Seasonal trends of viral respiratory tract infections in the tropics.

To evaluate the seasonal trends of viral respiratory tract infections in a tropical environment, a retrospective survey of laboratory virus isolation, serology and immunofluorescence microscopy in two large general hospitals in Singapore between September 1990 and September 1994 was carried out. Respiratory tract viral outbreaks, particularly among infants who required hospitalization, were found to be associated mainly with respiratory syncytial (RSV) infections (72%), influenza (11%) and parainfluenza viruses (11%). Consistent seasonal variations in viral infections were observed only with RSV (March-August) and influenza A virus (peaks in June, December-January). The RSV trends were associated with higher environmental temperature, lower relative humidity and higher maximal day-to-day temperature variation. Although the influenza A outbreaks were not associated with meteorological factors, influenza B isolates were positively associated with rainfall. These data support the existence of seasonal trends of viral respiratory tract infections in the tropics.

Multicentre evaluation of dengue IgM dot enzyme immunoassay.

BACKGROUND: The traditional methods used in the diagnosis of dengue infection do not lend themselves to field application. As such, clinical specimens have to be sent to a central laboratory for processing which invariably leads to delay. This affects patient management and disease control. The development of the dengue IgM dot enzyme immunoassay has opened up the possibility of carrying out the test in peripheral health settings. OBJECTIVES: This multicentre study was conducted to evaluate a new, commercial nitrocellulose membrane based IgM capture enzyme immunoassay. STUDY DESIGN: The sensitivity and specificity of the test were compared with in-house dengue IgM enzyme-linked immunoassays routinely performed by each of the selected centres. Known positive and negative dengue specimens, as well as specimens from non-dengue cases, were included in the evaluation. RESULTS: Based on 402 specimens tested by the six centres, the sensitivity was 92.1% and specificity 88.1%, with an overall agreement of 92.8% when compared with IgM EIA assays performed on microplates. CONCLUSIONS: The results suggest that this commercial kit has a role to play in the diagnosis of dengue infection, especially in peripheral health settings.

A severe case of hemorrhagic fever with renal syndrome in Singapore.

The incidence of human hantavirus infection in Singapore is low. Hitherto, only 2 cases of hemorrhagic fever with renal syndrome (HFRS) have been reported. A third case is reported here of a ragman who had the classical manifestations of HFRS, confirmed by serology. In addition, his condition was complicated by liver dysfunction and neurological disturbance. After a protracted stay, the patient was finally discharged from hospital 5 months after the onset of his severe illness.

Adult dengue deaths in Singapore.

BACKGROUND: Dengue haemorrhagic fever (DHF) is a leading cause of hospitalization of children in Southeast Asia and regarded mainly as a problem of childhood. In Singapore, however, both dengue fever (DF) and DHF now occur most frequently in those aged 16-25 years and case fatality rates are higher among adults than children. OBJECTIVE: To describe adults who died from DHF in Singapore. STUDY DESIGN: The clinical, laboratory and, where performed, autopsy records of adults reported to the Ministry of the Environment to have died from DHF were reviewed. RESULTS: Four of 10 adults had clinical, serological and/or virological evidence of acute dengue virus infection. All 4 patients, who were between 27 and 58 years old, had dengue IgM antibodies. Two of them had elevated dengue IgG antibodies consistent with a recent infection. Dengue type 2 virus was isolated from one of these two patients who had bled into the lungs, skin, pericardial and pleural surfaces and succumbed to shock. The other patient had no evidence of overt bleeding. A third patient, who suffered massive intractable retroperitoneal haemorrhage and shock, seroconverted in the haemagglutination inhibition test for dengue antibodies. The fourth patient had bleeding into her skin, urinary and gastrointestinal tracts, acute pulmonary oedema, ascites and hypotension. Her stillborn baby also had ascites. CONCLUSION: Deaths from DHF are not mainly a childhood occurrence. Adults do die from severe DHF, whether the infection be primary or secondary.

