An Overview Of The Communicable Disease Situation In Singapore, 2000 Communicable Disease Disease Situation In Singapore, 2000... 1-1
I AN OVERVIEW OF THE COMMUNICABLE DISEASE SITUATION IN SINGAPORE, 2000 The infectious disease situation in Singapore was closely monitored through a comprehensive and well-established system of epidemiological surveillance (Fig.1.1). A high level of vigilance on the disease activity was also maintained on emerging infectious diseases throughout the world to prevent their introduction into Singapore as far as possible and to deal with them swiftly and effectively should they be introduced. As of 1 st of October 2000, three new infectious diseases were made legally notifiable, viz. hand, foot and mouth disease, legionellosis and Nipah virus infection. Table 1.1 gives the list of notifiable diseases. The morbidity, mortality and case-fatality rates of the infectious diseases notifiable to the Ministry of the Environment in 2000 and the trend of vector-borne, food-borne and air-borne diseases are shown in Table 1.2 and Fig. 1.2, respectively. Vector-borne diseases There was a marked decrease in the incidence of dengue fever (DF)/dengue haemorrhagic fever (DHF) from 1,355 cases in 1999 to 673 cases in 2000. Two deaths were reported. The Figure 1.1 System for notification of infectious diseases Department of Pathology Singapore General Hospital Private Medical Practitioners Department of Mircobiology National University of Singapore SAF Medical Corps MINDEF Death Registry Ministry of Health Ministry of the Environment Hospitals Family Health Service School Health Service Clinical Laboratories OTHER001/CMH/300399 Disease Situation In Singapore, 2000... 1-1
Table 1.1 Notifiable diseases in Singapore Notifiable to ENV under the Infectious Diseases Act Notifiable to MOH under the Infectious Diseases Act Chickenpox Tuberculosis Cholera Venereal diseases Dengue - Chancroid Dengue haemorrhagic fever - Gonorrhoea Diphtheria - Non-specific urethritis Encephalitis - Syphilis Viral hepatitis - AIDS/HIV infection Malaria Leprosy Poliomyelitis Plague Typhoid Paratyphoid Mumps Hand, foot and mouth disease Yellow fever Measles Rubella Legionellosis Nipah virus infection Administratively notifiable to ENV Food-borne diseases - Campylobacteriosis - E. coli 0157 - Salmonellosis - Listeriosis - Food poisoning Rodent-borne diseases - Typhus - Leptospirosis - Hantavirus infection Environment-related diseases - Melioidosis - Cryptococcosis Vaccine-preventable diseases - Meningococcal meningitis - Haemophilus influenza B Disease Situation In Singapore, 2000... 1-2
Table 1.2 Morbidity, mortality and case-fatality rates of notifiable infectious diseases in Singapore, 2000 Diseases No. of cases No. of deaths Rate per 100,000 population* Morbidity rate Mortality rate Casefatality rate (%) Cholera 10 (3) 0 0.3 0 0 Plague 0 0 0 0 0 Yellow Fever 0 0 0 0 0 Chickenpox 24,074 1 737.7 0.03 0.004 DF/DHF 673 (271) 2 (2) 20.6 0.06 0.3 DF 663 (265) 0 20.3 0 0 DHF 10 (6) 2 (2) 0.3 0.06 20 Diphtheria 0 0 0 0 0 Enteric fevers 101 (85) 0 3.1 0 0 Typhoid fever 80 (66) 0 2.5 0 0 Paratyphoid fever 21 (19) 0 0.6 0 0 Malaria 266 (264) 3 (3) 8.2 0.09 1.1 Poliomyelitis 0 0 0 0 0 Viral hepatitis 211 (152) 4 6.5 0.12 1.9 Hepatitis A 77 (63) 0 2.4 0 0 Hepatitis B 117 (74) 0 3.6 0 0 Hepatitis E 17 (14) 0 0.5 0 0 Viral encephalitis 4 2 0.12 0.06 50 Japanese encephalitis 0 0 0 0 0 Other 4 2 0.12 0.06 50 Measles 141 (40) 0 4.3 0 0 Mumps 5,981 0 183 0 0 Rubella 312 (39) 0 9.6 0 0 Nipah virus infection+ 0 0 0 0 0 Hand, foot and mouth disease+ 6,402 4 196.2 0.12 0.06 Legionellosis+ 65 (10) 3 2.0 0.09 4.6 ( ) Imported cases * Rates are based on 2000 census population obtained from the Department of Statistics + Notifiable as from 1 Oct 2000 Disease Situation In Singapore, 2000... 1-3
Figure 1.2 Annual incidence rates of specified vector-borne, food-borne and air-borne diseases in Singapore, 1990-2000 Rate per 100,000 population 200 150 100 50 0 Dengue fever/dengue haemorrhagic fever Japanese encephalitis+ Malaria Vector-borne diseases Rate per 100,000 population 50 40 30 20 10 0 Cholera Typhoid fever Pa ra typhoid fe ve r He pa titis A Food poisoning Food-borne diseases Rate per 100,000 population 2000 1500 1000 500 0 Air-borne diseases Measles Chickenpox Mumps Rubella 91 92 93 94 95 96 97 98 99 00 Year * No local cases of diphtheria and poliomyelitis were reported during this period + Three cases of Japanese encephalitis were reported in 1990, one imported case in 1996, two imported cases in 1997, one imported case in 1998and one imported case in 1999 MIX002/CMH/111001 Disease Situation In Singapore, 2000... 1-4
incidence rate was highest in the 15-24 year age group. Residents of compound houses had an incidence rate five times higher than that of HDB flat dwellers. Most of these occurred in the southeastern and southern parts of the island. The main circulating dengue virus serotypes were dengue 1 and dengue 2. A total of 266 cases of malaria, including three deaths from falciparum malaria, were reported. Virtually all the cases were imported, mainly from the Indian subcontinent and Southeast Asia. Two sporadic cases with no recent travel history could have acquired the infection locally. No case of Japanese encephalitis was reported. Food-borne diseases The incidence of cholera remained low with 7 indigenous and 3 imported cases reported. A local resident was infected with Vibrio cholerae 0139. This strain was last isolated in 1993 and 1994 among imported cases from India