Infectious causes of encephalitis and meningoencephalitis in Thailand, 2003-2005.

Acute encephalitis is a severe neurologic syndrome. Determining etiology from among ≈100 possible agents is difficult. To identify infectious etiologies of encephalitis in Thailand, we conducted surveillance in 7 hospitals during July 2003-August 2005 and selected patients with acute onset of brain dysfunction with fever or hypothermia and with abnormalities seen on neuroimages or electroencephalograms or with cerebrospinal fluid pleocytosis. Blood and cerebrospinal fluid were tested for >30 pathogens. Among 149 case-patients, median age was 12 (range 0-83) years, 84 (56%) were male, and 15 (10%) died. Etiology was confirmed or probable for 54 (36%) and possible or unknown for 95 (64%). Among confirmed or probable etiologies, the leading pathogens were Japanese encephalitis virus, enteroviruses, and Orientia tsutsugamushi. No samples were positive for chikungunya, Nipah, or West Nile viruses; Bartonella henselae; or malaria parasites. Although a broad range of infectious agents was identified, the etiology of most cases remains unknown.

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

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.

Strengthening public health laboratory capacity in Thailand for International Health Regulations (IHR) (2005).

INTRODUCTION: Thailand conducted a national laboratory assessment of core capacities related to the International Health Regulations (IHR) (2005), and thereby established a baseline to measure future progress. The assessment was limited to public laboratories found within the Thai Bureau of Quality and Safety of Food, National Institute of Health and regional medical science centres. METHODS: The World Health Organization (WHO) laboratory assessment tool was adapted to Thailand through a participatory approach. This adapted version employed a specific scoring matrix and comprised 16 modules with a quantitative output. Two teams jointly performed the on-site assessments in December 2010 over a two-week period, in 17 public health laboratories in Thailand. The assessment focused on the capacity to identify and accurately detect pathogens mentioned in Annex 2 of the IHR (2005) in a timely manner, as well as other public health priority pathogens for Thailand. RESULTS: Performance of quality management, budget and finance, data management and communications was considered strong (>90%); premises quality, specimen collection, biosafety, public health functions, supplies management and equipment availability were judged as very good (>70% but ≤90%); while microbiological capacity, staffing, training and supervision, and information technology needed improvement (>60% but ≤70%). CONCLUSIONS: This assessment is a major step in Thailand towards development of an optimized and standardized national laboratory network for the detection and reporting of infectious disease that would be compliant with IHR (2005). The participatory strategy employed to adapt an international tool to the Thai context can also serve as a model for use by other countries in the Region. The participatory approach probably ensured better quality and ownership of the results, while providing critical information to help decision-makers determine where best to invest finite resources.

Optimization of one-step real-time reverse transcription-polymerase chain reaction assays for norovirus detection and molecular epidemiology of noroviruses in Thailand.

Noroviruses (NoVs) are an important human pathogen associated with acute viral gastroenteritis worldwide. NoVs display a significant amount of genetic heterogeneity, making it difficult to develop comprehensive detection assays. In this study, primer sets and probes were designed for a TaqMan(®)-based real-time reverse transcription-polymerase chain reaction (RT-PCR) for norovirus detection purposes. The assay was optimized and utilized as a multiplex real-time RT-PCR assay for genogroup I (GI) detection, and a singleplex real-time RT-PCR assay for genogroup II (GII) detection. The assays showed high specificity for NoV detection and no cross-reactivity was observed between GI and GII. The detection limit of the assay was as low as 10 and 50 RNA copies per reaction for GI and GII, respectively. The optimized protocol was employed to assess the presence of NoV strains in clinical samples collected throughout Thailand during December 2005 to November 2006. The percentage of NoV infections among children with acute gastroenteritis (case) was 23.8% (119/500) and for children without acute gastroenteritis (control) it was 6.8% (30/441). The frequency of NoV infections varied geographically, with the highest frequency observed in the central region and the lowest frequency in the northern region (P>0.0001). Of the 149 positive case and control specimens, GII was found to be the predominant genogroup (98.6%). Partial capsid sequences were successfully obtained from 67 NoV-positive specimens and a phylogenetic analysis was performed to genotype the viral strains. GII.4 was the most common genotype detected.

