Vector-borne Diseases - Ministry of Health

• Dengue• Leptospirosis• Malaria• Murine typhus

Air-/D

roplet-B

orneD

iseases

Vector-Borne/

ZoonoticD

iseases

Food-/Water-

Borne

Diseases

Blood-B

orneD

iseasesE

nvironment-

Related

Diseases

Childhood

Imm

unisation

Communicable Diseases Surveillance in Singapore 2003

IIVECTOR-BORNE DISEASES

Vector-borne and zoonotic diseases are diseases transmitted to humans by insects or animals. Vectors may transmit infectious diseases to humans by the blood-feeding of arthropods such as mosquitoes and ticks or through contaminated

urine, tissues or bites of infected animals such as rats or dogs. The causative organism may be viral, bacterial, fungal, protozoan or parasitic and the transmission could be direct or via food and water.

Dengue fever is an acute febrile viral disease characterised by sudden onset of fever for 3-5 days, intense headache, myalgia, arthralgia, retro-orbital pain, anorexia, gastrointestinal disturbances and rash. Early generalised erythema may occur in some cases. The infectious agents are flaviviruses comprising four serotypes (dengue-1, 2, 3 and 4) and are

DENGUE FEVER/DENGUE HAEMORRHAGIC FEVER (DF/DHF)transmitted by the Aedes mosquito.

In 2003, a total of 4788 cases of DF/DHF were reported compared to 3945 cases in 2002. The majority of the cases (78%) received inpatient treatment. The incidence was highest in June, during e-week 23. (Figure 2.1)

0

50

100

150

200

250

300

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 53Week

No.

of c

ases

2002 2003

Figure 2.1E-weekly distribution of DF/DHF cases, 2002 - 2003

23

The incidence rate among local residents was highest in the 15-24 years age group. (Table 2.1) Among the three major ethnic groups, Chinese residents had the highest incidence rate, followed

by Indians and Malays. Foreigners comprised 22.5% of the indigenous cases (Table 2.2), with majority employed as labourers or related workers in the construction and manufacturing industry.

Table 2.2Ethnic-gender distribution and ethnic-specific incidence rates of indigenous# DF/DHF cases, 2003

Male

1647

152

102

45

692

2638

Singapore Resident

Chinese

Malay

Indian

Others

Foreigner

Total

Total (%)

3011 (66.3)

253 (5.6)

179 (3.9)

78 (1.7)

1021 (22.5)

4542 (100.0)

Female

1364

101

77

33

329

1904

Incidence rateper 100,000 population*

# Cases acquired locally among Singaporeans, permanent and temporary residents.* Rates are based on 2003 estimated mid-year population.

(Source: Singapore Department of Statistics)

Table 2.1Age-gender distribution and age-specific incidence rates of indigenous# DF/DHF cases, 2003

Male

27

232

481

714

599

332

253

2638

Age (Yrs)

0 – 4

5 – 14

15 – 24

25 – 34

35 – 44

45 – 54

55+

Total

Total (%)

48 (1.1)

417 (9.2)

858 (18.9)

1102 (24.3)

974 (21.4)

619 (13.6)

524 (11.5)

4542 (100.0)

Female

21

185

377

388

375

287

271

1904


# Cases acquired locally among Singaporeans, permanent and temporary residents.* Rates are based on 2003 estimated mid-year population.


22.3

77.7

138.4

128.1

126.5

106.9

86.7

108.5

114.9

53.4

63.1

132.7

136.5

108.5

24


Table 2.3Economic/occupational profile of indigenous DF/DHF cases, 2003

Economic status/occupation

Economically active

Working

Senior officials & managers

Professionals

Associate professionals & technicians

Clerical workers

Service & sales workers

Production craftsmen & related workers

Plant & machine operators & assemblers

Cleaners, labourers & related workers

Workers not classifiable by occupation

Unemployed

Economically inactive

Homemakers

Students

Others

Total

%

7.3

10.0

4.3

4.2

5.6

0.7

0.6

13.2

8.3

7.7

14.0

17.9

6.2

100.0

No.

332

454

197

189

255

32

29

599

376

350

637

811

281

4542

The economic/occupational profile of indigenous DF/DHF cases is given in Table 2.3. Students accounted for 17.9%, 14.0% were homemakers

and 13.2% were cleaners, labourers and related workers.

