Changes in the prevalence of comorbidity of mental and physical disorders in Singapore between 2010 and 2016

INTRODUCTION@#Few studies have examined the changes in the prevalence of comorbidity of mental and physical disorders in recent years. The present study sought to examine whether the prevalence of comorbidity of mental and physical disorders in Singapore showed any changes between 2010 and 2016.@*METHODS@#We extracted data from two repeated nationally representative cross-sectional surveys conducted among resident adults aged ≥ 18 years in Singapore. Significant changes were tested using pooled multinomial logistic regression analyses.@*RESULTS@#The prevalence of comorbid mental and physical disorders increased significantly from 5.8% in 2010 to 6.7% in 2016. Among those with physical disorders, there were significant increases over time in the prevalence of comorbid generalised anxiety disorder (GAD) (0.1% vs. 0.4%) and obsessive-compulsive disorder (OCD) (1.4% vs. 3.9%) in diabetes mellitus, and alcohol dependence in cardiovascular disorders (0.1% vs. 1.3%). Among those with mental disorders, there were significant increases over time in the prevalence of comorbid diabetes mellitus in OCD (4.1% vs. 10.9%), cancer in major depressive disorder (0.4% vs. 2.4%), and cardiovascular disorders in GAD (0.4% vs. 6.7%) and alcohol dependence (0.9% vs. 11.8%). Significant changes in the overall prevalence of comorbid mental and physical disorders were also observed across age group, education and employment status.@*CONCLUSION@#The prevalence of comorbid mental and physical disorders increased significantly over time. This finding supports the need for more appropriate clinical management with better integration between mental health and general medical care professionals across all aspects of the healthcare system to treat this comorbidity in Singapore.

Assessment of the risk posed to Singapore by the emergence of artemisinin-resistant malaria in the Greater Mekong Subregion

Objective@#To assess the public health risk to Singapore posed by the emergence of artemisinin-resistant (ART-R) malaria in the Greater Mekong Subregion (GMS).@*Methods@#We assessed the likelihood of importation of drug-resistant malaria into Singapore and the impact on public health of its subsequent secondary spread in Singapore. Literature on the epidemiology and contextual factors associated with ART-R malaria was reviewed. The epidemiology of malaria cases in Singapore was analysed. The vulnerability and receptivity of Singapore were examined, including the connectivity with countries reporting ART-R malaria, as well as the preparedness of Singaporean health authorities. Sources of information include international journals, World Health Organization guidelines, data from the Singapore Ministry of Health and National Public Health Laboratory of the National Centre for Infectious Diseases, and the International Air Transport Association.@*Results@#The importation of ART-R malaria into Singapore is possible given the close proximity and significant travel volume between Singapore and the GMS countries reporting artemisinin resistance. Singapore’s vulnerability is further enhanced by the presence of foreign workers from neighbouring endemic countries. Nonetheless, the overall likelihood of such an event is low based on the rarity and decreasing trend of imported malaria incidence. With the presence of Anopheles vectors in Singapore, imported cases of drug-resistant malaria could cause secondary transmission. Nevertheless, the risk of sustained spread is likely to be mitigated by the comprehensive surveillance and control system in place for both infected vectors and human cases.@*Discussion@#This risk assessment highlights the need for a continued high degree of vigilance of ART-R malaria locally and globally to minimize the risk and public health impact of drug-resistant malaria in Singapore.

Assessment of the risk posed to Singapore by the 2015 Middle East respiratory syndrome outbreak in the Republic of Korea

