Results of a Search for Sub-GeV Dark Matter Using 2013 LUX Data.

The scattering of dark matter (DM) particles with sub-GeV masses off nuclei is difficult to detect using liquid xenon-based DM search instruments because the energy transfer during nuclear recoils is smaller than the typical detector threshold. However, the tree-level DM-nucleus scattering diagram can be accompanied by simultaneous emission of a bremsstrahlung photon or a so-called "Migdal" electron. These provide an electron recoil component to the experimental signature at higher energies than the corresponding nuclear recoil. The presence of this signature allows liquid xenon detectors to use both the scintillation and the ionization signals in the analysis where the nuclear recoil signal would not be otherwise visible. We report constraints on spin-independent DM-nucleon scattering for DM particles with masses of 0.4-5 GeV/c^{2} using 1.4×10^{4} kg day of search exposure from the 2013 data from the Large Underground Xenon (LUX) experiment for four different classes of mediators. This analysis extends the reach of liquid xenon-based DM search instruments to lower DM masses than has been achieved previously.

Epidemiology of tuberculosis and HIV coinfections in Singapore, 2000-2014.

Cross-matching of records between Singapore's tuberculosis and HIV registries showed that 3.3% of individuals with tuberculosis (TB) were coinfected with HIV (2000-2014), the TB incidence among individuals with HIV infection was 1.65 per 100 person-years, and 53% of coinfections were diagnosed within 1 month of each other. The findings supported joint prevention programmes for early diagnosis and treatment.

First Searches for Axions and Axionlike Particles with the LUX Experiment.

The first searches for axions and axionlike particles with the Large Underground Xenon experiment are presented. Under the assumption of an axioelectric interaction in xenon, the coupling constant between axions and electrons g_{Ae} is tested using data collected in 2013 with an exposure totaling 95 live days ×118 kg. A double-sided, profile likelihood ratio statistic test excludes g_{Ae} larger than 3.5×10^{-12} (90% C.L.) for solar axions. Assuming the Dine-Fischler-Srednicki-Zhitnitsky theoretical description, the upper limit in coupling corresponds to an upper limit on axion mass of 0.12 eV/c^{2}, while for the Kim-Shifman-Vainshtein-Zhakharov description masses above 36.6 eV/c^{2} are excluded. For galactic axionlike particles, values of g_{Ae} larger than 4.2×10^{-13} are excluded for particle masses in the range 1-16 keV/c^{2}. These are the most stringent constraints to date for these interactions.

Limits on Spin-Dependent WIMP-Nucleon Cross Section Obtained from the Complete LUX Exposure.

We present experimental constraints on the spin-dependent WIMP-nucleon elastic cross sections from the total 129.5 kg yr exposure acquired by the Large Underground Xenon experiment (LUX), operating at the Sanford Underground Research Facility in Lead, South Dakota (USA). A profile likelihood ratio analysis allows 90% C.L. upper limits to be set on the WIMP-neutron (WIMP-proton) cross section of σ_{n}=1.6×10^{-41} cm^{2} (σ_{p}=5×10^{-40} cm^{2}) at 35 GeV c^{-2}, almost a sixfold improvement over the previous LUX spin-dependent results. The spin-dependent WIMP-neutron limit is the most sensitive constraint to date.

Results from a Search for Dark Matter in the Complete LUX Exposure.

We report constraints on spin-independent weakly interacting massive particle (WIMP)-nucleon scattering using a 3.35×10^{4} kg day exposure of the Large Underground Xenon (LUX) experiment. A dual-phase xenon time projection chamber with 250 kg of active mass is operated at the Sanford Underground Research Facility under Lead, South Dakota (USA). With roughly fourfold improvement in sensitivity for high WIMP masses relative to our previous results, this search yields no evidence of WIMP nuclear recoils. At a WIMP mass of 50 GeV c^{-2}, WIMP-nucleon spin-independent cross sections above 2.2×10^{-46} cm^{2} are excluded at the 90% confidence level. When combined with the previously reported LUX exposure, this exclusion strengthens to 1.1×10^{-46} cm^{2} at 50 GeV c^{-2}.

A large common-source outbreak of norovirus gastroenteritis in a hotel in Singapore, 2012.

