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

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.

Epidemiology and Transmission of Respiratory Infections in Thai Army Recruits: A Prospective Cohort Study

Military recruits are at high risk of respiratory infections. However, limited data exist on military populations in tropical settings, where the epidemiology of respiratory infections differs substantially from temperate settings. We enrolled recruits undertaking a 10-week military training at two Royal Thai Army barracks between May 2014 and July 2015. We used a multiplex respiratory panel to analyze nose and throat swabs collected at the start and end of the training period, and from participants experiencing respiratory symptoms during follow-up. Paired sera were tested for influenza seroconversion using a hemagglutinin inhibition assay. Overall rates of upper respiratory illness and influenza-like illness were 3.1 and 2.0 episodes per 100 person-weeks, respectively. A pathogen was detected in 96% of samples. The most commonly detected microbes were Haemophilus influenzae type B (62.7%) or non–type B (58.2%) and rhinovirus (22.4%). At baseline, bacterial colonization was high and included H. influenzae type B (82.3%), H. influenzae non–type B (31.5%), Klebsiella pneumoniae (14.6%), Staphylococcus aureus (8.5%), and Streptococcus pneumoniae (8.5%). At the end of follow-up, colonization with H. influenzae non–type B had increased to 74.1%, and S. pneumoniae to 33.6%. In the serology subset, the rate of influenza infection was 3.4 per 100 person-months; 58% of influenza infections resulted in clinical disease. Our study provides key data on the epidemiology and transmission of respiratory pathogens in tropical settings. Our results emphasize the need for improved infection prevention and control in military environments, given the high burden of illness and potential for intense transmission of respiratory pathogens.

Cell-mediated immune responses to different formulations of a live-attenuated tetravalent dengue vaccine candidate in subjects living in dengue endemic and non-endemic regions

Three phase II randomized trials evaluated the safety/immunogenicity of two formulations of live-attenuated tetravalent dengue virus (TDEN) vaccine in dengue-endemic (Puerto Rico, Thailand) and non-endemic (US) regions (NCT00350337/NCT00370682/NCT00468858). We describe cell-mediated immune (CMI) responses; safety and humoral responses were reported previously. Participants received two doses of vaccine or control (placebo or the precursor live-attenuated TDEN vaccine) 6 months apart. Selected US participants received a booster 5–12 months post-dose 2. Evaluated subsets of the per-protocol cohorts included 75 primarily dengue virus (DENV)-unprimed US adults, 69 primarily flavivirus-primed Thai adults, and 100 DENV-primed or DENV-unprimed Puerto Rican adults/adolescents/children. T-cell responses were quantified using intracellular cytokine staining (ICS; DENV-infected cell-lysate or DENV-1/DENV-2 peptide-pool stimulation) or IFN-γ ELISPOT (DENV-2 peptide-pool stimulation). Memory B-cell responses were quantified using B-cell ELISPOT. Across populations and age strata, DENV serotype-specific CD4⁺ T-cell responses were slightly to moderately increased (medians ≤0.18% [ICS]), DENV-2–biased, and variable for both formulations. Responses in unprimed subjects were primarily detected post-dose 1. Response magnitudes in primed subjects were similar between doses. Multifunctional CD8⁺ T-cell responses were detected after peptide-pool stimulation. T-cell responses were mostly directed to DENV nonstructural proteins 3 and 5. Memory B-cell responses were tetravalent, of low-to-moderate magnitudes (medians ≤0.25%), and mainly observed post-dose 2 in unprimed subjects and post-dose 1 in primed subjects. A third dose did not boost CMI responses. In conclusion, both formulations of the live-attenuated TDEN vaccine candidate were poorly to moderately immunogenic with respect to B-cell and T-cell responses, irrespective of the priming status of the participants.

Abbreviation ATP: according-to-protocol; ICS: Intracellular Cytokine Staining; NS3: Nonstructural protein 3; ELISPOT: Enzyme-Linked ImmunoSpot; JEV: Japanese encephalitis virus; PBMC: peripheral blood mononuclear cells

Association between semi-quantitative microbial load and respiratory symptoms among Thai military recruits: a prospective cohort study

BACKGROUND

Multiplex real-time polymerase chain reaction assays have improved diagnostic sensitivity for a wide range of pathogens. However, co-detection of multiple agents and bacterial colonization make it difficult to distinguish between asymptomatic infection or illness aetiology. We assessed whether semi-quantitative microbial load data can differentiate between symptomatic and asymptomatic states for common respiratory pathogens.

