Establishing seasonal and alert influenza thresholds in Cambodia using the WHO method: implications for effective utilization of influenza surveillance in the tropics and subtropics
DOI:
https://doi.org/10.5365/wpsar.2017.8.1.002Abstract
Objective: To establish seasonal and alert thresholds and transmission intensity categories for influenza to provide timely triggers for preventive measures or upscaling control measures in Cambodia.
Methods: Using Cambodia’s influenza-like illness (ILI) and laboratory-confirmed influenza surveillance data from 2009 to 2015, three parameters were assessed to monitor influenza activity: the proportion of ILI patients among all outpatients, proportion of ILI samples positive for influenza and the product of the two. With these parameters, four threshold levels (seasonal, moderate, high and alert) were established and transmission intensity was categorized based on a World Health Organization alignment method. Parameters were compared against their respective thresholds.
Results: Distinct seasonality was observed using the two parameters that incorporated laboratory data. Thresholds established using the composite parameter, combining syndromic and laboratory data, had the least number of false alarms in declaring season onset and were most useful in monitoring intensity. Unlike in temperate regions, the syndromic parameter was less useful in monitoring influenza activity or for setting thresholds.
Conclusion: Influenza thresholds based on appropriate parameters have the potential to provide timely triggers for public health measures in a tropical country where monitoring and assessing influenza activity has been challenging. Based on these findings, the Ministry of Health plans to raise general awareness regarding influenza among the medical community and the general public. Our findings have important implications for countries in the tropics/subtropics and in resource-limited settings, and categorized transmission intensity can be used to assess severity of potential pandemic influenza as well as seasonal influenza.
References
Fact sheet on Influenza (seasonal) [Internet]. Geneva: World Health Organization; 2014. Available from: http://www.who.int/mediacentre/factsheets/fs211/en/ [accessed 31 December 2016]
Molinari N-AM, Ortega-Sanchez IR, Messonnier ML, Thompson WW, Wortley PM, Weintraub E, et al. The annual impact of seasonal influenza in the US: measuring disease burden and costs. Vaccine. 2007 Jun 28;25(27):5086–96.
Homaira N, Luby SP, Alamgir ASM, Islam K, Paul R, Abedin J, et al. Influenza-associated mortality in 2009 in four sentinel sites in Bangladesh. Bull World Health Organ. 2012 Apr 1;90(4):272–8.
Nair H, Brooks WA, Katz M, Roca A, Berkley JA, Madhi SA, et al. Global burden of respiratory infections due to seasonal influenza in young children: a systematic review and meta-analysis. Lancet. 2011 Dec 3;378(9807):1917–30.
Simmerman JM, Chittaganpitch M, Levy J, Chantra S, Maloney S, Uyeki T, et al. Incidence, seasonality and mortality associated with influenza pneumonia in Thailand: 2005-2008. PLoS ONE. 2009;4(11):e7776.
Simmerman JM, Uyeki TM. The burden of influenza in East and South-East Asia: a review of the English language literature. Influenza Other Respir Viruses. 2008 May;2(3):81–92.
Viboud C, Alonso WJ, Simonsen L. Influenza in tropical regions. PLoS Med. 2006 Apr;3(4):e89.
Yang L, Ma S, Chen PY, He JF, Chan KP, Chow A, et al. Influenza associated mortality in the subtropics and tropics: results from three Asian cities. Vaccine. 2011 Nov 8;29(48):8909–14.
Azziz Baumgartner E, Dao CN, Nasreen S, Bhuiyan MU, Mah-E-Muneer S, Mamun A Al, et al. Seasonality, timing, and climate drivers of influenza activity worldwide. J Infect Dis. 2012 Sep 15;206(6):838–46.
Saha S, Chadha M, Mamun A Al, Rahman M, Sturm-Ramirez K, Chittaganpitch M, et al. Influenza seasonality and vaccination timing in tropical and subtropical areas of southern and south-eastern Asia. Bull World Health Organ. 2014 May 1;92(5):318–30.
Meeting Report for WHO Expert Group Meeting on Seasonal Influenza Vaccine Composition for Tropics and Subtropics. Geneva: World Health Organization. Available from: http://apps.who.int/iris/handle/10665/183954 [accessed 31 December 2016]
Mardy S, Ly S, Heng S, Vong S, Huch C, Nora C, et al. Influenza activity in Cambodia during 2006-2008. BMC Infect Dis. 2009;9:168.
Horm SV, Mardy S, Rith S, Ly S, Heng S, Vong S, et al. Epidemiological and virological characteristics of influenza viruses circulating in Cambodia from 2009 to 2011. PLoS ONE. 2014;9(10):e110713.
Vega T, Lozano JE, Meerhoff T, Snacken R, Mott J, Ortiz de Lejarazu R, et al. Influenza surveillance in Europe: establishing epidemic thresholds by the moving epidemic method. Influenza Other Respir Viruses. 2013 Jul;7(4):546–58.
