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Fulltext Seroepidemiology of human herpesvirus 6 in a population seen in the University Hospital, Kuala Lumpur, Malaysia

Chua KB, Khairullah NS, Hooi PS

Southeast Asian J. Trop. Med. Public Health, 1996 Mar;27(1):91-5.
PMID: 9031408

Sera from healthy donors and patients stored over a period of 2 years, aged 1 to 83 years, were examined for reactivity to human herpes virus 6 (HHV-6) by the standard indirect immunofluorescence assay (IFA). Of the 600 serum specimens screened, 502 showed positive reactivity to HHV-6. This gives an overall seropositive rate of 83.7%. There is no significant difference in the overall positive rate between the ethnic groups (Chinese, Malays, Indians) (chi 2 = 0.35 df = 2 p > 0.05). However, there is significant difference in the positive rates at the extreme age groups of 1 year as well as 61 years and above. From birth up to below 1 year of age, the seroprevalence rate was 82%. At one year of age the positive rate decreased to 66% before gradually rising so that the percentage seropositivity of 6 to 10 years old becomes similar to that in older children and adults (11 to 40 years). The positive rate then starts to decline after 40 years of age. Using a standardized scoring system, the corresponding antibody titer was found to be high in the very young population and starts to decline after the age of 15 years. This suggests that in our population group, primary infection occurs mainly in the pediatric age group. It also accounts for the low positive rate in the age group of 61 years and above, as by then the titer had fallen to the level below the detection limits of the assay system.
Displacement of predominant respiratory syncytial virus genotypes in Malaysia between 1989 and 2011

Khor CS, Sam IC, Hooi PS, Chan YF

Infect Genet Evol, 2013 Mar;14:357-60.
PMID: 23305888 DOI: 10.1016/j.meegid.2012.12.017

From 1989 to 2011 in Kuala Lumpur, Malaysia, multiple genotypes from both respiratory syncytial virus (RSV) subgroups were found co-circulating each year. RSV-A subgroup predominated in 12 out of 17years with the remaining years predominated by RSV-B subgroup. Local RSV strains exhibited temporal clustering with RSV strains reported in previous epidemiological studies. Every few years, the existing predominant genotype was replaced by a new genotype. The RSV-A genotypes GA2, GA5 and GA7 were replaced by NA1 and NA2, while BA became the predominant RSV-B genotype. A unique local cluster, BA12, was seen in 2009, and the recently-described ON1 genotype with 72-nt duplication emerged in 2011. Our findings will have important implications for future vaccine intervention.
Fulltext A retrospective review of mucocutaneous infections by human herpesvirus 1 and 2 in an urban population in Malaysia

Hooi PS, Chua BH, Karunakaran R, Lam SK, Chua KB

Med J Malaysia, 2002 Mar;57(1):80-7.
PMID: 14569722 MyJurnal

This is a 10-year retrospective review of mucocutaneous infection by human herpesvirus 1 (HHV1) and human herpesvirus 2 (HHV2) carried out by the virus diagnostic unit of University Malaya Medical Centre (UMMC). A total of 504 specimens from UMMC and a private clinic in the same city (KLSC) were tested; 198 samples from patients with oral lesions and 306 from patients with genital lesions. HHV1 was found to be responsible for 98.4% of oral lesions whereas HHV2 was the cause of 83.6% of all genital lesions. Detailed analysis showed no statistical difference by age group, race or gender among the patients with oral and genital lesions. Two laboratory methods were used in this study. Of the total 504 specimens tested, 18.0% specimens were positive by direct immunofluorescence (IF), 55.0% by virus isolation and 56.5% when both methods were used in combination. Although IF can provide a more rapid diagnosis, it is, however, less sensitive and can be attributed partly to inadequate collection of specimens.
Fulltext The Use of NS1 Rapid Diagnostic Test and qRT-PCR to Complement IgM ELISA for Improved Dengue Diagnosis from Single Specimen

Teoh BT, Sam SS, Tan KK, Johari J, Abd-Jamil J, Hooi PS, et al.