OBJECTIVE: To assess the public health risk to Singapore posed by the Middle East respiratory syndrome (MERS) outbreak in the Republic of Korea in 2015. METHODS: The likelihood of importation of MERS cases and the magnitude of the public health impact in Singapore were assessed to determine overall risk. Literature on the epidemiology and contextual factors associated with MERS coronavirus infection was collected and reviewed. Connectivity between the Republic of Korea and Singapore was analysed. Public health measures implemented by the two countries were reviewed. RESULTS: The epidemiology of the 2015 MERS outbreak in the Republic of Korea remained similar to the MERS outbreaks in Saudi Arabia. In addition, strong infection control and response measures were effective in controlling the outbreak. In view of the air traffic between Singapore and MERS-affected areas, importation of MERS cases into Singapore is possible. Nonetheless, the risk of a serious public health impact to Singapore in the event of an imported case of MERS would be mitigated by its strong health-care system and established infection control practices. DISCUSSION: The MERS outbreak was sparked by an exported case from the Middle East, which remains a concern as the reservoir of infection (thought to be camels) continues to exist in the Middle East, and sporadic cases in the community and outbreaks in health-care settings continue to occur there. This risk assessment highlights the need for Singapore to stay vigilant and to continue enhancing core public health capacities to detect and respond to MERS coronavirus.

Determinants of late-stage HIV disease at diagnosis in Singapore, 1996 to 2009

<p><b>INTRODUCTION</b>The delay in HIV diagnosis has been identified as a significant reason for late presentation to medical care. This research aims to elucidate the significant determinants of late-stage HIV infection in Singapore between 1996 and 2009, after the advent of highly active anti-retroviral therapies.</p><p><b>MATERIALS AND METHODS</b>We included 3735 patients infected via sexual mode of transmission from the National HIV Registry diagnosed between 1996 and 2009. Late-stage HIV infection is defined as CD4 count less than 200 mm(3) or AIDS-defining opportunistic infections at fi rst diagnosis or within one year of HIV diagnosis. We determined independent epidemiological risk factors for late-stage HIV infection at first diagnosis using multivariate logistic regression.</p><p><b>RESULTS</b>Multivariate analysis showed that older age corresponded significantly with increasing odds of late-stage HIV infection. Compared to persons diagnosed at 15 to 24 years of age, those diagnosed at age 55 years and above were associated with 5-fold increased likelihood of late-stage infection (adjusted odds ratio (AOR): 5.17; 95% CI, 3.21 to 8.33). Chinese ethnicity, singlehood, and non-professional occupations were also significantly associated with late-stage HIV infection. Persons detected in the course of medical care had over 3.5 times the odds of late-stage infection (AOR: 3.55; 95% CI, 2.71 to 4.65). Heterosexual mode of transmission and having sex workers and social escorts as sexual partners, were the other epidemiological risk factors with significant associations.</p><p><b>CONCLUSION</b>The findings of this study emphasises the need to increase HIV awareness and to encourage early and regular HIV testing among at-risk persons.</p>

Changing epidemiological patterns of hepatitis A infection in Singapore

<p><b>INTRODUCTION</b>Singapore has experienced remarkable socioeconomic progress over the last few decades, with a corresponding rise in standards of sanitation and living conditions. We undertook a study to describe its epidemiological trends of hepatitis A over the last 2 decades.</p><p><b>MATERIALS AND METHODS</b>We analysed the epidemiological data on all laboratory-confirmed cases of hepatitis A from 1990 to 2009. We also described 3 outbreaks which occurred in 1991, 1992 and 2002. To determine the changing prevalence of hepatitis A virus (HAV) infection, we compared the findings from a seroepidemiological study conducted in 1993 with earlier surveys in 1975 and 1984/1985.</p><p><b>RESULTS</b>The incidence of indigenous hepatitis A cases per 100,000 population declined significantly from 1.8 in 1989 to 0.7 in 2009, and more than half were imported. While majority of the imported cases were Singapore residents, the proportion of imported cases among Singapore residents had decreased significantly. Most of the Singapore residents contracted the disease from Southeast Asia and the Indian subcontinent. The overall prevalence of HAV infection in the population declined from 31.8% in 1984/85 to 25.9% in 1993.</p><p><b>CONCLUSION</b>The incidence and seroprevalence of hepatitis A in Singapore are comparable to other developed countries. As Singapore is situated in a region highly endemic for HAV, it is very vulnerable to the introduction of the disease because of the high volume of regional travel and import of food, especially shellfish. While we note that there have been no further shellfish-associated outbreaks since 2002, sustained vigilance, strict control of food import by the authorities and public health education on the risk of consuming shellfish, especially cockles, raw and half-cooked, should be maintained.</p>

