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Biomedical subjects

W L Lim

Publications and source records attributed to W L Lim.

At least 19 recordsLinked to original sources
PubMed2005

Surveillance of acute flaccid paralysis in Hong Kong: 1997 to 2002.

OBJECTIVES: To describe the characteristics of patients reported with acute flaccid paralysis between 1997 and 2002, and to evaluate the performance of the acute flaccid paralysis surveillance system using indicators recommended by the World Health Organization. DESIGN: Retrospective study. SETTING: Department of Health, Hong Kong. PARTICIPANTS: Children aged younger than 15 years who were reported to the Department of Health between 1997 and 2002 with acute flaccid paralysis. RESULTS: Of 120 children with acute flaccid paralysis reported between 1997 and 2002, 42% were younger than 5 years of age. None of the cases were acute poliomyelitis or polio-compatible. A neurological cause was identified in 67.5% of cases, of which the most common was Guillain-Barre syndrome (42%), followed by transverse myelitis (15%). All except one of the performance indicators consistently met World Health Organization requirements and thus demonstrated the effectiveness of the acute flaccid paralysis surveillance programme. The acute flaccid paralysis notification rate consistently exceeded 1.0 per 100 000 population below 15 years of age. The requirement for adequate stool investigation was the single indicator that did not satisfy World Health Organization requirements. This highlighted the importance of maintaining physicians' awareness of acute flaccid paralysis surveillance. CONCLUSION: Hong Kong should remain vigilant for acute flaccid paralysis. The effective surveillance system and its evaluation may serve as a model for surveillance of other infectious diseases.

Acute Disease↗
PubMed2004

Re-emergence of fatal human influenza A subtype H5N1 disease.

Human disease associated with influenza A subtype H5N1 re-emerged in January, 2003, for the first time since an outbreak in Hong Kong in 1997. Patients with H5N1 disease had unusually high serum concentrations of chemokines (eg, interferon induced protein-10 [IP-10] and monokine induced by interferon gamma [MIG]). Taken together with a previous report that H5N1 influenza viruses induce large amounts of proinflammatory cytokines from macrophage cultures in vitro, our findings suggest that cytokine dysfunction contributes to the pathogenesis of H5N1 disease. Development of vaccines against influenza A (H5N1) virus should be made a priority.

Animals↗
PubMed2004

The lack of epidemiological link between the HIV type 1 infections in Hong Kong and Mainland China.

Blood samples were collected from 139 newly reported HIV-1 infections in Hong Kong over a 3-year period between 1999 and 2001, representing 22.8% of all reported cases. A majority of the patients were male (85.6%), Chinese (74%), and adult (97.1%) and acquired HIV-1 through sexual transmission (88.2%). The B and CRF01_AE were the major subtypes detected--49.6% and 44.6%, respectively. Over time, the frequency of CRF01_AE subtype increased, the B subtype decreased, and new subtypes of C (4) 2.8%, B' (1) 0.7%, and CRF07_BC (3) 2.2% emerged. The CRF01_AE subtype was commoner in female, Chinese, heterosexuals, and injection drug users whereas B subtype was commoner in male, white, and people with homosexual/bisexual contacts. There was no common source of infection from the analysis except a discernible cluster of Vietnamese injection drug users with the CRF01_AE subtype. The molecular findings did not suggest an epidemiological link between HIV infection in Hong Kong and Mainland China. Hong Kong's longstanding and extensive methadone treatment network may have contributed to the phenomenon.

Adult↗
PubMed2003

Cavitation phenomena in mechanical heart valves: the role of squeeze flow velocity and contact area on cavitation initiation between two impinging rods.