Sci Rep, 2016 06 09;6:27663.
PMID: 27278716 DOI: 10.1038/srep27663

Timely and accurate dengue diagnosis is important for differential diagnosis and immediate implementation of appropriate disease control measures. In this study, we compared the usefulness and applicability of NS1 RDT (NS1 Ag Strip) and qRT-PCR tests in complementing the IgM ELISA for dengue diagnosis on single serum specimen (n = 375). The NS1 Ag Strip and qRT-PCR showed a fair concordance (κ = 0.207, p = 0.001). While the NS1 Ag Strip showed higher positivity than qRT-PCR for acute (97.8% vs. 84.8%) and post-acute samples (94.8% vs. 71.8%) of primary infection, qRT-PCR showed higher positivity for acute (58.1% vs. 48.4%) and post-acute (50.0% vs.41.4%) samples in secondary infection. IgM ELISA showed higher positivity in samples from secondary dengue (74.2-94.8%) than in those from primary dengue (21.7-64.1%). More primary dengue samples showed positive with combined NS1 Ag Strip/IgM ELISA (99.0% vs. 92.8%) whereas more secondary samples showed positive with combined qRT-PCR/IgM ELISA (99.4% vs. 96.2%). Combined NS1 Ag Strip/IgM ELISA is a suitable combination tests for timely and accurate dengue diagnosis on single serum specimen. If complemented with qRT-PCR, combined NS1 Ag Strip/IgM ELISA would improve detection of secondary dengue samples.
Real-time polymerase chain reaction for diagnosis and quantitation of negative strand of chikungunya virus

Chiam CW, Chan YF, Loong SK, Yong SS, Hooi PS, Sam IC

Diagn Microbiol Infect Dis, 2013 Oct;77(2):133-7.
PMID: 23886793 DOI: 10.1016/j.diagmicrobio.2013.06.018

Quantitative real-time polymerase chain reaction (qRT-PCR) is useful for diagnosis and studying virus replication. We developed positive- and negative-strand qRT-PCR assays to detect nsP3 of chikungunya virus (CHIKV), a positive-strand RNA alphavirus that causes epidemic fever, rash, and arthritis. The positive- and negative-strand qRT-PCR assays had limits of quantification of 1 and 3 log10 RNA copies/reaction, respectively. Compared to a published E1 diagnostic assay using 30 laboratory-confirmed clinical samples, the positive-strand nsP3 qRT-PCR assay had higher R(2) and efficiency and detected more positive samples. Peak viral load of 12.9 log(10) RNA copies/mL was reached on day 2 of illness, and RNA was detectable up to day 9, even in the presence of anti-CHIKV IgM. There was no correlation between viral load and persistent arthralgia. The positive-strand nsP3 assay is suitable for diagnosis, while the negative-strand nsP3 assay, which uses tagged primers to increase specificity, is useful for study of active viral replication kinetics.
Seroprevalence of seasonal and pandemic influenza a in Kuala Lumpur, Malaysia in 2008-2010

Sam IC, Shaw R, Chan YF, Hooi PS, Hurt AC, Barr IG

J Med Virol, 2013 Aug;85(8):1420-5.
PMID: 23765779 DOI: 10.1002/jmv.23622

Relatively little is known about the burden of influenza in tropical countries. The seroprevalence of pandemic influenza A (H1N1) 2009, seasonal H1N1 and H3N2 was determined in Kuala Lumpur, Malaysia. Pre- and post-pandemic residual laboratory sera were tested by hemagglutination-inhibition. The seroprevalence of A(H1N1)pdm09 increased from 3.7% pre-pandemic to 21.9% post-pandemic, giving an overall cumulative incidence of 18.1% (95% CI, 13.8-22.5%), mainly due to increases in those <5, 5-17, and 18-29 years old. In contrast with findings from USA, Europe, and Australia, pre-existing seroprevalence to A(H1N1)pdm09 was low at 5.6% in the elderly age group of >55 years. A(H1N1)pdm09 affected almost a third of those <30 years in Kuala Lumpur. Pre-pandemic seroprevalence was 14.7% for seasonal H1N1 and 21.0% for H3N2, and these rates did not change significantly after the pandemic. Seasonal and pandemic influenza cause a considerable burden in tropical Malaysia, particularly in children and young adults.
Fulltext Epidemiology and seasonality of respiratory viral infections in hospitalized children in Kuala Lumpur, Malaysia: a retrospective study of 27 years

