Epidemiology of Dengue in Sri Lanka: past, present and future

Hasitha Tissera MBBS, MSc, MDConsultant Epidemiologist

Ministry of Health Epidemiology Unit

Ministry of Health Sri Lanka

Dengue SeminarSeptember, 2011

Outline

• Background

• Pre-endemic period

• Endemic period

• How we could change the epidemiology

Dengue

• Most important mosquito borne viral infection in the world

• Very common infection in tropics • Large epidemics occur • Nearly 90% of infections in children• Wide spectrum of infection outcomes Asymptomatic infection → Death • High morbidity, relatively low mortality disease

Transmission Modulating FactorsTransmission Modulating Factors

Vector Host (human) Virus

Dispersion

Density

Deposited eggs

Vector’s competency

Individual immnunity

Herd immnunity

Sequential Infections

Individual factors

Magnitude of the Epidemics (DF/DHF)

Serotypes

(Previous Circulation)

Genetic differences

Virulence

Probability of Transmission

Source: Prof. Maria Gloria Teixeira, London May 2008

Dengue: Global burden Dengue ploriferates from 20th to 21st century with increasing burden, despite a lot of hard work on control and prevention

1960 2004

Why Epidemiology ?

• To aid in setting health priorities

• To aid in setting research priorities

• To identify prospective health interventions

• To provide a comparable measure of output for interventions

Pre-endemic History• Clinical dengue-like illness from beginning of 20th century

• Serologically confirmed in 1962

• First outbreak in 1965

• D1-D4 circulating since at least 1966

• 1965-68 had 51 cases and 15 deaths

• 1969 – 88’ multiple outbreaks of DF with occasional DHF

• Mostly from Western Province• School cohort study 1980-85’ (pre DHF): Dengue sero- prevalence 50% (7000, 5-7 year olds in Colombo MC)

Endemic Period – 1989 onwards

• DHF became endemic in 1989*• 1989 – 203 hospitalized with 20 deaths (CFR 9.8%)• 1990 – sharp increase to 1300 cases and 54 deaths

(CFR 4%)• 1991- 95’ – multiple outbreaks • 1996 – became nationally notifable disease

*Source: Vitarana T, Jayakuru WS and Withane N, Ministry of Science Technology and Human Resources, 1993

Temporal and Spatial Spread, 1996 - 2009

1996 2004 2005 2006 2009

N=1294 N=15463 N=5994 N=11980 N=35007

Reported Cases to National Epidemiological UnitReported Cases to National Epidemiological Unit

Dengue Trends in Sri Lanka

2009 CFR – 0.99%2010 CFR – 0.71%2011 CFR - 0.71%

2004 : 7 districts >100 2009 : 13 districts >100

Geographic Expansion 2004 - 2010

Incidence 80/100,000 Incidence 170/100,000

2010 : 21 districts >100

Incidence 170/100,000

2004 2009 2010

6

197

318

181

73104 92

36 38 28 15 6 526

< 1 year 1-4 5-9 10-14 15-19 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 >60

Age group

0

100

200

300

400

Nu

mb

er

Dengue cases by age groups Sri Lanka - 1996 and 2006

38

209

352

261

339

513

366

257

189141

10958 38

64

< 1 year 1-4 5-9 10-14 15-19 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 >60

Age group

0

100

200

300

400

500

600

Num

ber

No. of cases analysed N= 2934

38

327

493

395

532

904

808

510425

318260

198127

218

< 1 year 1-4 5-9 10-14 15-19 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 >60

Age group

0

200

400

600

800

1000

Num

ber

No. of cases analysed N= 5553

Data as 22/01/2008

1996

No. of cases analysed N= 1125

Source: Epidemiology Unit Sri Lanka

Overall Sero-prevalence among children < 12 – 52% study supported by PDVI

Seasonality

• South-western monsoon peak: May – July • North-eastern monsoon peak: Oct - Jan

South-west monsoon North-east monsoon

What we did to control & prevent

• Vector control through awareness – until 2004 • With epidemic shift in 2004:

- Active social mobilization- Aggressive vector control- Attempt improvement in clinical management

Where are we today

• In general to date , the targeted health interventions largely not sustainable, less effective than expected. Why?

• A few model countries on effective surveillance (Brazil), Vector control (Singapore, Cuba) and effective clinical management (Thailand, Vietnam) exist, but are exceptions.

WHY IS DENGUE SUCH A BIG PROBLEM TODAY?

• Global population growth

• Rural to urban migration

• Growth of cities• Deterioration of

cities

• Jet travel• Health services

poorly organized/ underfunded

• Lack of vector control professionals

Slide courtesy of Dr. Scott Halstead

Which Perspective Do We Take?

SOCIETY

PATIENT

FAMILY

GOVERNMENT

ALL OTHER STAKE HOLDERS

SCIENCE

Slide courtesy of Dr. Ananda Amarasinghe

National Plan: Outputs

1. Improved Case Management2. Strengthened Surveillance – disease,

laboratory, entomological3. Capacity building – at all levels infrastructure,

staff, equipment, 4. Strengthened control activities at National,

Provincial, District, & Divisional levels5. Enhanced intersectoral & community

participation for sustainable programme

Dengue Epidemiology

• Primary Prevention:(A)Reduce disease transmission (interruption) –

solidifying evidence based vector control approach;

- improved entomological assistance - adult vector control

(B) Vaccine – preparation for vaccine introduction when become available (earliest 2015) – need to plan now

Dengue Epidemiology…

• Secondary Prevention: (A)Early case detection – Iry care & pvt. sector

through improved diagnostics:- Full Blood Count - NS1 (cost implications)

(B) Improving Clinical Management - reducing disease severity- reducing case fatality

National Guidelines 2010

1%

49%

37%

13%DF

DHF I & II

DHF III

DHF IV

Statistics LRH Ward 04 - 2009Statistics LRH Ward 04 - 2009

Source: Infection Control Unit LRH + Ward 04 records Slide courtesy of Dr. Padmakanthi Wijesuriya, Consultant Paediatrician LRH

DF

DHF I & II

DHF III

DHFIV

Total Dengue Patients : 333(Jan-Aug 2009)

5,565

12,422

Source: Epidemiology Unit Data

Dengue Situation by Month201120102009

To bring down mortality…

Scott B. Halstead, M.D.

Providing Micro-haematocrit Machines to Hospitals

Setting up of National ‘Hotline’

Standardized teaching and training curricula at all levels

Advocacy - Highest Level

• Health

•Local Govt.

• Environment

• Defense

• Education

• Media

High - risk areas June - July 2011

Major Breeding Habitats Urban Breeding Sites Rural Breeding Sites

Discarded containers – plastic cups, tins, cans, bottles.…

Discarded containers – coconut shells, clay pots, bottles ….

Water Storage –tanks, barrels, buckets Water storage – tanks, barrels, buckets

Used Tyres - domestic, workshops, depots

Used Tyres – domestic, workshops, depots

Roof Gutters - domestic, offices, high-rising building tops Roof Gutters – domestic, sun shades

Other – ornamental items, blocked drains, construction sites, natural breeding -ornamental plants, underprivileged communities, bare lands

Other – spare part yards, natural breeding sites -bamboo shoots, tree axills/holes, fallen tree leaves, plantations

www.epid.gov.lk

Regular update on dengue situation

Thank You!