25

Year

Southeast Asia Indonesia Malaysia Thailand Philippines Vietnam Cambodia Brunei Myanmar Laos East Timor

South Asia India Bangladesh Sri Lanka Pakistan Nepal

Other Regions

Total

1999

11665

91220300

74600

2

217

2000

17164

53025000

69300

3

271

2001

1427732

5082801

198310

2

308

2002

155139

436040200

143910

9

385

2003

93100

182280100

141311

2

246

There were 246 (5.1%) imported cases, defined as cases with a history of travel to endemic areas seven days prior to the onset of illness.

The majority of these cases (92%) were from neighbouring countries: 93 from Indonesia and 100 from Malaysia. (Table 2.4)

Table 2.4Imported DF/DHF cases, 1999-2003

Residents in Housing and Development Board (HDB) flats, compound houses and condominiums accounted for 55.0%, 31.9%, and 12.9%, respectively, of the cases. However, the incidence rate for residents of compound houses was ten times higher than that of HDB dwellers.

(Table 2.5)

Most of the cases were concentrated in the south-eastern (39.1%) and central (33%) areas of Singapore. (Figure 2.2)

Table 2.5Incidence rates of reported indigenous DF/DHF cases

(Singaporeans and Permanent Residents) by housing type, 2003

%

31.9

55.0

12.9

0.2

100.0

Incidence rateper 100,000 population Cases

1124

1937

453

7

3521

Housing Types

Compound houses (including shophouses)

HDB flats

Condominiums

Bangsals, containers/workers’ quartersand others

Total

633.7

63.9

220.4

-

102.9

26


Figure 2.2Geographical distribution of DF/DHF clusters having 10 or more reported cases, 2003

A total of 180 clusters involving 1405 epidemiologically linked cases were identified. The median number of cases in each cluster

was 4.5 (range 2 to 59) and the median duration of transmission was 12 days (range 1 to 79). (Table 2.6)

No. ofClusters*

40

74

134

33

75

118

143

198

239

54

9

93

73

180

No. of cases in cluster area

(% total cases)

270 (16.5)

414 (20.1)

733 (26.7)

183 (23.0)

424 (39.1)

679 (38.7)

1088 (37.8)

1124 (27.8)

1197 (23.4)

230 (20.2)

40 (10.0)

531 (25.7)

725 (20.4)

1405 (31.0)

Median no. of cases

per cluster

4.5

3.5

3.0

3.0

3.0

3.0

3.0

3.0

2.0

3.0

4.0

3.0

7.0

4.5

Median duration of transmission

(days)

10.0

6.0

5.0

8.0

7.0

7.0

6.0

5.0

7.0

11.0

15.0

8.0

20.0

12.0

Year

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

No. ofindigenous

cases

1640

2062

2741

794

1084

1756

2877

4039

5105

1138

402

2064

3560

4542

No. of clusters with 10 cases

(% total clusters)

11 (27.5)

9 (12.2)

13 (9.7)

4 (12.1)

8 (10.7)

16 (13.6)

27 (18.9)

24 (12.1)

23 (9.6)

6 (11.1)

1 (11.1)

15 (16.1)

30 (41.1)

38 (21.1)

Table 2.6Dengue clusters identified during the period 1990-2003

*A cluster is defined as two or more cases epidemiologically linked by place (within 250 metres) and time (within three weeks or approximately two incubation periods)

2 or more epidemiologically linked cases in a locality

27

Of the 180 clusters identified, there were 38 clusters (21.1%) having 10 cases or more. They were in the areas listed below:

S/No

123456789

1011121314151617181920212223242526272829303132333435363738

Location

Bishan St 24/Bishan St 22

Jalan Lembah Thomson/Soo Chow WalkAng Mo Kio Ave 2/Ang Mo Kio St 11Tampines Ave 4/Tampines Ave 1Bright Hill Road/Fulton RoadSerangoon Garden Way/Medway DriveSims Drive/Aljunied RoadMinbu Road/Mandalay RoadUbi Road 1/Ubi Ave 2Bedok North Ave 4Jalan Tua Kong/Jalan Ulu SiglapLorong 1 Toa Payoh/Toa Payoh NorthLorong 4 Geylang/Mountbatten RoadKallang Bahru MUP 14Whampoa Drive/Kim Keat RoadPark Road/Eu Tong Sen StChancery Hill Road/Dyson RoadAng Mo Kio Ave 4/Ang Mo Kio St 13Clover Crescent/Binjang Rise areaPoh Huat Road/Park Villas TerraceFidelio Street/Siglap Road areaBoon Teck/Jalan Ampas areaHougang Ave 7Bayshore Road/Upper East Coast RoadKew Ave/Kew DriveDefu Lane 6/Defu Lane 5Tanjong Katong Road/Amber RoadChai Chee St/Bedok North RoadJalan Seaview/Meyer RoadSerangoon Ave 3/Serangoon Ave 2Melrose Drive/Jalan Girang areaChuan Hoe Ave/Limbok TerracePoh Huat Road West/Yio Chu Kang RoadProposed Armanda CondominiumSerangoon North Ave 1Jalan Ikan Merah/Jalan SembilangGlasgow Road/Jansen RoadLichfield Road/Raglan Grove area