Khor CS, Sam IC, Hooi PS, Quek KF, Chan YF

BMC Pediatr, 2012;12:32.
PMID: 22429933 DOI: 10.1186/1471-2431-12-32

Viral respiratory tract infections (RTI) are relatively understudied in Southeast Asian tropical countries. In temperate countries, seasonal activity of respiratory viruses has been reported, particularly in association with temperature, while inconsistent correlation of respiratory viral activity with humidity and rain is found in tropical countries. A retrospective study was performed from 1982-2008 to investigate the viral etiology of children (≤ 5 years old) admitted with RTI in a tertiary hospital in Kuala Lumpur, Malaysia.
Fulltext Seroprevalence of Malassezia furfur in an urban population in Malaysia

Chua KB, Devi S, Hooi PS, Chong KH, Phua KL, Mak JW

Malays J Pathol, 2003 Jun;25(1):49-56.
PMID: 16196378

An in-house prepared M. furfur antigen was used to carry out a seroprevalence study in an urban population in Malaysia by indirect immunofluorescence assay. Of the 800 serum samples from all ages screened, 738 samples were positive for M. furfur specific IgG, giving an overall seropositive rate of 92.3%. There was no significant difference in the seropositive rates among the different gender group and races. However, there was a statistical significant difference in the seropositive rate among different age groups with a lower rate (73%) for the age group 5 years old and below, which increased rapidly to 99% for the 16 to 20 years old age group but declined slightly for the oldest age group. The degree of seropositivity, which semi-quantitatively reflect the anti-M. furfur specific IgG titre, did not show any significant difference among the gender and racial groups. On the other hand, there was a significant difference in the degree of seropositivity among the various age groups, with the 16 to 20 years old age group having the highest antibody titre and the extreme of age groups having the lower antibody titre.
Seasonal variation in respiratory syncytial virus chest infection in the tropics

Chan PW, Chew FT, Tan TN, Chua KB, Hooi PS

Pediatr Pulmonol, 2002 Jul;34(1):47-51.
PMID: 12112797 DOI: 10.1002/ppul.10095

Respiratory syncytial virus (RSV) is the most important cause of lower respiratory tract infection (LRTI) in young children. We determined if there was a seasonal variation in Malaysia in the incidence of RSV infection in young children admitted with LRTI, and possible associations of RSV infection with local meteorological parameters. A total of 5,691 children, aged less than 24 months and hospitalized with LRTI (i.e., bronchiolitis and pneumonia) between 1982-1997, were included in this study. Nasopharyngeal samples were collected and examined for RSV by immunofluorescence, viral culture, or both. Seasonal variations were determined by analyzing the monthly RSV-positive isolation rate via time series analysis. Possible correlations with local meteorological parameters were also evaluated.RSV was isolated in 1,047 (18.4%) children. Seasonal variations in RSV infection rate were evident and peaked during the months of November, December, and January (test statistics [T] = 53.7, P < 0.001). This seasonal variation was evident for both bronchiolitis and pneumonia categories (T = 42.8 and 56.9, respectively, P < 0.001). The rate of RSV infection appeared to correlate with the monthly number of rain days (r = 0.26, P < 0.01), and inversely with the monthly mean temperature (r = -0.38, P < 0.001). In the tropics, seasonal variations in the incidence of RSV infection are evident, with an annual peak in November, December, and January. This information provides a guide for healthcare provisions and implementation of RSV prevention.
The presence of Nipah virus in respiratory secretions and urine of patients during an outbreak of Nipah virus encephalitis in Malaysia

Chua KB, Lam SK, Goh KJ, Hooi PS, Ksiazek TG, Kamarulzaman A, et al.

J Infect, 2001 Jan;42(1):40-3.
PMID: 11243752

To study the excretion of Nipah virus in the upper respiratory secretions and urine of infected patients in relation to other clinical features.
Fulltext Seroprevalence of human parvovirus B19 infection in an urban population in Malaysia

