Melioidosis, Singapore, 2003-2014.

In contrast with northern Australia and Thailand, in Singapore the incidence of melioidosis and co-incidence of melioidosis and pneumonia have declined. Burkholderia pseudomallei deep abscesses increased 20.4% during 2003-2014. These trends could not be explained by the environmental and climatic factors conventionally ascribed to melioidosis.

Epidemiological characteristics associated with uptake of pneumococcal vaccine among older adults living in the community in Singapore: Results from the National Health Surveillance Survey 2013.

AIMS: In Singapore, pneumococcal vaccination is recommended for the elderly (i.e. those ≥65 years of age) and people with chronic medical conditions. We investigated epidemiological characteristics associated with the uptake of pneumococcal vaccine based on a nationally representative cross-sectional sample of community-living adults aged ≥50 years. METHODS: The data were obtained from the National Health Surveillance Survey (NHSS) 2013. Associations between pneumococcal vaccination and sociodemographic and health-related variables were analysed using univariable and multivariable logistic regression models. RESULTS: Among 3672 respondents aged ≥50 years in the NHSS, 7.8% had taken the pneumococcal vaccination. A higher level of education and higher monthly household income were sociodemographic characteristics independently associated with pneumococcal vaccine uptake. Health-related characteristics predictive of pneumococcal vaccine uptake were better self-rated health and having a regular family doctor/general practitioner. Among those who responded to the two questions on vaccinations, 3.9% had been vaccinated against both seasonal influenza and pneumococcal infection, while 11.1% had taken only seasonal influenza vaccination in the past year. CONCLUSIONS: There is a need to boost pneumococcal vaccination coverage among community-dwelling older adults. These findings provide insights into reviewing and tailoring public-health strategies and programmes to increase vaccine uptake in at-risk population groups.

Characterization of influenza activity based on virological surveillance of influenza-like illness in tropical Singapore, 2010-2014.

Singapore is situated in the tropics where the seasonality of influenza is not as well defined as that of temperate countries. We examined the circulation of influenza viruses in the community in terms of the characteristics of influenza activity. We reviewed laboratory-confirmed virological data collected between 2010 and 2014 under the national influenza surveillance programme. Influenza activity was measured by the proportion of specimens from outpatients with influenza-like illness tested positive for influenza virus based on 4-weekly moving interval. Seasonal epidemics occurred around the end of previous year or the beginning and middle of the year. Increases in influenza positivity were more pronounced when there was a change in the predominant circulating influenza virus type/subtype to influenza A(H3N2). Influenza epidemics lasted about 12 weeks on average, with longer duration when there was a change in the predominant influenza type/subtype and especially when it was associated with influenza A(H3N2). Continuous influenza surveillance is important as it could provide early warning of imminent surges in virus transmission, and allow for timely implementation of public health prevention and control interventions to minimize influenza-associated disease burden. J. Med. Virol. 88:2069-2077, 2016. © 2016 Wiley Periodicals, Inc.

Association of melioidosis incidence with rainfall and humidity, Singapore, 2003-2012.

Soil has been considered the natural reservoir for the bacterium Burkholderia pseudomallei, which causes melioidosis. We examined 550 melioidosis cases that occurred during a 10-year period in the highly urbanized city of Singapore, where soil exposure is rare, and found that rainfall and humidity levels were associated with disease incidence.

Seroprevalence of past dengue virus infection among children and adolescents in Singapore.

We conducted a pediatric seroprevalence study of dengue virus (DENV) infection in Singapore, a dengue endemic city-state. Residual sera from 1,200 Singapore residents aged 1-17 years seen in two hospitals between 2008 and 2010 were tested for anti-DENV IgG antibodies. The overall seroprevalence was 10.4% (95%CI: 8.7-12.1%). There had been a marked decline in seroprevalence in the 15-19-year age group over the last three decades, while the prevalence in the 1-5-year olds (12.6%) was significantly higher than that of the 1996-1997 pediatric survey (0.8%). The overall dengue seroprevalence in children and adolescents remained low.

Microsporidial keratoconjunctivitis after rugby tournament, Singapore.