An outbreak of gastroenteritis affected 453 attendees (attack rate 28·5%) of six separate events held at a hotel in Singapore. Active case detection, case-control studies, hygiene inspections and microbial analysis of food, environmental and stool samples were conducted to determine the aetiology of the outbreak and the modes of transmission. The only commonality was the food, crockery and cutlery provided and/or handled by the hotel's Chinese banquet kitchen. Stool specimens from 34 cases and 15 food handlers were positive for norovirus genogroup II. The putative index case was one of eight norovirus-positive food handlers who had worked while they were symptomatic. Several food samples and remnants tested positive for Escherichia coli or high faecal coliforms, aerobic plate counts and/or total coliforms, indicating poor food hygiene. This large common-source outbreak of norovirus gastroenteritis was caused by the consumption of contaminated food and/or contact with contaminated crockery or cutlery provided or handled by the hotel's Chinese banquet kitchen.

Factors associated with influenza vaccine uptake in older adults living in the community in Singapore.

In Singapore, influenza vaccination is recommended for persons at higher risk of complications of seasonal influenza, including those with chronic medical conditions and the elderly (individuals aged ⩾65 years). We investigated the factors associated with influenza vaccine uptake based on a nationally representative sample of community-dwelling adults aged >50 years. The data for this study were obtained from the National Health Surveillance Survey (NHSS) 2013. The association between influenza vaccine uptake and socio-demographic and health-related variables was analysed using univariable and multivariable logistic regression models. Of 3700 respondents aged ⩾50 years in the NHSS, 15·2% had received seasonal influenza vaccination in the past year. Older age, single marital status and economic inactivity were the socio-demographic variables independently associated with vaccine uptake. Health-related factors which were predictive of influenza vaccine uptake were sufficient total physical activity, better self-rated health, having at least one medical condition at risk of influenza complications and a regular family doctor/general practitioner. Influenza vaccine uptake in community-dwelling older adults was low. Our findings are of relevance in the formulation of public health policies and targeted health promotion strategies to increase vaccine uptake in this population group.

Improved Limits on Scattering of Weakly Interacting Massive Particles from Reanalysis of 2013 LUX Data.

We present constraints on weakly interacting massive particles (WIMP)-nucleus scattering from the 2013 data of the Large Underground Xenon dark matter experiment, including 1.4×10^{4} kg day of search exposure. This new analysis incorporates several advances: single-photon calibration at the scintillation wavelength, improved event-reconstruction algorithms, a revised background model including events originating on the detector walls in an enlarged fiducial volume, and new calibrations from decays of an injected tritium ß source and from kinematically constrained nuclear recoils down to 1.1 keV. Sensitivity, especially to low-mass WIMPs, is enhanced compared to our previous results which modeled the signal only above a 3 keV minimum energy. Under standard dark matter halo assumptions and in the mass range above 4 GeV c^{-2}, these new results give the most stringent direct limits on the spin-independent WIMP-nucleon cross section. The 90% C.L. upper limit has a minimum of 0.6 zb at 33 GeV c^{-2} WIMP mass.

Results on the Spin-Dependent Scattering of Weakly Interacting Massive Particles on Nucleons from the Run 3 Data of the LUX Experiment.

We present experimental constraints on the spin-dependent WIMP (weakly interacting massive particle)-nucleon elastic cross sections from LUX data acquired in 2013. LUX is a dual-phase xenon time projection chamber operating at the Sanford Underground Research Facility (Lead, South Dakota), which is designed to observe the recoil signature of galactic WIMPs scattering from xenon nuclei. A profile likelihood ratio analysis of 1.4×10^{4} kg day of fiducial exposure allows 90% C.L. upper limits to be set on the WIMP-neutron (WIMP-proton) cross section of σ_{n}=9.4×10^{-41} cm^{2} (σ_{p}=2.9×10^{-39} cm^{2}) at 33 GeV/c^{2}. The spin-dependent WIMP-neutron limit is the most sensitive constraint to date.

Seroepidemiology of dengue virus infection in the adult population in tropical Singapore.