Epidemiological characteristics of the 2005 and 2007 dengue epidemics in Singapore – similarities and distinctions

INTRODUCTION: We investigated the epidemiological features of the 2007 dengue outbreak to determine the factors that could have triggered it two years after the previous large outbreak in 2005. METHODS: All laboratory-confirmed cases of dengue reported during the year, as well as entomological and virological data, were analysed. RESULTS: A total of 8826 cases including 24 deaths were reported in 2007, giving an incidence of 192.3 cases per 100 000 residents and a case-fatality rate of 0.27%. The median age of the cases was 37 years (interquartile range 25 to 50), with an age range from two days to 101 years, which was higher than the median age of 31 years (interquartile range 20 to 42), with a range from four days to 98 years, in 2005. The overall Aedes premises index in 2007 was 0.68%, lower than the 1.15% observed in 2005. The predominant dengue serotype in 2007 was dengue virus DENV-2 which re-emerged with a clade replacement in early 2007, and overtook the predominant serotype (DENV-1) of 2005. Seroprevalence studies conducted in the three largest outbreak clusters revealed that 73.2% of residents with recent infection were asymptomatic. DISCUSSION: With the exception of an increase in the median age of the cases, and a change in the predominant dengue serotype, the epidemiological features of the 2007 epidemic were largely similar to those of 2005. Singapore remains vulnerable to major outbreaks of dengue, despite sustained vector control measures to maintain a consistently low Aedes premises index.

Influenza A (H1N1-2009) pandemic in Singapore--public health control measures implemented and lessons learnt

We describe the public health control measures implemented in Singapore to limit the spread of influenza A (H1N1-2009) and mitigate its social effects. We also discuss the key learning points from this experience. Singapore's public health control measures were broadly divided into 2 phases: containment and mitigation. Containment strategies included the triage of febrile patients at frontline healthcare settings, admission and isolation of confirmed cases, mandatory Quarantine Orders (QO) for close contacts, and temperature screening at border entry points. After sustained community transmission became established, containment shifted to mitigation. Hospitals only admitted H1N1-2009 cases based on clinical indications, not for isolation. Mild cases were managed in the community. Contact tracing and QOs tapered off, and border temperature screening ended. The 5 key lessons learnt were: (1) Be prepared, but retain flexibility in implementing control measures; (2) Surveillance, good scientific information and operational research can increase a system's ability to manage risk during a public health crisis; (3) Integrated systems-level responses are essential for a coherent public health response; (4) Effective handling of manpower surges requires creative strategies; and (5) Communication must be strategic, timely, concise and clear. Singapore's effective response to the H1N1-2009 pandemic, founded on experience in managing the 2003 SARS epidemic, was a whole-of-government approach towards pandemic preparedness planning. Documenting the measures taken and lessons learnt provides a learning opportunity for both doctors and policy makers, and can help fortify Singapore's ability to respond to future major disease outbreaks.

International health regulations: lessons from the influenza pandemic in Singapore

