Blood lead levels of a population group not occupationally exposed to lead in Singapore.

A survey was conducted between 1995 and 1997 to assess the impact of introduction of unleaded petrol and other public health measures on the blood lead level of the population. The geometric mean blood lead level of 269 government employees as determined by graphite furnace atomic absorption spectroscopy, was 66.0 microg/l, much lower than that recorded before introduction of lead-free petrol. Using multiple regression analysis, factors significantly associated with blood lead levels were: exposure to traffic, age (>50 years) and active smoking. Passive smoking, exposure to recent paint work, consumption of alcohol and traditional medicine were found not to be significantly associated with the blood lead level.

An institutional outbreak of Salmonella enteritidis in Singapore.

A large outbreak of food poisoning occurred in Singapore in March 1995 when a total of 188 inmates in an institution was taken ill. Salmonella enteritidis was isolated from the stool cultures of 35 inmates (16 symptomatic and 19 asymptomatic). All the isolates were of the serotype profile 0:1, 9, 12 and H:g, m (antigen phase I); all were sensitive to ampicillin, ceftriaxone, chloramphenicol, co-trimoxazole and ciprofloxacin. Plasmid profile analysis and restriction enzyme fragmentation patterns (REFPs), as generated with EcoRI and HindIII, of a 60 kb plasmid obtained from these isolates were all identical, confirming that the outbreak resulted from a single source of infection. Stratified statistical analysis of food-specific attack rates strongly implicated imported canned luncheon pork consumed by the inmates on 26 March 95 as the single most probable cause of the food poisoning [p < 10(6), Mantel-Haenszel weighted odds ratio (OR) = 14.33; 95% confidence interval (CI) = 6.20-33.15]. The median incubation period of this outbreak was 19.3 hours and the median duration of illness was three days. The outbreak was rapidly brought under control through prompt implementation of epidemic control measures which comprised active search for diarrheal cases, rectal swabbing of asymptomatic inmates, isolation of those found to be infected, and maintenance of a high standard of personal, food and environmental hygiene.

Prevalence of varicella-zoster virus infection in Singapore.

The incidence of chickenpox in Singapore has been increasing since 1984. A seroepidemiological survey was conducted in 1989-90 to determine the prevalence of varicella-zoster virus-specific IgG antibody in the healthy population in Singapore aged from 6 months to over 45 years. Overall, 42.8% of 500 samples assayed qualitatively by the ELISA method were positive, with less than one fifth of those aged under 15 years and less than half of the 15-24 year olds possessing antibody to the virus. However, antibody prevalence increased markedly to between 86% and 98% in those over 25 years of age. No significant sex or ethnic difference was noted. The survey confirmed the low herd immunity and the higher susceptibility of the young adult population to varicella infection in a tropical city compared to that of temperate countries.

Epidemiological aspects of an outbreak of dengue fever/dengue haemorrhagic fever in Singapore.

A nation-wide outbreak of 260 cases of DF/DHF with 1 death occurred in Singapore from Apr-Sept 1986. The outbreak originated from 3 separate foci of transmission at the western, south-eastern and north-eastern parts of the island and then spread to other dengue receptive urban and suburban areas. The morbidity rate was highest in young male Chinese adults between 15 and 24 years of age. The outbreak was rapidly brought under control through destruction of adult Aedes mosquitoes, surveys and source reduction of larval breeding habitats, health education and to a certain extent law enforcement. The Aedes population was high in the main foci of transmission although the overall house index was only 1.1. Other factors which could have precipitated the outbreak included waning herd immunity of the human population and continuous introduction of dengue virus into the country.

Social and economic aspects of malaria in Singapore.

Singapore is both receptive and vulnerable to the introduction of malaria because of its location in a malarious zone. The social and economic factors that determined the incidence of malaria included rapid urban and industrial developments which created suitable environmental conditions for the breeding of Anopheles vectors, influx of foreign workers from the endemic countries and increased travel to the malarious areas. The public health significance of the interactions of these factors was exemplified by the occurrence of periodic localized outbreaks. The problem of introduction of drug-resistant falciparum malaria by travellers into the country was another matter of concern. However, the health authorities were fully committed in bringing these problems under control, with political support as well as regional and international collaboration. The result of these efforts was realised in 1982 when Singapore was certified malaria-free by the WHO. The strategies implemented included epidemiological and vector surveillance, health education and environmental health supervision of all major development projects in receptive areas.