Ooi SL, Hooi PS, Chua BH, Lam SK, Chua KB

Med J Malaysia, 2002 Mar;57(1):97-103.
PMID: 14569725 MyJurnal

A seroepidemiological study carried out on 800 stored serum samples collected between January 1999 to December 2000 derived from an urban population in Malaysia showed that the overall seropositive rate of human paravovirus B19 infection was 37.6%, with an overall geometric mean titre (GMT) of 18.3 IU. The seropositive rates of B19 among the male and female populations were 39.0% and 36.3% respectively. The seropositive rates among the racial groups were 37.2%, 38.2%, 38.1% and 29.4% respectively for the Malays, Chinese, Indians and other races. There was no statistical significant gender and racial differences in the B19 seropositive rates. When compared with the seroprevalence of B19 infection in other Asian countries, the seropositive rate of B19 in Malaysia was low in the younger age group and increased steadily with age. The unusual finding in this study was the presence of a high seropositive rate in those between six months to five years of age, especially in children in the one year old age group.
Viral aetiology of lower respiratory tract infection in young Malaysian children

Chan PW, Goh AY, Chua KB, Kharullah NS, Hooi PS

J Paediatr Child Health, 1999 Jun;35(3):287-90.
PMID: 10404452

OBJECTIVE: To study the viral aetiology of lower respiratory tract infection (LRTI) in young Malaysian children.
METHODOLOGY: A retrospective review was performed of LRTI patients aged less than 24 months who were admitted to the University Malaya Medical Centre between 1982 and 1997. Respiratory viruses in their nasopharyngeal secretion were identified by indirect immunofluorescence, viral culture, or both.
RESULTS: A total of 5691 children were included in the study. The mean age was 8.6 +/- 6.6 months and the M:F ratio was 1.6:1. The most common diagnosis was pneumonia (52%) followed by bronchiolitis (45%) and croup (2%). Positive viral isolation rate was 22.0%. Respiratory syncytial virus (RSV) was the commonest virus isolated (84%), followed by parainfluenza virus (8%), influenza virus (6%) and adenovirus (2%). Patients with positive virus isolation were younger (7.8 +/- 6.2 vs 8.7 +/- 6.7 months, P = 0.0001) and were more likely to have bronchiolitis.
CONCLUSION: Young Malaysian children admitted with LRTI had a 22% viral isolation rate and RSV was the commonest virus isolated.
Fulltext Hand, foot and mouth disease: University Malaya Medical Centre experience

Hooi PS, Chua BH, Lee CSM, Lam SK, Chua KB

Med J Malaysia, 2002 Mar;57(1):88-91.
PMID: 14569723 MyJurnal

The prevalence of HFMD as well as the causative agents was unknown in peninsular Malaysia prior to May 1997. From May 1997 to June 2001, 585 patients suspected to have enterovirus infections, with 467 patients clinically diagnosed as having HFMD, were investigated in the diagnostic virology unit of the University Malaya Medical Centre. Data from this study showed that HFMD is endemic in Malaysia with the occurrence of two outbreaks during the study period. In each outbreak, a number of viruses were isolated but enterovirus 71 was the main virus isolated in both outbreaks. Echovirus 7 (Eo7) was isolated from 5 patients with HFMD in the second outbreak, a clinical entity that has not been attributed to it previously. Children aged 4 years and below, particularly those between 1 and 2 years of age, were in the main group of patients affected by the illness. HFMD by itself and without neurological involvement was relatively benign and self-limiting. There was no significant difference in the virus isolation rate with respect to gender and ethnic groups. Virus isolation was attempted in a total of 764 clinical specimens consisting of 342 stool specimens, 285 oral secretions specimens and 137 vesicular fluid specimens. Oral specimens gave the highest virus isolation rate (33.3%) followed by vesicular specimens (27.0%). Stool specimens only yielded an isolation rate of 14.0%.
Fulltext Retrospective review of serologic rubella activity in University Hospital Kuala Lumpur

Chua KB, Lam SK, Hooi PS, Chua BH, Lim CT

Med J Malaysia, 2000 Sep;55(3):299-303.
PMID: 11200707

A retrospective review of rubella serological results carried out in the Virus Diagnostic Unit, University Hospital Kuala Lumpur (UHKL) from January 1993 to September 1999 showed the presence of rubella infection annually which appeared to increase periodically every two to three years. There was no statistical significant difference in the rubella positive rate between male and female population aged 14 to 48 years. Congenital rubella infections (CRI) occurred in babies delivered in UHKL yearly from 1993 to 1998 with an average incidence rate of 48 per 100,000 deliveries. Peaks of rubella cases appeared to be followed by an increase in incidence of CRI cases 6 to 9 months later. The study showed that only 50.8% clinically diagnosed rubella was confirmed by laboratory finding. This study also showed an increase of rubella activity for the months of July, August and September 1999 and this may herald an increase of CRI cases in the coming millennium.
Evaluation of rapid influenza diagnostic tests for influenza A and B in the tropics

