Tan Boon Huan
Email Address
ephtbh@nus.edu.sg
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Publication Case Report: Hepatitis E in Singapore: A Case-Series and Viral Phylodynamics Study(AMER SOC TROP MED & HYGIENE, 2017-01-01) Teo, Esmeralda Chi-Yuan; Tan, Boon-Huan; Purdy, Michael A; Wong, Pui-San; Ting, Pei-Jun; Chang, Pik-Eu Jason; Oon, Lynette Lin-Ean; Sue, Amanda; Teo, Chong-Gee; Tan, Chee-Kiat; Prof Chee Kiat Kenneth Tan; DEAN'S OFFICE (DUKE-NUS MEDICAL SCHOOL); DUKE-NUS MEDICAL SCHOOLThe incidence of hepatitis E in Singapore appears to be increasing. A retrospective case-series study of patients diagnosed with hepatitis E in a tertiary hospital from 2009 to 2013 was conducted. Of 16 cases, eight (50%) were solid-organ transplant recipients (SOTRs), and 14 (88%) were found infected by genotype 3 hepatitis E virus (HEV-3). Bayesian inferences based on HEV subgenomic sequences from seven cases suggest that HEV-3 strains were introduced to Singapore as two principal lineages. Within limitations of the study, it can be inferred that one lineage, in the 3efg clade, emerged about 83 years ago, probably originating from Japan, whereas the other, in the 3abchij clade, emerged about 40 years ago, from the United States. Establishment and subsequent transmissions of strains from these two lineages likely contribute to the current endemicity of hepatitis E in Singapore.Publication Risk factors for pandemic (H1N1) 2009 virus seroconversion among hospital staff, Singapore(2010-10) Chen, M.I.C.; Lee, V.J.M.; Barr, I.; Lin, C.; Goh, R.; Lee, C.; Singh, B.; Tan, J.; Lim, W.-Y.; Cook, A.R.; Ang, B.; Chow, A.; Tan, B.H.; Loh, J.; Shaw, R.; Chia, K.S.; Lin, R.T.P.; Leo, Y.S.; STATISTICS & APPLIED PROBABILITY; DUKE-NUS GRADUATE MEDICAL SCHOOL S'PORE; EPIDEMIOLOGY & PUBLIC HEALTHWe describe incidence and risk factors for pandemic (H1N1) 2009 virus infection in healthcare personnel during the June-September 2009 epidemic in Singapore. Personnel contributed 3 serologic samples during June-October2009, with seroconversion defined as a ≥4-fold increase in hemagglutination inhibition titers to pandemic (H1N1) 2009.Of 531 participants, 35 showed evidence of seroconversion. Seroconversion rates were highest in nurses (28/290) and lowest in allied health staff (2/116). Significant risk factor son multivariate analysis were being a nurse (adjusted odd sratio [a OR] 4.5, 95% confidence interval [CI] 1.0-19.6) and working in pandemic (H1N1) 2009 isolation wards (aOR4.5, 95% CI 1.3-15.6). Contact with pandemic (H1N1)2009-infected colleagues (a OR 2.5, 95% CI 0.9-6.6) and larger household size (a OR 1.2, 95% CI 1.0-1.4) were of borderline significance. Our study suggests that seroconversion was associated with occupational and nonoccupational risk factors.Publication 2009 Influenza A(H1N1) seroconversion rates and risk factors among distinct adult cohorts in Singapore(2010) Chen, M.I.C.; Lee, V.J.M.; Lim, W.-Y.; Koh, G.C.H.; Tan, L.W.L.; Chia, K.S.; Yap, J.; Barr, I.G.; Laurie, K.; Shaw, R.; Durrant, C.; Kelso, A.; Lin, R.T.P.; Lin, C.; Cook, A.R.; Loh, J.; Leo, Y.S.; Tan, B.H.; Chow, V.T.K.; CENTRE FOR MOLECULAR EPIDEMIOLOGY; STATISTICS & APPLIED PROBABILITY; DUKE-NUS GRADUATE MEDICAL SCHOOL S'PORE; EPIDEMIOLOGY & PUBLIC HEALTH; MICROBIOLOGYPublication Molecular evidence of transmission of influenza A/H1N1 2009 on a University Campus(Public Library of Science, 2017) Virk R.K.; Gunalan V.; Lee H.K.; Inoue M.; Chua C.; Tan B.-H.; Tambyah P.A.; MEDICINE; UNIVERSITY HEALTH CENTRE; NATIONAL UNIVERSITY MEDICAL INSTITUTES; SAW SWEE HOCK SCHOOL OF PUBLIC HEALTHBackground In the recent years, the data on the molecular epidemiology of influenza viruses have expanded enormously because of the availability of cutting-edge sequencing technologies. However, much of the information is from the temperate regions with few studies from tropical regions such as South-east Asia. Despite the fact that influenza has been known to transmit rapidly within semi-closed communities, such as military camps and educational institutions, data are limited from these communities. Objectives To determine the phylogeography of influenza viruses on a university campus, we examined the spatial distribution of influenza virus on the National University of Singapore (NUS) campus. Methods Consenting students from the NUS who sought medical attention at the UHC provided two nasopharyngeal swabs and demographic data. PCR was used for detection of influenza viruses. 