METHODS

We obtained throat and nasal swab samples from military trainees at two Thai Army barracks. Specimens were collected at the start and end of 10-week training periods (non-acute samples), and from individuals who developed upper respiratory tract infection during training (acute samples). We analysed the samples using a commercial multiplex respiratory panel comprising 33 bacterial, viral and fungal targets. We used random effects tobit models to compare cycle threshold (Ct) value distributions from non-acute and acute samples.

RESULTS

We analysed 341 non-acute and 145 acute swab samples from 274 participants. Haemophilus influenzae type B was the most commonly detected microbe (77.4% of non-acute and 64.8% of acute samples). In acute samples, nine specific microbe pairs were detected more frequently than expected by chance. Regression models indicated significantly lower microbial load in non-acute relative to acute samples for H. influenzae non-type B, Streptococcus pneumoniae and rhinovirus, although it was not possible to identify a Ct-value threshold indicating causal etiology for any of these organisms.

CONCLUSIONS

Semi-quantitative measures of microbial concentration did not reliably differentiate between illness and asymptomatic colonization, suggesting that clinical symptoms may not always be directly related to microbial load for common respiratory infections.

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

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Next-generation Sequencing (NGS) was adopted in routine respiratory pathogen surveillance from South/South East (S/SE) Asia during 2010–2013.

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From 12,865 respiratory collections from ILI patients, 324 CPE-positive from 4,478 viral isolations were negative by standard assays.

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The CPE-positive samples were pooled, screened using NGS and validated the presence of the pathogens identified from NGS.

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Herpes simplex virus type 1, parainfluenza, adenovirus, coronavirus, human metapneumovirus, mumps virus and enterovirus genus were detected.

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NGS on pooled samples can be applied to surveillance work, identifying medically important viruses which may have missed by conventional methods.

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%).

Metagenomics Study of Viral Pathogens in Undiagnosed Respiratory Specimens and Identification of Human Enteroviruses at a Thailand Hospital

Numerous pathogens cause respiratory infections with similar symptoms. Routine diagnostics detect only a limited number of pathogens, leaving a gap in respiratory illness etiology surveillance. This study evaluated next-generation sequencing for unbiased pathogen identification. Respiratory samples collected in Thailand, Philippines, Bhutan, and Nepal, that were negative by several molecular and immunofluorescence assays, underwent viral cultivation. Samples which demonstrated cytopathic effect in culture (N = 121) were extracted and tested by Luminex xTAG respiratory viral panel (RVP) assay and deep sequencing by Roche 454 FLX Titanium system. Using RVP assay, 52 (43%) samples were positive for enterovirus or rhinovirus and another three were positive for respiratory syncytial virus B, parainfluenza 4, and adenovirus. Deep sequencing confirmed the Luminex assay results and identified additional viral pathogens. Human enteroviruses, including Enterovirus A type 71 and 12 types of Enterovirus B (EV-B) were identified from a hospital in Bangkok. Phylogenetic and recombination analysis showed high correlation of VP1 gene-based phylogeny with genome-wide phylogeny and the frequent genetic exchange among EV-B viruses. The high number and diversity of enteroviruses in the hospital in Bangkok suggests prevalent existence. The metagenomic approach used in our study enabled comprehensive diagnoses of respiratory viruses.

Long-Term Safety and Immunogenicity of a Tetravalent Live-Attenuated Dengue Vaccine and Evaluation of a Booster Dose Administered to Healthy Thai Children

We evaluated the safety and immunogenicity of two doses of a live-attenuated, tetravalent dengue virus vaccine (F17/Pre formulation) and a booster dose in a dengue endemic setting in two studies. Seven children (7- to 8-year-olds) were followed for 1 year after dose 2 and then given a booster dose (F17/Pre formulation), and followed for four more years (Child study). In the Infant study, 49 2-year-olds, vaccinated as infants, were followed for approximately 3.5 years after dose 2 and then given a booster dose (F17) and followed for one additional year. Two clinically notable events were observed, both in dengue vaccine recipients in the Infant study: 1 case of dengue approximately 2.7 years after dose 2 and 1 case of suspected dengue after booster vaccinations. The booster vaccinations had a favorable safety profile in terms of reactogenicity and adverse events reported during the 1-month follow-up periods. No vaccine-related serious adverse events were reported during the studies. Neutralizing antibodies against dengue viruses 1–4 waned during the 1–3 years before boosting, which elicited a short-lived booster response but did not provide a long-lived, multivalent antibody response in most subjects. Overall, this candidate vaccine did not elicit a durable humoral immune response.

