Fourteen countries responded to the survey. ILI case definitions, surveillance approach and intensity varied across countries, as did the number of years of reporting.
The definition of ILI varied across sentinel surveillance schemes within countries and areas and across countries (). Seven countries and one area reported applying the WHO definition: a person with sudden onset of fever >38°C and cough or sore throat in the absence of other diagnoses. Other definitions applied by reporting countries used broader clinical symptoms, separated definitions for different age groups or limited the timeframe for onset of different symptoms.
Surveillance and ILI case definitions in Western Pacific Region countries, 2006–2010.
All 14 countries reported using a sentinel site approach for influenza surveillance (). The number and type of sites varied widely across countries and areas, and some countries incrementally increased the number of surveillance sites during 2006–2010, especially in response to the A(H1N1)pdm09 pandemic. Confirmatory testing of a proportion of ILI cases was conducted through the surveillance systems. The number of specimens collected by surveillance schemes varied within and across countries and areas. Data were not collected on methods for selecting cases for specimen collection.
During the study period, 1,070,792 influenza virus detections were reported to FluNet globally, of which 301,195 (28%) were reported from NICs in the Western Pacific Region (). Within the Western Pacific Region, China contributed the most data for virus detections (57%), followed by Japan (19%) and the Republic of Korea (7%).
Figure 2 Proportion of influenza specimens reported by Western Pacific Region countries to GISN, 2006–2010∧.
∧ The proportion of contribution of viruses reported to FluNet from NICs in the Western Pacific Region ranged from 25–43% (more ...)
The number of Western Pacific Region countries submitting virus information to FluNet and the reported number of specimens tested for influenza increased over the five-year study period (). From 2006 through 2008, an average of 84,105 specimens was tested each year (range: 65,103 to 94,274). In 2009, the number of specimens tested increased to 366,164, a 4.3-fold compared to the average tested in the previous three years, and remained elevated in 2010. Of the total 926,064 specimens tested throughout the study period, 21.2% (n
196,720) were influenza positive. From 2006 through 2008, the weighted average proportion of specimens found positive for influenza was 11.7% (range: 11.4% to 12.0%). The overall proportion of specimens found positive for influenza increased 2.7-fold to 31.6% in 2009 compared to the 2006–2008 average, but decreased to 16.8% in 2010.
Specimens tested and specimens positive for influenza by type/subtype/lineage in Western Pacific Region countries, 2006–2010. ∧
Influenza A viruses accounted for the majority of viruses reported between 2006 and 2009, but an equal proportion of influenza A and influenza B viruses was detected in 2010. By subtype or lineage, a large proportion of viruses reported were seasonal A(H1) (40%) and B (lineage not determined) (30%) in 2006. This changed in 2007 when 48% of all influenza positive specimens were A(H3), which continued to be commonly detected in 2008 (18%) along with a resurgence of seasonal A(H1) viruses (38%).
In 2009, 64% of all viruses reported were A(H1N1)pdm09. Other viruses detected in 2009 were A(H3) (16%) and A(not subtyped) (10%), but very few influenza B viruses were reported. However, there was an increase in influenza B(lineage not determined) reports in 2010 (39% of all viruses reported) along with frequent detection of the A(H1N1)pdm09 and A(H3). B(Victoria) was reported more frequently than B(Yamagata) in 2006, 2009 and 2010 but less frequently in 2007 and 2008.
ILI case numbers and total all-cause consultations were provided by 10 of the 14 countries in this study. Australia, China (including Hong Kong), the Republic of Korea, Malaysia, Mongolia and Viet Nam provided data for the five year study period. New Zealand provided aggregate data for the five years, and was analyzed separately. Japan provided the total number of ILI cases but not the total number of all-cause consultations for the study period, and was also analyzed separately. Lao PDR provided ILI data for three years (2008–2010) and Cambodia, the Philippines and Singapore provided ILI data for two years (2009–2010) (). Data for total specimens tested and number positive for influenza were available for all countries except Japan, where only the number of specimens positive for influenza was provided.
Over the five year period, peaks in ILI reporting appeared to be coincident with the proportion of specimens positive for influenza (). This was particularly evident for the northern and southern hemispheres (Panels A & D, ).