Prevalence of hepatitis B virus (HBV) infection in Singapore men with sexually transmitted diseases and HIV infection: role of sexual transmission in a city state with intermediate HBV endemicity.

STUDY OBJECTIVES: To describe the prevalence of hepatitis B virus (HBV) infection in patients with sexually transmitted diseases (STD) and human immunodeficiency virus (HIV) infection, and to determine the role of sexual transmission of HBV infection in Singapore. DESIGN: A cross sectional study of all consecutive men presenting with a new episode of STD at a government outpatient clinic and all men with HIV infection on routine follow up at a government hospital. The prevalence of various HBV markers was compared with that of healthy males aged 15 years and above (controls). SETTING: Singapore, a city state of intermediate HBV endemicity. SUBJECTS: These comprised 497 STD patients, 47 HIV infected patients, and 418 controls. MAIN RESULTS: The overall seroprevalences of HBV infection in STD patients, HIV infected patients, and control subjects were 41.2%, 61.7%, and 33.3%, respectively (p < 0.001). The seroprevalences of hepatitis B surface antigen (6.2%, 8.5%, and 4.5%, respectively) were comparable in the three groups. Using stepwise logistic regression analysis, the adjusted seroprevalences of HBV infection in STD and HIV infected patients were respectively 2.4 times (95% confidence interval (CI), 1.7, 3.3) and 3.3 times (95% CI 1.7, 6.3) higher than in controls. HBV infection rates were higher among Chinese (odds ratio (OR), 1.9; 95% CI 1.6, 3.4) than non-Chinese, and among those aged 25-34 years (OR 2.4; 95% CI 1.6, 3.4), 35-44 years (OR 3.9; 95% CI 2.5, 5.9), and 45+ years (OR 6.2; 95% CI 3.8, 10.2) than in those aged 15-24 years. Sex related factors significantly associated with higher infection rates, independent of age and ethnic group, were reactive VDRL test (OR 2.4; 95% CI 1.2, 4.7), participation in anal intercourse (OR 2.3; 95% CI 1.2, 4.3), and having 10 or more lifetime sexual partners (OR 1.5; 95% CI, 1.0, 2.1). CONCLUSION: The importance of sexual transmission of HBV in an area of intermediate HBV endemicity was confirmed. Patients attending STD clinics should be routinely screened for HBV markers and those found to be seronegative should be strongly advised to be immunised against this virus.

A descriptive profile and the immune status of some hospitalised patients with measles.

The incidence of measles in Singapore has declined with the introduction of measles vaccination in 1976. However, a progressive increase in notified measles cases has occurred since 1990. To characterise the current profile of hospitalised patients with measles, particularly their measles immunity status, we analysed 46 cases over a period of 3 months. The majority (69.6%) were school-going children (aged 5-19 years). Of the 25 patients (54.3%) classified as preventable by immunisation according to the current strategy, 68% were school-age persons. Five previously vaccinated patients had measles enzyme immunoassay immunoglobulin M and immunoglobulin G antibodies present. The occurrence of preventable cases among school-age children indicates that the implementation of the current immunisation programme should be improved.

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.

Comparative analysis of the restriction endonuclease profiles of the Dumas and Singapore strains of varicella-zoster virus.

The incidence of varicella in Singapore has been increasing since 1984. In 1991, 17,930 cases were reported in a population of about 3 million. A serological survey completed in 1990 demonstrated that only 43% of the cohort had antibodies to varicella-zoster virus (VZV), indicating inadequate herd immunity. To exclude novel VZV strains, representative VZV isolates from 9 chicken pox and 4 zoster patients were characterised by restriction endonuclease analysis. DNAs were extracted from viral isolates propagated in MRC5 human embryo lung cells and were digested separately with BglII, EcoRI, PstI, SalI, and XbaI enzymes. The cleavage profiles of these VZV strains derived from both chicken pox and zoster lesions revealed no distinct differences. This observation implies that the current upsurge of chicken pox most likely stems from closely related VZV genotypes infecting a susceptible population with insufficient herd immunity. Comparison of the restriction fragments of the Singapore and the Dumas strains revealed polymorphisms of the SalI-D, SalI-E, and XbaI-I fragment lengths, which correlated with variable regions I, II, and III of the VZV genome, thereby representing geographically distinct genotypic variants of VZV.

