharyngeal specimens from acute influenza-like illness (ILI) patients in five countries in South/South East Asia during 2010-2013. Three hundred and twenty-four samples which were found to be negative for influenza virus after screening with real-time RT-PCR and cell-based culture techniques demonstrated the potential for viral infection with evident cytopathic effect (CPE) in several cell lines.

Objective: To assess whether whole genome next-generation sequencing (WG-NGS) together with conventional molecular assays can be used to reveal the etiology of influenza negative, but CPE positive specimens.

Study Design: The supernatant of these CPE positive cell cultures were grouped in 32 pools containing 2-26 supernatants per pool. Three WG-NGS runs were performed on these supernatant pools. Sequence reads were used to identify positive pools containing viral pathogens. Individual samples in the positive pools were confirmed by qRT-PCR, RT-PCR, PCR and Sanger sequencing from the CPE culture and original clinical specimens.

Results: WG-NGS was an effective way to expand pathogen identification in surveillance studies. This enabled the identification of a viral agent in 71.3% (231/324) of unidentified surveillance samples, including common respiratory pathogens (100/324; 30.9%): enterovirus (16/100; 16.0%), coxsackievirus (31/100; 31.0%), echovirus (22/100; 22.0%), human rhinovirus (3/100; 3%), enterovirus genus (2/100; 2.0%), influenza A (9/100; 9.0%), influenza B, (5/100; 5.0%), human parainfluenza (4/100; 4.0%), human adenovirus (3/100; 3.0%), human coronavirus (1/100; 1.0%), human metapneumovirus (2/100; 2.0%), and mumps virus (2/100; 2.0%), in addition to the non-respiratory pathogen herpes simplex virus type 1 (HSV-1) (172/324; 53.1%) and HSV-1 co-infection with respiratory viruses (41/324; 12.7%).
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http://dx.doi.org/10.1016/j.jcv.2017.07.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7106496PMC
September 2017

Absence of neutralizing antibodies against influenza A/H5N1 virus among children in Kamphaeng Phet, Thailand.

J Clin Virol 2015 Aug 3;69:78-80. Epub 2015 Jun 3.

Department of Virology, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.

Background: Influenza A/H5N1 actively circulated in Kamphaeng Phet (KPP), Thailand from 2004 to 2006. A prospective longitudinal cohort study of influenza virus infection in 800 adults conducted during 2008-2010 in KPP suggested that subclinical or mild H5N1 infections had occurred among this adult cohort. However, this study was conducted after the peak of H5N1 activity in KPP. Coincidentally, banked serum samples were available from a prospective longitudinal cohort study of primary school children who had undergone active surveillance for febrile illnesses from 2004 to 2007 and lived in the same district of KPP as the adult cohort.

Objectives: We sought to investigate whether subclinical or mild H5N1 infections had occurred among KPP residents during the peak of H5N1 activity from 2004 to 2006.

Study Design: H5N1 microneutralization (MN) assay was performed on banked serum samples from a prospective longitudinal cohort study of primary school children who had undergone active surveillance for febrile illnesses in KPP. Annual blood samples collected from 2004 to 2006 from 251 children were selected based on the criteria that they lived in villages with documented H5N1 infection.

Result: No H5N1 neutralizing antibodies were detected in 753 annual blood samples from 251 children.

Conclusion: During 2004-2006, very few subclinical or mild H5N1 infections occurred in KPP. Elevated H5N1 MN titers found in the adult cohort in 2008 were likely due to cross-reactivity from other influenza virus subtypes highlighting the complexities in interpreting influenza serological data.
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http://dx.doi.org/10.1016/j.jcv.2015.05.025DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4515272PMC
August 2015

Improving dengue virus capture rates in humans and vectors in Kamphaeng Phet Province, Thailand, using an enhanced spatiotemporal surveillance strategy.

Am J Trop Med Hyg 2015 Jul 18;93(1):24-32. Epub 2015 May 18.

Viral Diseases Branch, Walter Reed Army Institute of Research, Silver Spring, Maryland; Department of Virology, United States Army Medical Component, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand; Department of Geography, University at Buffalo, Buffalo, New York; Department of Entomology, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand; Bureau of Epidemiology, Department of Disease Control Sciences, Ministry of Public Health, Nonthaburi, Thailand; Department of Entomology, University of California, Davis, Davis, California; Institute for Immunology and Informatics, University of Rhode Island, Providence, Rhode Island; Insect-Virus Interactions Group, Department of Genomes and Genetics, Institut Pasteur, Centre National de la Recherche Scientifique, Paris, France; Department of Infectious Diseases, State University of New York, Syracuse, New York; Fogarty International Center, National Institutes of Health, Bethesda, Maryland.

