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

- 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

2008-2010 (n = 50390)

0

200

400

600

800

1000

1200

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

No

. cas

es

2008 2009 2010

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

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

• WHO• US-CDC• NIID, Tokyo • Other partners