We investigated an outbreak of 47 probable and 6 confirmed cases of microsporidial keratoconjunctivitis involving participants of an international rugby tournament in Singapore in April 2012.The mode of transmission was eye contact with soil. Vittaforma corneae was identified in 4 of 6 corneal scrapings and in 1 of 12 soil water samples.

Seroprevalence of hepatitis B virus infection among children and adolescents in Singapore, 2008-2010.

A national pediatric survey was undertaken to determine the prevalence of hepatitis B virus markers in Singapore. The aim was to assess the impact of the national childhood immunization program against hepatitis B implemented for all newborns since 1987. The survey involved prospective collection of residual sera from Singapore residents aged 1-17 years attending inpatient services or day surgery in two public hospitals between August 2008 and July 2010. A total of 1,200 sera were collected comprising 400 in each of the three age groups of 1-6, 7-12, and 13-17 years. The sera were tested for hepatitis B surface antigen (HBsAg) and antibody to HBsAg (anti-HBs). Four of the 1,200 samples tested positive for HBsAg, giving an overall prevalence of 0.3%. One and three in the 7-12 years and 13-17 years age groups, respectively, were positive for HBsAg. About 40% possessed anti-HBs (≥10 mIU/ml); the antibody prevalence decreased significantly from 63.8% in children aged 1-6 years to 32.8% in 7-12 year olds, and 23.5% in 13-17 year olds (P < 0.0005). The successful implementation of the national childhood hepatitis B immunization program over the last two decades has resulted in a low prevalence of HBsAg among children and adolescents. Singapore has achieved the World Health Organization Western Pacific Region's goal in reducing the prevalence of chronic HBV infection to below 2% among children aged 5 years and older by 2012 and to below 1% by 2017.

Epidemiology and control of legionellosis, singapore.

To determine trends and clinical and epidemiologic features of legionellosis in Singapore, we studied cases reported during 2000-2009. During this period, 238 indigenous and 33 imported cases of legionellosis were reported. Cases were reported individually and sporadically throughout each year. Although the annual incidence of indigenous cases had decreased from 0.46 cases per 100,000 population in 2003 to 0.16 cases per 100,000 in 2009, the proportion of imported cases increased correspondingly from 6.2% during 2000-2004 to 27.3% during 2005-2009 (p<0.0005). The prevalence of Legionella bacteria in cooling towers and water fountains was stable (range 12.1%-15.3%) during 2004-August 2008.

Melioidosis in a tropical city state, Singapore.

The incidence of melioidosis in Singapore decreased during 1998-2007, with the exception of the first quarter of 2004. After heavy rainfalls, an increase in pneumonic cases with a high case-fatality rate was detected. We show that melioidosis has the potential to reemerge following adverse climate events.

Twentieth century influenza pandemics in Singapore.

INTRODUCTION: Singapore was substantially affected by three 20th Century pandemics. This study describes the course of the pandemics, and the preventive measures adopted. MATERIALS AND METHODS: We reviewed and researched a wide range of material including peer-reviewed journal articles, Ministry of Health reports, Straits Settlements reports and newspaper articles. Monthly mortality data were obtained from various official sources in Singapore. RESULTS: The 1918 epidemic in Singapore occurred in 2 waves--June to July, and October to November--resulting in up to 3500 deaths. The 1957 epidemic occurred in May, and resulted in widespread morbidity, with 77,000 outpatient attendances in government clinics alone. The 1968 epidemic occurred in August and lasted a few weeks, with outpatient attendances increasing by more than 65%. The preventive measures instituted by the Singapore government during the pandemics included the closure of schools, promulgation of public health messages, setting up of influenza treatment centres, and screening at ports. Students, businessmen and healthcare workers were all severely affected by the pandemics. CONCLUSIONS: Tropical cities should be prepared in case of a future pandemic. Some of the preventive measures used in previous pandemics may be applicable during the next pandemic.

The 2005 dengue epidemic in Singapore: epidemiology, prevention and control.

