diseases borne air-/droplet- zoonotic...air-/droplet-borne diseases vector-borne/ zoonotic diseases...

Communicable Diseases Surveillance in Singapore 2007

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HIV

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S, S

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• Dengue • Leptospirosis • Malaria • Murine Typhus

Air-/D

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• Chikungunya Fever• Dengue• Japanese Encephalitis • Leptospirosis • Malaria • Murine Typhus


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IIVECTOR-BORNE DISEASES

Vector-borne and zoonotic diseases are diseases transmitted to humans by insects or animals. Vectors may transmit infectious diseases to humans through the blood-feeding 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 or protozoan and the transmission could be via direct contact, food and water.

CHIKUNGUNYA FEVERChikungunya fever is an acute febrile disease caused by the chikungunya virus. The disease is characterised by sudden onset of fever, chills, headache, nausea, vomiting, joint pain with or without swelling and low back pain. Some patients may develop a rash affecting the trunk and limbs. The illness is usually self-limiting. Most symptoms lasts for 3-10 days and the joint pain may last for weeks to months. The main vector is Aedes mosquito, the same type of mosquito that can transmit dengue fever.

In 2007, a total of 10 laboratory-confirmed cases of chikungunya fever were reported. Of these, seven were local residents who contracted the disease overseas. The remaining three cases were foreigners not resid-ing in Singapore who reportedly acquired the infection overseas and came to Singapore for medical treatment. All the cases were imported (Table 2.1 and 2.2).

Table 2.1Age-gender distribution and age-specific incidence rates of reported

chikungunya fever cases#, 2007

Age (Yrs) Male Female Total (%) Incidence rate per 100,000 population*

0 – 4 0 0 0 ( 0.0) 0.0

5 – 14 0 0 0 ( 0.0) 0.0

15 – 24 1 0 1 ( 14.3) 0.1

25 – 34 0 2 2 ( 28.6) 0.2

35 – 44 1 0 1 ( 14.3) 0.1

45 – 54 1 0 1 ( 14.3) 0.2

55+ 1 1 2 ( 28.6) 0.3

Total 4 3 7 (100.0) 0.2

#Excluding three foreigners seeking medical treatment in Singapore.*Rates are based on 2007 estimated mid-year population.

(Source: Singapore Department of Statistics)

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Table 2.2Ethnic-gender distribution and ethnic-specific incidence rates of reported

chikungunya fever cases#, 2007

Male Female Total (%) Incidence rate per 100,000 population*

Singapore Resident

Chinese 0 0 0 ( 0.0) 0.0

Malay 1 0 1 (14.3) 0.2

Indian 2 2 4 (57.1) 0.8

Others 0 0 0 ( 0.0) 0.0

Foreigner 1 1 2 (28.6) 0.2

Total 4 3 7 (100.0) 0.2

#Excluding three foreigners seeking medical treatment in Singapore.*Rates are based on 2007 estimated mid-year population.


Dengue fever is an acute febrile viral disease charac-terised by sudden onset of fever for 3 – 5 days, intense headache, myalgia, arthralgia, retro-orbital pain, an-orexia, gastrointestinal disturbances and rash. Early generalised erythema may occur in some cases. The infectious agents are flaviviruses comprising four sero-types (dengue-1, 2, 3 and 4) and are transmitted by the Aedes mosquito. In some cases, dengue haemorrhagic fever - a potentially fatal complication characterised by high fever, thrombocytopaenia, haemorrhagic manifesta-tions, and evidence of plasma leakage may develop.

DENGUE FEVER/DENGUE HAEMORRHAGIC FEVER (DF/DHF)A total of 8,826 laboratory confirmed cases of DF/DHF [comprising 8,637 cases of dengue fever (DF) and 189 cases of dengue haemorrhagic fever (DHF)] were report-ed in 2007, an increase of almost thrice from the 3,127 dengue cases reported in 2006. Of these, 8,426 were local residents with 139 imported and 8,287 indigenous cases. The remaining 400 cases were mainly foreigners not residing in Singapore and who reportedly acquired the infection overseas; majority of whom had come to Singapore for medical treatment. The incidence remains low throughout the year except the surge between May and August (Figure 2.1).

0

100

200

300

400

500

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

Week

No

. of

case

s

2006 2007

Figure 2.1E-weekly distribution of DF/DHF cases, 2006 – 2007


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The incidence rate among indigenous cases was high-est in the 55 years and above age group with a male to female ratio of 1.5:1 (Table 2.3). Among the three major

ethnic groups, Chinese had the highest incidence rate, followed by Malays and Indians. Foreigners comprised 28% of the indigenous cases (Table 2.4).

Table 2.3Age-gender distribution and age-specific incidence rates of indigenous# DF/DHF cases, 2007

Age (Yrs) Male Female Total (%)Incidence rate per 100,000

population*

0 – 4 58 42 100 ( 1.2) 48.0

5 – 14 272 258 530 ( 6.4) 102.6

15 – 24 797 473 1,270 (15.3) 176.7

25 – 34 1,135 667 1,802 (21.8) 188.8

35 – 44 1,140 637 1,777 (21.4) 219.7

45 – 54 662 472 1,134 (13.7) 174.4

55+ 869 805 1,674 (20.2) 228.9

Total 4,933 3,354 8,287 (100.0) 180.6

#Cases acquired locally among Singaporeans, permanent and temporary residents.*Rates are based on 2007 estimated mid-year population.