To assess the impact of past dengue epidemics in Singapore, we undertook a national seroepidemiological study to determine the prevalence of past dengue virus (DENV) infection in the adult population in 2010 and make comparisons with the seroprevalence in 2004. The study involved residual sera from 3293 adults aged 18-79 years who participated in a national health survey in 2010. The overall prevalence of anti-DENV IgG antibodies was 56·8% (95% confidence interval 55·1-58·5) in 2010. The seroprevalence increased significantly with age. Males had significantly higher seroprevalence than females (61·5% vs. 53·2%). Among the three major ethnic groups, Malays had the lowest seroprevalence (50·2%) compared to Chinese (57·0%) and Indians (62·0%). The age-standardized seroprevalence in adults was significantly lower in 2010 (54·4%) compared to 2004 (63·1%). Older age, male gender, Indian ethnicity, permanent residency and being home-bound were independent risk factors significantly associated with seropositivity. About 43% of the Singapore adult resident population remain susceptible to DENV infection as a result of the successful implementation of a comprehensive nationwide Aedes surveillance and control programme since the 1970s. Vector suppression and concerted efforts of all stakeholders in the community remain the key strategy in the prevention and control of dengue.

Surveillance of tuberculosis treatment outcomes of Singapore citizens and permanent residents, 2002-2011.

SETTING: Singapore, which had a tuberculosis (TB) incidence rate of 41 per 100,000 resident population in 2011. OBJECTIVE: To report the outcomes of Singapore citizens and permanent residents treated for TB from 2002 to 2011. METHODS: A computerised treatment surveillance module (TSM) was launched in 2001 to track the progress and outcome of TB patients nationally. Physicians were required to submit an electronic or paper return for every patient at each clinic visit. Treatment adherence, drugs prescribed, treatment delivery mode and final outcome, specified as 'completed treatment', 'lost to follow-up', 'death', 'transferred out', 'permanent cessation of treatment' and 'still on treatment/no final outcome', were captured. Quarterly cohort outcomes at 12-15 months after starting treatment were combined to generate annual treatment outcomes. RESULTS: Treatment completion rates increased from 73.4% to 82.8%. The proportion of patients lost to follow-up decreased from 3.4% to 1.7%, while that of patients still on treatment or with no final outcome decreased from 10.5% to 4.4%. The death rate ranged between 10.2% and 11.7%; the majority were not attributed to TB. CONCLUSION: TB treatment completion among Singapore citizens and permanent residents has improved since 2002 as the likely result of the TSM and other initiatives introduced over the past decade.

Notified tuberculosis among Singapore residents by ethnicity, 2002-2011.

SETTING: The National Tuberculosis Programme in Singapore where, among resident cases, higher tuberculosis (TB) rates have been reported in ethnic Malays. OBJECTIVE: To describe the socio-demographic and clinical characteristics of resident TB cases by ethnicity, and to assess whether Malays differ from other groups in terms of the above parameters. DESIGN: Cross-sectional review of records from the tuberculosis registry's electronic database. RESULTS: Among 15 622 resident cases notified, 72.2% were Chinese, 18.7% Malay, 5.8% Indian and 2.9% were from other minorities. Compared to other ethnicities, Malays were more likely to be incarcerated at the time of notification (odds ratio [OR] 3.70, 95%CI 3.03-4.52) and clustered at the same residential address (OR 1.65, 95%CI 1.44-1.89), but were less likely to be aged ≥65 years (OR 0.61, 95%CI 0.54-0.70) or to reside in high-cost housing (OR 0.11, 95%CI 0.07-0.17). In terms of disease characteristics, more Malays had diabetes mellitus (OR 1.54, 1.37-1.73), a highly-positive acid-fast bacilli smear (OR 1.64, 95%CI 1.47-1.83) and cavitary disease on chest X-ray (OR 1.41, 95%CI 1.28-1.55). CONCLUSION: Compared to other ethnicities, reported TB cases among Malays were more severe and were likely to be more infectious. Increased vigilance in case management and contact investigations, as well as an improvement in the socio-economic conditions of this community, are required to reduce TB rates in this ethnic group.

Prevalence of antibodies against measles, mumps and rubella in the childhood population in Singapore, 2008-2010.