Safety and Immunogenicity of a Tetravalent Dengue Vaccine Candidate in Healthy Children and Adults in Dengue-Endemic Regions: A Randomized, Placebo-Controlled Phase 2 Study

BACKGROUND

A safe, effective tetravalent dengue vaccine is a global health priority. The safety and immunogenicity of a live attenuated, recombinant tetravalent dengue vaccine candidate (TDV) were evaluated in healthy volunteers from dengue-endemic countries.

METHODS

This multicenter, double-blind, phase 2 study was conducted in Puerto Rico, Colombia, Singapore, and Thailand. During stage I, 148 volunteers aged 1.5-45 years were sequentially enrolled into 4 age-descending groups and randomized at a ratio of 2:1 to receive TDV or placebo. In stage II (group 5), 212 children aged 1.5-11 years were randomized at a ratio of 3:1 to receive TDV or placebo. Participants received a subcutaneous injection of TDV or placebo on days 0 and 90 and were followed for analysis of safety, seropositivity, and neutralizing antibodies to DENV-1-4.

RESULTS

Injection site pain, itching, and erythema (mostly mild) were the only solicited adverse events more frequently reported with TDV than with placebo in all age groups. After 2 TDV doses, seropositivity was >95% in all 5 groups for DENV-1-3 and 72.7%-100% for DENV-4; geometric mean titers ranged from 582 to 1187 for DENV-1, from 582 to 1187 for DENV-2, from 196 to 630 for DENV-3, and from 41 to 210 for DENV-4 among the 5 groups.

CONCLUSIONS

TDV was well tolerated and immunogenic in volunteers aged 1.5-45 years, irrespective of prevaccination dengue exposure.

Elevated transmission of upper respiratory illness among new recruits in military barracks in Thailand

BACKGROUND

New recruits within military barracks present conditions favorable for the spread of respiratory pathogens. However, respiratory pathogen transmission in such confined settings in the tropics has not been well studied.

METHODS

Recruits in four successive Royal Thai Army basic training classes living in military barracks were monitored for the symptoms of influenza-like illness (ILI) or upper respiratory illness (URI). Classes 1 and 2 were also monitored after basic training. Nasal/throat swabs from acute illnesses were collected and tested by influenza RT-PCR (all four classes). In addition, class 1 had multiplex PCR performed along with the analysis of bed locations within the barracks.

RESULTS

Influenza-like illness/upper respiratory illness rates ranged from 4·7 to 6·9 per 100 recruit-weeks in the four classes and generally decreased during the course of basic training (P < 0·05 in three of four classes). Rates during basic training were 1·7 (95% CI: 1·29, 2·29) and 2·5 (95% CI: 1·5, 4·1) times higher than after basic training (classes 1 and 2, respectively). In class 1, coronavirus, parainfluenza virus, and rhinovirus were the most commonly identified respiratory pathogens; only one influenza PCR-positive infection was detected in all four classes. Bed locations of URI/ILI cases in class 1 tended to be in closer proximity to each other.

CONCLUSION

Basic training recruits in military barracks in the tropics had high rates of acute respiratory illnesses with illness patterns consistent with external seeding followed by substantial internal transmission. Our findings may contribute to control measures in similar confined settings both within and outside the military.

Influenza vaccine effectiveness in the tropics: moderate protection in a case test-negative analysis of a hospital-based surveillance population in Bangkok between August 2009 and January 2013

Influenza in the tropics occurs year round with peaks that correspond variably to temperate regions. However, data on influenza vaccine effectiveness (VE) in the tropics is sparse. We report on the effectiveness of influenza vaccine to prevent medically attended laboratory confirmed influenza from sentinel surveillance conducted at a Thai military medical facility in Bangkok, Thailand from August 2009 to January 2013. Patients ≥6 months old presenting with influenza-like illness underwent combined nasal/throat swabs which were tested by influenza RT-PCR. A case test-negative study design was used to evaluate VE. Of 2999 samples available for analysis,1059 (35.3%) were PCR-positive (cases) and 1940 (64.6%) were PCR-negative (test-negative controls). Five hundred and seven (16.9%) of these patients reported being vaccinated within the previous 12 months. Periods of high and low influenza activity were defined based on publicly available Thai Ministry of Public Health data. Overall VE adjusted for age and epiweek was found to be 50.1% (95%CI: 35.0, 61.9%). The May to April adjusted VE for year 2010, 2011 and 2012 was 57.7% (95%CI: 33.7, 73.8%), 57.1% (95% CI: 35.2, 68.3%) and 37.6% (95% CI: 3.5, 62.9%).During high influenza activity in years with the same vaccine formulation, the adjusted VE was 54.9% (95%CI: 38.9, 66.9%). VE appeared to be much higher during high versus low influenza activity periods. The adjusted point estimate for VE was highest in the 18-49 year age group (76.6%) followed by 6-23 months (58.1%) and 2-17 years (52.5%). Adjusted estimates were not done for those ≥50 years of age due to small numbers. VE in patients with underlying disease was 75.5% compared to 48.0% in those without. Our findings demonstrate moderate protection by influenza vaccination and support the utility of influenza vaccination in the tropics including in very young children and those with underlying disease.