INTRODUCTION: We investigated the 2005 outbreak of dengue fever (DF)/dengue haemorrhagic fever (DHF) to determine its epidemiological, virological and entomological features to further understand the unprecedented resurgence. MATERIALS AND METHODS: All physician-diagnosed, laboratory-confirmed cases of DF/DHF notified to the Ministry of Health, Singapore during the outbreak as well as entomological and virological data were analysed retrospectively. RESULTS: A total of 14,006 cases of DF/DHF comprising 13,625 cases of DF and 381 cases of DHF, including 27 deaths were reported, giving an incidence rate of 322.6 per 100,000 and a case-fatality rate of 0.19%. The median age of the cases and deaths were 32 and 59.5 years, respectively. The incidence rate of those living in compound houses was more than twice that of residents living in public and private apartments. The distribution of DF/DHF cases was more closely associated with Aedes aegypti compared to Aedes albopictus breeding sites and the overall Aedes premises index was 1.15% (2.28% in compound houses and 0.33% to 0.8% in public and private apartments). The predominant dengue serotype was DEN-1. A significant correlation between weekly mean temperature and cases was noted. The correlation was strongest when the increase in temperature preceded rise in cases by a period of 18 weeks. CONCLUSION: The resurgence occurred in a highly densely populated city-state in the presence of low Aedes mosquito population. Factors contributing to this resurgence included lower herd immunity and change in dominant dengue serotype from DEN-2 to DEN-1. There was no evidence from gene sequencing of the dengue viruses that the epidemic was precipitated by the introduction of a new virulent strain. The current epidemiological situation is highly conducive to periodic dengue recurrences. A high degree of vigilance and active community participation in source reduction should be maintained.

Seroprevalence of antibodies against chikungunya virus in Singapore resident adult population.

OBJECTIVES: We determined the seroprevalence of chikungunya virus (CHIKV) infection in the adult resident population in Singapore following local outbreaks of chikungunya fever (CHIKF) in 2008-2009. METHODS: Our cross-sectional study involved residual sera from 3,293 adults aged 18-79 years who had participated in the National Health Survey in 2010. Sera were tested for IgG antibodies against CHIKV and dengue virus (DENV) and neutralizing antibodies against CHIKV. RESULTS: The prevalence of CHIKV-neutralizing antibodies among Singapore residents aged 18-79 years was 1.9% (95% confidence interval: 1.4%- 2.3%). The CHIKV seroprevalence was highest in the elderly aged 70-79 years at 11.5%, followed by those aged 30-39 years at 3.1%. Men had significantly higher CHIKV seroprevalence than women (2.5% versus 1.3%, p = 0.01). Among the three main ethnic groups, Indians had the highest seroprevalence (3.5%) compared to Chinese (1.6%) and Malays (0.7%) (p = 0.02 and p = 0.01, respectively). Multivariable logistic regression identified adults aged 30-39 years and 70-79 years, men, those of Indian ethnicity and ethnic minority groups, and residence on ground floor of public and private housing apartments as factors that were significantly associated with a higher likelihood of exposure to CHIKV. The overall prevalence of anti-DENV IgG antibodies was 56.8% (95% CI: 55.1%- 58.5%), while 1.5% (95% CI: 1.1%- 2.0%) of adults possessed both neutralizing antibodies against CHIKV and IgG antibodies against DENV. CONCLUSIONS: Singapore remains highly susceptible to CHIKV infection. There is a need to maintain a high degree of vigilance through disease surveillance and vector control. Findings from such serological study, when conducted on a regular periodic basis, could supplement surveillance to provide insights on CHIKV circulation in at-risk population.

Epidemiology and control of SARS in Singapore.

Severe acute respiratory syndrome (SARS) was imported into Singapore in late February 2003 by a local resident who returned from a holiday in Hong Kong and started an outbreak in the hospital where she was admitted on 1 March 2003. The disease subsequently spread to 4 other healthcare institutions and a vegetable wholesale centre. During the period between March and May 2003, 238 probable SARS cases, including 8 imported cases and 33 deaths, were reported. Transmission within the healthcare and household settings accounted for more than 90% of the cases. Factors contributing to the spread of infection included the failure to recognise the high infectivity of this novel infection, resulting in a delay in isolating initial cases and contacts and the implementation of personal protective measures in healthcare institutions; and the super-spreading events by 5 index cases, including 3 with co-morbid conditions presenting with atypical clinical manifestations of SARS. Key public health measures were directed at prevention and control within the community and hospitals, and the prevention of imported and exported cases. An isolated laboratory-acquired case of SARS was reported on 8 September 2003. Based on the lessons learnt, Singapore has further strengthened its operational readiness and laboratory safety to respond to SARS, avian flu and other emerging diseases.

