Influenza surveillance in southern Thailand during 2009-2010

Influenza SurveIllance In ThaIland INFLUENZA SURVEILLANCE IN SOUTHERN THAILAND DURING 2009-2010 Sawan Kanchana1, Supannakhon Kanchana1, Slinporn Prachayangprecha, Jarika Makkoch, Charas Chantrakul1 and Yong Poovorawan 1 Thung Song Hospital, Nakhon Si Thammarat; 2Center of Excellence in Clinical Virology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand Abstract. The aim of this study was to determine the epidemiology of inluenza infection among patients with inluenza-like illness by real-time RT-PCR in southern Thailand from August 2009 to January 2011. The predominant strain in Thung Song District was inluenza A. Sporadic cases of inluenza occured year round but the incidence peaked from August to November 2009 and July to November 2010. During August to November 2009, pandemic H1N1 (pH1N1) activity was observed along with a low level of seasonal inluenza co-circulation. Subsequently, seasonal inluenza (H3) activity increased and became the predominant inluenza strain, with co-circulation with pH1N1 and inluenza B during the 2010 inluenza season. Continual surveillance of inluenza activity is useful for public health planning in southern Thailand and plays a major role in future inluenza control and prevention measures. Keywords: Inluenza, surveillance, real time RT-PCR INTRODUCTION Inluenza virus infection is a yearly global health problem. Several inluenza pandemics have been reported, such as the Spanish influenza outbreak responsible for high mortality on a global scale (Reference? Year of outbreak?). An outbreak of human pandemic inluenza (pH1N1) occurred in North America in April 2009 and subsequently spread throughout the world. In June 2009, the World Health Organization (WHO) deCorrespondence: Prof Yong Poovorawan, Center of Excellence in Clinical Virology, Department of Pediatrics, Faculty of Medicine, Chulalongkorn University, Bangkok 10330, Thailand. Fax: +66 (0) 2256 4929 E-mail: [email protected] Vol 43 No. 4 July 2012 clared this new virus a pandemic strain which became an international public health problem. In August 2010, the WHO declared the pH1N1 infection to be in a post-pandemic stage with viral activity resembling seasonal inluenza with continuous circulation in the human population as a seasonal strain (WHO, 2010). pH1N1 infection rate was higher among children, unlike seasonal inluenza, with higher rate among adults aged ≥ 60 years (Chieochansin et al, 2009). Most pH1N1 clinical characteristics were similar to typical seasonal inluenza, such as cough, sore throat, fever and nasal congestion. Unless the patient had any underlying medical condition, the symptoms were not usually severe. The pH1N1 virus was detected in Mexico in April 2009 and rapidly spread 1 SouTheaST aSIan J Trop Med publIc healTh throughout the world. In Thailand, the first case was conirmed in a traveler from Mexico in May 2009, as reported by the Bureau of Emerging Infectious Diseases, Department of Disease Control, Ministry of Public Health (Department of Disease Control, 2009). Spread was facilitated by population density in certain areas, such as schools in Bangkok, the largest metropolitan area and capital city of Thailand. From this epicenter the virus spread to other regions of the country. In southern Thailand, the outbreak was detected in Thung Song District, Nakhon Si Thammarat Province on June 28, 2009. Since then the disease has persisted and become seasonal inluenza. In this study, we investigated inluenza virus activity in Thung Song District, Nakhon Si Thammarat Province, Thailand by performing real-time reverse transcription polymerase chain reaction (rRT-PCR) for inluenza virus detection among samples obtained from randomly selected patients with inluenzaFig 1–Map of Thailand showing the location of Thung Song like illness (ILI). We obtained District, Nakhon Si Thammarat Province. samples thoughout the influenza season from 2009 to 2010 to monitor inluenza activity and assist enza surveillance representing southern in prevention and control measures for Thailand. This district is 612 km south of inluenza in Thailand. Bangkok, on the Malay Peninsula. There are 2 seasons: rainy and summer (Reference?). The district has a population of MATERIALS AND METHODS 150,671 and is subdivided into 13 subdistricts (Reference?). Thung Song is an Thung Song District is located in agricultural area (rubber plantation and southwestern Nakhon Si Thammarat palm oil). Most of the residents work in Province, southern Thailand (Fig 1). It agriculture (Fig 1). was selected as the sentinel site for inlu2 Vol 43 No. 4 July 2012 Influenza SurveIllance In ThaIland Sources of specimens and ethical approval In total, 1,209 nasopharyngeal or throat swab samples were collected from approximately 15-20 patients weekly (10-15 out-patients and 5 in-patients) diagnosed with ILI, having fever, cough, sore throat, nasal congestion or rhinorrhea, from August 2009 to January 2011. We examined 519 males and 690 females ranging in age from 13 days to 90 years (mean age 35 years). The specimens were collected in viral transport medium containing penicillin G 2 x 106 U/l and streptomycin (200 mg/l) kept on ice and sent to the Center for Excellence in Clinical Virology within 48 hours of obtaining the specimen. The collected samples were screened for seasonal inluenza A, inluenza B and p H1N1. The study was approved by the Ethics Committee of Thung Song Hospital, Nakhon Si Thammarat and the Faculty of Medicine, Chulalongkorn University. All the subjects or their parents were informed of the purpose of the surveillance and gave written informed consent prior to participation. Detection of inluenza viruses by realtime RT-PCR RNA was extracted from each sample using a Viral Nucleic Acid Extraction Kit (RBC Bioscience, Taiwan) according to the manufacturer’s protocol and subsequently transcribed into cDNA. The reaction mixtures for ampliication, including the primers, speciic TaqMan probes and thermal proiles have been described previously (Kendal et al, 1982; Suwannakarn et al, 2008; WHO, 2009). RTPCR was performed using the SuperScript III Platinum One-Step RT-PCR system (Invitrogen, Foster City, CA) in a RotorGene 3000 (Corbett Research, New South Wales, Australia). Vol 43 No. 4 July 2012 RESULTS During July 2009 - January 2011, there was sporadic inluenza activity in Thung Song. Of 1,209 samples collected, 214 (18%) tested positive for inluenza viruses with inluenza A viruses being the most common subtype identiied. Of the positive samples, 50% (108/214) were positive for pH1N1, 44% (95/214) were positive for seasonal inluenza H3 and 5% (11/214) were positive for inluenza B virus. The mean age of the positive cases was 37 years. The irst inluenza peak occurred during August to November 2009, the majority being pH1N1. Additional cases were reported during January and March 2010 with seasonal inluenza (H3) and pH1N1 circulating low levels during January and February, 2010. After a decrease in inluenza circulation during April to June 2010, there was an increase in pH1N1 along with low levels of inluenza B virus. During September to October 2010, inluenza peaked again with most cases positive for seasonal inluenza (H3), this peak started to decline in November 2010 (Fig 2). DISCUSSION Since the pH1N1 outbreak in Thailand in June 2009, there have been 3 waves of inluenza activity dominated by pH1N1. The irst pH1N1 peak was between August and October 2009 with sporadic cases of inluenza infection occurring during December 2009 to June 2010. In July 2010, the inluenza positive cases began to increase and by October 2010, influenza activity had started to decrease. This study shows the activity of inluenza viruses from August 2009 to January 2011 with inluenza A viruses predominating in the Thung Song area. 3 SouTheaST aSIan J Trop Med publIc healTh Total samples Negative Positive for pH1N1 120 Positive for seasonal flu (H3) 50 45 40 Number of samples Positive for influenza B 100 % positive for influenza A % positive for pH1N1 80 35 30 25 60 40 20 15 10 20 5 Percent positive for influenza 140 peaks, from December to February, during the cooler months, and from July to October, during the rainy season in this region (Prachayangprecha et al, 2010). In Sa Kaeo Province, eastern Thailand, inluenza is at its highest activity from June to August (Simmerman et al, 2007). Seasonal inluenza activity is associated with many factors, such Month as weather that can afFig 2–Number of inluenza cases in Thung Song District, Nakhon fect the transmission of Si Thammarat, Thailand. the virus (Lowen et al, 2007). The higher numThe strain circulating during the outbreak ber of inluenza positive samples might in August to October 2009 was pH1N1 have been due to the weather. Cold, dry resulting in a large number of cases, since weather facilitates inluenza virus transthe majority of the population had no antimission as it helps stabilize the particle bodies against pH1N1 since the virus was and increases spreading distance (Linde the result of a triple re-assortment among et al, 2009). These factors are inadequate human, avian and swine inluenza viruses to explain the inluenza activity pattern (Trifonov et al, 2009). since transmission patterns differed by region (Soebiyanto et al, 2010). In this study, The pH1N1 virus is still circulating inluenza activity increased between July in Thung Song District but at lower levels and November, which is the rainy season than during 2009 - 2010, most likely due in southern Thailand. This is considered to waxing immunity in the population. unfavorable weather for inluenza virusOnly a small number of inluenza vies. Other factors could be associated with ruses were detected in Thung Song during inluenza transmission, such as El Nino November 2009 to June 2010, but the activor seasonal luctuations in host immune ity increased between July and December response or social behavior (Viboud et al, 2010, which is the rainy season in southern 2004; Truscott et al, 2009). Thailand. The rainy season in this part The activity of speciic inluenza viof Thailand persists longer than in the ruses has been shown to vary by region. rest of the country. Inluenza activity has Seasonal inluenza (H3) was predominant shown various season related patterns in the Thung Song area, pH1N1 was more in different areas of Thailand. In Chum common in Chum Phae District, Khon Phae District, northeastern Thailand, apKaen Province with a peak activity during proximately 449 km Northeast of BangJuly 2009 to September 2010; in October kok, inluenza activity has two distinct 0 Au g 0 Se 9 p 09 O ct 0 No 9 v 0 De 9 c 09 Ja n 1 Fe 0 b 10 M ar 10 Ap r1 M 0 ay 10 Ju n 10 Ju l1 Au 0 g 1 Se 0 p 10 O ct 1 No 0 v 10 De c 10 Ja n 11 0 4 Vol 43 No. 4 July 2012 Influenza SurveIllance In ThaIland 2010 seasonal inluenza (H3) and inluenza B virus activity started to increase (Prachayangprecha et al, 2010). This study investigated influenza activity in Thung Song area, focusing on inluenza strains currently circulating. ACKNOWLEDGEMENTS We would like to express our gratitude to the Thai Health Promotion Foundation, Center for Excellence in Clinical Virology, Chulalongkorn University, CU Centenary Academic Development Project, King Chulalongkorn Memorial Hospital, Graduate School of Biomedical Science, Chulalongkorn University, the RGJ PhD program, the Thailand Research Fund (RGJ and DPG5480002), the Ratchadaphiseksomphot fund and the National Research University Project for Thailand, Commission of Higher Education (HR1155A) for their generous support. We also would like to thank the staff and nurses of Thung Song Hospital, Nakhon Si Thammarat Province, Thailand for collecting the clinical data, specimens and the advisory members for their assistance. Finally we would like to thank Ms Petra Hirsch for reviewing the manuscript. REFERENCES Chieochansin T, Makkoch J, Suwannakarn K, Payungporn S, Poovorawan Y. Novel H1N1 2009 inluenza virus infection in Bankok, Thailand: effects of school closures. 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