Viral subpopulation diversity in influenza virus isolates compared to clinical specimens

BACKGROUND

Influenza virus (IFV) isolates obtained from mammalian cell cultures are valuable reagents used for vaccine production, antigenic characterization, laboratory assays, and epidemiological and evolutionary studies. Complete genomic comparison of IFV isolates with their original clinical specimens provides insight into cell culture-driven genomic changes which may sequentially alter the virus phenotype.

OBJECTIVES

The genome of the viral isolates and of the viruses in the clinical specimens was examined by deep sequencing in order to determine nucleotide heterogeneity (measured number of variances or numbers of mixed bases) as a marker for IFV population diversity.

STUDY DESIGN

Clinical respiratory specimens were collected between July and October 2012 and identified by RT-PCR as positive for influenza A H3N2 or H1N1, or influenza B. The viruses in the clinical specimens were amplified using mammalian cell culture. Next generation sequencing (NGS) was used to investigate genomic differences between IFV isolates and their corresponding clinical specimens.

RESULTS

There was less nucleotide heterogeneity in 5 of 6 viral isolates compared to the corresponding clinical specimens, especially for influenza B. A phylogenetic analysis of the hemagglutinin (HA) gene consensus sequences obtained from deep and Sanger sequencing showed that the viral isolates and their corresponding clinical specimens contained the same IFV strains with less than 5% pair-wise genetic distance.

CONCLUSION

The IFV sequence data analysis detected a substantial decrease in nucleotide heterogeneity from clinical specimens to viral cultures in 5 out of 6 investigated cases.

C-reactive protein as a single useful parameter for discontinuation of antibiotic treatment in Thai neonates with clinical sepsis

BACKGROUND

Clinical sepsis is a common diagnosis in neonate and is usually treated with antibiotic. The duration of treatment is usually more than five days or until all cultures from the patient's samples reveal negative.

OBJECTIVE

To determine whether quantitative C-reactive protein (CRP) level less than 10 mg/L could be used as a reliable index for discontinuation of antibiotic treatment in Thai neonates with clinical sepsis.

MATERIAL AND METHOD

All neonates with birth weight greater than 1,500 grams, diagnosed as clinical sepsis, were enrolled to the study. Serum CRP was measured at 24 to 48 hours after the first dose of antibiotics. If CRP level was less than 10 mg/L, infants were randomly divided to groups Ia and Ib. If CRP level was 10 mg/L or more, infants were randomly divided to groups IIa and IIb. Antibiotics were discontinued promptly after the CRP level was reported in group Ia, while CRP level was measured daily and antibiotics were discontinued after it returned to less than 10 mg/L in group IIa. In controlled groups (Ib and IIb), antibiotics were continued until all bacterial cultures were negative. The outcome measurements were the number ofpatients who required retreatment for clinical sepsis within three days and 28 days after discontinuing antibiotics.

RESULTS

Of 98 neonates with clinical sepsis, 76 (77.6%) were in group I. The duration of antibiotic treatment in group Ia was shorter than group Ib significantly, 1.68 vs. 5.47 days (p < 0.01). One neonate in group Ia was retreated on the third day after discontinuing antibiotics due to positive blood and urine cultures. The negative predictive value of CRP for discontinuation of antibiotics in group I was 97.4%. The durations of antibiotic treatments were 5.27 and 7.09 days in group IIa and IIb, respectively. One neonate in group IIa was retreated on the second day after discontinuing antibiotics since the patient's clinical and laboratory results suggested severe sepsis although all bacterial cultures were negative. No patient was readmitted for treatment of sepsis within 28 days after discontinuing antibiotics.

CONCLUSION

CRP levels were less than 10 mg/L in the majority of neonates with clinical sepsis. The negative predictive value for using this level as a guide for antibiotic discontinuation was 97.4%.