No. of cases

1214161559102131122029171214412228152513101048102211251219501323111242101225

Month

JanFeb

Jan-FebJan-MarFeb-MarJan-MarFeb-Mar

MarMar-Apr

AprApr-JunApr-MayApr-MayApr-MayMay-JunApr-MayMay-JunMay-JunMay-JunMay-JunMay-JunMay-Jun

Jun-JulJun-Jul

Jun-SepAug

Aug-SepAug

Aug-SepSep-OctSep-OctSep-OctSep-Oct

OctOct-DecNov-Dec

DecDec-Jan

The median number of cases in these 38 clusters was 15.5 (range 10 to 59) and the median duration of transmission was 32 days (range 13 to 79).

28


There were six deaths from dengue, of which five were classified as local and one as imported.

The first case was a 41-year-old Chinese male security guard from Clementi. He had no history of travel prior to his onset of illness; however his job required him to travel around Singapore. He was admitted to Alexandra Hospital with high fever, headache, malaise, abdominal discomfort, vomiting and diarrhoea for five days duration. Dengue IgM antibody tested positive on admission and he developed haemorrhagic features over the following two days. His condition deteriorated over the following two weeks and he died on 3 January 2003 from Dengue Shock Syndrome (DSS) with multi-organ failure.

The second case was a 70-year-old Malay male retiree with a travel history of a trip to Johor Bahru four days prior to the onset of symptoms. He developed fever on 9 January and was treated by a general practitioner and prescribed antibiotics. The fever persisted and on 13 January, he was admitted to Singapore General Hospital. Dengue IgM antibody tested positive. Following admission, the platelet count dropped from 60,000/mm3 to 14,000/mm3 and he developed gastrointestinal bleeding. His condition deteriorated rapidly over two days and he died on 17 January 2003 from DSS and bleeding from GI tract.

The third case was a 31-year-old Indian labourer residing at a work-site in an industrial area. He had no history of travel prior to his onset of illness. He was admitted to Changi General Hospital on 2 February 2003 and Dengue IgM antibody tested positive. He died on 6 February 2003 from DHF.

The fourth case was a 71-year-old Chinese retiree

DHF Deaths residing in Serangoon. He had previous history of stroke and hypertension. He developed high fever and myalgia and sought treatment from a general practitioner. He was subsequently admitted to East Shore Hospital on 5 April 2003 in an unconscious state. On admission he was found to have a low platelet count of 43,000/mm3 and a CT scan indicated a cerebral haemorrhage. His condition did not improve despite platelet and plasma transfusion and died on 6 April 2003. The cause of death was cerebral haemorrhage associated with DHF.

The fifth case was a 59-year-old Chinese housewife residing in Hougang area. She developed high fever on 26 June 2003 and presented to Tan Tock Seng Hospital on 29 June 2003 with giddiness and a history of fall at home. At admission she was managed for septic shock in the Intensive Care Unit (ICU). Laboratory findings revealed Dengue PCR positive and marked thrombocytopenia. Her condition deteriorated despite ventilation support and fresh frozen plasma transfusion. She died of DSS and multi-organ failure on 4 July 2003.

The sixth case was a 77-year-old Chinese housewife residing in Joo Chiat area. She had no history of travel prior to the onset of illness. She developed fever, myalgia and rash on 28 August 2003, and sought treatment from a general practitioner. She was subsequently referred to Gleneagles Hospital and was admitted on 30 August 2003. The Dengue PCR tested positive on 1 September 2003. The patient died on 3 September 2003 due to DSS with multi-organ failure, sepsis with disseminated intravascular coagulation (DIVC), fulminant hepatitis and severe acidosis.

29

All reported cases of dengue fever were confirmed by one or more laboratory tests; viz. anti-dengue IgM antibody, enzyme linked immunosorbent assay (ELISA), and polymerase chain reactions (PCR).

