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Epidemiological and virologic characteristics of seasonal
influenza in Lao PDR, 2008-2010
Ms Bouphanh Khamphaphongphanh, Epidemiology Department, NCLE
• 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
- 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:
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
ILI increases during the wet season (May to October)
Number of patients meeting ILI case definition, 3 central hospitals, Vientiane Capital
• 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
Age-group of patients presenting to 3 central hospitals, Vientiane Capital, 2008-2010
0.010.020.030.040.050.060.070.0
0 to <3 3 to <5 5 to <18 18 to <65 ≥65 years Unknown
Age-group (years)
Perc
enta
ge (%
)
OPD & ER(n=509313 )
ILI (n =50390)
ILI specimen (n =1511)
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
0%10%20%30%40%50%60%70%80%90%100%
0255075
100125150175200225
Jan-
08Fe
b-08
Mar
-08
Apr
-08
May
-08
Jun-
08Ju
l-08
Aug
-08
Sep-
08O
ct-0
8N
ov-0
8D
ec-0
8Ja
n-09
Feb-
09M
ar-0
9A
pr-0
9M
ay-0
9Ju
n-09
Jul-0
9A
ug-0
9Se
p-09
Oct
-09
Nov
-09
Dec
-09
Jan-
10Fe
b-10
Mar
-10
Apr
-10
May
-10
Jun-
10Ju
l-10
Aug
-10
Sep-
10O
ct-1
0N
ov-1
0D
ec-1
0
Prop
orti
on P
ositi
ve (
%)
No.
ILI S
peci
men
s Te
sted
Date Received (month/year)
No. ILI specimens tested and proportion positive for influenza in Lao PDR, 2008-2010
No. Negative 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
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
Proportion of influenza sub-types by quarter in Lao PDR, 2008-2010
0%
20%
40%
60%
80%
100%
Q1-2008
Q2-2008
Q3-2008
Q4-2008
Q1-2009
Q2-2009
Q3-2009
Q4-2009
Q1-2010
Q2-2010
Q3-2010
Q4-2010
Date received (quarter, year)
Prop
ortio
n (%
)
0
100
200
300
400
500
No
ILI S
pecim
en te
sted
% Flu B
% Flu A/H1N1 2009
% Flu A/H3
% Flu A/H1
% Other Flu (Co-infection/untype)
% Flu Neg
No Specimen Tested
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