Dengue is of public health importance in tropical and sub-tropical regions. Dengue virus (DENV) transmission dynamics was studied in Kamphaeng Phet Province, Thailand, using an enhanced spatiotemporal surveillance of 93 hospitalized subjects with confirmed dengue (initiates) and associated cluster individuals (associates) with entomologic sampling. A total of 438 associates were enrolled from 208 houses with household members with a history of fever, located within a 200-m radius of an initiate case. Of 409 associates, 86 (21%) had laboratory-confirmed DENV infection. A total of 63 (1.8%) of the 3,565 mosquitoes collected were dengue polymerase chain reaction positive (PCR+). There was a significant relationship between spatial proximity to the initiate case and likelihood of detecting DENV from associate cases and Aedes mosquitoes. The viral detection rate from human hosts and mosquito vectors in this study was higher than previously observed by the study team in the same geographic area using different methodologies. We propose that the sampling strategy used in this study could support surveillance of DENV transmission and vector interactions.
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http://dx.doi.org/10.4269/ajtmh.14-0242DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4497898PMC
July 2015

Sequential dengue virus infections detected in active and passive surveillance programs in Thailand, 1994-2010.

BMC Public Health 2015 Mar 14;15:250. Epub 2015 Mar 14.

US Army Institute of Surgical Research, San Antonio, TX, USA.

Background: The effect of prior dengue virus (DENV) exposure on subsequent heterologous infection can be beneficial or detrimental depending on many factors including timing of infection. We sought to evaluate this effect by examining a large database of DENV infections captured by both active and passive surveillance encompassing a wide clinical spectrum of disease.

Methods: We evaluated datasets from 17 years of hospital-based passive surveillance and nine years of cohort studies, including clinical and subclinical DENV infections, to assess the outcomes of sequential heterologous infections. Chi square or Fisher's exact test was used to compare proportions of infection outcomes such as disease severity; ANOVA was used for continuous variables. Multivariate logistic regression was used to assess risk factors for infection outcomes.

Results: Of 38,740 DENV infections, two or more infections were detected in 502 individuals; 14 had three infections. The mean ages at the time of the first and second detected infections were 7.6 ± 3.0 and 11.2 ± 3.0 years. The shortest time between sequential infections was 66 days. A longer time interval between sequential infections was associated with dengue hemorrhagic fever (DHF) in the second detected infection (OR 1.3, 95% CI 1.2-1.4). All possible sequential serotype pairs were observed among 201 subjects with DHF at the second detected infection, except DENV-4 followed by DENV-3. Among DENV infections detected in cohort subjects by active study surveillance and subsequent non-study hospital-based passive surveillance, hospitalization at the first detected infection increased the likelihood of hospitalization at the second detected infection.

Conclusions: Increasing time between sequential DENV infections was associated with greater severity of the second detected infection, supporting the role of heterotypic immunity in both protection and enhancement. Hospitalization was positively associated between the first and second detected infections, suggesting a possible predisposition in some individuals to more severe dengue disease.
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http://dx.doi.org/10.1186/s12889-015-1590-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4371716PMC
March 2015

Monitoring and improving the sensitivity of dengue nested RT-PCR used in longitudinal surveillance in Thailand.

J Clin Virol 2015 Feb 12;63:25-31. Epub 2014 Dec 12.

Department of Virology, Armed Forces Research Institute of Medical Sciences, 315/6 Rajvithi Road, Bangkok, Thailand.

Background: AFRIMS longitudinal dengue surveillance in Thailand depends on the nested RT-PCR and the dengue IgM/IgG ELISA.

Objective: To examine and improve the sensitivity of the nested RT-PCR using a panel of archived samples collected during dengue surveillance.

