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
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
Methods: ILI Sentinel Virologic
Surveillance in Laos, 2007-2010
ILI sentinel
surveillance
objectives:
- 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 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
Results: ILI aggregate data trends,
Vientiane Capital
Number of patients meeting ILI case definition,
3 central hospitals, Vientiane Capital
2008-2010 (n = 50390)
1200
No. cases
1000
800
600
400
200
0
1
3
5
7
9
11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53
Week
2008
2009
2010
ILI increases during the wet season (May to October)
Results: Comparing Age Groups
Percentage (%)
Age-group of patients presenting to 3 central
hospitals, Vientiane Capital, 2008-2010
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
OPD & ER
(n=509313 )
ILI (n =
50390)
ILI specimen
(n =1511)
0 to <3
3 to <5
5 to <18
18 to <65 ≥65 years Unknown
Age-group (years)
• 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
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%
Seasonality
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
No. Negative
Date Received (month/year)
No. Positive
Proportion Positive (%)
• 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
Proportion Positive (%)
225
200
175
150
125
100
75
50
25
0
Jan-08
Feb-08
Mar-08
Apr-08
May-08
Jun-08
Jul-08
Aug-08
Sep-08
Oct-08
Nov-08
Dec-08
Jan-09
Feb-09
Mar-09
Apr-09
May-09
Jun-09
Jul-09
Aug-09
Sep-09
Oct-09
Nov-09
Dec-09
Jan-10
Feb-10
Mar-10
Apr-10
May-10
Jun-10
Jul-10
Aug-10
Sep-10
Oct-10
Nov-10
Dec-10
No. ILI Specimens Tested
No. ILI specimens tested and proportion positive for influenza
in Lao PDR, 2008-2010
Influenza Sub-types
Proportion of influenza sub-types by quarter in Lao PDR, 2008-2010
100%
500
80%
400
60%
300
40%
200
20%
100
0%
0
No ILI Specimen tested
Proportion (%)
% Flu B
Q1- Q2- Q3Q4- Q1- Q2- Q3- Q4- Q1Q2- Q3- Q42008 2008 2008 2008 2009 2009 2009 2009 2010 2010 2010 2010
% Flu A/H1N1 2009
% Flu A/H3
% Flu A/H1
% Other Flu (Coinfection/untype)
% Flu Neg
No Specimen Tested
Date received (quarter, year)
• 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
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
Acknowledgment
• National Center for Laboratory and Epidemiology
(NCLE), Ministry of Health, Lao People’s
Democratic Republic
• WHO
• US-CDC
• NIID, Tokyo
• Other partners