Sopon Iamsirithaworn

Serological Response to the 2009 Pandemic Influenza A (H1N1) Virus for Disease Diagnosis and Estimating the Infection Rate in Thai Population

Background Individuals infected with the 2009 pandemic virus A(H1N1) developed serological response which can be measured by hemagglutination-inhibition (HI) and microneutralization (microNT) assays. Methodology/Principal Findings MicroNT and HI assays for specific antibody to the 2009 pandemic virus were conducted in serum samples collected at the end of the first epidemic wave from various groups of Thai people: laboratory confirmed cases, blood donors and health care workers (HCW) in Bangkok and neighboring province, general population in the North and the South, as well as archival sera collected at pre- and post-vaccination from vaccinees who received influenza vaccine of the 2006 season. This study demonstrated that goose erythrocytes yielded comparable HI antibody titer as compared to turkey erythrocytes. In contrast to the standard protocol, our investigation found out the necessity to eliminate nonspecific inhibitor present in the test sera by receptor destroying enzyme (RDE) prior to performing microNT assay. The investigation in pre-pandemic serum samples showed that HI antibody was more specific to the 2009 pandemic virus than NT antibody. Based on data from pre-pandemic sera together with those from the laboratory confirmed cases, HI antibody titers ≥40 for adults and ≥20 for children could be used as the cut-off level to differentiate between the individuals with or without past infection by the 2009 pandemic virus. Conclusions/Significance Based on the cut-off criteria, the infection rates of 7 and 12.8% were estimated in blood donors and HCW, respectively after the first wave of the 2009 influenza pandemic. Among general population, the infection rate of 58.6% was found in children versus 3.1% in adults.

Modeling seasonal leptospirosis transmission and its association with rainfall and temperature in Thailand using time-series and ARIMAX analyses

OBJECTIVE To study the number of leptospirosis cases in relations to the seasonal pattern, and its association with climate factors. METHODS Time series analysis was used to study the time variations in the number of leptospirosis cases. The Autoregressive Integrated Moving Average (ARIMA) model was used in data curve fitting and predicting the next leptospirosis cases. RESULTS We found that the amount of rainfall was correlated to leptospirosis cases in both regions of interest, namely the northern and northeastern region of Thailand, while the temperature played a role in the northeastern region only. The use of multivariate ARIMA (ARIMAX) model showed that factoring in rainfall (with an 8 months lag) yields the best model for the northern region while the model, which factors in rainfall (with a 10 months lag) and temperature (with an 8 months lag) was the best for the northeastern region. CONCLUSION The models are able to show the trend in leptospirosis cases and closely fit the recorded data in both regions. The models can also be used to predict the next seasonal peak quite accurately.

Modeling Seasonal Influenza Transmission and Its Association with Climate Factors in Thailand Using Time-Series and ARIMAX Analyses

Influenza is a worldwide respiratory infectious disease that easily spreads from one person to another. Previous research has found that the influenza transmission process is often associated with climate variables. In this study, we used autocorrelation and partial autocorrelation plots to determine the appropriate autoregressive integrated moving average (ARIMA) model for influenza transmission in the central and southern regions of Thailand. The relationships between reported influenza cases and the climate data, such as the amount of rainfall, average temperature, average maximum relative humidity, average minimum relative humidity, and average relative humidity, were evaluated using cross-correlation function. Based on the available data of suspected influenza cases and climate variables, the most appropriate ARIMA(X) model for each region was obtained. We found that the average temperature correlated with influenza cases in both central and southern regions, but average minimum relative humidity played an important role only in the southern region. The ARIMAX model that includes the average temperature with a 4-month lag and the minimum relative humidity with a 2-month lag is the appropriate model for the central region, whereas including the minimum relative humidity with a 4-month lag results in the best model for the southern region.

A modeling study of school closure to reduce influenza transmission: A case study of an influenza A (H1N1) outbreak in a private Thai school

Abstract The A/H1N1 influenza pandemic has been in the spotlight since the virus was first detected in Mexico in early 2009. To prevent the repetition of the 1918 influenza pandemic, the global response to this pandemic has been strong. In Thailand and in many other countries, schools have been a major source of outbreaks, which then spreads to the general population. Understanding the dynamics of school outbreaks and the impact of disease intervention in school settings is crucial for the effective mitigation of a pandemic. Using data from outbreaks in School G, a private school in Bangkok where detailed epidemiological data were collected, we estimated the basic reproduction number ( R 0 ) to be 3.58 [95% confidence interval: 2.88 to 4.28]. We then modeled outbreaks in school settings with Susceptible-Exposed-Infectious-Recovered (SEIR) equations and tested various interventions such as school closure and student screenings. We found that closing the school on the date with the peak number of daily incidences usually appeared to be effective in preventing further outbreaks. However, if the school was closed too early, subsequent cases would appear after reopening. With no intervention, the number of total cases reaches 83%. Individual student screenings appeared to reduce the number of total cases by up to 40%. In a situation in which the widespread outbreak of a mild disease is unavoidable and in which the goal is to slowly reach sufficient herd immunity while minimizing the number of cases, closing the school at the predicted date with the peak number of daily incidences and screening for respiratory symptoms appear to be the most appropriate intervention methods.