Safety and immunogenicity of a rederived, live-attenuated dengue virus vaccine in healthy adults living in Thailand: a randomized trial

Safety and immunogenicity of two formulations of a live-attenuated tetravalent dengue virus (TDEN) vaccine produced using rederived master seeds from a precursor vaccine were tested against a placebo control in a phase II, randomized, double blind trial (NCT00370682). Two doses were administered 6 months apart to 120 healthy, predominantly flavivirus-primed adults (87.5% and 97.5% in the two vaccine groups and 92.5% in the placebo group). Symptoms and signs reported after vaccination were mild to moderate and transient. There were no vaccine-related serious adverse events or dengue cases reported. Asymptomatic, low-level viremia (dengue virus type 2 [DENV-2], DENV-3, or DENV-4) was detected in 5 of 80 vaccine recipients. One placebo recipient developed a subclinical natural DENV-1 infection. All flavivirus-unprimed subjects and at least 97.1% of flavivirus-primed subjects were seropositive to antibodies against all four DENV types 1 and 3 months post-TDEN dose 2. The TDEN vaccine was immunogenic with an acceptable safety profile in flavivirus-primed adults.

Simultaneous and complete genome sequencing of influenza A and B with high coverage by Illumina MiSeq Platform

Active global surveillance and characterization of influenza viruses are essential for better preparation against possible pandemic events. Obtaining comprehensive information about the influenza genome can improve our understanding of the evolution of influenza viruses and emergence of new strains, and improve the accuracy when designing preventive vaccines. This study investigated the use of deep sequencing by the next-generation sequencing (NGS) Illumina MiSeq Platform to obtain complete genome sequence information from influenza virus isolates. The influenza virus isolates were cultured from 6 respiratory acute clinical specimens collected in Thailand and Nepal. DNA libraries obtained from each viral isolate were mixed and all were sequenced simultaneously. Total information of 2.6 Gbases was obtained from a 455±14 K/mm2 density with 95.76% (8,571,655/8,950,724 clusters) of the clusters passing quality control (QC) filters. Approximately 93.7% of all sequences from Read1 and 83.5% from Read2 contained high quality sequences that were ≥Q30, a base calling QC score standard. Alignments analysis identified three seasonal influenza A H3N2 strains, one 2009 pandemic influenza A H1N1 strain and two influenza B strains. The nearly entire genomes of all six virus isolates yielded equal or greater than 600-fold sequence coverage depth. MiSeq Platform identified seasonal influenza A H3N2, 2009 pandemic influenza A H1N1and influenza B in the DNA library mixtures efficiently.

Safety and immunogenicity of a tetravalent live-attenuated dengue vaccine in flavivirus-naive infants

A Phase I/II observer-blind, randomized, controlled trial evaluated the safety and immunogenicity of a dengue virus (DENV) vaccine candidate in healthy Thai infants (aged 12-15 months) without measurable pre-vaccination neutralizing antibodies to DENV and Japanese encephalitis virus. Fifty-one subjects received two doses of either DENV (N = 34; four received 1/10th dose) or control vaccine (N = 17; dose 1, live varicella; dose 2, Haemophilus influenzae type b). After each vaccine dose, adverse events (AEs) were solicited for 21 days, and non-serious AEs were solicited for 30 days; serious AEs (SAEs) were recorded throughout the study. Laboratory safety assessments were performed at 10 and 30 days; neutralizing antibodies were measured at 30 days. The DENV vaccine was well-tolerated without any related SAEs. After the second dose, 85.7% of full-dose DENV vaccinees developed at least trivalent and 53.6% developed tetravalent neutralizing antibodies ≥ 1:10 to DENV (control group = 0%). This vaccine candidate, therefore, warrants continued development in this age group (NCT00322049; clinicaltrials.gov).

Invasive pneumococcal disease in Phramongkutklao Hospital 2004-2008: clinical data, serotype distribution and antimicrobial resistance patterns

OBJECTIVE

To describe the clinical course, serotype distribution and antimicrobial resistance patterns of invasive pneumococcal disease (IPD) cases in a public hospital.

MATERIAL AND METHOD

Retrospective review of IPD cases occurring from January 2004 through December 2008 was performed. Antibiotic susceptibility testing and serotyping were performed for available isolates.

RESULTS

Fifty one IPD cases occurred during the study period, of which 47 had medical records available for review. The majority of cases occurred among children under 5 years of age (23.4%) and adults over 60 years of age (36.1%). Underlying diseases were identified in 72.3% of patients. Fifty-three percent of cases were associated with pneumonia, while 17% had meningitis, and 15% had isolated bacteremia. Serotype could be determined for 15 (31.9%) isolates, and 6B was most common. Based on current antibiotic susceptibility breakpoints for meningitis, 4 of the 7 available isolates from meningitis cases were penicillin resistant and one had reduced susceptibility to cefotaxime. Among non-meningitis isolates, 96.7% were penicillin susceptible and 3.3% had intermediate susceptibility to penicillin. Overall case fatality proportion was 19%.