Vega T, Lozano JE, Meerhoff T, Snacken R, Beauté J, Jorgensen P, et al. Influenza surveillance in Europe: comparing intensity levels calculated using the moving epidemic method. Influenza Other Respir Viruses. 2015 Sep;9(5):234–46.
Overview of Influenza Surveillance in the United States [Internet] Atlanta: The United States Centers for Disease Control and Prevention; 2015. Available from: http://www.cdc.gov/flu/weekly/overview.htm [accessed 31 December 2016]
WHO Global Epidemiological Surveillance Standards for Influenza. Geneva: World Health Organization; 2014. Available from: http://www.who.int/influenza/resources/documents/influenza_surveillance_manual/en/ [accessed 31 December 2016]
Strengthening Response to Pandemics and Other Public-Health Emergencies. Geneva: World Health Organization; 2011. Available from: http://apps.who.int/gb/ebwha/pdf_files/WHA64/A64_10-en.pdf [accessed 31 December 2016]
Tay EL, Grant K, Kirk M, Mounts A, Kelly H. Exploring a proposed WHO method to determine thresholds for seasonal influenza surveillance. PLoS ONE. 2013;8(10):e77244.
Beigel JH, Farrar J, Han AM, Hayden FG, Hyer R, de Jong MD, et al. Avian influenza A (H5N1) infection in humans. N Engl J Med. 2005 Sep 29;353(13):1374–85.
Azziz-Baumgartner E, Alamgir ASM, Rahman M, Homaira N, Sohel BM, Sharker MAY, et al. Incidence of influenza-like illness and severe acute respiratory infection during three influenza seasons in Bangladesh, 2008-2010. Bull World Health Organ. 2012 Jan 1;90(1):12–9.
Chadha MS, Broor S, Gunasekaran P, Potdar VA, Krishnan A, Chawla-Sarkar M, et al. Multisite virological influenza surveillance in India: 2004-2008. Influenza Other Respir Viruses. 2012 May;6(3):196–203.
Chittaganpitch M, Supawat K, Olsen SJ, Waicharoen S, Patthamadilok S, Yingyong T, et al. Influenza viruses in Thailand: 7 years of sentinel surveillance data, 2004-2010. Influenza Other Respir Viruses. 2012 Jul;6(4):276–83.
Influenza and Other Respiratory Viruses Situation Report [Internet]. Washington D.C.: Regional Office for the Americas of the World Health Organization. Available from: http://www.paho.org/hq/index.php?option=com_content&view=article&id=3352&Itemid=2469&lang=en [accessed 31 December 2016]
Khamphaphongphane B, Ketmayoon P, Lewis HC, Phonekeo D, Sisouk T, Xayadeth S, et al. Epidemiological and virological characteristics of seasonal and pandemic influenza in Lao PDR, 2008-2010. Influenza Other Respir Viruses. 2013 May;7(3):304–11.
Kosasih H, Roselinda, Nurhayati, Klimov A, Xiyan X, Lindstrom S, et al. Surveillance of influenza in Indonesia, 2003–2007. Influenza Other Respir Viruses. 2013 May;7(3):312–20.
Members of the Western Pacific Region Global Influenza Surveillance and Response System. Epidemiological and Virological Characteristics of Influenza in the Western Pacific Region of the World Health Organization, 2006–2010. PLoS ONE [Internet]. 2012 May 29;7(5):e37568. Available from: http://dx.doi.org/10.1371/journal.pone.0037568 [accessed 31 December 2016]
Bi-weekly Influenza Situation Update [Internet]. Manila: World Health Organization. Available from: http://www.wpro.who.int/emerging_diseases/Influenza/en/ [accessed 31 December 2016]
Flu Express [Internet]. Hong Kong: Department of Health. Available from: http://www.chp.gov.hk/en/guideline1_year/29/134/441/304.html [accessed 31 December 2016]
Pacific Syndromic Surveillance [Internet]. New Caledonia: Pacific Public Health Surveillance Network. Available from: http://www.spc.int/phs/PPHSN/Surveillance/Syndromic.htm [accessed 31 December 2016]
Weekly Report [Internet]. China: Chinese National Influenza Center. Available from: http://www.chinaivdc.cn/cnic/en/Surveillance/WeeklyReport/ [accessed 31 December 2016]
Steffen C, Debellut F, Gessner BD, Kasolo FC, Yahaya AA, Ayebazibwe N, et al. Improving influenza surveillance in sub-Saharan Africa. Bull World Health Organ. 2012 Apr 1;90(4):301–5.
Radin JM, Katz MA, Tempia S, Talla Nzussouo N, Davis R, Duque J, et al. Influenza surveillance in 15 countries in Africa, 2006-2010. J Infect Dis. 2012 Dec 15;206(Suppl 1):S14–21.