<p><b>INTRODUCTION</b>Singapore's defense against imported novel influenza A (H1N1-2009) comprised public health measures in compliance with the World Health Organization's (WHO) International Health Regulations (IHR), 2005. We report herein on the epidemiology and control of the fi rst 350 cases notified between May and June 2009.</p><p><b>MATERIALS AND METHODS</b>We investigated the fi rst 350 laboratory-confirmed cases of novel influenza A (H1N1-2009) identified from the healthcare institutions between 27 May and 25 June 2009. Epidemiological details of these cases were retrieved and analysed. Contact tracing and active case finding were also instituted for each reported case, and relevant particulars including flight information were provided to WHO and overseas counterparts.</p><p><b>RESULTS</b>The fi rst 350 novel influenza A (H1N1-2009) cases comprised 221(63%) imported cases, 124 (35%) locally acquired cases and 5 (2%) cases with unknown source. The imported cases consisted of three waves involving the United States (US), Australia and Southeast Asia. In the fi rst wave, 11 (69%) of the 16 imported cases had visited the US within seven days prior to their onset of illness between 25 May and 4 June 2009. In the second wave, 20 (74%) of the 27 imported cases between 5 June and 12 June had travelled to Melbourne, Australia. In the third wave, 90 (51%) of the 178 imported cases between 13 June and 25 June were acquired from intra-regional travel in Southeast Asia. Specifically, 49 cases were from the Philippines and 40 (82%) of them had travelled to Manila. A total of 667 communications were effected through the IHR mechanism; a majority within 24 hours of disease notification.</p><p><b>CONCLUSION</b>Singapore experienced an unprecedented need for international cooperation in surveillance and response to this novel Influenza A (H1N1-2009) pandemic. The IHR mechanism served as a useful channel to engage in regional cooperation concerning disease surveillance and data sharing, but requires improvement.</p>

Epidemiological characteristics of cholera in Singapore, 1992-2007

<p><b>INTRODUCTION</b>We carried out an epidemiological review of cholera in Singapore to determine its trends and the factors contributing to its occurrence.</p><p><b>MATERIALS AND METHODS</b>Epidemiological data of all notified cases of cholera maintained by the Communicable Diseases Division, Ministry of Health, for the period 1992 to 2007 were collated and analysed. Case-control studies were carried out in outbreaks to determine the source of infection and mode of transmission. Linear patterns in age and ethnic distribution of cholera cases were assessed using chi2 test for trend.</p><p><b>RESULTS</b>There were a total of 210 cholera cases reported between 1992 and 2007. The incidence of cholera declined from 17 cases in 1992 to 7 cases in 2007. About a quarter of the cases were imported from endemic countries in the region. Between 76% and 95% of the reported cases were local residents. Four elderly patients with comorbidities and who sought medical treatment late died, giving a case-fatality rate of 1.9%. Vibrio cholerae 01, biotype El Tor, serotype Ogawa, accounted for 83.8% of the cases. The vehicles of transmission identified in outbreaks included raw fi sh, undercooked seafood and iced drinks cross-contaminated with raw seafood.</p><p><b>CONCLUSION</b>With the high standard of environmental hygiene and sanitation, a comprehensive epidemiological surveillance system and licensing and control of food establishments, cholera could not gain a foothold in Singapore despite it being situated in an endemic region. However, health education of the public on the importance of personal and food hygiene is of paramount importance in preventing foodborne outbreaks. Physicians should also maintain a high level of suspicion of cholera in patients presenting with severe gastroenteritis, especially those with a recent travel history to endemic countries.</p>

Evaluation on the effectiveness of the national childhood immunisation programme in Singapore, 1982-2007

<p><b>INTRODUCTION</b>We undertook a study to evaluate the effectiveness of the National Childhood Immunisation Programme (NCIP) over the past 26 years by reviewing the epidemiological trends of the diseases protected, the immunisation coverage and the changing herd immunity of the population during the period of 1982 to 2007.</p><p><b>MATERIALS AND METHODS</b>The epidemiological data of all cases of diphtheria, pertussis, poliomyelitis, measles, mumps, rubella and acute hepatitis B notified to the Communicable Diseases Division, Ministry of Health (MOH) from 1982 to 2007 were collated and analysed. Data on tuberculosis (TB) cases were obtained from the TB Control Unit, Tan Tock Seng Hospital. Cases of neonatal tetanus and congenital rubella syndrome (CRS) among infants born in Singapore were identified from the Central Claims Processing System. The number of therapeutic abortions performed for rubella infections was retrieved from the national abortion registry. Coverage of the childhood immunisation programme was based on the immunisation data maintained by the National Immunisation Registry, Health Promotion Board. To assess the herd immunity of the population against the various vaccine-preventable diseases protected, the findings of several serological surveys conducted from 1982 to 2005 were reviewed.</p><p><b>RESULTS</b>The incidence of vaccine-preventable diseases covered under the NCIP had declined over the last 26 years with diphtheria, neonatal tetanus, poliomyelitis and congenital rubella virtually eliminated. The last case of childhood TB meningitis and the last case of acute hepatitis B in children below 15 years were reported in 2002 and 1996, respectively.</p><p><b>CONCLUSION</b>The NCIP has been successfully implemented as evidenced by the disappearance of most childhood diseases, excellent immunisation coverage rate in infants, preschool and school children, and high level of herd immunity of the childhood population protected.</p>