CONCLUSION

At this tertiary care hospital in Bangkok, IPD has disproportionately affected young children and the elderly. High rates of penicillin resistance among meningitis cases, the most severe form of IPD, underscore the need of appropriate treatment strategies and vaccine usage.

Pediatric disease burden and vaccination recommendations: understanding local differences

BACKGROUND

Diphtheria (D), tetanus (T), pertussis (P), hepatitis B (HepB), invasive Haemophilus influenzae type b (Hib) disease, and measles cause substantial global morbidity and mortality.

METHODS

This unique review highlights geographic differences in disease burden across certain countries in the African, Americas, Mediterranean, South-East Asian, and Western Pacific World Health Organization (WHO) regions, and relates this to vaccination coverage and local vaccine recommendations using the authors' countries as illustrations.

RESULTS

Substantial differences were observed in the incidence of these diseases and in vaccination coverage between the countries studied. Disease incidence often reflected inadequate surveillance, but also variable or poor vaccination coverage. Vaccination coverage against HepB was particularly low in the African and South-East Asian WHO regions; vaccination coverage against invasive Hib disease was low in these regions and in the Eastern Mediterranean and Western Pacific WHO regions. Vaccination schedules within some countries in these regions do not include, or have only recently included, vaccinations against HepB and Hib disease. The use of DTwP-HepB-Hib (diphtheria, tetanus, whole-cell pertussis, HepB, Hib) combination vaccines has now been adopted by some countries to help increase vaccination coverage.

CONCLUSIONS

Vaccination coverage and vaccination schedules vary markedly between the countries studied, often according to the resources available. DTwP-HepB-Hib combination vaccines represent a cost-effective option, with the potential to substantially reduce the burden associated with these diseases by increasing coverage and compliance.

Safety and immunogenicity of a tetravalent live-attenuated dengue vaccine in flavivirus naive children

A live-attenuated tetravalent dengue virus (DENV) vaccine candidate has been well tolerated and immunogenic in healthy, US flavivirus naive adult volunteers. We conducted a pilot, safety, and immunogenicity trial of the vaccine candidate in healthy Thai children (6-7 years of age) to prepare for its eventual evaluation in Thai infants. In an uncontrolled, open clinical trial, the investigational vaccine was administered on study Days 0 and 180 to seven volunteers residing in Bangkok without neutralizing antibodies to DENV1-4 or to Japanese encephalitis virus (JEV). Clinical and laboratory safety assessments were completed during the 30 days after each vaccine dose, and immunogenicity was determined at Day 30. In this study, the vaccine was well tolerated with no serious adverse events or alert laboratory values. One volunteer experienced fever (38.2 degrees C, < 2 days) and associated DENV4 vaccine viremia 7 days after Dose 2. One month after Dose 2, six volunteers in the per-protocol analysis exhibited a tetravalent neutralizing antibody response with DENV1-4 geometric mean titers of 55, 475, 350, and 171, respectively. Ten weeks (~75 days) after Dose 2, five of the six volunteers continued to exhibit a tetravalent neutralizing antibody profile; one volunteer's DENV4 PRNT50 titer fell below the assay cut-off (29 --> < 10); (clinicaltrials.gov NCT00384670).

The study transplacental chikungunya virus antibody kinetics, Thailand

Antibodies to chikungunya virus were detected by hemagglutination-inhibition assay in 33.6% of 2,000 infants' cord sera at delivery. Follow-up of 24 seropositive infants showed that the half-life of antibody persistence was 35.5 days. Chikungunya virus infection is common in Thailand, and routine use of diagnostic assays is needed.

Transplacental Chikungunya Virus Antibody Kinetics, Thailand

Antibodies to chikungunya virus were detected by hemagglutination-inhibition assay in 33.6% of 2,000 infants' cord sera at delivery. Follow-up of 24 seropositive infants showed that the half-life of antibody persistence was 35.5 days. Chikungunya virus infection is common in Thailand, and routine use of diagnostic assays is needed.