Surveillance, prevention, and control of legionellosis in a tropical city-state.

Legionellosis is endemic in Singapore, with sporadic cases reported throughout the year. The absence of outbreak could be due to the low prevalence of the highly pathogenic Pontiac subtype of Legionella pneumophila in the urban environment. Mandatory maintenance of cooling towers and water fountains has been put in place, and the effectiveness of legislation in minimizing the occurrence and risk of outbreak of legionellosis is being evaluated.

An epidemiological assessment towards elimination of rubella and congenital rubella syndrome in Singapore.

OBJECTIVE: In line with regional and global goals for the elimination of rubella and congenital rubella syndrome (CRS), we reviewed the epidemiological situation in Singapore, based on surveillance reports on rubella and CRS, national immunization coverage and seroprevalence surveys. The aim of our review was to identify current gaps and steps taken to achieve the targets set by the World Health Organization (WHO) Western Pacific Regional Office (WPRO). METHODS: Epidemiological data on clinical and laboratory-confirmed rubella cases, including CRS, notified to the Communicable Diseases Division, Ministry of Health, Singapore, from 2003 to 2013 were collated and analyzed. Vaccination coverage against rubella was obtained from the National Immunization Registry and School Health Services of the Health Promotion Board. The changing prevalence of rubella was determined from periodic serological surveys. FINDINGS: The incidence of indigenous rubella cases per million population decreased from 37.2 in 2008 to 7.6 in 2013 and there had been no indigenous case of CRS in 2012 and 2013. Therapeutic abortions performed due to rubella infections had become uncommon. The annual measles, mumps, and rubella (MMR) vaccination coverage in childhood population remained high ranging from 93% to 96%. The overall susceptibility to rubella in women aged 18-44 years had reduced significantly from 15.8% in 2004 to 11.0% in 2010. The prevalence of IgG antibody against rubella among Singapore children aged 1-17 years was maintained at 87.3% in 2008-2010. CONCLUSION: All available data indicated that Singapore has made good progress towards the elimination of rubella and CRS. It has attained the targets set by the WHO WPRO for 2015. In preparation for verification of rubella elimination, an enhanced surveillance system has been implemented to ensure that all reported cases are laboratory confirmed, and genotyping of rubella virus strains isolated is carried out to provide evidence for interruption of endemic transmission.

Seroepidemiology of Coxsackievirus A6, Coxsackievirus A16, and Enterovirus 71 Infections among Children and Adolescents in Singapore, 2008-2010.

Coxsackieviruses A6 (CV-A6) and A16 (CV-A16) and Enterovirus 71 (EV-A71) have caused periodic epidemics of hand, foot and mouth disease (HFMD) among children in Singapore. We conducted a cross-sectional study to estimate the seroprevalence of these enteroviruses among Singapore children and adolescents. The study was conducted between August 2008 and July 2010. It involved 700 Singapore residents aged 1-17 years whose residual sera were obtained following the completion of routine biochemical investigations in two public acute-care hospitals. The levels of neutralizing antibodies (NtAb) against CV-A6, CV-A16 and EV-A71 were analyzed by the microneutralization test. The age-specific geometric mean titer (GMT) of antibodies against each of the three enteroviruses and the 95% confidence intervals (CI) were calculated. The seroprevalence of CV-A6 and CV-A16 was high at 62.7% (95% CI: 59.1-66.2%) and 60.6% (95% CI: 56.9-64.1%), respectively. However, the seroprevalence of EV-A71 was significantly lower at 29.3% (95% CI: 26.0-32.8%). About 89.7% of the children and adolescents had been infected by at least one of the three enteroviruses by 13-17 years of age. About half (52.3%) were seropositive for two or all three enteroviruses, while only 16.1% had no NtAb against any of the three enteroviruses. High NtAb levels were observed in the younger age groups. CV-A6 and CV-A16 infections are very common among Singapore children and adolescents, while EV-A71 infections are less common. Infection is continually acquired from early childhood to adolescent age.