Dengue virus serotype identification was performed on a total of 525 blood samples by

Laboratory Surveillancethe Department of Pathology Singapore General Hospital and Environmental Health Institute at the National Environment Agency.

The predominant strain in Singapore in 2003 was DEN-2 serotype. All four serotypes were isolated. 8 DEN-1, 58 DEN-2, 4 DEN-3 and 5 DEN-4. (Table 2.7)

DEN-1

4(2.6)

1(0.4)

8(2.6)

20(7.8)

10(3.9)

18(7.1)

12(4.5)

11(3.2)

4(1.2)

1(0.3)

16(4.8)

8(1.5)

Year

1992 (May - Dec)

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

Total no. of samples

tested

154

257

309

257

255

254

266

348

327

354 [119]

331[99]

525

DEN-2

5(3.2)

14(5.4)

16(5.2)

8(3.1)

5(2.0)

15(5.9)

19(7.1)

8(2.3)

4(1.2)

12(3.4)

28(8.5)

70(13.3)

DEN-3

21(13.6)

4(1.6)

20(6.5)

17(6.6)

2(0.8)

0

3(1.1)

2(0.6)

1(0.3)

0

2(0.6)

4(0.8)

DEN-4

0

0

0

2(0.8)

1(0.4)

0

0

0

2(0.6)

2(0.6)

6(1.8)

5(1.0)

Untyped

0

2(0.8)

1(0.3)

0

0

0

0

0

0

0

0

0

No. of positive isolates (%)

[ ] denotes specimens from Dengue Project (general physicians and construction sites)

Table 2.7Surveillance of dengue serotypes, 1992-2003

30


Serangoon Ave 3/Serangoon Ave 2 areasOn 16 September 2003, the Ministry of Health was notified of six cases of dengue fever involving students of Nanyang Junior College and residents of Serangoon Avenue 2 and 3. Within the next five days, four more cases from the same area were confirmed to be dengue fever. As soon as the cluster of cases was identified, vector control operations were carried out.

A total of 50 serologically confirmed cases were identified in the outbreak. Illness onsets were between 7 September and 5 October 2003. Seventy per cent of the cases were hospitalised.

The cases comprised of 18 students, 14 working adults, 8 construction workers, 3 retirees, 3

Outbreaks of Dengue

Table 2.8Age-gender distribution of reported DF/DHF cases at Serangoon Ave 3/Serangoon Ave 2

September–October 2003

Male

0

5

4

7

7

3

3

29

Age (Yrs)

0 – 4

5 – 14

15 – 24

25 – 34

35 – 44

45 – 54

55+

Total

Total (%)

0 (0)

7 (14)

11 (22)

14 (28)

9 (18)

6 (12)

3 (6)

50 (100)

Female

0

2

7

7

2

3

0

21

Figure 2.3 Geographical distribution of 50 DF/DHF cases at Serangoon Ave 2/3 area, September-October 2003

One Case

Culex Breeding

Aedes albopictus Breeding

Aedes aegypti Breeding

Aedes Breeding

307

308

309

310

313 312

314 315

311

316

317318

302

303

305

306

304301

319

239

238

243

244

245

240

232 234

236

237

242

241

246

322

321 325

324

327

328

329

326

323

332

333

331

330

334

335

267266

265264

263

261

262

254A254

253

Nanyang Junior College

Yangzheng Pri Sch

ZhonghuaSec Sch

Chuan Park

Lor C

huan

Serangoon A

ve 2

TheSunnydale

Serangoon Ave 3

AmandaGarden

unemployed, 2 maids and 2 housewives. The majority of the cases were in the 25–34 years age group with a male to female ratio of 1.4:1. (Table 2.8)

All cases were clustered within a 250-metre radius from the initial focus of transmission. (Figure 2.3)

Aedes mosquito breeding habitats were identified in 63 (1.7%) of 3682 premises inspected. Abundant breeding habitats were found in ornamental containers (42.0%), domestic containers (14.8%) and bamboo pole holders (14.8%). Aedes aegypti and Aedes albopictus accounted for 51.4% and 47.9% of the breeding detected respectively.

31

Bright Hill Road/Fulton Road areasOn 11 February 2003, a case of dengue fever involving a resident of Fulton Ave was notified. Two days later, another 16 cases from a construction site in the same area were reported. The NEA was immediately alerted when the cluster of cases in the area was identified on 13 February 2003. Vector control measures were implemented to prevent further disease transmission.