We undertook a national paediatric seroprevalence survey of measles, mumps and rubella (MMR) in Singapore to assess the impact of the national childhood immunization programme against these three diseases after introduction of the trivalent MMR vaccine in 1990. The survey involved 1200 residual sera of Singapore residents aged 1-17 years collected from two hospitals between 2008 and 2010. The overall prevalence of antibodies against measles, mumps and rubella was 83∙1% [95% confidence interval (CI) 80∙9-85∙1], 71.8% (95% CI 69∙1-74∙2) and 88∙5% (95% CI 86∙6-90∙2), respectively. For all three diseases, the lowest prevalence was in children aged 1 year (47∙8-62∙3%). The seroprevalence of the vaccinated children declined over time. The national MMR immunization programme is effective in raising the herd immunity of the childhood population, although certain age groups are more susceptible to infection, in particular, those who are not eligible for vaccination at age <15 months.

Comparative seroepidemiology of pertussis, diphtheria and poliovirus antibodies in Singapore: waning pertussis immunity in a highly immunized population and the need for adolescent booster doses.

BACKGROUND: We assessed the seroepidemiology of pertussis, diphtheria and poliovirus antibodies in a cohort of highly immunized children, together with the burden of these diseases in Singapore. METHODS: Hospital residual sera collected between August 2008 and July 2010 from 1200 children aged 1-17 years were tested for the prevalence of IgG antibodies against Bordetella pertussis, diphtheria toxoid, and all three poliovirus types by enzyme-linked immunosorbent assays. RESULTS: We found an overall seroprevalence of 99.4% (95% CI 98.8-99.7%) for diphtheria, and 92.3% (95% CI 90.6-93.6%) for poliomyelitis, along with no indigenous cases of these diseases since 1993. However, the seroprevalence for pertussis was 60.8% (95% CI 58.0-63.5%) only. Among the subjects who had completed three doses of pertussis vaccination by the age of 2 years (n=1092), the pertussis seroprevalence was 85.0% (95% CI 79.7-89.2%) in those who received the last vaccination within a year before the study, and it decreased to 75.0% (95% CI 64.5-83.2%) and 63.1% (95% CI 50.9-73.8%) in those who had the last vaccination 1 year and 2 years before the study, respectively. The seroprevalence remained at about 50% for those whose last pertussis vaccination was administered 4 years and longer before the study. CONCLUSIONS: The high seroprevalence for poliomyelitis and diphtheria confer solid herd immunity to eliminate these diseases in Singapore. In contrast, immunity against pertussis waned considerably over time, and routine boosters should be given to adolescents to ensure sustained immunity against pertussis.

Correlations between clinical illness, respiratory virus infections and climate factors in a tropical paediatric population.

Weekly (August 2003-December 2008) numbers of five common paediatric diseases and the incidence of respiratory viruses were obtained from a children's hospital in Singapore and correlated with climate data using multivariate time-series techniques. Upper respiratory tract infections were positively correlated with the incidences of influenza A, B, respiratory syncytial virus (RSV) and parainfluenza viruses (types 1-3 combined). Lower respiratory tract infections were positively correlated with only the incidence of RSV. Both upper and lower respiratory tract infections were negatively correlated with relative humidity. Asthma admissions were negatively correlated with maximum temperature and positively correlated with the incidence of influenza B and increasing hours of sunshine. Although sporadic cases of adenovirus infection were identified, not enough cases were available for a more detailed analysis. Gastroenteritis and urinary tract infections, included as control diseases, were not correlated significantly with any climate parameters. These correlations are compatible with current understanding of respiratory virus survival under certain climate conditions and may assist the prediction of disease burdens and hospital resource planning in such tropical environments.

Mortality among tuberculosis patients on treatment in Singapore.

OBJECTIVE: To identify the risk factors associated with mortality among tuberculosis (TB) patients on treatment in Singapore. DESIGN: A retrospective cohort study of 7433 TB patients notified and started on TB treatment from 2000 to 2006 was conducted. Cox regression analysis was used to determine independent risk factors for mortality. RESULTS: Of 7433 patients who started TB treatment between 2000 and 2006, there were 884 deaths (11.9%) from any cause. Older age, male sex, being in a long-term care facility, having comorbidity, absence of cough, more than one site of TB, bacteriologically confirmed laboratory results, resistance to at least isoniazid (INH) and rifampicin (RMP) and absence of cavity were strongly associated with all-cause mortality among TB patients. A total of 203 patients (2.7%) died of TB. Risk factors for death due to TB were older age, male sex, Malay ethnicity, being in a long-term care facility, absence of cough, more than one site of TB, bacteriologically confirmed laboratory results and resistance to at least INH and RMP or to at least INH but not RMP. CONCLUSION: It is important to identify TB patients with risk factors related to mortality so that appropriate and timely interventions can be instituted to prevent deaths among TB patients.