In this study, the closing dynamics of two impinging rods were experimentally analyzed to simulate the cavitation phenomena associated with mechanical heart valve closure. The purpose of this study was to investigate the cavitation phenomena with respect to squeeze flow between two impinging surfaces and the parameter that influences cavitation inception. High-speed flow imaging was employed to visualize and identify regions of cavitation. The images obtained favored squeeze flow as an important mechanism in cavitation inception. A correlation study of the effects of impact velocities, contact areas and squeeze flow velocity on cavitation inception showed that increasing impact velocities results in an increase in the risk of cavitation. It was also shown that for similar impact velocities, regions near the point of impact were found to cavitate later for those with smaller contact areas. It was found that the decrease in contact areas and squeeze flow velocities would delay the onset and reduce the intensity of cavitation. It is also interesting to note that the squeeze flow velocity alone does not provide an indication if cavitation inception will occur. This is corroborated by the wide range of published critical squeeze flow velocity required for cavitation inception. It should be noted that the temporal acceleration of fluid, often neglected in the literature, can also play an important role on cavitation inception for unsteady flow phenomenon. This is especially true in mechanical heart valves, where for the same leaflet closing velocity, valves with a seat stop were observed to cavitate earlier. Based on these results, important inferences may be made to the design of mechanical heart valves with regards to cavitation inception.

Blood Flow Velocity↗
PubMed2003

The long-term efficacy of plasma-derived hepatitis B vaccine in babies born to carrier mothers.

The long-term efficacy of a childhood hepatitis B vaccination programme was evaluated. A total of 112 newborn babies of hepatitis B carrier mothers were given hepatitis B immune globulin (HBIG) and a 10-microg three-dose regimen of plasma-derived vaccine administered at a conventional (0, 1, 6 months), delayed (2, 3, 8 months) or accelerated (0, 1, 2 months) schedule. The vaccinees were followed up to determine their anti-HBs status over a 16-year period. Upon completion of the vaccination schedules, 92.6% developed antibody against surface antigen (anti-HBs) seroconverion, the rate of which fell to 33.3% at year 16. The three schedules were equally effective in preventing chronic infection, with a protective efficacy of 88.9% from hepatitis B surface antigen (HBsAg) carriage, compared with historical control. Vaccinees on the delayed schedule had a slightly higher seroconversion rate over years, and were better able to maintain an anti-HBs level of > or = 100 iu/L. Overall, a quarter demonstrated evidence of exposure to the virus, being positive for antibody against core antigen or HBsAg, or mounting a rise in anti-HBs during the follow-up period. We conclude that a three-dose hepatitis B vaccination regimen is generally effective in protecting newborns of hepatitis B carrier mothers from infection and chronic carriage. Booster is not needed even after 16 years of monitoring.

Carrier State↗
PubMed2003

Perioperative death in Malaysia: the transition phase from a developing nation to a developed one.

This paper examines the surgical pathology associated with perioperative deaths in a country that is undergoing the transition from a developing to a developed nation status. The data from an ongoing nation-wide perioperative mortality study was prospectively collected for the period July 1996 to December 1997 and analyzed. The surgical pathology related to perioperative deaths in Malaysia is different from other developing and developed countries. While death from trauma and the late presentation of surgical conditions are similar to developing countries, infective gastrointestinal conditions were rarely encountered. Diseases associated with advanced age such as colorectal cancer, peptic ulcer, urological diseases and vascular conditions are beginning to emerge. As the country races towards a developed nation status, increasing life expectancy and changing life-styles are expected to influence the disease pattern. The planning of surgical facilities and manpower development must recognize the changes taking place.

Adolescent↗
PubMed2002

The implication of a reduced-dose hepatitis B vaccination schedule in low risk newborns.

Five hundred and seventy-four babies born to HBsAg negative mothers in Hong Kong received either a regular (5 micro g) or reduced (2.5 micro g) three-dose regimen of recombinant hepatitis B vaccine. A significantly higher anti-HBs positivity rate (>or=10 mIU/ml), geometric mean titer (GMT) and the maintenance of a high anti-HBs level (>or=100 mIU/ml) were observed with the regular-dose regimen. The differences persisted, however, only up to 1 year post-vaccination. Over an 8-year period, only 1% of the vaccinees demonstrated anti-HBc seroconversion and none had become HBsAg positive. The long-term efficacy of the reduced-dose regimen was confirmed, even in an HBV endemic population.

Dose-Response Relationship, Immunologic↗
PubMed2001

Pulsatile flow studies of a porcine bioprosthetic aortic valve in vitro: PIV measurements and shear-induced blood damage.

