Kee Tai Goh

Influenza excess mortality from 1950–2000 in tropical Singapore

Introduction Tropical regions have been shown to exhibit different influenza seasonal patterns compared to their temperate counterparts. However, there is little information about the burden of annual tropical influenza epidemics across time, and the relationship between tropical influenza epidemics compared with other regions. Methods Data on monthly national mortality and population was obtained from 1947 to 2003 in Singapore. To determine excess mortality for each month, we used a moving average analysis for each month from 1950 to 2000. From 1972, influenza viral surveillance data was available. Before 1972, information was obtained from serial annual government reports, peer-reviewed journal articles and press articles. Results The influenza pandemics of 1957 and 1968 resulted in substantial mortality. In addition, there were 20 other time points with significant excess mortality. Of the 12 periods with significant excess mortality post-1972, only one point (1988) did not correspond to a recorded influenza activity. For the 8 periods with significant excess mortality periods before 1972 excluding the pandemic years, 2 years (1951 and 1953) had newspaper reports of increased pneumonia deaths. Excess mortality could be observed in almost all periods with recorded influenza outbreaks but did not always exceed the 95% confidence limits of the baseline mortality rate. Conclusion Influenza epidemics were the likely cause of most excess mortality periods in post-war tropical Singapore, although not every epidemic resulted in high mortality. It is therefore important to have good influenza surveillance systems in place to detect influenza activity.

Prevalence of hepatitis A virus infection among sewage workers in Singapore.

To determine whether or not occupational exposure to sewage is associated with a higher seroprevalence of hepatitis A virus (HAV) infection, 600 sewage workers in Singapore were tested for total (IgG and IgM) antibody to HAV by enzyme immunoassay. Using logistic regression with stepwise procedure, the adjusted seroprevalence of sewage workers was 2.2 times higher than that of another non-occupationally exposed population group. Seroprevalence was significantly correlated with age and educational levels, the association being independent of the occupational association. The epidemiological data in the study show that sewage workers have an increased occupational risk of acquiring HAV infection and should be protected by active immunization.

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.

Person-to-person transmission of cholera in a psychiatric hospital

An outbreak of cholera caused by Vibrio cholerae O1, biotype el tor, serotype Ogawa, phage type 4, was reported in a psychiatric hospital in Singapore. A total of 74 inmates (18 symptomatic and 56 asymptomatic) were infected; two of them died. Extensive epidemiological investigations showed that the organism was not transmitted by contaminated food or water but through close person-to-person contact. Early recognition of the outbreak and prompt implementation of epidemic control measures comprising surveillance of diarrhoea, rectal swabbing of all asymptomatic inmates, isolation of those found to be infected, maintenance of a high standard of environmental sanitation and mass chemoprophylaxis with doxycycline, rapidly brought the outbreak under control.

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.

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.

Statistical modeling reveals the effect of absolute humidity on dengue in Singapore.

Weather factors are widely studied for their effects on indicating dengue incidence trends. However, these studies have been limited due to the complex epidemiology of dengue, which involves dynamic interplay of multiple factors such as herd immunity within a population, distinct serotypes of the virus, environmental factors and intervention programs. In this study, we investigate the impact of weather factors on dengue in Singapore, considering the disease epidemiology and profile of virus serotypes. A Poisson regression combined with Distributed Lag Non-linear Model (DLNM) was used to evaluate and compare the impact of weekly Absolute Humidity (AH) and other weather factors (mean temperature, minimum temperature, maximum temperature, rainfall, relative humidity and wind speed) on dengue incidence from 2001 to 2009. The same analysis was also performed on three sub-periods, defined by predominant circulating serotypes. The performance of DLNM regression models were then evaluated through the Akaikes Information Criterion. From the correlation and DLNM regression modeling analyses of the studied period, AH was found to be a better predictor for modeling dengue incidence than the other unique weather variables. Whilst mean temperature (MeanT) also showed significant correlation with dengue incidence, the relationship between AH or MeanT and dengue incidence, however, varied in the three sub-periods. Our results showed that AH had a more stable impact on dengue incidence than temperature when virological factors were taken into consideration. AH appeared to be the most consistent factor in modeling dengue incidence in Singapore. Considering the changes in dominant serotypes, the improvements in vector control programs and the inconsistent weather patterns observed in the sub-periods, the impact of weather on dengue is modulated by these other factors. Future studies on the impact of climate change on dengue need to take all the other contributing factors into consideration in order to make meaningful public policy recommendations.

Molecular characterization of hepatitis B virus surface antigen mutants in Singapore patients with hepatocellular carcinoma and hepatitis B virus carriers negative for HBsAg but positive for anti-HBs and anti-HBc

Background and Aims : Mutations on the a‐determinant of hepatitis B virus surface antigen (HBsAg), capable of escaping detection and vaccination, are identified in HBsAg‐positive/anti‐HBs‐positive vaccinated infants. We studied the prevalence of these mutants in HBsAg‐negative/anti‐HBc‐positive chronic HBV carriers and patients with hepatocellular carcinoma (HCC).

Epidemiology of typhoid fever in Singapore

A total of 1452 cases of typhoid fever was notified in Singapore from 1980-9. The morbidity rates of indigenous cases showed a steady decline from 5.9 per 100,000 population in 1980 to 1.2 per 100,000 population in 1989. The mean case fatality was 0.8%. Children, adolescents and young adults were most susceptible to typhoid fever. There was no significant difference in morbidity rates between the major ethnic groups. The vast majority of indigenous cases were sporadic while outbreaks accounted for almost one third of them. Food was the main vehicle of transmission. The commonest indigenous phage types were B1, D1 and A. Antimicrobial resistance was infrequently seen. The proportion of imported cases rose from 32% in 1980 to 72% in 1989. Almost half (48.5%) of all imported cases were local residents who contracted typhoid fever while travelling in endemic countries. As imported cases assume greater importance in the epidemiology of typhoid fever in Singapore, further drop in typhoid fever incidence would require reduction of travel-related cases through greater awareness of food hygiene and effective vaccination.

Epidemiological characteristics of an institutional outbreak of cholera

An outbreak of cholera caused by Vibrio cholerae 01, biotype El Tor, serotype Inaba, phage type 4, occurred in an institution for the aged in Singapore in August and September 1984. 96 inmates were infected (21 symptomatic and 75 asymptomatic) and 5 died. The index case was a 72-year-old male inmate who continued to assist in food preparation in the kitchen from the time of onset of diarrhoea until he was seriously ill and hospitalized 4 days later. Another kitchen helper was found to have asymptomatic V. cholerae 01 infection. The infection rate for males was significantly higher than that for females (P less than 0.025), associated with the use of unsanitary toilets. The main mode of transmission was through food contaminated by the 2 kitchen helpers who probably accounted for most of the infections, while poor personal hygiene of the inmates helped to sustain person-to-person spread. The outbreak was confined within the institution as the result of the prompt and effective implementation of control measures.