Study Design: A retrospective analysis of 16,454 dengue IgM/IgG ELISA positive cases collected between 2000 and 2013 was done to investigate the sensitivity of the nested RT-PCR. From these cases, 318 acute serum specimens or extracted RNA, previously found to be negative by the nested RT-PCR, were tested using TaqMan real-time RT-PCR (TaqMan rRT-PCR). To improve the sensitivity of nested RT-PCR, we designed a new primer based on nucleotide sequences from contemporary strains found to be positive by the TaqMan rRT-PCR. Sensitivity of the new nested PCR was calculated using a panel of 87 samples collected during 2011-2013.

Results And Conclusion: The percentage of dengue IgM/IgG ELISA positive cases that were negative by the nested RT-PCR varied from 17% to 42% for all serotypes depending on the year. Using TaqMan rRT-PCR, dengue RNA was detected in 194 (61%) of the 318 acute sera or extracted RNA previously found to be negative by the nested RT-PCR. The newly designed DENV-1 specific primer increased the sensitivity of DENV-1 detection by the nested RT-PCR from 48% to 88%, and of all 4 serotypes from 73% to 87%. These findings demonstrate the impact of genetic diversity and signal erosion on the sensitivity of PCR-based methods.
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http://dx.doi.org/10.1016/j.jcv.2014.12.009DOI Listing
February 2015

Dengue virus neutralizing antibody levels associated with protection from infection in thai cluster studies.

PLoS Negl Trop Dis 2014 Oct 16;8(10):e3230. Epub 2014 Oct 16.

Department of Virology, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.

Background: Long-term homologous and temporary heterologous protection from dengue virus (DENV) infection may be mediated by neutralizing antibodies. However, neutralizing antibody titers (NTs) have not been clearly associated with protection from infection.

Methodology/principal Findings: Data from two geographic cluster studies conducted in Kamphaeng Phet, Thailand were used for this analysis. In the first study (2004-2007), cluster investigations of 100-meter radius were triggered by DENV-infected index cases from a concurrent prospective cohort. Subjects between 6 months and 15 years old were evaluated for DENV infection at days 0 and 15 by DENV PCR and IgM ELISA. In the second study (2009-2012), clusters of 200-meter radius were triggered by DENV-infected index cases admitted to the provincial hospital. Subjects of any age ≥6 months were evaluated for DENV infection at days 0 and 14. In both studies, subjects who were DENV PCR positive at day 14/15 were considered to have been "susceptible" on day 0. Comparison subjects from houses in which someone had documented DENV infection, but the subject remained DENV negative at days 0 and 14/15, were considered "non-susceptible." Day 0 samples were presumed to be from just before virus exposure, and underwent plaque reduction neutralization testing (PRNT). Seventeen "susceptible" (six DENV-1, five DENV-2, and six DENV-4), and 32 "non-susceptible" (13 exposed to DENV-1, 10 DENV-2, and 9 DENV-4) subjects were evaluated. Comparing subjects exposed to the same serotype, receiver operating characteristic (ROC) curves identified homotypic PRNT titers of 11, 323 and 16 for DENV-1, -2 and -4, respectively, to differentiate "susceptible" from "non-susceptible" subjects.

Conclusions/significance: PRNT titers were associated with protection from infection by DENV-1, -2 and -4. Protective NTs appeared to be serotype-dependent and may be higher for DENV-2 than other serotypes. These findings are relevant for both dengue epidemiology studies and vaccine development efforts.
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http://dx.doi.org/10.1371/journal.pntd.0003230DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4199527PMC
October 2014

The spatial dynamics of dengue virus in Kamphaeng Phet, Thailand.

PLoS Negl Trop Dis 2014 Sep 11;8(9):e3138. Epub 2014 Sep 11.

Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, United States of America.

Background: Dengue is endemic to the rural province of Kamphaeng Phet, Northern Thailand. A decade of prospective cohort studies has provided important insights into the dengue viruses and their generated disease. However, as elsewhere, spatial dynamics of the pathogen remain poorly understood. In particular, the spatial scale of transmission and the scale of clustering are poorly characterized. This information is critical for effective deployment of spatially targeted interventions and for understanding the mechanisms that drive the dispersal of the virus.

