Communicable Diseases Surveillance in Singapore 2009

21

IIVeCtoR-BoRne DIseAses

Vector-borne and zoonotic diseases are diseasesthat are transmitted to humans by insects or animals. Vectors may transmit infectious diseases to humans through 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 organismmay be viral, bacterial, fungal or protozoanand transmission can 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 fever, chills, headache, nausea, vomiting, joint pain with or without swelling and lower back pain. Some patients may develop a rash affecting the trunk and limbs. The

disease is usually self-limiting. Most symptoms last for 3 -10 days and the joint pain may last for weeks to months. The main vector is the Aedes mosquito.

Atotalof341laboratory-confirmedcasesofchikungunyafever were reported in 2009. Out of the 341 cases, 136 were Singaporean or permanent residents with 35 imported and 101 indigenous cases. The remaining 205 cases were foreigners including work permits holdersconsistingof31 importedand174 indigenouscases. The year began with a high incidence of cases thatdecreasedsharply in thefirstquarterof theyear;followed by a steady decrease towards end of third quarter before a slight rise of cases until the end of 2009 (Figure 2.1).

Figure 2.1e-weekly distribution of Chikungunya fever cases, 2008 2009

The incidence rate among indigenous cases was highest in the 25 34 years age group with a male to female ratio of 5.2:1 (Table 2.1). Amongst the three major

ethnic groups, Chinese had the highest incidence rate, followed by Indians and Malays. Foreigners comprised of 63.3 %ofindigenouscases(Table2.2).

22

table 2.1Age-gender distribution and age-specific incidence rates of indigenous#

chikungunya fever cases, 2009

Age (yrs) male Female total (%) Incidence rate per 100,000 population*

0 4 1 0 1 (0.4) 0.5

5 14 1 7 8 (2.9) 1.6

15 24 42 6 48(17.5) 6.0

25 34 68 13 81 (29.4) 7.5

35 44 43 13 56 (20.3) 6.4

45 54 31 11 42 (15.3) 6.1

55+ 24 15 39 (14.2) 4.8

total 210 65 275 (100.0) 5.5

#Cases acquired locally among singaporeans, permanent and temporary residents.*Rates are based on 2009 estimated mid-year population.

(source: singapore Department of statistics)

table 2.2Ethnic-gender distribution and ethnic-specific incidence rates of indigenous#

chikungunya fever cases, 2009

male Female total (%) Incidence rate per 100,000 population*

Singapore Resident

Chinese 53 32 85 (30.9) 3.1

Malay 2 1 3 (1.1) 0.6

Indian 7 1 8 (2.9) 2.3

Others 4 1 5 (1.8) 4.2

Foreigner 144 30 174(63.3) 13.9

total 210 65 275 (100.0) 5.5

#Cases acquired locally among singaporeans, permanent and temporary residents.*Rates are based on 2009 estimated mid-year population.

(source: singapore Department of statistics)

There were 66 (19.4%) imported cases, defined asresidents and non-residents with a history of travel to chikungunya endemic countries twelve days prior to the

onsetofillness.30(45.5%)and26(39.4%)caseswerefrom India and Malaysia respectively(Table 2.3).

Communicable Diseases Surveillance in Singapore 2009

23

table 2.3Imported chikungunya fever cases, 2006 2009

year2006 2007 2008 2009

Southeast Asia

Cambodia 0 0 1 0

Thailand 0 0 0 2

Myanmar 0 0 0 2

Malaysia 0 1 166 26

Indonesia 0 1 6 4

South Asia

India 2 6 4 30

Sri Lanka 1 0 2 0

Maldives 0 0 0 2

Other Regions 0 2 2 0

total 3 10 181 66

Residents in the Housing and Development Board (HDB) flats,condominiumsandcompoundhousesconstituted24.0%6.2%and30.2%ofthecases,respectively.109

cases (39.6%)were residing in temporary residencesanddormitoriesthatcannotbeclassifiedunderthethreemain residence types (Table 2.4).

table 2.4Incidence rates of reported indigenous# chikungunya fever cases by housing type, 2009

Housing type no. % Incidence rate per 100,000 population*

Compound houses (including shophouses) 83 30.2 22.1

HDB Flats 66 24.0 1.8

Condominiums 17 6.2 5.0

Others 109 39.6 17.3

total 275 100.0 5.5

#Cases acquired locally among singaporeans, permanent and temporary residents.*Rates are based on census of population 2000.

(source: singapore Department of statistics)

A total of 123 caseswere identified in 37 clusters. Aclusterisdefinedastwoormorecasesoccurringwithin300 meters of each other with onset dates at most 24 daysapart.Atotalof7(18.9%)clusterswith5ormorecaseswereidentified(Table2.5).Themediannumberofcasesinthese7largeclusterswas5(range511)and the median duration of transmission for clusters with

5 or more cases was 21 days (range 19 60).