Prospective study of avian influenza virus infections among rural Thai villagers.

BACKGROUND: In 2008, 800 rural Thai adults living within Kamphaeng Phet Province were enrolled in a prospective cohort study of zoonotic influenza transmission. Serological analyses of enrollment sera suggested this cohort had experienced subclinical avian influenza virus (AIV) infections with H9N2 and H5N1 viruses. METHODS: After enrollment, participants were contacted weekly for 24 mos for acute influenza-like illnesses (ILI). Cohort members confirmed to have influenza A infections were enrolled with their household contacts in a family transmission study involving paired sera and respiratory swab collections. Cohort members also provided sera at 12 and 24 months after enrollment. Serologic and real-time RT-PCR assays were performed against avian, swine, and human influenza viruses. RESULTS: Over the 2 yrs of follow-up, 81 ILI investigations in the cohort were conducted; 31 (38%) were identified as influenza A infections by qRT-PCR. Eighty-three household contacts were enrolled; 12 (14%) reported ILIs, and 11 (92%) of those were identified as influenza infections. A number of subjects were found to have slightly elevated antibodies against avian-like A/Hong Kong/1073/1999(H9N2) virus: 21 subjects (2.7%) at 12-months and 40 subjects (5.1%) at 24-months. Among these, two largely asymptomatic acute infections with H9N2 virus were detected by >4-fold increases in annual serologic titers (final titers 1:80). While controlling for age and influenza vaccine receipt, moderate poultry exposure was significantly associated with elevated H9N2 titers (adjusted OR = 2.3; 95% CI, 1.04-5.2) at the 24-month encounter. One subject had an elevated titer (1:20) against H5N1 during follow-up. CONCLUSIONS: From 2008-10, evidence for AIV infections was sparse among this rural population. Subclinical H9N2 AIV infections likely occurred, but serological results were confounded by antibody cross-reactions. There is a critical need for improved serological diagnostics to more accurately detect subclinical AIV infections in humans.

Influenza viruses in Thailand: 7 years of sentinel surveillance data, 2004-2010.

BACKGROUND: The re-emergence of avian influenza A (H5N1) in 2004 and the pandemic of influenza A (H1N1) in 2009 highlight the need for routine surveillance systems to monitor influenza viruses, particularly in Southeast Asia where H5N1 is endemic in poultry. In 2004, the Thai National Institute of Health, in collaboration with the U.S. Centers for Disease Control and Prevention, established influenza sentinel surveillance throughout Thailand. OBJECTIVES: To review routine epidemiologic and virologic surveillance for influenza viruses for public health action. METHODS: Throat swabs from persons with influenza-like illness and severe acute respiratory illness were collected at 11 sentinel sites during 2004-2010. Influenza viruses were identified using the standard protocol for polymerase chain reaction. Viruses were cultured and identified by immunofluorescence assay; strains were identified by hemagglutination inhibition assay. Data were analyzed to describe frequency, seasonality, and distribution of circulating strains. RESULTS: Of the 19,457 throat swabs, 3967 (20%) were positive for influenza viruses: 2663 (67%) were influenza A and able to be subtyped [21% H1N1, 25% H3N2, 21% pandemic (pdm) H1N1] and 1304 (33%) were influenza B. During 2009-2010, the surveillance system detected three waves of pdm H1N1. Influenza annually presents two peaks, a major peak during the rainy season (June-August) and a minor peak in winter (October-February). CONCLUSIONS: These data suggest that March-April may be the most appropriate months for seasonal influenza vaccination in Thailand. This system provides a robust profile of the epidemiology of influenza viruses in Thailand and has proven useful for public health planning.

Evidence for subclinical avian influenza virus infections among rural Thai villagers.