Table 2.4Ethnic-gender distribution and ethnic-specific incidence rates of indigenous#

DF/DHF cases, 2007

Male Female Total (%)Incidence rate per 100,000

population*

Singapore Resident

Chinese 2,578 2,118 4,696 (56.7) 174.8

Malay 383 288 671 ( 8.1) 136.8

Indian 216 138 354 ( 4.3) 113.0

Others 134 110 244 ( 2.9) 264.9

Foreigner 1,622 700 2,322 (28.0) 230.9

Total 4,933 3,354 8,287 (100.0) 180.6

#Cases acquired locally among Singaporeans, permanent and temporary residents.*Rates are based on 2007 estimated mid-year population.


There were 139 (1.6%) imported cases, defined as local residents with a history of travel to endemic areas seven days prior to the onset of illness. The majority of these cases (74.1%) were from Southeast Asian countries:

34 from Indonesia, 31 from Malaysia, 14 from Thailand, eight from Viet Nam, six from Philippines, four from Cambodia, four from Myanmar, one from Brunei and one from East Timor (Table 2.5).

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Table 2.5Imported DF/DHF cases, 2003 – 2007

Year

2003 2004 2005 2006 2007

Southeast Asia

Brunei 0 0 0 0 1

Cambodia 8 4 0 4 4

East Timor 0 0 0 0 1

Indonesia 93 17 11 34 34

Laos 0 0 0 1 0

Malaysia 100 22 2 25 31

Myanmar 1 1 0 0 4

Philippines 2 1 0 5 6

Thailand 18 3 1 8 14

Viet Nam 2 0 0 2 8

South Asia

Bangladesh 1 1 0 5 2

India 14 7 0 12 20

Maldives 0 0 0 2 0

Nepal 1 0 0 0 0

Pakistan 1 0 0 0 0

Sri Lanka 3 2 0 1 2

Other Regions 2 3 0 4 12

Total 246 61 14 103 139

Residents in Housing & Development Board (HDB) flats, condominiums and compound houses constituted 63.2%, 17.2% and 14.7% of the cases, respectively.

However, the incidence rate of residents of compound houses (351.5 per 100,000) was over double that of residents in HDB flats (156.5 per 100,000) (Table 2.6).

Table 2.6Incidence rates of reported indigenous DF/DHF cases by housing type, 2007

Housing Type No. %Incidence rate per 100,000

population*

Compound houses (including shophouses) 1,217 14.7 351.5

HDB Flats 5,242 63.2 156.5

Condominiums 1,420 17.2 453.8

Others 408 4.9 70.2

Total 8,287 100.0 180.6

*Rates are based on census of population 2000.(Source: Singapore Department of Statistics)

Though cases were concentrated in the central (29.0%) and south-eastern (20.4%) parts of Singapore, cases were reported from around the island [according to the

boundary demarcated by the Community Development Council / National Environment Agency (NEA) Regional Office] (Figure 2.2).


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A total of 949 clusters involving 3,877 epidemiologically linked cases were identified. The median number of cases in each cluster was three (range 2 to 117) and the

median duration of transmission was 10 days (range 1 to 81) (Table 2.7). The number of clusters increased by 9.0% compared to the previous year.

Figure 2.2Geographical distribution of dengue cases, 2007

Table 2.7Dengue clusters identified, 1990 – 2007

YearNo. of indig-enous cases

No. ofclusters*

No. of cases incluster area

(% total cases)

No. of clusterswith ≥ 10 cases

(% total clusters)

Median no.of cases

per cluster

Median duration of transmission

(days)

1990 1,640 40 270 (16.5) 11 (27.5) 4.5 10

1991 2,062 74 414 (20.1) 9 (12.2) 3.5 6

1992 2,741 134 733 (26.7) 13 ( 9.7) 3 5

1993 794 33 183 (23.0) 4 (12.1) 3 8

1994 1,084 75 424 (39.1) 8 (10.7) 3 7

1995 1,756 118 679 (38.7) 16 (13.6) 3 7

1996 2,877 143 1,088 (37.8) 27 (18.9) 3 6

1997 4,039 198 1,124 (27.8) 24 (12.1) 3 5

1998 5,105 239 1,197 (23.4) 23 ( 9.6) 2 7

1999 1,138 54 230 (20.2) 6 (11.1) 3 11

2000 402 9 40 (10.0) 1 (11.1) 4 15

2001 2,064 93 531 (25.7) 15 (16.1) 3 8

2002 3,560 73 725 (20.4) 30 (41.1) 7 20

2003 4,542 180 1,405 (30.9) 38 (21.1) 4.5 12

2004 9,297 559 2,434 (26.2) 34 ( 6.1) 3 4

2005 14,032 1,190 5,362 (37.7) 93 ( 7.8) 3 5

2006 2,844 172 871 (30.6) 19 (11.0) 3 5

2007 8287 949 3,877 (46.8) 58 ( 6.1) 3 10

*A cluster is defined as two or more cases epidemiologically linked by place [within 150m (200m till 2002)] and time (within 14 days)

Dengue cases

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Table 2.8Dengue clusters identified, 2007 (10 or more cases)

S/No LocationNo. of cases

Month

1 Bukit Batok Street 31 / Bukit Batok Street 32 / Bukit Batok Street 33 / Bukit Batok Street 34 117 Jul - Sep

2 Pasir Ris Drive 6 / Pasir Ris Drive 3 71 May - Jul

3 Woodlands Street 83 / Woodlands Street 82 / Woodlands Street 81 67 Jul - Aug

4 Construction site at West Coast Road / Clementi Road 42 Jun - Jul

5 West Coast Drive / West Coast Walk / West Coast Road / Jalan Mas Puteh 34 May - Jun

6Jalan Songket / Hougang Street 21 / Aroozoo Avenue / Surin Avenue / Jalan Samarinda / Jalan Mastuli / Jalan Pelikat