A two-dimensional particle image tracking velocimetry (PIV) system has been used to map the velocity vector fields and Reynolds stresses in the immediate downstream vicinity of a porcine bioprosthetic heart valve at the aortic root region in vitro under pulsatile flow conditions. Measurements were performed at five different time steps of the systolic phase of the cardiac cycle. The velocity vector fields and Reynolds stress mappings at different time steps allowed us to chart a time history of the stress levels experienced by fluid particles as they move across the aortic root. This Lagrangian description of the stresses experienced by individual blood cells enabled us to estimate the propensity of shear-induced damage to platelets and red blood cells. Coupled with flow visualization techniques, the hydrodynamic consequences of introducing a porcine bioprosthetic heart valve into the aortic root was examined. Although the PIV measurements may lack the accuracy of single point measuring systems, the overall view of the flow in the aortic root region compensates for the shortcoming.

Animals↗
PubMed2001

Hepatitis B surface antigen variants in vaccinees, blood donors and an interferon-treated patient.

Variants of hepatitis B virus (HBV), with amino acid substitutions in the major antigenic "a" determinant of hepatitis B surface antigen (HBsAg), have been described mainly in vaccinated children. In the present study in addition to vaccinated children, we have investigated Chinese blood donors positive for anti-HBc alone, and a patient with continuing liver disease after interferon-induced seroconversion to anti-HBs. Variants were detected in two of four children with break-through infections. One child had a double mutation (P142S and G145R) and the other a G145A substitution. Three of seven anti-HBc positive Chinese blood donors had a T131I substitution, whilst the interferon-treated patient had a treble amino acid substitution (P142S, G145R and N146D). The present results indicate that HBsAg variants may exist in individuals other than vaccinated children.

Amino Acid Sequence↗
PubMed2001

Epidemiology and detection of human immunodeficiency virus among pregnant women in Hong Kong.

OBJECTIVES: To determine the epidemiology of human immunodeficiency virus infection among pregnant women and the neonatal outcomes in Hong Kong. DESIGN: Retrospective observational study composed of two parts: record review of pregnant women and unlinked anonymous screening of cord blood from neonates. SETTING: Two human immunodeficiency virus clinics and the Government Virus Unit. PARTICIPANTS: Female patients attending the two clinics who became pregnant and neonates who underwent routine metabolic screening by the Government Virus Unit between 1992 and 1999. MAIN OUTCOME MEASURES: The outcomes of neonates born to women who had human immunodeficiency virus infection during pregnancy. RESULTS: Forty-one human immunodeficiency virus-related pregnancies were recorded among 32 infected women. Fifteen pregnancies were terminated, of which 14 were in women who knew their infection status before conception. Twenty-six pregnancies continued to term, resulting in 26 live births. Twelve babies were born to women who knew their infection status before delivery. One baby was confirmed to be infected. Six women were given zidovudine for prophylaxis against vertical transmission and none of the babies were infected at birth. Of the remaining 14 human immunodeficiency virus-related pregnancies, the mothers' status became known only at a later date and nine (64.3%) babies were confirmed to be infected at the age of 18 months or older. The rate ratio of giving birth to an infected baby was 8.18 from mothers who did not know their status antenatally. Unlinked anonymous screening showed that the seroprevalence rate for human immunodeficiency virus in pregnant women was 0.032% (1/3125) in Hong Kong in 1999. CONCLUSIONS: Human immunodeficiency virus-related pregnancy is not rare in Hong Kong and the majority of infected mothers were not identified and treated. Detection of these pregnancies will be invaluable for the prevention of mother-to-child transmission. Universal antenatal screening of human immunodeficiency virus antibody is proposed as an effective strategy.

AIDS Serodiagnosis↗
PubMed2000

A case-controlled study on the use of HBsAg-positive donors for allogeneic hematopoietic cell transplantation.