Clusters were distributed in the northwest, northeast, central and southwest parts of Singapore and coincided with areas where Aedes albopictus mosquitoes were present (Figure 2.2).

24

table 2.5Chikungunya clusters identified, 2009 (5 or more cases)

s/no Location no. of cases month1 Sussex Garden 11 Mar Apr2 Tuas South Avenue 4 8 Feb Apr3 Kranji Loop 6 Apr May4 Queen Astrid Park 5 JanFeb5 Dalvey Road 5 AprJun6 Cluny Road 5 MayJun7 Lorong Buangkok 5 Nov Dec

Figure 2.2geographical distribution of Aedes albopictus and chikungunya fever cases, 2009

(source: national environment Agency)

Chikungunya Deaths There were no deaths for the year 2009. No chikungunya-related deaths have been reported in Singapore before.

DengUe FeVeR/DengUe HAemoRRHAgIC FeVeR (DF/DHF)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 fourserotypes (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 manifestations, and evidence of plasma leakage may develop.

Atotalof4,497laboratoryconfirmedcasesofDF/DHF[comprising 4,451 cases of dengue fever (DF) and 46 cases of dengue haemorrhagic fever (DHF)] were reported in 2009, a decrease of more than 30 percent from the 7,031 dengue fever cases reported in 2008.Of these,2,907were local residentswith85 importedand 2822 indigenous cases. The remaining 1,590 cases were foreigners, of which 1365 cases were infected locally and 225 cases acquired the infection overseas.

Aedes albopictus

Chikungunya cases

Communicable Diseases Surveillance in Singapore 2009

25

Figure 2.3e-weekly distribution of DF/DHF cases, 2008 2009

The incidence rate among indigenous cases was highest in theagegroupof55+ with a male to female ratio of 1:1 (Table 2.6). Among the three major ethnic groups,

Chinese had the highest incidence rate, followed by MalaysandIndians.Foreignerscomprised32.4%oftheindigenouscases(Table2.7).

table 2.6Age-gender distribution and age-specific incidence rates of indigenous# DF/DHF cases, 2009

Age (yrs) male Female total (%) Incidence rate per 100,000 population*0 4 24 25 49 (1.2) 22.6

5 14 143 75 218 (5.2) 43.1

15 24 499 279 778(18.6) 97.9

25 34 643 336 979(23.4) 90.6

35 44 526 281 807(19.3) 91.8

45 54 312 222 534(12.7) 77.1

55+ 405 417 822 (19.6) 100.5

total 2,552 1,635 4,187 (100.0) 83.9

#Cases acquired locally among singaporeans, permanent and temporary residents.*Rates are based on 2009 estimated mid-year population.

(source: singapore Department of statistics)

Majority of those who acquired the infection overseas were foreigners who came to Singapore for medical treatment. The incidence remains low throughout the

year except for a slight increase during the second half of the year (Figure 2.3).

26

table 2.7Ethnic-gender distribution and ethnic-specific incidence rates of indigenous#

DF/DHF cases, 2009

male Female total (%) Incidence rate per 100,000 population*

Singapore Resident

Chinese 1,227 970 2,198 (52.5) 79.3

Malay 158 125 283 (6.8) 56.6

Indian 106 86 191 (4.6) 55.9

Others 93 64 157(3.7) 130.8

Foreigner 968 390 1,358 (32.4) 108.3

total 2,552 1,635 4,187 (100.0) 83.9

#Cases acquired locally among singaporeans, permanent and temporary residents.*Rates are based on 2009 estimated mid-year population.

(source: singapore Department of statistics)

Therewere83(1.8%)importedcases,definedaslocalresidents with a history of travel to endemic areas seven days prior to the onset of illness. The majority of these cases(87.4%)werefromSoutheastAsiancountries:32

from Malaysia, 19 from Indonesia, four from Vietnam, three from Cambodia, three from Philippines, two from Thailand, one from Myanmar, one from Brunei, one from Laos and one from East Timor (Table 2.8).

table 2.8Imported DF/DHF cases, 2005 2009

year2005 2006 2007 2008 2009

Southeast Asia

Brunei 0 0 1 0 1

Cambodia 0 4 4 4 3

East Timor 0 0 1 1 1

Indonesia 11 34 34 40 19

Laos 0 1 0 0 1

Malaysia 2 25 31 42 32

Myanmar 0 0 4 1 1

Philippines 0 5 6 4 3

Thailand 1 8 14 15 2

Viet Nam 0 2 8 8 4

South Asia

Bangladesh 0 5 2 2 0

India 0 12 20 13 9

Maldives 0 2 0 1 0

Nepal 0 0 0 0 1

Pakistan 0 0 0 0 0

Sri Lanka