Methodology/principal Findings: We geocoded the home locations of 4,768 confirmed dengue cases admitted to the main hospital in Kamphaeng Phet province between 1994 and 2008. We used the phi clustering statistic to characterize short-term spatial dependence between cases. Further, to see if clustering of cases led to similar temporal patterns of disease across villages, we calculated the correlation in the long-term epidemic curves between communities. We found that cases were 2.9 times (95% confidence interval 2.7-3.2) more likely to live in the same village and be infected within the same month than expected given the underlying spatial and temporal distribution of cases. This fell to 1.4 times (1.2-1.7) for individuals living in villages 1 km apart. Significant clustering was observed up to 5 km. We found a steadily decreasing trend in the correlation in epidemics curves by distance: communities separated by up to 5 km had a mean correlation of 0.28 falling to 0.16 for communities separated between 20 km and 25 km. A potential explanation for these patterns is a role for human movement in spreading the pathogen between communities. Gravity style models, which attempt to capture population movement, outperformed competing models in describing the observed correlations.

Conclusions: There exists significant short-term clustering of cases within individual villages. Effective spatially and temporally targeted interventions deployed within villages may target ongoing transmission and reduce infection risk.
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http://dx.doi.org/10.1371/journal.pntd.0003138DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4161352PMC
September 2014

High rate of A(H1N1)pdm09 infections among rural Thai villagers, 2009-2010.

PLoS One 2014 4;9(9):e106751. Epub 2014 Sep 4.

College of Public Health and Health Professions and Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America.

Background: Pandemic influenza A(H1N1)pdm09 emerged in Thailand in 2009. A prospective longitudinal adult cohort and household transmission study of influenza-like illness (ILI) was ongoing in rural Thailand at the time of emergence. Symptomatic and subclinical A(H1N1)pdm09 infection rates in the cohort and among household members were evaluated.

Methods: A cohort of 800 Thai adults underwent active community-based surveillance for ILI from 2008-2010. Acute respiratory samples from ILI episodes were tested for A(H1N1)pdm09 by qRT-PCR; acute and 60-day convalescent blood samples were tested by A(H1N1)pdm09 hemagglutination inhibition assay (HI). Enrollment, 12-month and 24-month follow-up blood samples were tested for A(H1N1)pdm09 seroconversion by HI. Household members of influenza A-infected cohort subjects with ILI were enrolled in household transmission investigations in which day 0 and 60 blood samples and acute respiratory samples were tested by either qRT-PCR or HI for A(H1N1)pdm09. Seroconversion between annual blood samples without A(H1N1)pdm09-positive ILI was considered as subclinical infection.

Results: The 2-yr cumulative incidence of A(H1N1)pdm09 infection in the cohort in 2009/2010 was 10.8% (84/781) with an annual incidence of 1.2% in 2009 and 9.7% in 2010; 83.3% of infections were subclinical (50% in 2009 and 85.9% in 2010). The 2-yr cumulative incidence was lowest (5%) in adults born ≤ 1957. The A(H1N1)pdm09 secondary attack rate among household contacts was 47.2% (17/36); 47.1% of these infections were subclinical. The highest A(H1N1)pdm09 secondary attack rate among household contacts (70.6%, 12/17) occurred among children born between 1990 and 2003.

Conclusion: Subclinical A(H1N1)pdm09 infections in Thai adults occurred frequently and accounted for a greater proportion of all A(H1N1)pdm09 infections than previously estimated. The role of subclinical infections in A(H1N1)pdm09 transmission has important implications in formulating strategies to predict and prevent the spread of A(H1N1)pdm09 and other influenza virus strains.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0106751PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4154756PMC
December 2015

Relationship of preexisting influenza hemagglutination inhibition, complement-dependent lytic, and antibody-dependent cellular cytotoxicity antibodies to the development of clinical illness in a prospective study of A(H1N1)pdm09 Influenza in children.

Viral Immunol 2014 Oct 20;27(8):375-82. Epub 2014 Aug 20.

