Epidemiological and virologic characteristics of seasonal influenza in Lao PDR, 2008-2010

1. Epidemiological and virologic characteristics of seasonal influenza in Lao PDR, 2008-2010 Ms Bouphanh Khamphaphongphanh, Epidemiology Department, NCLE Khamphaphongphanh, Bouaphanh1; Chorcharoenying, Pakapak1,2; Lewis, Hannah2; Phonekeo, Darouny1; Thongchanh, Sisouk1, Xaysithideth, Sinakhone1; Ongkhamme, Somvay2;Vongphrachanh, Phengta1; Corwin, Andrew2 1. NCLE; 2. WHO; 3. US-CDC

2. Background • Information on influenza virology and epidemiology is limited • Seasonal patterns of influenza have not been previously described • The objectives of this study were to: • describe demographic characteristics, incidence and seasonality of ILI patients and confirmed influenza cases • describe the sub-types of influenza virus circulating in Lao PDR

3. - Determine proportion of samples that are influenza positive  - Monitor demographics, morbidity and mortality of community acquired ILI ;Seven sentinel hospitals in three regions (central, north, south); 2007- 2010 Methods: ILI Sentinel Virologic Surveillance in Laos, 2007-2010 ILI sentinel surveillance objectives:

4. Methods • ILI Case definition: • Fever >38oC with cough and/or sore throat • Weekly aggregated data collected from each ILI sentinel sites - Total number of outpatients - Total number of ILI outpatients • Specimen collection • Nasopharyngeal (NP) swab or combined NP with oropharyngeal swab • One day (central sites) or two days (provincial sites) per week • Case data collected from all providing swab • Specimens tested at NCLE • Luminex (2008) • Real-time PCR with US-CDC primers/probes (2009-2010) • Descriptive analysis of aggregate data and case data from ILI patients in Stata

5. Results: ILI aggregate data trends, Vientiane Capital ILI increases during the wet season (May to October)

6. Results: Comparing Age Groups • 10% of OPD/ER are ILI; ILI patients are younger than OPD/ER patients • Patients from which ILI samples taken & tested had similar age to those presenting with ILI to the hospital • For Vientiane Capital, 3% of total ILI patients were sampled and tested

7. Influenza results: all sentinel sites • ILI Samples • 2,348 samples were received nationwide • Most from central hospitals • 65% Central; 22% North; 13% South • Most received in 2010 • 50% 2010, 35% 2009, 15% 2008 • Median age: 7 years; range: <1 to 89 • Male to Female Ratio 1 : 1 • 22% (523/2,338) positive for influenza • Influenza positive • 523 positive specimens (22%) • Median age: 12 years; range: <1 to 60 • Positivity rate was similar year to year (20-23%). • Regional differences in positivity • Central: 23%; North: 16%; South 29%

8. Seasonality • Influenza was detected year-round • Highest proportion of positive specimens in the 3rd and 4th quarter • Variability in peak year to year (Aug-Sept); bi-modal seasonal pattern only in 2008

9. Influenza Sub-types • Each year 3-4 sub-types co-circulated with different predominant sub-types • Transformation of Pandemic A/H1N1 2009 into mix of seasonally occurring sub-types • Flu B not seen in Q3 & 4 2009 after emergence of A H1N1/2009, returned in 2010 • Seasonal Flu A/H1 not seen since emergence of A H1N1/2009

10. Conclusions • Results similar to findings of other countries in the region • Cambodia, Vietnam, Thailand • A large proportion of ILI patients are not influenza, particularly younger children • Built on previous study (Vongphrachanh et al. 2010) • Aggregate data to be collected from all sites • Influenza affects all ages but mostly older children • Influenza season is June to December and is dominated by a different strain each year • ILI surveillance is critical for: • Recognizing changing patterns of seasonal occurrence • Contributing to future influenza vaccination policy and strategy • Strengthened Severe Acute Respiratory Infection (SARI) surveillance required

11. Acknowledgment • National Center for Laboratory and Epidemiology (NCLE), Ministry of Health, Lao People’s Democratic Republic • WHO • US-CDC • NIID, Tokyo • Other partners