Hajj-associated outbreak strain of Neisseria meningitidis serogroup W135: estimates of the attack rate in a defined population and the risk of invasive disease developing in carriers.

An outbreak of disease due to Neisseria meningitidis serogroup W135 (W135) occurred in 2000 and 2001 among pilgrims returning from the annual Islamic pilgrimage to Saudi Arabia (the Hajj) and in their contacts. For the Hajj in 2000, the attack rate of W135 disease was 25 cases per 100,000 pilgrims. After the introduction of quadrivalent meningococcal vaccine for the Hajj in 2001, no pilgrim developed W135 disease. The estimated attack rates for household contacts of returning pilgrims were 18 cases and 28 cases per 100,000 contacts for the years 2000 and 2001, respectively. On the basis of rates of transmission of W135 carriage and national epidemiological data, the risk that an unvaccinated household contact who had acquired W135 carriage would develop invasive meningococcal disease was estimated to be 1 case per 70 acquisitions. Public health policies to protect household contacts of Hajj pilgrims need to be implemented.

Experience of severe acute respiratory syndrome in singapore: importation of cases, and defense strategies at the airport.

BACKGROUND: The importation of SARS was responsible for the outbreaks in Singapore, Hong Kong, Vietnam and Canada at a time when this new disease had not been identified. We report the incidence and impact of cases of SARS imported to Singapore between 25 February and 31 May 2003, and describe national measures to prevent further importation. METHODS: Information on imported cases of SARS and measures taken at entry points to Singapore was retrieved from the Ministry of Health and the Civil Aviation Authority of Singapore. RESULTS: Of the 6 imported cases, which all occurred before screening measures were implemented at the airport, only the first resulted in extensive secondary transmission. Of 442973 air passengers screened after measures were implemented, 136 were sent to a designated hospital for further SARS screening; none was diagnosed as having SARS. CONCLUSIONS: The SARS outbreak in Singapore can be traced to the first imported case. The absence of transmission from the other imported cases was probably a result of relatively prompt identification and isolation of cases, together with a low potential for transmission. New imported SARS cases therefore need not lead to major outbreaks if systems are in place to identify and isolate them early. Screening at entry points is costly, has a low yield and is not sufficient in itself, but may be justified in light of the major economic, social and international impact which even a single imported SARS case may have.

Changing seroprevalence of varicella zoster virus infection in a tropical city state, Singapore.

OBJECTIVE: To understand the seroepidemiology of varicella zoster virus (VZV) in the Singaporean population, based on a paediatric survey conducted in 2008-2010 and the 2010 National Health Survey. The findings were compared with previous studies carried out in 1989-1990, 1993, 1998, and 2004. METHODS: The paediatric survey involved 1200 subjects; residual diagnostic serum samples were collected from Singapore residents aged 1-17 years at two hospitals. The adult survey involved 3293 subjects; residual serum samples were obtained from Singapore residents aged 18-79 years who had participated in the 2010 National Health Survey. RESULTS: The seroprevalence in children under 5 years of age increased from 4% in 1989/1990 to 11.7% in 1998 and 33.2% in 2008-2010. For children aged 5-14 years, the corresponding seroprevalences were 22.8%, 59.5%, and 58.0%. The seroprevalence in children aged 5-14 years in 2008-2010 was not significantly different from that in 1998 (p=0.721). Among Singapore adults over 25 years of age, the seroprevalence remained consistently high at around 88% from 1998/1990 to 2010. CONCLUSIONS: Nearly two-thirds of pre-school children, 39.5% of primary school children, and 29% of adolescents aged 13-17 years are susceptible to VZV infection. At this level of immunity, it can be expected that outbreaks will continue to occur unless the varicella vaccine is introduced into the national childhood immunization programme.