Proportion of specimens positive for influenza and proportion of consultations meeting ILI case definition in Western Pacific Region countries, 2006–2010.*
A yearly seasonal pattern typical of temperate northern hemisphere countries was observed in the Republic of Korea and Mongolia (Panel A, ), where peaks in ILI activity were detected in January-March each year. A similar seasonal pattern was observed in Japan, where the reported number of ILI cases and the number of specimens positive for influenza were greatest in the first three months of each year (data not shown). A seasonal pattern typical of temperate southern hemisphere countries was observed in Australia (Panel D, ), where ILI activity and specimens positive for influenza peaked in July-September each year. A similar pattern was observed in New Zealand where ILI activity peaked approximately five weeks earlier than it did in Australia each year (data not shown). Two annual peaks in activity were observed in China (Panel B, ), one in January and one in July or August, from 2006 through 2008 and prior to the appearance of influenza A(H1N1)pdm09 in 2009. A temporal pattern was less evident in the group of six other reporting countries (Panel C, ).
ILI activity and the proportion of specimens positive for influenza were greater during July through December 2009 compared to previous years. This was observed in all reporting countries except Australia, where peak ILI activity in 2009 was of similar magnitude to previous years.
In 2006 and 2007, the predominant influenza viruses in the region were influenza B and seasonal A(H1) and influenza B and influenza A(H3), respectively. Influenza B was identified throughout this period, seasonal A(H1) was frequently identified in May through August 2006 and A(H3) detection increased in January through August 2007. This was followed by detection of A(H3) in Australia, Fiji, New Zealand and New Caledonia (France) in June through September 2007 (Panel D, ). Only influenza B and A(not subtyped) were detected in Mongolia and the Republic of Korea during the same time period.
Number of influenza viruses by type/subtype and proportion of specimens positive for influenza in Western Pacific Region countries, 2006–2010.*
In 2008, influenza B was most frequently reported by countries in the region. However, in the latter half of 2008 an increase in seasonal A(H1) was seen in China (Panel B, ), Japan (data not shown), Mongolia and the Republic of Korea (Panel A, ). Seasonal A(H1) viruses were reported from Mongolia from December 2008 through February 2009, but did not predominate among influenza viruses reported by other countries in the Western Pacific Region during 2008 (Panels C and D, ).
In 2009, pandemic A(H1N1)pdm09 was predominant in the region. A(H3) viruses were reported from all countries in the region, and peaked earliest in Japan, Mongolia and the Republic of Korea, followed by all other countries except China which saw a later A(H3) peak in August through September. Australia, the Philippines and Singapore were the first countries to report detection of the pandemic A(H1N1)pdm09 subtype to FluNet in May 2009 (although New Zealand was the first country in the region to detect this virus). The dominance of this virus in the Western Pacific Region countries was staggered, peaking during May to August 2009 in Cambodia, Lao PDR, Malaysia, Philippines, Singapore and Viet Nam, July to August 2009 in Australia, Fiji, New Zealand and New Caledonia (France), and October 2009 to January 2010 in China, Mongolia and the Republic of Korea. Japan had dual peaks of pandemic virus detection, with a large number of detections in August to September 2009 followed by resurgence in November to January 2010 (data not shown).
During the pandemic period (11 June 2009 to 10 August 2010), other influenza A virus sub-types, including A(H3), were reported. There was also resurgence of influenza B activity with peaks in China, Mongolia and the Republic of Korea during January to April 2010, followed by the remaining countries in July to September 2010 ().
Six countries reported data by age group for ILI cases and total consultations: Cambodia (2009–2010), Lao PDR (2008–2010), Mongolia (2006–2010), New Zealand (2006–2010), the Philippines (2009–2010) and Viet Nam (2008–2010). Cambodia, Mongolia and New Zealand reported greater ILI activity in the 0–5 years age group than other age groups (5 to <18, 18 to <65, and 65 years and over, data not shown). The Philippines and Lao PDR reported greater ILI activity in the 0 to <5 and 5 to <18 age groups, while Viet Nam reported greater ILI activity in the 5 to <18 and 18 to <65 age groups (data not shown).