Disease-bearing insects brought in by international aircraft into Singapore.

Fifty-seven (17.3%) of 330 incoming aircraft landing at Changi International Airport were found to harbour mosquitoes and other insects on board. The frequency of insects detected in aircraft from the Southeast Asian countries varied from 7.1% to 32.2%. Live insects were found in 5 (6.1%) of 82 aircraft disinsectized by the "block away" method. The species of mosquitoes brought in were: Culex quinquefasciatus (96), Culex tritaeniorhynchus (1), Aedes albopictus (2) and Aedes aegypti (1). None of the 51 female Culex quinquefasciatus dissected was found to be infected with microfilariae. They key to the prevention of introduction of exotic vectors and transmission of vector- borne diseases is to continue with the existing system of vector surveillance and control at the international airport, rather than routine disinsecting of aircraft landing in Singapore.

An epidemic of acute conjunctivitis caused by enterovirus-70 in Singapore in 1980.

The clinical, epidemiological and virological findings of the 1980 epidemic of acute conjunctivitis were described. Enterovirus 70 was isolated from 7 (35%) of 20 eye swabs submitted for virus isolation, and the paired sera of eight patients showed a four-fold or greater rise in neutralising antibody titre to Enterovirus 70. The disease mainly affected children and young adults of all ethnic groups. Most of the cases contracted the infection at home. The mean secondary attack rate was 72.6% and the mean incubation period, four days. The clinical features were similar to the 1970 and 1975 epidemics caused by Coxsackievirus A24. Subconjunctival haemorrhage was observed in 10% of the cases. Most of the cases recovered spontaneously within a week. Transmission of infection within the home was either indirect, probably through fomites contaminated with eye or respiratory discharges of cases, or direct, through intimate person-to-person contact. During outbreaks, health education on simple personal hygiene should be highlighted.

An outbreak of paratyphoid A in Singapore: clinical and epidemiological studies.

The epidemiological and clinical findings of 61 cases of laboratory-confirmed paratyphoid A reported in an outbreak in 1979 were described. Epidemiological investigations of 42 indigenous cases implicated imported fresh oysters as the vehicles of transmission (p less than 0.01). Although S. paratyphi A could not isolated from the implicated oysters, several observations presented tend to support the association between oyster consumption and illness. The clinical features were similar to typhoid, 82.8% of the organisms were isolated from blood cultures. The relapse rate was 8.6%. There were three stool and one urinary convalescent carriers. Two of the stool carriers were treated with cholecystectomy.

Enteric infections in Singapore with special reference to typhoid.

A review of the epidemiological features of the more important enteric infections in Singapore was given. Enteric fevers (typhoid and paratyphoid), Salmonella gastroenteritis and Shigellosis remained endemic at a rather constant level in spite of vast improvement in environmental sanitation, but amoebic dysentery showed marked decline. Vibrio parahaemolyticus is an important cause of food poisoning since it was first reported in 1973. El tor cholera is believed to be introduced through regional trade and travel. Control measures directed mainly at typhoid include detection of typhoid carriers in the community responsible for transmission of infection, control and licensing of public food handlers and health education.

Epidemiology of acute viral hepatitis in Singapore.

A total of 194 cases of acute viral hepatitis were notified between June and December 1976. Thirty-five (22.6%) out of 155 patients were positive for HBs Ag by counter-immuno-electrophoresis. The ethnic-specific morbidity rates per 100,000 were Chinese, 9.51; Malays, 3.20; Indians, 8.30 and others, 1.13; and the age specific attack rates were high in the 15 -- 24 and 25 -- 34 age groups, being 15.05 and 15.77 per 100,000 respectively. The male to female ratio was 3.04:1. Cases were not confined to areas with poor environmental sanitation. There were very few secondary cases. Unrecognized anicteric or subclinical cases probably play an important role in the transmission of viral hepatitis in the community. The possibility of transmission of hepatitis A by contaminated food was discussed.