32 Mar - May

7 Kim Keat Road / Kim Keat Close / Kim Keat Lane 32 May - Jun

8 Tampines Street 22 30 May - Jul

9 Clementi West Street 2 / West Coast Road 25 Jun - Jul

10 Ang Mo Kio Avenue 4 25 Aug - Oct

11 West Coast Road 24 May - Jun

12Lorong 14 Geylang / Lorong 16 Geylang / Lorong 17 Geylang / Lorong 19 Geylang / Lorong 21 Geylang / Lorong 12 Geylang

23 May - Jun

13 Pasir Ris Drive 6 / Pasir Ris Drive 4 23 Jun - Jul

14 Bukit Batok Central / Bukit Batok Street 21 / Bukit Batok East Avenue 3 23 Jul - Aug

15 Simei Street 4 20 Sep - Nov

16 Balestier Road / Martaban Road / Pegu Road / Minbu Road / Mandalay Road / Jalan Ampas 19 Apr - May

17 Admiralty Road West 19 Apr - Jun

18 Boon Lay Drive 19 May - Jun

19 Ang Mo Kio Avenue 9 18 Jun - Jul

20 Clementi Avenue 1 18 Sep - Nov

21 Construction site at East Coast Road / Lorong N Telok Kurau 18 Nov - Dec

22 Ho Ching Road / Tao Ching Road / Yung Sheng Road 17 May - Jun

23 Lorong Ah Soo / Hougang Avenue 1 17 May - Jun

24 Yio Chu Kang Gardens 17 Jun

25 Bukit Batok Street 33 17 Jul - Aug

26 Serangoon Road / Race Course Road 16 Mar - Apr

27Geylang Road / Lorong 20 Geylang / Lorong 22 Geylang / Guillemard Road / Westerhout Road / Lorong 23 Geylang / Sims Avenue

15 May - Jun

28 Pandan Gardens 15 Jun - Jul

29 Pasir Ris Drive 1 14 Jun - Jul

30 Geylang Road / Lorong 9 Geylang / Lorong 11 Geylang / Lorong 13 Geylang 14 Jul - Aug

31 Pipit Road / Paya Lebar Way / Circuit Road 14 Aug - Sep

32 Upper Changi Road North 13 Mar - Apr

33 Khalsa Crescent 13 May

34 Saujana Road / Jelepang Road 13 May - Jul

35 Jurong East Street 21 13 Jul - Aug

36 Bukit Batok Street 21 / Bukit Batok East Avenue 3 13 Oct

37 Lorong 40 Geylang / Lorong 42 Geylang 12 May

38 Jalan Senang / Senang Crescent / Chai Chee Drive 12 May - Jun

39 East Coast Road / Lorong M Telok Kurau / Lorong N Telok Kurau 12 May - Jun

40 Lorong Lew Lian / Lorong Ong Lye / Upp Paya Lebar Road 12 May - Jul

41 Bedok Reservoir Road 12 Jun - Jul

42 Dakota Crescent 12 Jun - Jul

43 Tampines Street 22 12 Jun - Jul

44 Lorong 6 Geylang / Lorong 10 Geylang / Geylang Road 12 Jun - Jul

45 Bukit Batok West Avenue 6 12 Jul - Aug

46 Jurong East Street 24 12 Aug - Sep

47 Lichi Avenue / Butterfly Avenue / Belimbing Avenue / Chempaka Avenue 12 Oct - Nov


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48 Tampines Street 83 / Tampines Avenue 5 11 Jan - Feb

49 Tampines Street 21 11 Jun - Jul

50 Lorong 4 Geylang / Lorong 8 Geylang 11 Aug

51 Barbary Walk / Alexandra Road / Merino Crescent / Angora Close 11 Aug - Sep

52 Bukit Batok Street 32 / Bukit Batok Street 33 11 Sep - Oct

53 Construction site at Martin Road 11 Dec - Jan

54 Tampines Street 11 10 May - Jun

55 Ang Mo Kio Avenue 8 10 Jun - Jul

56 Meyer Road / Meyer Place / Arthur Road 10 Jun - Jul

57 Pasir Panjang Road / Neo Pee Teck Lane / Clementi Road 10 Sep

58Lorong Pisang Emas / Lorong Pisang Udang / Lorong Pisang Hijau / Lorong Pisang Asam / Chun Tin Road

10 Nov

A total of 24 fatal cases of DF/DHF, comprising 8 DF and 16 DHF cases were reported in 2007. Of these, 20 cases were indigenous infections among local residents.

DHF Deaths The remaining four cases consisted of a tourist and three non-resident foreigners who sought treatment in Singapore; all had acquired the infection overseas.

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

A total of 1,044 blood samples obtained from both inpa-tients and outpatients tested positive for dengue virus by Polymerase Chain Reactions (PCR) at the Department of Pathology and Laboratory Medicine, Tan Tock Seng Hospital, National University Hospital’s Laboratory and

Laboratory Surveillancethe Environmental Health Institute, National Environ-mental Agency.

All four dengue serotypes were detected, comprising DEN-1 (5.7%), DEN-2 (78.7%), DEN-3 (4.1%) and DEN-4 (0.6%). 10.9% was indeterminate (Figures 2.3 and 2.4).

There is a change in the predominant circulating serotype from DEN-1 in 2006 to DEN-2 in 2007 (Figure 2.4).