Table 2.9Age-gender distribution of reported DF/DHF cases at Bright Hill Road/Fulton Road areas

February-March 2003

Male

0

1

2

22

21

3

1

50

Age (Yrs)

0 – 4

5 – 14

15 – 24

25 – 34

35 – 44

45 – 54

55+

Total

Total (%)

0 (0.0)

2 (3.4)

6 (10.2)

24 (40.6)

22 (37.3)

4 (6.8)

1 (1.7)

59 (100.0)

Female

0

1

4

2

1

1

0

9

All cases were clustered within a 250-metre radius from the initial focus of transmission. (Figure 2.4)

A total of 463 premises were checked. Eight were found to be breeding mosquitoes. In addition,

A total of 59 serologically confirmed cases were reported with onsets of illness between 1 February and 10 March 2003. Seventy-eight per cent of these cases received inpatient treatment.

The cases comprised of 43 construction workers, 6 working adults, 6 students, 1 unemployed, 1 housewife, 1 domestic helper and 1 retiree. The majority of the cases were in the 25–34 years age group and the overall male to female ratio was 5.6:1. (Table 2.9)

Figure 2.4 Geographical distribution of 59 DF/DHF cases at Bright Hill Road/Fulton Road,

February-March 2003

One Case

Aedes albopictus Breeding

Aedes aegypti Breeding

Bishan ParkSec Sch

Ai Tong Pri Sch

Sin

Min

g A

ve

Bishan Park

Sin

Min

g D

r

Kong Meng SanTempleProposed Extension

Bright HillEvergreen Home

Fulto

n R

d

Fulton Rd

Fulto

n Av

e

Brig

ht H

ill D

r

VicomVehicleInspectionCentre

402403

401

406

407408

405

404

there was one breeding habitat found in the public area. The main breeding habitats were plastic pails (55.6%) and flowerpot plates (16.7%). Aedes albopictus and Aedes aegypti accounted for 55.6% and 44.4%, respectively.

32


Leptospirosis is a zoonotic bacterial disease of variable clinical manifestations. The common presenting features are fever, headache, chills, severe myalgia and conjunctival suffusion. The etiologic agent is a spiral organism, Leptospires, a member of the order Spirochaetales found mainly in infected wild and domestic animals. The mode of transmission is through direct contact of the skin (especially if broken) or mucous membranes with the urine or tissues of infected animals. Soil or vegetation contaminated by

LEPTOSPIROSISinfected animals may also result in infection. Occasionally leptospirosis has occured following the ingestion of food contaminated by the urine of infected rats.

In 2003, there were 29 reported cases of Leptospirosis. Of these 12 were classified as imported cases. Leptospirosis is a disease of young males (male to female ratio 13.5:1). They tend to be foreigners in the 25-34 year age group. (Tables 2.10 and 2.11)

Table 2.10Age-gender distribution and age-specific incidence rates of reported leptospirosis cases, 2003

Male

0

0

5

10

6

2

3

1

27

Age (Yrs)

0 – 4

5 – 14

15 – 24

25 – 34

35 – 44

45 – 54

55+

Unknown

Total

Total (%)

0 (0.0)

0 (0.0)

5 (17.2)

10 (34.5)

6 (20.7)

2 (6.9)

5 (17.2)

1 (3.5)

29 (100.0)

Female

0

0

0

0

0

0

2

0

2


* Rates are based on 2003 estimated mid-year population.(Source: Singapore Department of Statistics)

Table 2.11Ethnic-gender distribution and ethnic-specific incidence rates of reported leptospirosis cases, 2003

Male

7

2

2

0

16

27

Singapore Resident

Chinese

Malay

Indian

Others

Foreigner

Total

Total (%)

8 (27.6)

2 (6.9)

2 (6.9)

0 (0.0)

17 (58.6)

29 (100.0)

Female

1

0

0

0

1

2


* Rates are based on 2003 estimated mid-year population.(Source: Singapore Department of Statistics)

0.3

0.4

0.7

0.0

2.3

0.7

0.0

0.0

0.8

1.2

0.8

0.4

0.8

-

0.7

33

Malaria is a parasitic disease characterised by fever and chills. Serious malarial infections may present with cough, diarrhoea, respiratory distress and headache. The infectious agent is a protozoan parasite, Plasmodium, and there are four different species namely, P. vivax, P. malariae, P. faciparum and P. ovale. The mode of transmission is via a bite

MALARIAfrom an infective female Anopheles mosquito.