Dengue vaccine

Dengue is an expanding health problem. About two-fifths of the world population are at risk for acquiring dengue with 50-100 million cases of acute febrile illness yearly including about 500,000 cases of DHF/DSS. No antiviral drugs active against the flavivirus exist. Attempts to control mosquito vector has been largely unsuccessful. Vaccination remains the most hopeful preventive measure. Dengue vaccine has been in development for more than 30 years, yet none has been licensed. The fact that enhancing antibody from previous infection and high level of T cell activation during secondary infection contribute to immunopathology of DHF, the vaccine must be able to induce protective response to four dengue serotypes simultaneously. Inactivated vaccine is safe but needs a repeated booster thus, development is delayed. Tetravalent live attenuated vaccine and chimeric vaccine using yellow fever or dengue viruses as a backbone are being carried out in human trials. DNA vaccine and subunit vaccine are being carried out in animal trials.

Transplacentally transferred maternal-infant antibodies to dengue virus

Antibodies of all four dengue virus serotypes were detected by hemagglutination inhibition (HI) in 97% of 2,000 infants' cord sera at the time of delivery. In comparison with 250 mother-infant's paired sera, we found that 53% of the infants' serum HI titers were higher than those of the mother's. The mother/infant IgG subclasses 1, 2, 3, and 4 titers were 53.1/87.0, 8.4/11.7, 0.14/0.11, and 1.1/1.0 mg/dL, respectively. In 18 months of follow-up of 100 infants studied, we observed that antibody to dengue virus disappeared in 3% by two months of age, in 19% by four months of age, in 72% by six months of age, in 99% by nine months of age, and in 100% by 12 months of age, with a half-life of 41 days. We conclude that the antibodies to dengue virus disappeared in the first year of life. We suggest that the most appropriate age for vaccination with a live-attenuated dengue vaccine in an endemic area is one year of age.

Safety and immunogenicity of combined or associated administration of PRP-T vaccine with diphtheria, tetanus and pertussis vaccine in Thai children

To assess whether the combination of a diphtheria, tetanus and pertussis vaccine with a Haemophilus influenzae type b conjugate vaccine (PRP-T) had any effect on immunogenicity or safety compared with separate administration of the vaccines, 158 infants were randomized to receive the vaccines either in association or as a combination at 2, 4, and 6 months of age. A total of 126 infants (59 associated, 67 combination) completed the three-dose regimen and were analysed for immunogenicity and safety. With respect to safety, there were no significant differences between the two groups. The combination vaccine was well tolerated with adverse reactions consisting mainly of transient pain, redness, induration and some low-grade fever. With respect to immunogenicity, response to PRP-T vaccine was good. Following just two doses, all infants achieved anti-PRP titers >0.15 microg/ml, regardless of whether the vaccine was given in combination or association. Following three doses, 98.5 per cent of infants in the combination group and 98.3 per cent in the association group had titers higher than 1.0 microg/ml.

Adverse impact of infections on antibody responses to measles vaccination

Antibody titres were determined in 102 Thai infants who were vaccinated at 9-months of age during the respiratory disease season. The symptom densities of illnesses at or following vaccination, including rhinorrhea and diarrhea, were significantly lower among seroconverters, although the simple presence or absence of specific symptoms was not significantly related to seroconversions. Logistic regression indicated that neutralization test antibody titres below the median titre of 1:80 following vaccination were significantly more frequent among those with rhinorrhea when vaccinated and among those with diarrhea after vaccination. Compared with a referent group without these symptoms, titres were lower in those who had rhinorrhea when vaccinated, rhinorrhea during the first week post vaccination, and diarrhea in either of the two follow-up weeks. Illnesses concurrent or subsequent to measles vaccination adversely affected antibody responses in these study objects.

Measles vaccination of Thai infants by intranasal and subcutaneous routes: possible interference from respiratory infections

Reactogenicity and seroresponses were studied after standard doses of Edmonston-Zagreb measles vaccine were given intranasally (i.n.) and subcutaneously (s.c.) to 6-month-old Thai children. Few children given i.n. vaccine (2/31), but most (13/21) given s.c. vaccine, seroconverted. All but 1 of 51 children were seropositive after receiving vaccine s.c. at 9 months-of-age. Upper respiratory infection (URI) outbreaks with onsets in the week following vaccination occurred after each vaccination session and were equally common in all groups. URIs following i.n. vaccination at 6 months may have adversely affected response to i.n. vaccine, while URIs after s.c. vaccination at 9 months adversely affected final geometric mean antibody titers. I.n. measles vaccination does not appear to be an acceptable route for routine vaccination.