0

50

100

150

200

250

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Months

No

. of

po

siti

ve s

amp

les

DEN-1 DEN-2 DEN-3 DEN-4

Figure 2.3Surveillance of dengue virus serotypes, 2007

(Source: Environmental Health Institute, Tan Tock Seng Hospital Department of Pathology and Laboratory Medicine, and National University Hospital Laboratory)

0

50

100

150

200

250

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Months

No

. of

po

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amp

les


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Figure 2.4Surveillance of dengue virus serotypes, 1992 – 2007

(Source: Singapore General Hospital Department of Pathology, Environmental Health Institute, Tan Tock Seng Hospital Department of Pathology and Laboratory Medicine, National University Hospital Laboratory, and KK Hospital Laboratory)

0

10

20

30

40

50

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May1992

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Year

% o

f p

osi

tive

sam

ple

s


Aedes Surveillance and Control Singapore adopts a multi-pronged approach to the con-trol of dengue. Since September 2005, the National En-vironment Agency (NEA) has enhanced measures in the areas of mosquito surveillance and control, enforcement, community outreach and education as well as research to minimise the potential of dengue outbreaks.

One key feature of NEA’s dengue surveillance system is preventive surveillance. Everyday, there are about 500 NEA officers that carry out regular inspection island-wide to systematically uncover and destroy mosquito-breeding habitats. The focus is primarily on areas that are prone to dengue and/or high density of Aedes mosquitoes (e.g. construction sites, schools, compounds of landed properties). Under the surveillance system, NEA has dedicated teams of vector control officers responsible for the regular auditing, inspections and enforcement in each of the 84 constituencies. The effectiveness of these teams lies in their familiarity with the areas under their charge and their local knowledge of problematic spots. NEA also promotes an intersectoral preventive surveillance approach. Through the Inter-agency Den-gue Task Force, NEA plays a leadership role in building Aedes surveillance systems into the daily routines of other government agencies and departments.

In 2007, NEA inspected some 1.5 million premises and carried out over 46,000 ground surveys. In addition,

more than 2,500 ovitraps were placed around Singapore for Aedes monitoring (Figure 2.5). The distribution of dengue cases was more closely associated with Aedes aegypti than Aedes albopictus (Figure 2.6). (Note: Aedes aegypti and Aedes albopictus are now known as Stego-myia aegypti and Stegomyia albopictus respectively.)

Over and above routine surveillance checks, pre-emp-tive “Intensive Source Reduction Exercises” (ISREs) are carried out from April to September ahead of the warmer months (typically June to October when the weekly incidence of dengue cases traditionally peak) to minimise the mosquito population and the impact of dengue outbreaks. NEA together with other land agen-cies, Town Councils and their pest control operators carried out ISREs successfully in 2007, which helped to curb the surge in dengue cases traditionally experienced during the warmer months. The agencies coordinated their search and destroy operations in their respective premises and public areas including residential estates. Breedings are destroyed immediately and potential breeding habitats uncovered during the exercise are re-corded for follow-up actions. ISRE will continue to be an important event in NEA’s dengue operations calendar.

The overall Aedes premises index was about 0.68%, with the highest percentage detected in compound houses (Figure 2.7). The top five breeding habitats


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for Aedes aegypti were domestic containers (32%), ornamental containers (21%), flower pot plate (11%), toilet bowl/cistern (3%) and bamboo pole holders (2%) (Figure 2.8). In the case of Aedes albopictus, the most common breeding habitats were flower pot plate (19%), domestic containers (19%), ornamental containers (15%), discarded receptacles (4%) and roof gutters (3%) (Figure 2.9).

To reduce the number of breedings found in TC-main-tained areas, NEA has helped Town Councils implement dedicated mosquito control programmes from Septem-ber 2005. Apart from providing technical specifications for dengue control works, NEA also trained officers in these 15 TCs to be Estate Environmental Officers so that they can supervise the performance of the dedicated pest control operators. Since the implementation of this programme, the reduction of Aedes breeding found in these estates had reduced from 19% in 2005 to about 5.8% and 5.7% in 2006 and 2007 respectively.

NEA has been working closely with the community and grassroots voluntary groups. To engage the community

in our fight against dengue, NEA also makes use of both multimedia advertising (“broadcast”) and target-group specific outreach programmes. NEA will continue to refine its public outreach efforts to bring about greater awareness and to make the practice of keeping homes mosquito-free a way of life for members of the commu-nity. This will be part of our long-term effort to encourage ownership in dengue prevention.

Research is an integral part of Singapore’s Aedes surveil-lance and control programme to establish an evidence-based Aedes control strategy. The Environmental Health Institute (EHI), a research arm of the NEA, has four key programmes, Surveillance, Epidemiology, Vector Control and Diagnostics. The Surveillance Programme seeks to develop better mosquito surveillance tools and strategy. A key activity of the programme is the monitoring of viral serotypes circulating in Singapore. The Epidemiology Programme seeks to understand the factors contrib-uting to dengue outbreaks. Under the Vector Control Programme, new tools are evaluated and developed for vector control. The Diagnostics Programme develops and evaluates dengue diagnostic tools, to facilitate early and accurate notification of dengue cases.