Chong YM, Tan XH, Hooi PS, Lee LM, Sam IC, Chan YF

J Med Virol, 2019 08;91(8):1562-1565.
PMID: 31032971 DOI: 10.1002/jmv.25495

Rapid diagnosis of influenza is important for early treatment and institution of control measures. In developing tropical countries such as Malaysia, influenza occurs all year round, but molecular assays and conventional techniques (such as immunofluorescence and culture) for diagnosis are not widely available. Rapid influenza diagnostic tests (RIDTs) may be useful in this setting. A total of 552 fresh respiratory specimens were assessed from patients with respiratory symptoms at a teaching hospital in Kuala Lumpur, Malaysia from November 2017 to March 2018. Two digital immunoassays (DIAs), STANDARD F Influenza A/B Fluorescence Immunoassay (STANDARD F) and Sofia Influenza A + B Fluorescence Immunoassay (Sofia) and one conventional RIDT (immunochromatographic assay), SD Bioline Influenza Ag A/B/A(H1N1) Pandemic rapid test kit (SD Bioline) were evaluated in comparison with a WHO-recommended reverse transcription quantitative PCR (RT-qPCR). Of the 552 samples, influenza A virus was detected in 47 (8.5%) and influenza B virus in 7 (1.3%). The digital immunoassays STANDARD F and Sofia had significantly higher overall sensitivity rates (71.7% and 70.6%, respectively) than the conventional RIDT SD Bioline and immunofluorescence/viral culture (55.8% and 52.8%, respectively). Sensitivity rates were higher for influenza A than influenza B, and specificity rates were uniformly high, ranging from 98% to 100%. Digital readout RIDTs can be used in tropical settings with year-round influenza if PCR is unavailable.
Isolation of Waddlia malaysiensis, a novel intracellular bacterium, from fruit bat (Eonycteris spelaea)

Chua PK, Corkill JE, Hooi PS, Cheng SC, Winstanley C, Hart CA

Emerg Infect Dis, 2005 Feb;11(2):271-7.
PMID: 15752446

An obligate intracellular bacterium was isolated from urine samples from 7 (3.5%) of 202 fruit bats (Eonycteris spelaea) in peninsular Malaysia. The bacterium produced large membrane-bound inclusions in human, simian, and rodent cell lines, including epithelial, fibroblastlike, and lymphoid cells. Thin-section electron microscopy showed reticulate bodies dividing by binary fission and elementary bodies in the inclusions; mitochondria surrounded the inclusions. The inclusions were positive for periodic acid-Schiff stain but could not be stained by fluorescein-labeled anti-Chlamydia trachomatis major outer membrane protein monoclonal antibody. The bacterium was resistant to penicillin and streptomycin (MICs > 256 mg/L) but susceptible to tetracycline (MIC = 0.25 mg/L) and chloramphenicol (MIC = 0.5 mg/L). Sequence analysis of the 16SrRNA gene indicated that it was most closely related to 2 isolates of Waddlia chondrophila (94% and 96% identity). The 16S and 23S rRNA gene signatures were only 91% identical. We propose this novel bacterium be called W. malaysiensis.
Fulltext Enterovirus 71 outbreak, Brunei

AbuBakar S, Sam IC, Yusof J, Lim MK, Misbah S, MatRahim N, et al.

Emerg Infect Dis, 2009 Jan;15(1):79-82.
PMID: 19116058 DOI: 10.3201/eid1501.080264

Enterovirus 71 (EV71) outbreaks occur periodically in the Asia-Pacific region. In 2006, Brunei reported its first major outbreak of EV71 infections, associated with fatalities from neurologic complications. Isolated EV71 strains formed a distinct lineage with low diversity within subgenogroup B5, suggesting recent introduction and rapid spread within Brunei.
Fulltext Reemergence of endemic Chikungunya, Malaysia