To compare the clinical and serological outcomes of patients receiving donors' marrow positive or negative for hepatitis B surface antigen (HBsAg), we studied 18 patients of allogeneic hematopoietic cell transplantation receiving HBsAg-positive marrow (group 1) and 18 receiving HBsAg-negative marrow (group 2). The recipients of the 2 groups were matched for hepatitis B virus (HBV) serology, sex, age, underlying hematological diseases, conditioning regimen, and prophylaxis against graft-versus-host diseases. Eight (44.4%) recipients in group 1 and 2 (11.1%) in group 2 suffered from HBV-related hepatitis posttransplant (P =.03). Furthermore, HBV-related hepatic failure was seen in 6 group 1 patients, but in none of the group 2 patients (P =.007). Five of the 9 (55.5%) HBsAg-negative recipients in group 1 became positive after receiving HBsAg-positive marrow. Serum HBV DNA was positive in all 5 donors of these patients, but in none of the donors of recipients who remained HBsAg negative (P =.008). Group 1 patients developing HBV-related hepatitis posttransplant were more likely to have a donor carrying a precore A(1896 )and/or core promoter T(1762)/A(1764) HBV variant (62. 5% versus 0%, P =.007). This study has demonstrated that a high incidence of HBV-related hepatitis was associated with the use of HBsAg-positive marrow for transplant, and a high viral load in the donor appeared to predispose recipients to the development of HBV-related hepatitis posttransplant. Further clinical trials will be necessary to determine the optimal management approach to this problem, including the use of the antiviral agents in the donors and the recipients. (Blood. 2000;96:452-458)

Adolescent↗
PubMed1999

Twelve-year follow-up of a prospective randomized trial of hepatitis B recombinant DNA yeast vaccine versus plasma-derived vaccine without booster doses in children.

A total of 318 children were prospectively randomized in group 1 with two 5-microg doses of recombinant vaccine given at 0 and 1 month; in group 2 with three 5-microg doses of recombinant vaccine given at 0, 1, and 6 months; or in group 3 with three doses of plasma-derived vaccine given at 0, 1, and 6 months. Eleven subjects with a hepatitis B surface antigen antibody (anti-HBs) titer of less than 10 mIU/mL at 12 months were given an extra dose of vaccine and were excluded from analysis. No booster doses were given to any other subjects. All children were followed up yearly for the level of anti-HBs titers and for the detection of hepatitis B infection. At the 12th year of follow-up, there were significantly fewer subjects with anti-HBs of 10 mIU/mL or above in group 1 (60.4%) when compared with group 2 (81.4%; P =.0287) and group 3 (79.0%; P =. 0381). The geometric mean titers (GMTs) of subjects of group 1 were significantly lower than those of group 2 and group 3 throughout the 12 years of follow-up. A total of 65 subjects had one or more episodes of anamnestic response. No subject became positive for hepatitis B surface antigen (HBsAg); 2 became positive for hepatitis B core antigen antibody (anti-HBc). In conclusion, the long-term protective immunity was better with three doses of hepatitis B vaccine (either the recombinant or plasma-derived) than with two doses. However, protection from hepatitis B infection could be equally achieved by either two doses or three doses of the vaccine. Booster doses were not necessary, probably because of effective anamnestic response.

Child↗
PubMed1998

Steady flow dynamics of prosthetic aortic heart valves: a comparative evaluation with PIV techniques.

Particle Image Velocimetry (PIV), capable of providing full-field measurement of velocities and flow stresses, has become an invaluable tool in studying flow behaviour in prosthetic heart valves. This method was used to evaluate the performances of four prosthetic heart valves; a porcine bioprostheses, a caged ball valve, and two single leaflet tilting disc valves with different opening angles. Flow visualization techniques, combined with velocity vector fields and Reynolds stresses mappings in the aortic root obtained from PIV, and pressure measurements were used to give an overall picture of the flow field of the prosthetic heart valves under steady flow conditions. The porcine bioprostheses exhibited the highest pressure loss and Reynolds stresses of all the valves tested. This was mainly due to the reduction in orifice area caused by the valve mounting ring and the valve stents. For the tilting disc valves, a larger opening angle resulted in a smoother flow profile, and thus lower Reynolds stresses and pressure drops. The St. Vincent valve exhibited the lowest pressure drop and Reynolds stresses.

Algorithms↗
PubMed1998

Fatal enterovirus 71 encephalomyelitis.

During an outbreak of hand-foot-mouth disease caused by enterovirus 71 (EV-71) in 1997, 4 children presented with sudden cardiopulmonary collapse and minimal neurologic features. All children received cardiopulmonary resuscitation but died within a few hours of admission. Postmortem studies showed infection by EV-71 with extensive damage to the medulla and pons. We postulate an etiologic link between EV-71 and brainstem encephalomyelitis as the cause of pulmonary edema and death.