Figure 2.5Locations of 2,500 ovitraps used for Aedes surveillance

(Source: National Environment Agency)

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Figure 2.6Geographical distribution of Aedes albopictus, Aedes aegypti and dengue cases, 2007


Aedes albopictusAedes aegyptiDengue cases

Figure 2.7Percentage of premises breeding Aedes mosquitoes, 1998 – 2007


1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Year

% o

f pre

mis

es b

reed

ing

0

1

2

3

4

5

6

7

HDB flats Condominiums Compound houses


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Figure 2.8Distribution of Aedes aegpyti by top five breeding habitats, 2007


Figure 2.9Distribution of Aedes albopictus by top five breeding habitats, 2007


Domestic Containers

Ornamental Containers

Flower Pot Plate/Tray

Toilet Bowl/Cistern

Bamboo Pole Holder

Others

21%11%

3%

2%

31% 32%

Flower Pot Plate/Tray

Domestic Containers

Ornamental Containers

Others

Discarded Receptacles

Roof Gutters

40%

4%3%

15%

19%

19%

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On 5 July 2007, the Ministry of Health was notified of a case of dengue fever residing in Bukit Batok Street 34. Within one week, another seven cases among residents in the same area were reported. As soon as the cluster was identified, epidemiological investigations and vector control operations were carried out.

Outbreak of dengue at Bukit Batok Street 31 / Bukit Batok Street 32 / Bukit Batok Street 33 / Bukit Batok Street 34

A total of 117 serologically confirmed cases were identified in this outbreak. All of them had onset of illness between 2 July 2007 and 23 September 2007. The epidemic curve is shown in Figure 2.10.

0

1

2

3

4

5

6

7

8

9

10

01-Jul-07 09-Jul-07 17-Jul-07 25-Jul-07 02-Aug-07 10-Aug-07 18-Aug-07 26-Aug-07 03-Sep-07 11-Sep-07 19-Sep-07 27-Sep-07

Date of onset

No

.of

ca

ses

Search &

destroy

Indoor fogging

Major

Breeding

Cluster notification on 11 Jul 07

First case notification

on 6 Jul 07

Outdoor Fogging

Figure 2.10 Time distribution of 117 DF/DHF cases in Bukit Batok Street 31 / Bukit Batok Street 32 / Bukit

Batok Street 33 / Bukit Batok Street 34, July – September 2007

A breakdown by occupation showed that the cases comprised 39 working adults, 20 students, seven housewives, three unemployed, two domestic maids, two retirees and one infant. The remaining cases were uncontactable. The majority of the cases were in the 35 - 54 years age group (44.5%). The female to male ratio was 1:1.17.

All of the cases were clustered by residential/workplace addresses within a 150-metre radius from the initial focus

of transmission (Figure 2.11). As part of vector control operations, Aedes mosquito breeding habitats were identified in 81 (3%) of the 2735 premises inspected. 40.7% of the breeding habitats were found in domestic containers (dish trays, pails etc.) and 21% were found in toilet bowl/cistern. It was noted that most of the breeding habitats were detected in residential premises. Aedes aegypti and Aedes albopictus accounted for 85% and 15% of the breeding respectively.


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Figure 2.11Geographical distribution of 117 DF/DHF cases in Bukit Batok Street 31 / Bukit Batok Street 32 /

Bukit Batok Street 33 / Bukit Batok Street 34, July – September 2007

JAPANESE ENCEPHALITISJapanese encephalitis is an arthropod-borne disease, characterised by sudden onset of high fever, chills, severe headache, meningismus, photophobia, nau-sea, abdominal pain, drowsiness and obtundation. The infectious agent is the Japanese encephalitis virus (a Flavivirus), which the mosquitoes acquired mainly from domestic pigs and wild birds. The mode of transmission is through the bite of infective mosquitoes from the Culex tritaeniorhynchus group.

There was a local case of Japanese encephalitis (JE) reported in 2007. She was a 38 year old Indian domestic helper who had been working in Singapore since No-vember 2005. She had not travelled out of the country since then. Her symptoms include fever and confusion on 19 July 2007 and she was hospitalised between 21-27 July 2007. Molecular test detected JE virus in her cerebral spinal fluid. The case has returned to India on 28 July 2007

LEPTOSPIROSISLeptospirosis is a zoonotic bacterial disease of vari-able clinical manifestations. The common presenting features are fever, headache, chills, severe myalgia and conjunctival suffusion. The etiologic agent – Leptospires - is a spiral organism and a member of the order Spi-rochaetales 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 infected animals may also cause infection. Occasionally leptospirosis has oc-

curred following the ingestion of food contaminated by the urine of infected rats.

In 2007, a total of 26 laboratory-confirmed cases of leptospirosis were reported, compared with 29 in 2006. Of these 23 were local residents, comprising of 16 indig-enous and 7 imported cases. The remaining three cases were two foreigners who came to Singapore for medical treatment and leisure and one Singaporean who stayed overseas (Table 2.9 and 2.10).

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leptospirosis cases^, 2007

Age (Yrs) Male Female Total (%) Incidence rate per 100,000 population*

0 – 4 0 0 0 ( 0.0) 0.0

5 – 14 0 0 0 ( 0.0) 0.0

15 – 24 4 3 7 ( 30.4) 1.0

25 – 34 8 0 8 ( 34.8) 0.8

35 – 44 4 0 4 ( 17.4) 0.5

45 – 54 0 0 0 ( 0.0) 0.0

55+ 2 2 4 ( 17.4) 0.5

Total 18 5 23 (100.0) 0.5

^Excluding three non-resident cases.*Rates are based on 2007 estimated mid-year population.



leptospirosis cases^, 2007

Male Female Total (%) Incidence rate per 100,000 population*

Singapore Resident

Chinese 4 1 5 ( 24.0) 0.2

Malay 1 1 2 ( 8.0) 0.4

Indian 1 0 1 ( 4.0) 0.3

Others 0 0 0 ( 0.0) 0.0

Foreigner 12 3 15 ( 64.0) 1.5

Total 18 5 23 (100.0) 0.5

^Excluding three non-resident cases.*Rates are based on 2007 estimated mid-year population.