BACKGROUND: Regions of Thailand reported sporadic outbreaks of A/H5N1 highly pathogenic avian influenza (HPAI) among poultry between 2004 and 2008. Kamphaeng Phet Province, in north-central Thailand had over 50 HPAI poultry outbreaks in 2004 alone, and 1 confirmed and 2 likely other human HPAI infections between 2004 and 2006. METHODS: In 2008, we enrolled a cohort of 800 rural Thai adults living in 8 sites within Kamphaeng Phet Province in a prospective study of zoonotic influenza transmission. We studied participants' sera with serologic assays against 16 avian, 2 swine, and 8 human influenza viruses. RESULTS: Among participants (mean age 49.6 years and 58% female) 65% reported lifetime poultry exposure of at least 30 consecutive minutes. Enrollees had elevated antibodies by microneutralization assay against 3 avian viruses: A/Hong Kong/1073/1999(H9N2), A/Thailand/676/2005(H5N1), and A/Thailand/384/2006(H5N1). Bivariate risk factor modeling demonstrated that male gender, lack of an indoor water source, and tobacco use were associated with elevated titers against avian H9N2 virus. Multivariate modeling suggested that increasing age, lack of an indoor water source, and chronic breathing problems were associated with infection with 1 or both HPAI H5N1 strains. Poultry exposure was not associated with positive serologic findings. CONCLUSIONS: These data suggest that people in rural central Thailand may have experienced subclinical avian influenza infections as a result of yet unidentified environmental exposures. Lack of an indoor water source may play a role in transmission.

Japanese encephalitis virus remains an important cause of encephalitis in Thailand.

BACKGROUND: Japanese encephalitis virus (JEV) is endemic in Thailand and prevention strategies include vaccination, vector control, and health education. METHODS: Between July 2003 and August 2005, we conducted hospital-based surveillance for encephalitis at seven hospitals in Bangkok and Hat Yai. Serum and cerebrospinal (CSF) specimens were tested for evidence of recent JEV infection by immunoglobulin M (IgM) enzyme-linked immunosorbent assay (ELISA) and a plaque reduction neutralization test (PRNT). RESULTS: Of the 147 patients enrolled and tested, 24 (16%) had evidence of acute flavivirus infection: 22 (15%) with JEV and two (1%) with dengue virus. Of the 22 Japanese encephalitis (JE) cases, 10 (46%) were aged ≤ 15 years. The median length of hospital stay was 13 days; one 13-year-old child died. Ten percent of encephalitis patients enrolled in Bangkok hospitals were found to have JEV infection compared to 28% of patients enrolled in hospitals in southern Thailand (p < 0.01). Four (40%) of the 10 children with JE were reported as being vaccinated. CONCLUSIONS: JEV remains an important cause of encephalitis among hospitalized patients in Thailand. The high proportion of JE among encephalitis cases is concerning and additional public health prevention efforts or expanded vaccination may be needed.

Antimicrobial resistance surveillance of Vibrio cholerae in Thailand from 2000 to 2004.

OBJECTIVE: To study the trends of antimicrobial resistance pattern of Vibrio cholerae in Thailand between 2000 and 2004. MATERIAL AND METHOD: All isolates of Vibrio cholerae from 28 hospitals across Thailand between 2000 and 2004 were tested for their susceptibility to ampicillin, chloramphenicol, norfloxacin, tetracycline and trimethoprim/sulfamethoxazole by the disk diffusion method (Kirby Bauer). The relevant data were collected and analyzed by the WHONET software program supported by the World Health Organization (WHO). RESULTS: V. cholerae O1, serotype Inaba was much more common than serotype Ogawa. The most frequent type of clinical specimens that V. cholerae isolated was the stool. There was no trend of increasing resistance of all V. cholerae both O1 and non O1. Over all average rates of tetracycline resistance of V. cholerae O1, Inaba and Ogawa were 0.9% and 16.3% respectively and trimethoprim/sulfamethoxazole resistance were 0.4% and 60.5% respectively. The strains were not resistant to norfloxacin. CONCLUSION: In Thailand, V. cholerae O1 were still susceptible to tetracycline and norfloxacin which were the most frequently antimicrobial used for the treatment of cholera. The trend of increasing resistance during the study period was not detected.