Child, Preschool↗
PubMed1998

Use of famciclovir to prevent HBV reactivation in HBsAg-positive recipients after allogeneic bone marrow transplantation.

BACKGROUND/AIMS: Reactivation of chronic hepatitis B viral infection causes significant morbidity and mortality after bone marrow transplantation. Recently, nucleoside analogues, such as famciclovir, were found to have a direct suppressive effect on hepatitis B virus replication in both in vitro and in vivo studies. We have studied the effect of famciclovir on the incidence of hepatitis B virus reactivation and hepatitis after allogeneic bone marrow transplantation. METHODS: Eight hepatitis B surface antigen (HBsAg)-positive patients who received allogeneic bone marrow transplantation were given oral famciclovir 250 mg three times daily, starting at least 1 week prior to bone marrow transplantation and continuing for 24 weeks after transplantation. Clinical and serological outcomes in these patients were compared with 24 HBsAg-positive recipients of allogeneic bone marrow transplantation who did not receive famciclovir (historical controls). RESULTS: After bone marrow transplantation, there were five patients with hepatitis B virus reactivation among those who received famciclovir 250 mg three times daily. Four of these patients responded to increased dosages of 500 mg three times daily and did not develop hepatitis. The remaining patient suffered from hepatitis related to hepatitis B virus reactivation. Compared to historical controls, there were fewer cases of hepatitis due to hepatitis B virus reactivation and veno-occlusive disease. The median follow-up was 701.6 days (range: 50-2346 days) with ten deaths (three due to hepatic failure related to HBV reactivation) in those who did not receive famciclovir and one death (due to hepatic failure related to graft-versus-host disease) in those who received famciclovir. CONCLUSIONS: Use of famciclovir significantly reduced hepatitis due to hepatitis B virus reactivation in HBsAg-positive recipients after allogeneic bone marrow transplantation.

2-Aminopurine↗
PubMed1998

Clearance of persistent hepatitis B virus infection in Chinese bone marrow transplant recipients whose donors were anti-hepatitis B core- and anti-hepatitis B surface antibody-positive.

Thirteen hepatitis B surface antigen-positive Chinese patients who received hepatitis B surface antibody-positive marrow (hepatitis B core antibody-positive or -negative: 6 and 7, respectively) via allogeneic bone marrow transplantation (BMT) were studied. After BMT, 4 recipients had serologic clearance of hepatitis B surface antigen from hepatitis B core antibody-positive marrow, but none of the recipients of hepatitis B core antibody-negative marrow had serologic clearance (P=.02). There was no significant difference in the donors' hepatitis B surface antibody titer before BMT for patients with or without serologic clearance of hepatitis B surface antigen (2255.2+/-4244.0 vs. 854.2+/-2306.7 mIU/mL; P=not significant). Adoptive immunity clearance of hepatitis B surface antigen was favored by hepatitis B core antibody positive-donor marrow and was not related to donor pre-BMT hepatitis B surface antibody titer.

Adolescent↗
PubMed1998

The effectiveness of surfactant replacement therapy for preterm infants with respiratory distress syndrome.

Thirty preterm infants weighing > or = 800 g with clinical and radiological evidence of respiratory distress syndrome (RDS) requiring mechanical ventilation with FiO2 of > or = 40% were given modified bovine surfactant (Survanta). They were compared with equal number of historical controls. Infants who received surfactant showed prompt and highly significant improvement in FiO2, mean airway pressure, arterial/alveolar oxygen tension ratio and ventilatory index. There was significant improvement in mortality rate (10% vs 33%; p = 0.03). Among the survivors, surfactant-treated infants required shorter duration of continuous positive airway pressure (CPAP) (3.4 vs 9.6 days; p = 0.04). For survivors with birthweight of > 1000 g, surfactant-treated infants required shorter duration of ventilatory support (intermittent positive pressure ventilation + CPAP) (7.5 vs 18.9 days, p = 0.02). Overall, surfactant-treated infants achieved full enteral feeds sooner (15.7 days vs 24.6 days; p = 0.03) and required shorter duration of total parenteral nutrition (13.9 days vs 25.6 days; p = 0.02). We concluded that surfactant replacement therapy was effective in the treatment of preterm infants with RDS.

Animals↗