Changing seroprevalence of hepatitis B virus markers of adults in Singapore

<p><b>INTRODUCTION</b>We presented the findings from 2 seroprevalence studies conducted 6 years apart, so as to determine changes in the hepatitis B surface antigen (HBsAg) positivity rate and immunity to hepatitis B virus (HBV) among Singapore residents aged 18 to 69 years, and to assess the impact of a 4-year catch-up hepatitis B immunisation programme for adolescents and young adults launched in 2001.</p><p><b>MATERIALS AND METHODS</b>Two hepatitis B seroprevalence studies (HBSS) were conducted in 1999 and 2005 based on stored blood samples collected from 4698 participants aged 18 to 69 years during the national health survey (NHS) 1998 and from 3460 participants during the NHS 2004, respectively. Serology for HBsAg, hepatitis B e antigen (HBeAg) and antibody to HBsAg (anti-HBs) were tested by enzyme immunoassay in HBSS 1999 and electrochemiluminescence in HBSS 2005.</p><p><b>RESULTS</b>The overall age-standardised prevalence of HBsAg among Singapore residents aged 18 to 69 years decreased significantly from 4.0% in HBSS 1999 to 2.8% in HBSS 2005 (P = 0.002). The age-standardised prevalence of HBsAg in males (4.9% in 1999) and Chinese (4.7% in 1999) both decreased significantly to 2.7% and 2.8%, respectively in 2005. The overall age-standardised population immunity to HBV (anti-HBs >10 mIU/ml) increased from 39.7% in 1999 to 42.1% in 2005 (P = 0.019). In particular, the age-specific prevalence of anti-HBs showed a significant increase among those in the age group of 18 to 29 years from 27.9% in 1999 to 41.7% in 2005 (P <0.001) and among those in the age group of 30 to 39 years from 39.9% in 1999 to 44.7% in 2005 (P = 0.021).</p><p><b>CONCLUSION</b>There was an overall decline in the HBsAg positivity rate as well as an overall increase in population immunity to HBV. Following the 4-year catch-up immunisation programme, there was a significant increase in the immunity to HBV infection in the younger population aged 18 to 29 years.</p>

Changing epidemiology of enteric fevers in Singapore

<p><b>INTRODUCTION</b>We studied the epidemiological trends of enteric fevers (typhoid and paratyphoid fever) in Singapore from 1990 to 2009 and carried out a review of the current prevention and control measures.</p><p><b>MATERIALS AND METHODS</b>Epidemiological records of all reported enteric fevers maintained by the Communicable Diseases Division, Ministry of Health from 1990 to 2009 were analysed.</p><p><b>RESULTS</b>A total of 2464 laboratory confirmed cases of enteric fevers (1699 cases of typhoid and 765 cases of paratyphoid) were reported. Of these, 75% were imported, mainly from India and Indonesia. There had been a significant fall in the mean annual incidence rate of indigenous enteric fevers from 4.3 per 100,000 population in 1990 to 0.26 per 100,000 population in 2009 (P <0.005) with a corresponding increase in the proportion of imported cases from 71% between 1990 and 1993 to 92% between 2006 and 2009 (P <0.0005). Imported cases involving foreign contract workers increased significantly from 12.8% between 1990 and 1993 to 40.4% between 2006 and 2009 (P <0.0005).</p><p><b>CONCLUSION</b>Singapore has experienced a marked decline in the incidence of enteric fevers that is now comparable to that of other developed countries. Continued vigilance and proactive measures that address the changing epidemiology of enteric fevers in Singapore are necessary to sustain the milestone achieved in the past 2 decades.</p>