MALARIAMalaria is a parasitic disease characterised by fever and chills. Most serious malarial infections may present with cough, diarrhoea, respiratory distress and headache. The infectious agent is a protozoan parasite, Plas-modium, and there are four different species namely, P. vivax, P.malariae, P. faciparum and P. ovale. The mode of transmission is via a bite of an infective female Anopheles mosquito.

In 2007, a total of 154 laboratory-confirmed cases were reported, a decrease of 14.9% from the 181 cases reported in 2006 (Figure 2.12). However, 148 (96.1%) cases were reportedly acquired overseas. There was a cluster of simian malaria cases involving three local residents. Among the other 89 local residents affected, 86 were classified as imported cases, two were classified as introduced and one was classified as indigenous. The remaining were tourists (13) and foreigners seeking medical treatment in Singapore (49).


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0

2

4

6

8

10

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

Week

No

. o

f C

ases

2006 2007

Figure 2.12E-weekly distribution of reported malaria cases, 2006 – 2007

Among the 92 reported cases of malaria in local resi-dents, the age-specific incidence rate was highest in the 25 – 34 years age group. The male to female ratio was

3.6:1 (Table 2.11). Among the three major ethnic groups, the incidence rate was highest for Malays, followed by Indians and Chinese (Table 2.12).

Table 2.11Age-gender distribution and age-specific incidence rates of

reported malaria cases^, 2007


population*

0 – 4 0 0 0 ( 0.0) 0.0

5 – 14 0 1 1 ( 1.1) 0.2

15 – 24 17 6 23 ( 25.0) 3.2

25 – 34 32 5 37 ( 40.2) 3.5

35 – 44 10 2 12 ( 13.0) 1.5

45 – 54 10 5 15 ( 16.3) 2.3

55+ 3 1 4 ( 4.4) 0.5

Total 72 20 92 (100.0) 2.0

^Excluding 49 foreigners seeking medical treatment in Singapore and 13 tourists.*Rates are based on 2007 estimated mid-year population.


36

Table 2.12Ethnic-gender distribution and ethnic-specific incidence rates of

reported malaria cases^, 2007

Male Female Total (%)Incidence rate per

100,000 population*

Singapore Resident

Chinese 15 5 20 ( 21.7) 0.7

Malay 4 3 7 ( 7.6) 1.4

Indian 2 1 3 ( 3.3) 1.0

Others 1 2 3 ( 3.3) 3.3

Foreigner 50 9 59 ( 64.1) 5.9

Total 72 20 92 (100.0) 2.0

^Excluding 49 foreigners seeking medical treatment in Singapore and 13 tourists.*Rates are based on 2007 estimated mid-year population.


Table 2.13Classification of reported malaria cases by parasite species, 2007*

Classification

Parasite species

Total (%)P.v. P.f.

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

Mixed(P.f. & P.m.)

P.m.

Imported** 101 42 2 1 2 148 (98.0)

Introduced 2 0 0 0 0 2 (1.3)

Indigenous 0 1 0 0 0 1 (0.7)

Cryptic 0 0 0 0 0 0 (0.0)

Induced 0 0 0 0 0 0 (0.0)

Total 103 43 2 1 2 151 (100)

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

*Exclude the three simian malaria cases involving SAF personnel**Including relapsed and induced cases that were imported.

Overseas-acquired malariaThe majority of the malaria cases acquired overseas were infected in India (39.2%) and Indonesia (35.1%).

P. vivax accounted for 86.2% and 61.5% of the infec-tions acquired in India and Indonesia respectively (Table 2.14).

Malaria parasite speciesThe distribution of the cases by parasite species was P. vivax (68.2%), P. falciparum (28.5%), P. malariae (1.3%)

and mixed infection (2.0%) (Table 2.13).


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Table 2.14Imported malaria cases by country of origin and by parasite species, 2007

Countries P.v. P.f.Mixed

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

(P.f. & P.m.)P.m. Total %

Southeast Asia

Indonesia 32 18 1 0 1 52 35.1

Malaysia 4 3 0 1 0 8 5.4

Myanmar 6 1 0 0 0 7 4.7

Philippines 0 1 0 0 0 1 0.7

Thailand 5 2 0 0 0 7 4.7

South Asia

India 50 7 1 0 0 58 39.2

Pakistan 1 0 0 0 0 1 0.7

Other Asian countries

Papua New Guinea 2 1 0 0 0 3 2.0

Africa

Angola 0 1 0 0 0 1 0.7

Equatorial Guinea 0 1 0 0 0 1 0.7

Ghana 0 1 0 0 0 1 0.7

Mozambique 0 1 0 0 0 1 0.7

Nigeria 1 4 0 0 1 6 4.0

South Africa 0 1 0 0 0 1 0.7

Total 101 42 2 1 2 148 100.0


Most of the cases (86.4%) had onset of fever within three weeks of entry into Singapore (Table 2.15). For

P. vivax malaria, 16.8% did not develop symptoms until more than six weeks after entry.

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Table 2.15Imported malaria cases by interval between period of entry and onset of illness and

by parasite species, 2007

Interval in weeks

Parasite species

P.v. P.f.Mixed

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

(P.f. & P.m.)P.m. Total (%)

<2 70 40 2 1 1 114 (77.0)

2 – 3 12 1 0 0 1 14 (9.4)