In 2003, a total of 118 cases were reported compared with 175 cases in 2002. Of these, 81 were local residents, while the remaining were either tourists (13) or foreigners seeking medical treatment in Singapore (24).

Table 2.12Age-gender distribution and age-specific incidence rates of reported malaria cases^, 2003

Male

0

1

14

23

12

8

9

67

Age (Yrs)

0 – 4

5 – 14

15 – 24

25 – 34

35 – 44

45 – 54

55+

Total

Total (%)

0 (0.0)

2 (2.5)

18 (22.2)

26 (32.1)

13 (16.0)

11 (13.6)

11 (13.6)

81 (100.0)

Female

0

1

4

3

1

3

2

14

^excluding 24 foreigners seeking medical treatment in Singapore and 13 tourists *Rates are based on 2003 estimated mid-year population.


Figure 2.5 E-weekly distribution of reported malaria cases, 2002 - 2003

0

3

6

9

12

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.

of c

ases

2002 2003


0.0

0.4

2.9

3.0

1.7

1.9

1.8

1.9

Among the 81 reported cases of malaria in local residents, the age-specific incidence rate was highest in the 25-34 years age group and the male to female ratio was 4.8:1. (Table 2.12)

The ethnic-specific incidence rate for Malay residents was about 4 times that of Chinese and 1.3 times that of Indians. (Table 2.13)

34


Table 2.13Ethnic-gender distribution and ethnic-specific incidence rates of reported malaria cases^, 2003

^excluding 24 foreigners seeking medical treatment in Singapore and 13 tourists*Rates are based on 2003 estimated mid-year population.


Male

19

10

6

0

32

67

Singapore Resident

Chinese

Malay

Indian

Others

Foreigner

Total

Total (%)

21 (25.9)

15 (18.5)

7 (8.6)

0 (0.0)

38 (47.0)

81 (100.0)

Female

2

5

1

0

6

14


Malaria parasite speciesOf the total 118 reported cases, 113 (95.8%) were acquired overseas, 4 (3.4%) were introduced, and 1 (0.8%) was cryptic. No indigenous cases were reported.

The distribution of the cases by parasite species was P. vivax (64.4%), P. falciparum (33.9%), and mixed infection (1.7%). (Table 2.14)

P.f

40

0

0

0

0

40

Classifications

Imported*

Introduced

Indigenous

Cryptic

Induced

Total

P.v.

71

4

0

1

0

76

Total (%)

113 (95.8)

4 (3.4)

0 (0.0)

1 (0.8)

0 (0.0)

118 (100.0)

Mixed(P.v. & P.f.)

2

0

0

0

0

2

Mixed(P.v. & P.m.)

0

0

0

0

0

0

P.m.

0

0

0

0

0

0

Parasites species

P.v. - Plasmodium vivax P.m. - Plasmodium malariae P.f. - Plasmodium falciparum *Including relapsed and induced cases which were imported.

Table 2.14Classification of reported malaria cases by parasite species, 2003

0.8

3.2

2.5

0.0

5.1

1.9

35

The majority of the malaria cases acquired overseas were infected in Indonesia (47.8%) and

Table 2.15Malaria cases^ by country of origin and by parasite species, 2003

P.f

24

0

2

0

0

6

0

1

0

1

5

1

40

P.v.

29

4

1

1

1

32

1

0

1

0

1

0

71

Mixed(P.v. & P.f.)

1

0

0

0

0

0

0

0

0

0

1

0

2

Mixed(P.v. & P.m.)

0

0

0

0

0

0

0

0

0

0

0

0

0

P.m.

0

0

0

0

0

0

0

0

0

0

0

0

0

Countries

Southeast Asia

Indonesia

Malaysia

Myanmar

Thailand

Vietnam

South Asia

India

Nepal

Pakistan

Other Asian countries

Papua New Guinea

Taiwan

Africa

Central African Republic

South Africa

Total

Total (%)

54 (47.8)

4 (3.5)

3 (2.6)

1 (0.9)

1 (0.9)

38 (33.6)

1 (0.9)

1 (0.9)

1 (0.9)

1(0.9)

7 (6.2)

1 (0.9)

113 (100.0)

P.v. - Plasmodium vivax P.m. - Plasmodium malariae P.f. - Plasmodium falciparum

India (33.6%). (Table 2.15) P. falciparum accounted for 44.4% of the infections acquired in Indonesia.