Epidemiological surveillance and control of rubella in Singapore, 1991-2007

<p><b>INTRODUCTION</b>We reviewed the epidemiological features of rubella in Singapore and the impact of the national immunisation programme in raising the population herd immunity against rubella, with special reference to females in the reproductive age group, and in the elimination of congenital rubella syndrome (CRS).</p><p><b>MATERIALS AND METHODS</b>Epidemiological data on all reported cases of rubella and CRS were obtained from the Communicable Diseases Division and Central Claims Processing System, respectively, at the Ministry of Health. Coverage of the childhood immunisation programme against rubella was based on the immunisation data maintained by the National Immunisation Registry, Health Promotion Board. To assess the herd immunity of the population against rubella, 4 serological surveys were conducted from 1989 to 1990, in 1993, 1998 and 2004.</p><p><b>RESULTS</b>The incidence of rubella has decreased significantly from the peak of 13.3 per 100,000 population in 1996 to 1.8 per 100,000 in 2007. CRS has virtually disappeared. With more than 92% to 93% of primary school leavers and preschool children annually vaccinated against rubella since 1976 and 1990, respectively, the level of susceptibility to rubella among women in the reproductive age group has gradually decreased from 44% in 1975 to 28% in 1985, and maintained at between 10% and 20% from 1987 to 1998. A considerable proportion (15.8%) of women 18 to 44 years of age remained susceptible to rubella infection in 2004.</p><p><b>CONCLUSION</b>Rubella prevention and control has been successfully implemented. However, the relatively high level of susceptibility to rubella among women in the reproductive age group continues to be of concern. More public awareness and health educational efforts are needed and every opportunity should be taken to ensure that all susceptible women are identified and protected against the infection.</p>

Outbreak of pandemic influenza A (H1N1-2009) in Singapore, May to September 2009

<p><b>INTRODUCTION</b>The fi rst case of pandemic influenza A(H1N1) was detected in Singapore on 26 May 2009, 1 month after the fi rst cases of novel influenza A(H1N1) was reported in California and Texas in the United States. The World Health Organization declared the fi rst influenza pandemic of the 21st century on 11 June 2009.</p><p><b>MATERIALS AND METHODS</b>Confirmed cases notified to the Ministry of Health between 27 May and 9 July 2009 were analysed. Various indicators of influenza activity were monitored throughout the study period. Estimates of the number of cases of H1N1-2009 were made using the number of polyclinic attendances for acute respiratory infection and influenza-like illness and the weekly prevalence of H1N1-2009.</p><p><b>RESULTS</b>Cases in Singapore affected mainly young adults, youths and children. By the end of September 2009, it was estimated that at least 270,000 persons had been infected by pandemic influenza A (H1N1) in Singapore. The peak number of cases occurred during E-week 30 (26 July-1 August) when an estimated 45,000 cases were seen in polyclinics and GP clinics. The hospitalisation, severe illness and mortality rates were estimated at 6 per 1000 cases, 0.3 per 1000 cases and 6.7 per 100,000 cases, respectively. The most common risk factors among hospitalised adult cases were asthma and diabetes. For hospitalised children, the most common risk factors were being under 5 years of age and asthma. The most common risk factors among persons with severe illness were diabetes in adults and epilepsy and being under 5 years of age in children. About half of cases with severe illness required mechanical ventilation. In addition, one-fifth of cases with severe illness had acute respiratory distress syndrome.</p><p><b>CONCLUSIONS</b>The fi rst wave of the influenza pandemic lasted about 10 weeks. Morbidity and mortality resulting from pandemic influenza were low.</p>

An epidemiological study of 1348 cases of pandemic H1N1 influenza admitted to Singapore Hospitals from July to September 2009