4 – 5 2 1 0 0 0 3 (1.9)

6 – 7 1 0 0 0 0 1 (0.7)

8 – 9 2 0 0 0 0 2 (1.4)

10 – 11 2 0 0 0 0 2 (1.4)

12 – 13 1 0 0 0 0 1 (0.7)

14 – 15 0 0 0 0 0 0 (0.0)

16 – 17 0 0 0 0 0 0 (0.0)

18 – 19 2 0 0 0 0 2 (1.4)

20 – 23 2 0 0 0 0 2 (1.4)

24 – 27 3 0 0 0 0 3 (1.9)

28 – 31 0 0 0 0 0 0 (0.0)

32 – 35 2 0 0 0 0 2 (1.4)

36 – 39 1 0 0 0 0 1 (0.7)

40+ 1 0 0 0 0 1 (0.7)

Total 101 42 2 1 2 148 (100.0)


The overseas-acquired cases comprised 28 Singapore residents (18.9%), 51 work permit/employment pass holders (34.5%), five student pass holders (3.4%), two

other foreigners (1.3%), 49 foreigners seeking medical treatment in Singapore (33.1%) and 13 tourists (8.8%) (Table 2.16).

Table 2.16Classification of imported malaria cases by population group, 2006 – 2007

Classification2006 2007

Cases % Cases %

Local Residents

Singapore residents 55 33.2 28 18.9

Work permit/Employment pass holders 46 27.7 51 34.5

Student pass holders 6 3.6 5 3.4

Other foreigners 2 1.2 2 1.3

Foreigners seeking medical treatment 38 22.9 49 33.1

Tourists 19 11.4 13 8.8

Total 166 100.0 148 100.0

The majority of Singapore residents who contracted malaria whilst travelling overseas were on social visits

or holidays. All admitted that they did not take chemo-prophylaxis (Table 2.17 and 2.18).


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Table 2.17Purpose of travel for Singapore residents who contracted malaria overseas, 2003 – 2007

2003 2004 2005 2006 2007

Purpose of Travel

Social visits/holidays 30 34 35 44 23

Business 7 8 11 5 3

Military service 1 1 0 1 0

Employment 0 0 0 5 2

Total 38 43 46 55 28

Table 2.18History of chemoprophylaxis for Singapore residents who contracted malaria overseas,

2003 – 2007

2003 2004 2005 2006 2007

Chemoprophylaxis

Took complete chemoprophylaxis 0 1 0 0 0

No chemoprophylaxis 35 40 45 51 28

Irregular/Incomplete chemoprophylaxis

3 2 1 4 0

Total 38 43 46 55 28

A local case involving a 20 year old NS man who developed generalised body aches, fever and joint pains on 25 April 07 was admitted to CDC TTSH on 28 April 07. Prior to the onset of illness, he was undergoing jungle training in the vicinity of Lim Chu Kang Road/Neo Tiew Road area (military prohibited area) in early April 07. He is currently attached to Sungei Gedong Camp. He was earlier diagnosed to be suffering from P. malaria but PCR later confirmed to be P. knowlesi. Two more cases were reported in 20-year-old NSFs who developed fever, chills, body ache, myalgia and giddiness on 26 - 27 May 07 and were admitted to CDC on 2 Jun 07. These two soldiers resided in the same army camp. In view that their clinical presentation was similar to the first soldier, further laboratory investigations were conducted and

these were positive for Plasmodium knowlesi. Detailed movement history in the past 2 months showed that they were both attached to Selarang Camp in Changi, and prior to their onset of fever, had been to Pulau Tekong, western training areas including Neo Tiew/Sarimbun area, and Marsiling live firing area off Lorong Asrama.

In the absence of significant travel history, the above three infections were most probably acquired locally in the SAF forested training areas where macaques have been sighted. A total of 230 blood slides (for microscopy) and 208 venous samples (for PCR) taken from 230 people living within the area were screened negative for the presence of malaria parasite.

Cluster of simian malaria cases involving SAF personnel

40

Local P. falciparum malaria was diagnosed in a 38-year-old foreign construction worker who developed fever, epigastric pain and cough on 9 September 07. He was admitted to CDC on 14 September 07. The case had been working in a construction site on Jurong Island since 15 August 07. Prior to that, the case had

Sporadic local malaria case from the southern islands

been working on Marina Bay IR and Paya Lebar KPE projects. The case had no other travel history since arrival in 2006 and he stayed in the dormitory when he was not working. All the 308 blood slides collected from construction workers were tested negative for malaria parasites.

Blood film examination for malaria parasitesA total of 836 blood films were collected during routine epidemiological investigations and examined for ma-

laria parasites. Of these, none was tested positive for malaria parasite (Table 2.19).

There was a cluster of local P. vivax malaria case involving a 56-year-old odd job labourer and a 49-year-old driver who developed fever and other symptoms on 11 June 07. Both were admitted to SGH on 14 June 07 and 15 June 07, respectively. They had no recent travel history prior to the onsets of illnesses and movement history

Cluster of local malaria cases (probable introduced) involving Redhill residents

was confined to home surroundings and coffee shop at Blk 161 Bukit Merah Centre. 170 blood slides collected from construction workers, during our screening exercise dated 20 June 07, were all tested negative for malaria parasites. The source of infection was unknown.