Adoption of One Health in Thailand's National strategic plan for emerging infectious diseases.

This study illustrates how Thailand adopted the One Health concept. Massive socio-economic and health consequences of emerging infectious diseases, especially Avian Influenza in 2004, led to recognition of the importance of and need for One Health. Based on collaboration and consultative meetings between the national actors and international development partners, Thailand adopted One Health to drive more effective containment of Emerging Infectious Diseases. This concept gained support from the non-governmental and civil society organizations through processes of the National Health Assembly. In 2012, a Cabinet resolution endorsed a National Strategic Plan for Emerging Infectious Diseases (2013–2016), in which One Health appeared as a core principle. Collaboration among multi-disciplinary groups of professionals, particularly epidemiologists trained in Field Epidemiology Training Programs (FETP), including FETP, FETP-veterinarian, and FETP-wildlife veterinarians, promoted implementation of One Health.

Cross-reactive antibodies against H7N9 and H5N1 avian influenza viruses in Thai population.

BACKGROUD Avian influenza H5N1 and H7N9 viruses have jumped across species from avian to humans and become a threat to public health. Not much is known about pre-existing cross-reactive antibodies against these avian viruses in human population. OBJECTIVE To determine the prevalence of cross-reactive anti-HA and anti-NA antibodies to avian influenza H5N1 and H7N9 viruses in Thai population. METHOD Archival serum samples from 100 blood donors and 21 patients infected with 2009 pandemic influenza A (H1N1) (pdmH1N1) virus were investigated by hemagglutination-inhibition (HAI) and neuraminidase-inhibition (NAI) assays for anti-HA and anti-NA antibodies, respectively. The test antigens comprised 2 human viruses (pdmH1N1 and H3N2 viruses), and 6 reassortant viruses carrying HA and NA genes of avian H5N1 or H7N9 virus generated by reverse genetics. RESULTS HAI antibody titers ≥ 10 were found in 58, 89, 0 and 15% of blood donors as tested against pdmH1N1, H3N2, H5N1 and H7N9 viruses, respectively. On the other hand, NAI antibodies were detected in 98, 94, 73 and 53% of blood donors when reverse genetic-derived viruses harboring NA gene from pdmH1N1, H3N2, H5N1 or H7N9 virus were used as the test antigens. Moreover, 66.7% of pdmH1N1 patients who had > 4 fold increase in HAI antibody titers in paired sera developed > 4 fold increase in NAI antibody titers. CONCLUSIONS Anti-NA antibody has broader reactivity than anti-HA antibody, therefore, it can be a supplement to anti-HA antibody in the prevention against novel influenza viruses.

Kinetics, longevity and cross-reactivity of anti-neuraminidase antibody after natural infection with influenza A viruses

ABSTRACT The kinetics, longevity, and breadth of antibodies to influenza virus neuraminidase (NA) in archival, sequential serum/plasma samples from influenza A virus (IAV) H5N1 infection survivors and from patients infected with the 2009 pandemic IAV (H1N1) virus were determined using an enzyme-linked lectin-based assay. The reverse-genetics-derived H4N1 viruses harboring a hemagglutinin (HA) segment from A/duck/Shan Tou/461/2000 (H4N9) and an NA segment derived from either IAV H5N1 clade 1, IAV H5N1 clade 2.3.4, the 2009 pandemic IAV (H1N1) (H1N1pdm), or A/Puerto Rico/8/1934 (H1N1) virus were used as the test antigens. These serum/plasma samples were also investigated by microneutralization (MN) and/or hemagglutination inhibition (HI) assays. Neuraminidase-inhibiting (NI) antibodies against N1 NA of both homologous and heterologous viruses were observed in H5N1 survivors and H1N1pdm patients. H5N1 survivors who were never exposed to H1N1pdm virus developed NI antibodies to H1N1pdm NA. Seroconversion of NI antibodies was observed in 65% of the H1N1pdm patients at day 7 after disease onset, but an increase in titer was not observed in serum samples obtained late in infection. On the other hand, an increase in seroconversion rate with the HI assay was observed in the follow-up series of sera obtained on days 7, 14, 28, and 90 after infection. The study also showed that NI antibodies are broadly reactive, while MN and HI antibodies are more strain specific.