<p><b>INTRODUCTION</b>We reviewed the epidemiological features of 1348 hospitalised cases of influenza A (H1N1-2009) [pandemic H1N1] infection in Singapore reported between 15 July and 28 September 2009.</p><p><b>MATERIALS AND METHODS</b>Data on the demographic and epidemiological characteristics of hospitalised patients with confirmed pandemic H1N1 infection were collected from all restructured and private hospitals in Singapore using a standard template and were analysed retrospectively.</p><p><b>RESULTS</b>Of the 1348 cases, 92 were classified as severely ill (i.e. were admitted to an intensive care unit and/or who died). Of these severely ill cases, 50 (54.3%) required mechanical ventilation. While overall hospitalisation rates were highest in the 0 to 11 months age group, the incidence of severely ill cases was highest in patients aged 65 years and older. Fifty per cent of all hospitalised cases and 28% of all severely ill cases did not have any underlying medical conditions. The following factors were found to be independently associated with a higher likelihood of severe illness: older age and the presence of the following comorbidities: neuromuscular disorders, epilepsy and obesity.</p><p><b>CONCLUSION</b>Between 15 July and 28 September 2009, pandemic H1N1 infection caused significant illness requiring hospitalisation, as well as intensive care and mechanical ventilation in some cases. There were 18 deaths from pandemic H1N1 during this period, which corresponded to a case-fatality rate of 7 deaths for every 100,000 cases of pandemic H1N1.</p>

Outbreak of novel influenza A (H1N1-2009) linked to a dance club

<p><b>INTRODUCTION</b>This paper describes the epidemiology and control of a community outbreak of novel influenza A (H1N1-2009) originating from a dance club in Singapore between June and July 2009.</p><p><b>MATERIALS AND METHODS</b>Cases of novel influenza A (H1N1-2009) were confirmed using in-house probe-based real-time polymerase chain reaction (PCR). Contact tracing teams from the Singapore Ministry of Health obtained epidemiological information from all cases via telephone.</p><p><b>RESULTS</b>A total of 48 cases were identified in this outbreak, of which 36 (75%) cases were patrons and dance club staff, and 12 (25%) cases were household members and social contacts. Mathematical modelling showed that this outbreak had a reproductive number of 1.9 to 2.1, which was similar to values calculated from outbreaks in naïve populations in other countries.</p><p><b>CONCLUSION</b>This transmission risk occurred within an enclosed space with patrons engaged in intimate social activities, suggesting that dance clubs are places conducive for the spread of the virus.</p>

Seroepidemiology of dengue virus infection among adults in Singapore

<p><b>INTRODUCTION</b>To determine the seroepidemiology of dengue virus infection in a representative sample of the adult resident population aged 18 years old to 74 years old in Singapore and to estimate the proportion of asymptomatic dengue infection during the 2004 epidemic.</p><p><b>MATERIALS AND METHODS</b>The study was based on 4152 stored blood samples collected between September and December 2004 from participants aged 18 years old to 74 years old during the 2004 National Health Survey. Sera were tested for IgG and IgM antibodies using a commercial test kit (PanBio Capture/Indirect ELISA).</p><p><b>RESULTS</b>Of the study population, 59.0% and 2.6% tested positive for dengue IgG (past infection) and IgM/high-titre IgG (recent infection), respectively. Only 17.2% of young adults aged 18 years old to 24 years old were dengue IgG positive. Multivariate analyses showed that older age, Indian ethnicity and male gender were significantly associated with past infection, whereas only age was significantly associated with recent dengue infection. Based on the dengue cases notified during the period of survey, it was estimated that for every 23 individuals recently infected with dengue, only 1 was reported to the health authority as a clinical case.</p><p><b>CONCLUSION</b>The Singapore population is highly susceptible to dengue epidemics despite its aggressive Aedes prevention and control programme. The finding of a high proportion of unreported cases due to asymptomatic and subclinical infection poses a challenge for dengue control.</p>