Overseas-acquired malaria

^ Excluding 4 introduced cases and 1 cryptic case.

36


P.f

33

7

0

0

0

0

0

0

0

0

0

0

0

0

0

0

40

P.v.

38

10

3

4

1

0

3

0

2

0

1

2

3

1

1

2

71

Mixed(P.v. & P.f.)

0

1

1

0

0

0

0

0

0

0

0

0

0

0

0

0

2

Mixed(P.v. & P.m.)

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

P.m.

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Interval inweeks

< 2

2 - 3

4 - 5

6 - 7

8 - 9

10 - 11

12 - 13

14 - 15

16 - 17

18 - 19

20 - 23

24 - 27

28 - 31

32 - 35

36 - 39

40+

Total

Total (%)

71 (62.8)

18 (15.9)

4 (3.5)

4 (3.5)

1 (0.9)

0 (0.0)

3 (2.6)

0 (0.0)

2 (1.8)

0 (0.0)

1 (0.9)

2 (1.8)

3 (2.7)

1 (0.9)

1 (0.9)

2 (1.8)

113 (100.0)

P.v. - Plasmodium vivax P.m. - Plasmodium malariae P.f. - Plasmodium falciparum

Parasite species

Most of the cases (78.7%) had onset of fever within three weeks of entry into Singapore. (Table 2.16)

Table 2.16Malaria cases^ by interval between period of entry and onset of illness

and by parasite species, 2003

For vivax malaria, 7.1% did not develop symptoms until more than six months after entry.

^ Excluding 4 introduced cases and 1 cryptic case.

37

The overseas-acquired cases comprised 38 (33.6%) Singapore residents; 33 (29.2%) work permit/employment pass holders; 24

%

29.3

24.2

4.0

4.6

28.7

9.2

100.0

Cases

51

42

7

8

50

16

174

Local Residents

Singapore residents

Work permit holders

Employment pass holders

Other foreigners

Foreigners seeking medical treatment in Singapore

Tourists

Total

Classification 2002 2003

%

33.6

20.4

8.9

4.4

21.2

11.5

100.0

Cases

38

23

10

5

24

13

113

(21.2%) foreigners seeking medical treatment in Singapore; 13 (11.5%) tourists; and 5 (4.4%) foreigners residing in Singapore. (Table 2.17)

Table 2.17Classification of overseas-acquired malaria cases by population group, 2002-2003

A large proportion of the Singapore residents affected visited malaria endemic areas, without taking adequate personal precautionary measures. (Table 2.18)

Table 2.18Purpose of travel for Singapore residents who contracted malaria overseas, 1999-2003

Table 2.19History of chemoprophylaxis for Singapore residents who contracted malaria overseas, 1999-2003

1999

8

74

8

90

2000

1

71

11

83

2001

0

51

4

55

2002

1

47

3

51

2003

0

35

3

38

Chemoprophylaxis

Took complete chemoprophylaxis

No chemoprophylaxis

Irregular/incomplete chemoprophylaxis

Total

1999

73

9

8

90

2000

60

16

7

83

2001

47

8

0

55

2002

37

13

1

51

2003

30

7

1

38

Purpose of Travel

Social visit/holiday

Business

Military service

Total

Furthermore, none of the Singapore residents with imported malaria had taken a complete course of chemoprophylaxis. (Table 2.19)

38


Blood film examinationA total of 1955 blood films were collected during routine epidemiological investigations and examined for malaria parasites.

No. positive formalaria parasites

00

00

00

01000000000000

1

Locality

Lim Chu Kang areaPulau Ubin & Tekong area

Bedok South areaSungei Gedong areaSungei Khatib Bongus area

Yishun St 23

Tekong HQTekong Campsite 1Rivervale LinkSengkang areaWoodlands Ave 5/6Tampines St 22Mount Vernon areaMandai estate Senja RoadMandai LinkHindhede RoadBukit Batok areaMandai RoadBukit Batok East Ave 2

Total

No. of blood films examined

51496

2272

10

231

22261137182

74

624

6922222953

199

1955

Introduced/cryptic malariaThere were five introduced/cryptic cases of malaria. One cryptic case was detected in Yishun

Street 21 area and the four introduced cases were from Pulau Tekong.