Table 2.19Malaria Surveillance, 2007

Locality No. of blood films examined No. positive for malaria parasite

Yishun Avenue 6 95 0

Woodlands Street 13 33 0

Mandai Road 89 0

Neo Tiew Road 141 0

Red Hill construction sites 170 0

Jurong Island 43 0

Marina Bay 230 0

Kim Chuan Road 35 0

Total 836 0


41

MURINE TYPHUSMurine typhus is a rickettsial disease whose course resembles that of louse-borne 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 from its host. This contaminates the bite site and other fresh skin wounds. Occasionally cases occur following the inhalation of dried infective flea faeces.

In 2007, a total of 21 laboratory confirmed cases of murine typhus were reported, compared with 11 in 2006. Only four (19%) were Singapore residents and 17 (81%) were foreigners (16 workers and one student). The majority of cases were male. 19 cases were indigenous while two were imported. The incidence rate was highest for foreigners in the 35 – 44 years age group (Tables 2.20 and 2.21).


murine typhus cases, 2007

Age-group Male Female Total (%)Incidence rate per

100,000 population*

0 – 4 0 0 0 ( 0.0) 0.0

5 – 14 0 0 0 ( 0.0) 0.0

15 – 24 2 1 3 ( 14.3) 0.4

25 – 34 4 1 5 ( 23.8) 0.5

35 – 44 9 0 9 ( 42.8) 1.1

45 – 54 2 1 3 ( 14.3) 0.5

55+ 0 1 1 ( 4.8) 0.1

Total 17 4 21 (100.0) 0.5

* Rates are based on 2007 estimated mid-year population.(Source: Singapore Department of Statistics)



Male Female Total (%)Incidence rate per

100,000 population*

Singapore Resident

Chinese 1 2 3 ( 14.3) 0.1

Malay 1 0 1 ( 4.7) 0.2

Indian 0 0 0 ( 0.0) 0.0

Others 0 0 0 ( 0.0) 0.0

Foreigner 15 2 17 ( 81.0) 1.7

Total 17 4 21 (100.0) 0.5


MURINE TYPHUSMurine typhus is a rickettsial disease whose course resembles that of louse-borne 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 from its host. This contaminates the bite site and other fresh skin wounds. Occasionally cases occur following the inhalation of dried infective flea faeces.

In 2007, a total of 21 laboratory confirmed cases of murine typhus were reported, compared with 11 in 2006. Only four (19%) were Singapore residents and 17 (81%) were foreigners (16 workers and one student). The majority of cases were male. 19 cases were indigenous while two were imported. The incidence rate was highest for foreigners in the 35 – 44 years age group (Tables 2.20 and 2.21).




population*

0 – 4 0 0 0 ( 0.0) 0.0

5 – 14 0 0 0 ( 0.0) 0.0

15 – 24 2 1 3 ( 14.3) 0.4

25 – 34 4 1 5 ( 23.8) 0.5

35 – 44 9 0 9 ( 42.8) 1.1

45 – 54 2 1 3 ( 14.3) 0.5

55+ 0 1 1 ( 4.8) 0.1

Total 17 4 21 (100.0) 0.5




Male Female Total (%)Incidence rate per 100,000

population*

Singapore Resident

Chinese 1 2 3 ( 14.3) 0.1

Malay 1 0 1 ( 4.7) 0.2

Indian 0 0 0 ( 0.0) 0.0

Others 0 0 0 ( 0.0) 0.0

Foreigner 15 2 17 ( 81.0) 1.7

Total 17 4 21 (100.0) 0.5


42

Rodent surveillance and controlRodents can spread diseases such as leptospirosis, hanta fever and murine typhus. These medically impor-tant diseases can be transmitted through rodent urines, faeces and bites of infective fleas that live on the rodent bodies. Besides that, rodent urines and faeces can also pose a serious hygiene problem in food establishment. To eliminate the public health risks posed by rodents, a comprehensive rodent surveillance and control system is essential. In Singapore, this effort is overseen by the National Environment Agency (NEA).

To achieve a high standard of public health and prevent rodent-borne diseases, the NEA carries out rodent surveillance routinely. Areas that are prone to rodent infestation such as construction sites, workers’ quarters, bin centres, markets and food establishments are assessed regularly for rodent infestation. The NEA also carries out inspection according to public complaints and feedback on rodents, and MOH’s notification of local murine typhus and leptospirosis cases. In the latter, investigation will be conducted in the case’s residential addresses, work addresses and all other potential areas indicated through MOH’s epidemiological investigation.

In 2007, 257 of the sites surveyed were detected with rodent burrows. It was found that majority of the breeding sites were at Town Council maintained areas. Of the 257 infested sites:

• 77.4% (199 sites) had less than 6 burrows (low infestation);

• 12.5% (32 sites) had 6-10 burrows (medium infestation); and

• 10.1% (26 sites) had more than 10 burrows (high infestation).

Apart from NEA’s routine rodent surveillance and control actions by the respective stakeholders, NEA also sought the active participation of all stakeholders in the commu-nity to deny rodents of food and harbourage and to report rodent sightings. NEA works closely with all stakeholders to implement measures to improve the overall sanitation of the housing estates and the surrounding environment to prevent rodent infestation.

With rapid development and increasing population, ro-dent surveillance and control is becoming increasingly challenging. NEA will continue to monitor the rodent situation closely and take appropriate control meas-ures to ensure that Singapore maintains a low rodent population.

Figure 2.13Geographical distribution of rodent burrows detected, 2007


• Rodent burrows


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77.4%

12.5%

10.1%

Low (<6 burrows) Medium (6 - 10 burrows) High (>10 burrows)

Figure 2.14Rodent infestation levels in premises inspected, 2007


diseases borne air-/droplet- zoonotic...air-/droplet-borne diseases vector-borne/ zoonotic diseases...

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