Prevalence of varicella-zoster virus infection in Singapore.

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

Clinical and laboratory study of first episode genital herpes in Singapore.

A prospective study of the epidemiology, clinical aspects and laboratory features of first episode genital herpes was carried out in Middle Road Hospital, Singapore between June 1986 and December 1987. A total of 68 patients were studied. There were more women than men in the study population with a female to male ratio of 7.5 to 1. The peak incidence of first episode genital herpes was between 20 and 29 years of age. Specimens from 63 patients yielded positive culture for herpes simplex virus (HSV). HSV-1 was isolated from 21 patients (30.9%), HSV-2 from 41 patients (60.3%) and untyped HSV from one patient (1.5%). True primary genital herpes was diagnosed in 43 patients (68.3%) using a test for complement fixing antibodies to HSV. HSV-1 was found to be the causative agent in 18 (41.9%) of the true primary infections, HSV-2 in 24 (55.8%) and untyped HSV in one (2.3%). In comparison, HSV-1 was isolated in only 2 (10%) of the 20 patients with non-primary first episode genital herpes; HSV-2 was found in 13 patients (65%) and the culture was negative in 5 (25%).

PIP: A prospective study of the epidemiology, clinical aspects, and laboratory features of 1st episode genital herpes was conducted in Middle Road Hospital, Singapore between June 1986-December 1987. A total of 68 patients were studied and there were more women than men in the study population; the ratio of females:males was 7.5:1. The peak incidence of 1st episode genital herpes was between 20-29 years of age. Specimens from 63 patients yielded positive culture for herpes simplex virus (HSV). HSV-1 was isolated from 21 patients (30.9%), HSV-2 from 41 patients (60.3%), and untyped HSV from 1 patient (1.5%). True primary genital herpes was diagnosed in 43 patients (68.3%) using a test for complement fixing antibodies to HSV. HSV-1 was found to be the causative agent in 18 (41.9%) of the true primary infection, HSV-2 in 24 (55.8%), and untyped HSV in 1 (2.3%). In comparison, HSV-1 was isolated in only 2 (10%) of the 20 patients with nonprimary 1st episode genital herpes; HSV-2 was found in 13 patients (65%), and the culture was negative in 5 (25%).

The hepatitis B immunization programme in Singapore.

A voluntary immunization programme to prevent perinatal transmission of hepatitis B virus (HBV) infection in Singapore was implemented on 1 October 1985 as an integral component of the national childhood immunization programme. Up to April 1988, a total of 68,845 mothers who attended government maternal and child health clinics were screened for the disease. Of these, 2432 (3.5%) were positive for hepatitis B surface antigen (HBsAg) and 904 (1.3%) for hepatitis B e antigen (HBeAg). Virtually all the babies born to carrier mothers completed the full immunization schedule; and in addition, those of HBeAg-positive mothers were given a dose of hepatitis B immunoglobulin at birth. The hepatitis B immunization programme was extended on 1 September 1987 to cover all newborns. About 90% of the 15,943 babies delivered in government institutions from September 1987 to April 1988 were immunized at birth, with the subsequent doses being administered at maternal and child health clinics at 4-6 weeks and 5 months later. More than 85% of the children given the full course of plasma-derived and yeast-derived hepatitis B vaccine from birth continued to have protective antibody to HBV two years after immunization. The programme is being closely monitored to assess the duration of immunity and the need for booster doses, while seronegative adults are also being encouraged to be vaccinated.

Comparison of tube cultures of Madin Darby canine kidney cells with shell-vial cultures after low-speed centrifugation for influenza virus isolation.