A national study of the epidemiology of pneumococcal disease among hospitalised patients in Singapore: 1995 to 2004.

INTRODUCTION: Infections with Streptococcus pneumoniae cause significant morbidity and mortality. In this study, we describe the epidemiology of pneumococcal disease based on hospitalisation rates for all age groups in Singapore. This is important for evaluating prevention and control strategies of pneumococcal disease. METHODS: We conducted a retrospective study of hospitalisation cases admitted to all public and private hospitals from 1995 to 2004. 4,275 hospitalisation records were extracted, based on the International Classification of Diseases, Ninth Revision (ICD-9) codes for pneumococcal disease. We analysed the demographics, type of pneumococcal disease, length of stay and case fatality of these cases. RESULTS: Our study showed that the mean annual hospitalisation rate for pneumococcal disease was 10.9 per 100,000 population from 1995 to 2004. The mean annual hospitalisation rate was highest in the young and the elderly. CONCLUSION: Baseline information on the epidemiology of pneumococcal disease is important for the formulation and evaluation of a national prevention and control programme.

Outbreak of measles in primary school students with high first dose MMR vaccination coverage.

INTRODUCTION: Indigenous cases of measles continue to occur in Singapore despite the implementation of a two-dose mumps, measles and rubella (MMR) vaccination policy in 1998. We investigated a measles outbreak that took place in a primary school from April 17 to May 6, 2004 to identify all cases, evaluate vaccine efficacy (VE) and implement outbreak control measures. METHODS: A case of measles was defined as anyone having generalised rash and fever with or without cough, coryza or conjunctivitis during the outbreak period, and who had either laboratory-confirmed acute measles infection or was epidemiologically linked to a patient with laboratory-confirmed measles infection. Vaccination status was obtained from the studentos health booklet and confirmed with the National Immunisation Registry. Attack rates in unvaccinated (ARU) and vaccinated (ARV) students were calculated and VE was evaluated using the formula: VE (percent) = [(ARU-ARV) / ARU] x 100 percent. RESULTS: Nine students, aged between eight and 14 years, from five classes in primary three and primary six, were epidemiologically linked to have measles. None of them had received the second dose of the MMR vaccine. 93 percent of students in the affected classes (n = 184) had prior documented evidence of receiving at least one dose of MMR vaccination, as compared to 96.5 percent for the entire school enrolment (n = 1,309). The attack rate was 1.2 percent in the vaccinated group and 53.8 percent in the unvaccinated group. The VE for the primary dose of MMR in the affected classes was 97.8 percent. CONCLUSION: It is important to achieve a high coverage for the primary dose of MMR vaccine in order to prevent any potential outbreaks prior to receiving the booster dose.

Public health measures implemented during the SARS outbreak in Singapore, 2003.

The SARS outbreak hit Singapore between March and May 2003. Public health control measures were applied along three fronts; prevention and control within healthcare settings, community and at the borders. Nosocomial spread composed majority of SARS cases in Singapore. To prevent infection within healthcare facilities, cases were centralized in a SARS-designated hospital, a no-visitors rule was applied and movement of patients and healthcare staff were restricted. For triaging purposes, fever clinics were established. A dedicated ambulance service was used to transport possible cases to the SARS-designated hospital. Hospitals were surveyed for fever clusters. The challenge was to identify cases with atypical presentation. Effective and safe discharge criteria were established from the lessons learnt. To prevent community spread, contacts of cases were stringently traced, quarantined in their homes and monitored daily. For prompt identification of a case and to reduce the time between onset of symptoms and isolation, the Infectious Diseases Act was amended. A large wholesale market closure resulted in massive quarantine thereby limiting the spread of infection. A mass education campaign was implemented in order to educate and raise awareness of the public. At all air, sea and land points-of-entry, exit and entry screening took place that resulted in zero importation and exportation of SARS cases after implementation of screening. Coordinated effort of the cross sectional inter-ministerial collaboration and strong coordination by the Task Force and commitment from different professionals made it possible to conquer the disease.