AbuBakar S, Sam IC, Wong PF, MatRahim N, Hooi PS, Roslan N

Emerg Infect Dis, 2007 Jan;13(1):147-9.
PMID: 17370532

Chikungunya virus infection recently reemerged in Malaysia after 7 years of nondetection. Genomic sequences of recovered isolates were highly similar to those of Malaysian isolates from the 1998 outbreak. The reemergence of the infection is not part of the epidemics in other Indian Ocean countries but raises the possibility that chikungunya virus is endemic in Malaysia.
Fulltext Detection of Respiratory Viruses from ARTI Patients by xTAG RVP Fast v2 Assay and Conventional Methods

Kuan CS, Yew SM, Hooi PS, Lee LM, Ng KP

Malays J Med Sci, 2017 Oct;24(5):33-43.
PMID: 29386970 MyJurnal DOI: 10.21315/mjms2017.24.5.4

Introduction: Acute respiratory tract infections (ARTIs) are a major cause of morbidity and mortality in paediatric patients. Therefore, early detection of the viral aetiologies of ARTIs is essential for patient management and infection control. In this study, we evaluated the performance of a new multiplex polymerase chain reaction (PCR) assay (xTAG Respiratory Viral Panel [RVP] Fast v2) in the detection of respiratory viruses by comparing it with that of viral culture and direct immunofluorescence (IF) staining.
Methods: Nasopharyngeal swab and aspirate samples were collected prospectively from 199 patients who presented with ARTIs at the University Malaya Medical Centre (UMMC) in Kuala Lumpur, Malaysia during a 10-month period. The PCR assay was conducted in parallel with conventional culture and direct IF staining methods.
Results: The positive rate of the xTAG RVP Fast v2 assay (78.4%) in detecting respiratory viruses was higher than that of the viral isolation (7.5%) and direct IF (23.1%) methods. Using the xTAG RVP Fast v2 assay, human enterovirus/human rhinovirus (HEV/HRV) was the most frequently detected (46.2%). The xTAG RVP Fast v2 assay revealed mixed infection caused by two or three respiratory viruses in 40 specimens, and these were undetected by the viral isolation and direct IF methods.
Conclusion: The xTAG RVP Fast v2 assay was superior to conventional methods in the identification of common respiratory viruses, with higher sensitivity and shorter turnaround times for laboratory results.
Fulltext Detection of dengue viruses using reverse transcription-loop-mediated isothermal amplification

Teoh BT, Sam SS, Tan KK, Johari J, Danlami MB, Hooi PS, et al.

BMC Infect Dis, 2013;13:387.
PMID: 23964963 DOI: 10.1186/1471-2334-13-387

BACKGROUND: Early and rapid detection of dengue virus (DENV) infection during the febrile period is crucial for proper patient management and prevention of disease spread. An easy to perform and highly sensitive method is needed for routine implementation especially in the resource-limited rural healthcare settings where dengue is endemic.
METHODS: A single-tube reverse transcription-loop-mediated isothermal amplification (RT-LAMP) assay with a set of nine primers was developed for the detection of all four DENV serotypes and their different genotypes. The sensitivity and specificity of the RT-LAMP were evaluated. The clinical applicability of RT-LAMP assay for detection of DENV RNA was assessed in a total of 305 sera of clinically-suspected dengue patients. The test results of RT-LAMP were statistically compared to those of quantitative reverse transcription-polymerase chain reaction (qRT-PCR), IgM- and IgG-capture enzyme-linked immunosorbent assays (ELISA).
RESULTS: Acute DENV infection was confirmed in 171 samples (n = 305); 43.3% (74/171) and 46.8% (80/171) of the samples were positive for DENV using RT-LAMP and qRT-PCR, respectively. The combination of RT-LAMP with the dengue IgM and IgG ELISA increased detection of acute DENV infection to 97.7% (167/171), in comparison to only 70.8% (121/171) when dengue IgM and IgG ELISA alone were used. The RT-LAMP assays showed high concordance (κ = 0.939) with the qRT-PCR. The RT-LAMP assay detected up to 10 copies of virus RNA within an hour but 100% reproducibility (12/12) was achieved with 100 copies. There was no cross reactivity of RT-LAMP with other closely related arboviruses.
CONCLUSION: The RT-LAMP assay developed in this study is sensitive, specific and simple to perform. The assay improved the detection of dengue when used in combination with serological methods.

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