The efficacy of isolation of influenza viruses was compared in two systems--conventional tube cultures of Madin Darby canine kidney cells, and shell-vial cultures after low-speed centrifugation. One hundred and fifty eight throat and nasal swabs were inoculated and cultures screened by hemagglutination on days 1, 2, 3 and 5 post-inoculation. Twenty-four shell-vial cultures (15.2%) and 6 tube cultures (3.8%) were positive for influenza virus type B, indicating that shell-vial cultures with low-speed centrifugation are superior to tube cultures for influenza virus type B isolation (p less than 0.005 by McNemar's test for analysis of matched pairs data).

Influenza surveillance in Singapore: 1972-86.

Prospective laboratory surveillance of influenza viruses has been carried out since 1973 in Singapore. The results indicate that antigenic shift variants caused epidemics at various times of the year over this period, whereas drift variants were associated with a regular increase in incidence during the second and fourth calendar quarters. Outbreaks due to influenza A virus occurred every year and to influenza B virus at intervals of 16-24 months. Between outbreaks, viruses belonging to either of the two types could be detected during most months, and certain variants appeared several months before the outbreaks they subsequently caused. The factors that contribute to the seasonal pattern are at present unknown.

Acute hepatitis A in Singapore: importance of shellfish ingestion in a non-epidemic period.

A case-control study based on 28 serologically confirmed cases of hepatitis A and 42 home contacts with no recent or past evidence of hepatitis A virus (HAV) infection was conducted to determine the importance of shellfish exposure in the transmission of HAV during a non-epidemic period in Singapore. It was found that consumption of partially-cooked cockles (Anadara granosa) was significantly associated with the illness (p less than 0.001). No other types of locally available shellfish including oysters, mussels and clams were incriminated. The public should be constantly reminded to refrain from consuming raw and inadequately cooked bivalve molluscs all the time, and not just during epidemics.

Genital herpes in Singapore.

As in many parts of the world, the incidence of genital herpes has increased in Singapore, the increase occurring sharply from 1982 onwards, and affecting females to a greater extent than males. Peak incidence in both sexes was found to occur in the 15-34 year age group. Changes in sexual practices, a decreasing prevalence of age-specific antibody to herpes simplex type 1 virus in sexually active adults, and greater interest in the disease following publicity in the media, are factors which have contributed to both a real and an apparent increase in incidence. However, the incidence in Malay males is very low, and neonatal herpes is extremely rare in the local population. Herpes simplex virus type 1 is responsible for about 30% of initial genital infections and an even higher proportion of primary genital herpes infections. Approximately 16% of purulent penile ulcers in Singapore are associated with genital herpes infection.

Epidemiology of viral infections in Singapore.

As Singapore is a densely populated island, and also a major air and sea port, the importation and dissemination of viral infections is facilitated. Respiratory viral infections have the highest prevalence rates, influenza and respiratory syncytial virus (RSV) being the most important ones. Seasonal variation occurs with influenza, RSV and parainfluenza virus type 1 infections. The age distribution and clinical picture associated with infections due to the various respiratory viruses are similar to those reported in other countries. Carrier rates for hepatitis B are high, but differ in the three major ethnic groups, vertical transmission from infected mothers being an important mode of transmission. Outbreaks of hepatitis A have been associated with the consumption of inadequately cooked shellfish. Cytomegalovirus and Epstein-Barr virus infections are acquired early in life and herpes simplex, more slowly. Genital herpes is increasing in incidence. Coxsackievirus A24 and enterovirus 70 have caused major epidemics of acute haemorrhagic conjunctivitis at 5-10 year intervals. Outbreaks of hand, foot and mouth disease due to coxsackievirus A16 have also occurred. With the declining incidence of dengue haemorrhagic fever, the percentage of susceptible individuals in children under 10 years, has increased markedly. Epidemics of rubella which occurred during the past decade, together with immunisation, have increased herd immunity to this virus.