34 full-genomes of pH1N1/09 viruses were successfully sequenced by Sanger method and concatenated using Geneious R7. Phylogenetic analysis was conducted using these 34 sequences and 1518 global sequences. Phylogeographic analysis was done using BaTS software and Association index and Fitch parsimony scores were determined. Results Integrating whole genome sequencing data with epidemiological data, we found strong evidence of influenza transmission on campus as isolates from students residing on-campus were highly similar to each other (AI, P value = 0.009; PS, P value = 0.04). There was also evidence of multiple introductions from the community. Conclusions Such data are useful in formulating pandemic preparedness plans which can use these communities as sentinel sites for detection and monitoring of emerging respiratory viral infections. © 2017 Virk et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Publication A highly divergent Encephalomyocarditis virus isolated from nonhuman primates in Singapore(2013) Yeo, D.S.-Y.; Lian, J.E.; Fernandez, C.J.; Lin, Y.-N.; Liaw, J.C.-W.; Soh, M.-L.; Lim, E.A.-S.; Chan, K.-P.; Ng, M.-L.; Tan, H.-C.; Oh, S.; Ooi, E.-E.; Tan, B.-H.; SAW SWEE HOCK SCHOOL OF PUBLIC HEALTHBackground: In 2001 and 2002, fatal myocarditis resulted in the sudden deaths of four, two adult and two juvenile, orang utans out of a cohort of 26 in the Singapore Zoological Gardens. Methods. Of the four orang utans that underwent post-mortem examination, virus isolation was performed from the tissue homogenates of the heart and lung obtained from the two juvenile orang utans in Vero cell cultures. The tissue culture fluid was examined using electron microscopy. Reverse transcription and polymerase chain reaction with Encephalomyocarditis virus (EMCV)-specific primers targeting the gene regions of VP3/VP1 and 3D polymerase (3Dpol) confirmed the virus genus and species. The two EMCV isolates were sequenced and phylogenetic analyses of the virus genes performed. Serological testing on other animal species in the Singapore Zoological Gardens was also conducted. Results: Electron microscopy of the two EMCV isolates, designated Sing-M100-02 and Sing-M105-02, revealed spherical viral particles of about 20 to 30 nm, consistent with the size and morphology of members belonging to the family Picornaviridae. In addition, infected-Vero cells showed positive immunoflorescence staining with antiserum to EMCV. Sequencing of the viral genome showed that the two EMCV isolates were 99.9% identical at the nucleotide level, indicating a similar source of origin. When compared with existing EMCV sequences in the VP1 and 3Dpol gene regions, the nucleotide divergence were at a maximum of 38.8% and 23.6% respectively, while the amino acid divergence were at a maximum of 33.9% and 11.3% respectively. Phylogenetic analyses of VP1 and 3Dpol genes further grouped the Sing-M100-02 and Sing-M105-02 isolates to themselves, away from existing EMCV lineages. This strongly suggested that Sing-M100-02 and Sing-M105-02 isolates are highly divergent variants of EMCV. Apart from the two deceased orang utans, a serological survey conducted among other zoo animals showed that a number of other animal species had neutralizing antibodies to Sing-M105-02 isolate, indicating that the EMCV variant has a relatively wide host range. Conclusions: The etiological agent responsible for the fatal myocarditis cases among two of the four orang utans in the Singapore Zoological Gardens was a highly divergent variant of EMCV. This is the first report of an EMCV infection in Singapore and South East Asia. © 2013 Yeo et al.; licensee BioMed Central Ltd.Publication The incidence of human bocavirus infection among children admitted to hospital in Singapore(2009-01) Tan, B.-H.; Lim, E.A.-S.; Seah, S.G.-K.; Loo, L.-H.; Tee, N.W.S.; Lin, R.T.P.; Sugrue, R.J.; MICROBIOLOGYHuman bocavirus (HBoV) is a parvovirus, belonging to the genus Bocavirus. The virus was identified recently in Sweden, and has now been detected in several different countries. Although it is associated with lower respiratory tract infections in pediatric patients, the incidence of HBoV infection in a developed country in South East Asia, has not been examined. The objective of this study was to determine the importance of HBoV as a cause of lower respiratory tract infections among children admitted to hospital in Singapore. Five hundred nasopharyngeal swabs were collected from anonymized pediatric patients admitted to the Kandang Kerbau Women's and Children's Hospital for acute respiratory infections. The specimens were tested for the presence of HBoV using polymerase chain reactions. HBoV was detected in 8.0% of the patients tested, and a majority of these HBoV patients exhibited lower respiratory tract infections. A significant level of coinfection with respiratory syncytial viruses and rhinoviruses was also observed in these HBoV patients. The data suggest that HBoV is an important cause of lower respiratory tract infections among children admitted to hospital in Singapore, and is the first study examining the incidence of HBoV infection in a developed country in South East Asia. © 2008 Wiley-Liss, Inc.