Simultaneous administration of oral rhesus-human reassortant tetravalent (RRV-TV) rotavirus vaccine and oral poliovirus vaccine (OPV) in Thai infants

Rhesus-human reassortant tetravalent (RRV-TV) oral rotavirus vaccine was given at the same time as oral poliovirus vaccine (OPV) or inactivated parenteral poliovirus vaccine (IPV) to Thai infants at 2, 4 and 6 months of age. Sera for rotavirus antibody studies were taken prior to and one month after each vaccination. After the first dose of vaccine at 2 months of age, 37% of the infants receiving rotavirus vaccine with IPV but only 10% of those receiving it with OPV showed a seroconversion by rotavirus IgA ELISA antibody test (p < 0.001). Likewise, neutralizing antibody seroconversion rates in initially seronegative subjects to rhesus rotavirus type 3 (RRV-3) after the first dose of RRV-TV vaccine were higher if the vaccine was given with IPV (74%) than if given with OPV (39%) (p = 0.0069). After the second and third doses of vaccine, the rotavirus IgA ELISA and RRV-3-neutralizing antibody response rates were not different between groups. Development of neutralizing antibodies to human rotavirus serotypes 1, 2 and 4 in the first seven months of life in vaccinees receiving rotavirus vaccine with OPV tended to occur at a lower rate than in those receiving rotavirus vaccine with IPV but the antibody levels were not significantly different at 7 months of age. Poliovirus type 2 and type 3 antibody responses were not different in infants receiving the rotavirus vaccine with OPV as compared with infants receiving only OPV. The mean poliovirus type 1 antibody level was slightly but not significantly lower at 5 and 7 months of age in infants that received both rotavirus vaccine and OPV.(ABSTRACT TRUNCATED AT 250 WORDS)

Vaccination of Thai infants with rhesus-human reassortant tetravalent oral rotavirus vaccine

In a randomized double blind placebo-controlled study, the rhesus-human reassortant tetravalent oral rotavirus vaccine (dose 4 x 10(4) plaque-forming units) was evaluated in Thai infants immunized at ages 2, 4 and 6 months. To investigate dose responses and to compare vaccine-induced and naturally acquired rotavirus immunity in the study population blood specimens were collected before and 1 month after each vaccination and at 12 months of age. No adverse reactions attributable to the vaccine were detected in the vaccinees. Sixty-three of 94 (67%) vaccine recipients showed a seroconversion in rotavirus IgA enzyme-linked immunosorbent assay antibodies after one or more doses, whereas only 15 of 93 (16%) placebo-vaccinated control children showed an IgA enzyme-linked immunosorbent assay antibody response, suggestive of natural rotavirus infection, between 2 and 7 months of age. By measuring rhesus rotavirus-neutralizing antibodies a seroconversion was detected in 49% of the vaccinees and 14% of the controls between 2 and 7 months of age. The geometric mean titers of neutralizing antibodies to human rotavirus serotypes 1, 2, 3 and 4 after the completion of vaccinations and at 12 months of age were higher in the vaccinees than in the controls. It is concluded that, even though maternally acquired rotavirus antibodies are commonly present, the rhesus-human reassortant tetravalent vaccine is immunogenic in many Thai infants ages 2 to 6 months. The immunogenicity of this vaccine is enhanced by multiple doses.

Comparison of enhanced potency inactivated poliovirus vaccine (EIPV) versus standard oral poliovirus vaccine (OPV) in Thai infants

Enhanced potency inactivated poliovirus vaccine (EIPV), combined with diphtheria-tetanus-pertussis (DTP) vaccine, was compared with oral poliovirus vaccine (OPV) regarding immunogenicity in Thai infants, vaccinated at 2, 4 and 6 months of age. EIPV induced significantly higher seroconversion rates than OPV to all 3 poliovirus types after the second and third immunization. After 3 doses of each vaccine, at 7 months of age, all infants receiving EIPV proved seropositive for poliovirus type 1, type 2 and type 3 neutralizing antibodies, whereas of those receiving OPV, 9% remained seronegative (titre < 1:4) for type 1 (p = 0.0042) and 11% for type 3 (p = 0.0013). All participating children were given an additional dose of OPV at the age of 9 months and tested again at 12 months of age. At that point, virtually all infants had poliovirus neutralizing antibodies, but the geometric mean titres to each poliovirus type were significantly higher in the vaccinees who had received EIPV. It is concluded that the greater immunogenicity of EIPV vis-à-vis 3 doses of OPV may be biologically significant for protection against poliovirus types 1 and 3 in countries where cases of poliomyelitis occur in young children. These findings warrant considering EIPV, alone or in combination with OPV, for an immunization programme in Thailand and similar countries in the future.