1 Department of Medicine, University of Massachusetts Medical School , Worcester, Massachusetts.

The hemagglutination inhibition (HAI) antibody titer is considered the primary immune correlate of protection for influenza. However, recent studies have highlighted the limitations on the use of the HAI titer as a correlate in at-risk populations such as children and older adults. In addition to the neutralization of cell-free virus by antibodies to hemagglutinin and interference of virus release from infected cells by antibodies to neuraminidase, influenza virus-specific antibodies specifically can bind to infected cells and lyse virus-infected cells through the activation of complement or natural killer (NK) cells, via antibody-dependent cellular cytotoxicity (ADCC) or complement-dependent lysis (CDL). We evaluated preexisting HAI, CDL, and ADCC antibodies in young children enrolled in a prospective cohort study of dengue during the epidemic with influenza A(H1N1)pdm09 virus to determine associations between preexisting antibodies and the occurrence of clinical or subclinical influenza virus infection. Though both preexisting HAI and CDL antibodies were associated with protection against clinical influenza, our data suggested that CDL was not a better correlate than HAI. We found that ADCC antibodies behaved differently from HAI and CDL antibodies. Unlike HAI and CDL antibodies, preexisting ADCC antibodies did not correlate with protection against clinical influenza. In fact, ADCC antibodies were detected more frequently in the clinical influenza group than the subclinical group. In addition, in contrast to HAI and CDL antibodies, HAI and the ADCC antibodies titers did not correlate. We also found that ADCC, but not CDL or HAI antibodies, positively correlated with the ages of the children.
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http://dx.doi.org/10.1089/vim.2014.0061DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4183906PMC
October 2014

Characteristics of mild dengue virus infection in Thai children.

Am J Trop Med Hyg 2013 Dec 14;89(6):1081-7. Epub 2013 Oct 14.

Department of Virology, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand; University of Massachusetts Medical School, Worcester, Massachusetts; Department of Medicine, University of Toronto, Toronto, Ontario, Canada; Department of Entomology, University of California, Davis, Davis, California; Department of Geography, University at Buffalo, Buffalo, New York; Bureau of Epidemiology, Department of Medical Sciences, Ministry of Public Health, Nonthaburi, Thailand; Department of Infectious Diseases, State University of New York, Syracuse, Syracuse, New York; Institute for Immunology and Informatics, University of Rhode Island, Providence, Rhode Island; Fogarty International Center, National Institutes of Health, Bethesda, Maryland.

A four-year longitudinal cohort and geographic cluster study in rural Thailand was conducted to characterize the clinical spectrum of dengue virus (DENV) infection. Symptomatic DENV infections in the cohort were detected by active school absence-based surveillance that triggered cluster investigations around ill cohort children. Data from 189 cohort children with symptomatic DENV infection and 126 contact children in the clusters with DENV infection were analyzed. Of infected contacts, only 19% were asymptomatic; 81% were symptomatic, but only 65.9% reported fever. Symptom-based case definitions were unreliable for diagnosis. Symptomatic infections in contacts were milder with lower DENV RNA levels than the cohort. Infections in contacts with fever history were more likely to have detectable DENV RNA than infections without fever history. Mild infections identified by cluster investigations account for a major proportion of all DENV infections. These findings are relevant for disease burden assessments, transmission modeling, and determination of vaccine impact.
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http://dx.doi.org/10.4269/ajtmh.13-0424DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3854884PMC
December 2013

A shorter time interval between first and second dengue infections is associated with protection from clinical illness in a school-based cohort in Thailand.

J Infect Dis 2014 Feb 20;209(3):360-8. Epub 2013 Aug 20.

Department of Medicine, University of Minnesota Medical School, Minneapolis.

Background: Despite the strong association between secondary dengue virus (DENV) infections and dengue hemorrhagic fever (DHF), the majority of secondary infections are subclinical or mild. The determinants of clinical severity remain unclear, though studies indicate a titer-dependent and time-dependent role of cross-protective anti-DENV antibodies.

Methods: Data from 2 sequential prospective cohort studies were analyzed for subclinical and symptomatic DENV infections in schoolchildren in Kamphaeng Phet, Thailand (1998-2002 and 2004-2007). Children experiencing ≥ 1 DENV infection were selected as the population for analysis (contributing 2169 person-years of follow-up).

Results: In total, 1696 children had ≥ 1 DENV infection detected during their enrollment; 268 experienced 2 or more infections. A shorter time interval between infections was associated with subclinical infection in children seronegative for DENV at enrollment, for whom a second-detected DENV infection is more likely to reflect a true second infection (average of 2.6 years between infections for DHF, 1.9 for DF, and 1.6 for subclinical infections).

Conclusions: These findings support a pathogenesis model where cross-reactive antibodies wane from higher-titer, protective levels to lower-titer, detrimental levels. This is one of the first studies of human subjects to suggest a window of cross-protection following DENV infection since Sabin's challenge studies in the 1940s.
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http://dx.doi.org/10.1093/infdis/jit436DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3883164PMC
February 2014
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