Epidemiology and control of hand, foot and mouth disease in Singapore, 2001-2007

<p><b>INTRODUCTION</b>We reviewed the epidemiology of hand, foot and mouth disease (HFMD) in Singapore after the 2000 epidemic caused by Enterovirus 71 (EV71), with particular reference to the cyclical pattern, predominant circulating enteroviruses and impact of prevention and control measures in preschool centres.</p><p><b>MATERIALS AND METHODS</b>We analysed the epidemiological data from all clinical cases and deaths of HFMD diagnosed by medical practitioners and notified to the Ministry of Health, as well as laboratory data on enteroviruses detected among HFMD patients maintained by the Department of Pathology, Singapore General Hospital, and the Microbiology Laboratory, KK Women's and Children's Hospital from 2001 to 2007.</p><p><b>RESULTS</b>The incidence rate was highest in the 0 to 4 years old age group, with males being predominant. Three deaths were reported between January and February 2001. Nationwide epidemics occurred periodically; the predominating circulating virus was Coxsackievirus A16 (CA16) in the 2002, 2005 and 2007 epidemics, and EV71 in the 2006 epidemic. During the epidemic years between 2005 and 2007, 2 peaks were observed. The number of institutional outbreaks had increased 10-fold from 167 in 2001 to 1723 in 2007, although most of these outbreaks were rapidly brought under control with an attack rate of less than 10%.</p><p><b>CONCLUSION</b>HFMD remains an important public health problem in Singapore with the annual incidence rate per 100,000 population increasing from 125.5 in 2001 to 435.9 in 2007, despite stringent measures taken in preschool centres to prevent the transmission of infection. A high degree of vigilance should be maintained over the disease situation, in particular, surveillance of EV 71 which continues to cause severe complications and deaths in the region.</p>

Epidemiological characteristics of imported and locally-acquired malaria in Singapore

<p><b>INTRODUCTION</b>The objective of the study was to determine the trend of malaria, the epidemiological characteristics, the frequency of local transmission and the preventive and control measures taken.</p><p><b>MATERIALS AND METHODS</b>We analysed the epidemiological records of all reported malaria cases maintained by the Communicable Diseases Division, Ministry of Health, from 1983 to 2007 and the Anopheles vector surveillance data collected by the National Environment Agency during the same period.</p><p><b>RESULTS</b>The annual incidence of reported malaria ranged from 2.9 to 11.1 per 100,000 population, with a sharp decline observed after 1997. There were 38 deaths, 92.1% due to falciparum malaria and 7.9% due to vivax malaria. Of the reported cases, 91.4% to 98.3% were imported, with about 90% originating from Southeast Asia and the Indian subcontinent. Among the various population groups with imported malaria, the proportion of cases involving work permit/employment pass holders had increased, while that of local residents had decreased. Between 74.8% and 95.1% of the local residents with imported malaria did not take personal chemoprophylaxis when they travelled overseas. Despite the extremely low Anopheles vector population, a total of 29 local outbreaks involving 196 cases occurred. Most of the larger outbreaks could be traced to foreign workers with imported relapsing vivax malaria and who did not seek medical treatment early. One of the outbreaks of 3 cases in 2007 was caused by Plasmodium knowlesi, a newly recognised simian malaria which was probably acquired in a forested area where long-tail macaques had been sighted.</p><p><b>CONCLUSIONS</b>Singapore remains both vulnerable and receptive to the reintroduction of malaria and a high level of vigilance should be maintained indefinitely to prevent the re-establishment of endemicity. Medical practitioners should highlight the risk of malaria to travellers visiting endemic areas and also consider the possibility of simian malaria in a patient who has no recent travel history and presenting with daily fever spikes and with malaria parasite morphologically similar to that of P. malariae.</p>

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

<p><b>INTRODUCTION</b>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.</p><p><b>MATERIALS AND METHODS</b>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.</p><p><b>RESULTS</b>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.</p><p><b>CONCLUSION</b>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.</p>