Only one blood film was tested positive for malaria parasite. (Table 2.20)

Table 2.20Malaria surveillance, 2003

39

In addition, 14332 blood films were routinely examined at the clinical laboratories of restructured

Malaria Outbreak at P. Tekong area On 5 August 2003, the Ministry of Health was notified of an imported case of vivax malaria. He was a Nepalese, from the Gurkha Contingent deployed at Pulau Tekong with onset of fever on 29 July 2003.

Subsequently, on 10 and 12 August 2003, two more cases of vivax malaria were notified. Both cases were national servicemen who were undergoing basic military training at Pulau Tekong (since April 2003) and were hospitalised at Changi General Hospital. They had no recent travel history outside Singapore.

Three days later, another national serviceman from Pulau Tekong was diagnosed with vivax malaria using PCR. On 19 August 2003, yet another national serviceman from Pulau Tekong was diagnosed with vivax malaria. The Singapore Armed Forces and the National Environment Agency were alerted when local

transmission was suspected. Active case detection was immediately carried out in Pulau Tekong and in the vicinity of the cases’ homes on the mainland. This included blood film examination conducted for Gurkhas, contract foreign workers and foreign construction workers in Pulau Tekong as well as foreign construction workers in the vicinity of the cases’ homes on the mainland. Of the 1018 blood films examined, one was positive for vivax malaria parasite. Fever surveillance among residents of the areas was also conducted and the residents were advised to seek medical advice if they experienced symptoms of malaria.

Prevention and controlMosquito larval survey and thermal fogging were immediately carried out in Pulau Tekong and in the vicinity of the patients’ homes. Although no Anopheles breeding was detected at the vicinity of the cases’ homes, Anopheles breedings were detected in Pulau Tekong. (Figure 2.6)

Table 2.21Examination of blood films for malaria parasite at various government

and restructured institutions, 2003

%0.3

0.7

0.8

0.7

3.6

3.6

1.1

No. positive13

24

27

8

63

21

156

No. of blood films examined4140

3343

3434

1089

1744

582

14332

InstitutionSingapore General Hospital

Tan Tock Seng Hospital

Changi General Hospital

Alexandra Hospital

National University Hospital

KK Women’s & Children’s Hospital

Total

hospitals. Of these, 156 (1.1%) tested positive for malaria parasites. (Table 2.21)

40


Figure 2.6Geographical distribution of four reported local malaria cases in Pulau Tekong,

July–August 2003

Comments One possible source of infection in this outbreak could have been the index Nepalese imported relapse case. He had a history of similar illness in

December 2002 prior to arrival in Singapore and did not complete his medication during the first episode of illness.

41

MURINE TYPHUSMurine typhus is a rickettsial disease whose course resembles that of a louseborne typhus. The infectious agents are Rickettsia typhi (Rickettsia mooseri) and Rickettsia felis. Mode of transmission is by infective rat fleas that defecate ricketsiae while sucking blood. This contaminates the bite site and other fresh skin wounds. Occasionally cases occur following the inhalation of dried

infective flea faeces.

In 2003, there were 16 reported cases of Murine typhus; of these, 3 (18.8%) were Singapore residents and 13 (81.2%) were foreign workers. The incidence rate was highest in the 15-24 years age group and amongst foreigners. (Tables 2.22 and 2.23)

Table 2.22Age-gender distribution and age-specific incidence rates of reported murine typhus cases, 2003

Male

0

0

5

5

4

0

0

14

Age (Yrs)

0 – 4

5 – 14

15 – 24

25 – 34

35 – 44

45 – 54

55+

Total

Total (%)

0 (0.0)

0 (0.0)

5 (31.2)

5 (31.2)

5 (31.2)

0 (0.0)

1 (6.4)

16 (100.0)

Female

0

0

0

0

1

0

1

2


* Rates are based on 2003-estimated mid-year population.(Source: Singapore Department of Statistics)

Table 2.23Ethnic-gender distribution and ethnic-specific incidence rates of reported murine typhus cases, 2003

Male

1

0

0

0

13

14

Singapore Resident

Chinese

Malay

Indian

Others

Foreigner

Total

Total (%)

1 (6.3)

1 (6.3)

1 (6.3)

0 (0.0)

13 (81.1)

16 (100.0)

Female

0

1

1

0

0

2


* Rates are based on 2003-estimated mid-year population.(Source: Singapore Department of Statistics)

0.0

0.0

0.8

0.6

0.7

0.0

0.2

0.4

0.04

0.2

0.4

0.0

1.7

0.4

42

Documents

Vector-borne Diseases - Ministry of Health