and Thailand. The incidence of indigenous typhoid and paratyphoid was also low with 14 and 2 cases, respectively, reported. Majority of the notified cases of typhoid (82.5%) and paratyphoid (90.5%) were imported. A large proportion of the hepatitis A (81.8%) and hepatitis E (82.4%) cases were imported. Only 14 indigenous cases of hepatitis A and 3 indigenous cases of hepatitis E cases were reported. In 2000, there were 213 food poisoning notifications involving 1,542 cases. A common source food-borne outbreak of 269 cases in a secondary school was associated with the consumption of contaminated iced drink made from non-food-grade ice. A water-borne outbreak of 122 cases of gastroenteritis occurred in a shopping/office/residential complex at Bukit Timah. Investigation showed that the basement water tanks were contaminated with sewage leaking from the sewerage pipes located above a tank with missing cover. An outbreak of multidrug resistant Salmonella typhimurium definite type 104, involving mainly children below 18 months of age, was traced to the consumption of undercooked ground ikan bilis. Two cases of ciguatera fish poisoning were reported. The diagnosis was based on the typical clinical presentations. Ciguatoxin could not be detected in the implicated oral-reef fish imported from Fiji. Disease Situation In Singapore, 2000... 1-5
Air-borne diseases There were 509,966 attendances at restructured polyclinics for acute respiratory illnesses and 26,077 attendances for conjunctivitis. Influenza A and B viruses were detected throughout the year. Influenza A (H3N2), circulated in the beginning of the year and was replaced by the A (H1N1) strains in Mar-Jun. An increase in polyclinic attendances for conjunctivitis was noted during the Aug-Oct period. No virus study was carried out. The number of chickenpox decreased from 31,592 cases in 1999 to 24,074 cases in 2000. The resurgence of mumps, which started in 1999, declined by 6% with 5,981 cases reported in 2000. The resurgence was due to poor protection conferred by the Rubini mumps virus strain of the Swiss MMR vaccine, which was subsequently deregistered. The incidence rate was highest in children 5-14 years of age. Rubella incidence also declined from 432 cases in 1999 to 312 cases in 2000. The incidence of measles increased from 65 cases in 1999 to 141 cases in 2000. The incidence rate was highest in pre-school children below 5 year of age. No local cases of diphtheria or poliomyelitis were reported. Environment-related diseases A total of 65 cases of legionellosis were reported in 2000 compared to 79 cases in the previous year. The diagnosis was mainly based on serological finding of a single blood specimen (indirect fluorescent antibody titre of 1:1024) in the presence of characteristic clinical presentation. About 70% of the cases had concurrent medical illness. The incidence rate was highest in those above 65 years age. Of the cooling towers tested during the year, 59.5% were positive for legionella bacteria. The incidence of melioidosis remained stable with 77 cases reported. The highest incidence rate was among the elderly aged 65 years and above. Almost all the cases had some underlying medical conditions. There had been a sharp reduction in case-fatality rates from 60% in 1990 to 12% in 2000. This could be due to greater awareness among medical practitioners to diagnose and treat the disease early, as reflected by the decreasing proportion of bacteraemic cases from 91% to 36.4% during the same period. Emerging diseases Following reports of outbreaks of hand, foot and mouth disease (HFMD) in Sarawak in 1997 and Taiwan in 1998, a close surveillance of the disease was maintained in Singapore. A Standard Operation Procedure (SOP) was prepared and the HFMD Task Force established. Disease Situation In Singapore, 2000... 1-6
In September 2000, 4 deaths, including 2 siblings, were reported. Enterovirus 71 was isolated from the brain, lung and throat swabs of the 2 siblings. These deaths occurred when the disease incidence was increasing rapidly. With the notification of the deaths of the two siblings, the Task Force immediately activated the SOP by closing down all preschool centres from 1 Oct 16 Oct 2000. The measure taken was effective in reducing transmission among preschool children. The incidence dropped sharply from a peak of 308 cases per day on 10 Oct to 10 cases per day on 28 Oct. In April 2000, 6 cases of meningococcal disease, including one death, related to travel to Saudi Arabia were reported in Singapore. The disease was caused by an uncommon strain of Neisseria meningitidis serogroup W135. Two of the cases were family contacts of returning Haj pilgrims. Following this outbreak, the bivalent meningococcal vaccine (A/C) was replaced by the quadrivalent (A/C/Y/W135) vaccine for all Haj pilgrims. Campylobacter enteritits has been increasing from 84 cases in 1994 to 343 cases in 1999. It then dropped to 231 cases in the following year. The incidence rate was highest in preschool children below 5 years of age. The risk factor identified through a case-control study was failure of caregivers to wash their hands after handling raw poultry and before preparing milk formula. The Agri-food Veterinary Authority of Singapore is taking measures to reduce the high prevalence of Campylobacter contamination of imported poultry. An imported case of diarrhoea caused by E. coli O157:H7 and an imported case of listerosis were notified during the year. Disease Situation In Singapore, 2000... 1-7