Lai-Ming Ho

The University of Hong Kong | HKU

Few previous studies have investigated the association between the severity of an infectious disease and the length of incubation period. We estimated the association between the length of the incubation period and the severity of infection with the severe acute respiratory syndrome coronavirus, using data from the epidemic in 2003 in Hong Kong. We...

Surveillance systems utilizing early indicator of disease activity would be useful for monitoring community disease pattern and facilitating timely decision making on public health interventions in an evidence-based manner. We explored the feasibility and practicability of establishing an electronic school absenteeism surveillance system in Hong Ko...

Hong Kong experienced two large epidemics of pandemic influenza A(H1N1pdm09). We used regression methods to estimate the excess mortality associated with each epidemic. The first epidemic of H1N1pdm09 peaked in September 2009 and was associated with 2·13 [95% confidence interval (CI): -8·08, 11·82] excess all-cause deaths per 100 000 population. Th...

Background: Although deaths associated with laboratory-confirmed influenza virus infections are rare, the excess mortality burden of influenza estimated from statistical models may more reliably quantify the impact of influenza in a population. Methods: We applied age-specific multiple linear regression models to all-cause and cause-specific mor...

TO THE EDITOR: Potentially useful public health interventions, such as school closure, need to be introduced in a timely manner during the evolution of an ongoing epidemic to substantially affect community transmission (1,2). In most traditional surveillance systems that include health care use data, however, considerable delays occur between data...

Great strides have been made exploring and exploiting new and different sources of disease surveillance data and developing robust statistical methods for analyzing the collected data. However, there has been less research in the area of dissemination. Proper dissemination of surveillance data can facilitate the end user's taking of appropriate act...

In an emerging influenza pandemic, estimating severity (the probability of a severe outcome, such as hospitalization, if infected) is a public health priority. As many influenza infections are subclinical, sero-surveillance is needed to allow reliable real-time estimates of infection attack rate (IAR) and severity. We tested 14,766 sera collected d...

Flow chart of study recruitment. See Table S1 for the number of individuals at each stage in the process. (0.08 MB PDF)

Recruitment of households by random dialing and from parallel attitude's study. (0.06 MB PDF)

Characteristics of the study population compared with the population of Hong Kong. (0.08 MB PDF)

Age-specific proportions of individuals with antibody titers ≥1∶40 by viral MN in Hong Kong since June 2009. Markers and vertical bars indicate the MLE and 95% confidence intervals of weekly seroprevalence estimated using the exact binomial method applied to weekly serologic data. Data points with sample size <10 are not shown. The seroprevalence f...

Neutralization titres against H1N1pdm. The location of each pie chart indicates neutralization tire at baseline (x-axis) and at follow-up (y-axis). The radius of each pie chart is proportional to the number of individuals with a particular combination of baseline and follow-up titres, on a log scale (base 10, see legend). The color mix within each...

Dictionary of field names for Dataset S1 (data from serological study). (0.06 MB PDF)

Individual-level data from the serological study (see Table S4 for definition of fields). (0.05 MB CSV)

The relationship between age group, baseline neutralization titre, and seroconversion status. (0.06 MB PDF)

A statistical model for severity (0.18 MB PDF)

While patterns of incidence of clinical influenza have been well described, much uncertainty remains over patterns of incidence of infection. The 2009 pandemic provided both the motivation and opportunity to investigate patterns of mild and asymptomatic infection using serological techniques. However, to date, only broad epidemiological patterns ha...

Timely estimation of the transmissibility of a novel pandemic influenza virus was a public health priority in 2009. We extended methods for prospective estimation of the effective reproduction number (Rt) over time in an emerging epidemic to allow for reporting delays and repeated importations. We estimated Rt based on case notifications and hospit...

Serial cross-sectional data on antibody levels to the 2009 pandemic H1N1 influenza A virus from a population can be used to estimate the infection attack rates and immunity against future infection in the community. From April through December 2009, we obtained 12,217 serum specimens from blood donors (aged 16-59 years), 2520 specimens from hospita...

Characteristics of SARS patients in Hong Kong, Beijing and Taiwan (pooled data). The associated case-fatality ratios and adjusted odds ratios (95% confidence intervals) are also reported. CFR, case fatality ratio; AOR, adjusted odds ratio; CI, confidence interval. * Data on final outcome were not available for 12 patients in Taiwan and were exclude...

Factors affecting the onset-to-death and onset-to-discharge period of SARS patients in Hong Kong, Beijing (restricted to Hospitals 302 and 309 only and Taiwan. CI, confidence interval. * The acceleration factor is computed as exp(β). It indicates the relative increase (>1) or decrease (<1) in the median time from onset of symptoms to death or disch...

Case fatality ratio by different onset-to-admission periods, Hong Kong, Beijing and Taiwan. CFR, case fatality ratio; CI, confidence interval. * Excluding 16 patients with unknown admission dates or discharge outcome.

Factors affecting the onset-to-death and onset-to-discharge period of SARS patients in Hong Kong, Beijing and Taiwan. CI, confidence interval. * The acceleration factor is computed as exp(β). It indicates the relative increase (>1) or decrease (<1) in the median time from onset of symptoms to death or discharge. † also adjusted for interaction betw...

Characteristics of SARS patients in Hong Kong, Beijing and Taiwan. The associated case-fatality ratios and adjusted odds ratios (95% confidence intervals) are also reported. CFR, case fatality ratio; AOR, adjusted odds ratio; CI, confidence interval. * Patients with unknown age, pre-existing comorbid conditions or admission date were excluded. † Ad...

Case fatality ratio by different onset-to-admission periods in Beijing, XTS Hospital, Hospital 302 and Hospital 309. CFR, case fatality ratio; CI, confidence interval.

Technical Details of the Transmission Model and Sensitivity Analyses.

In Hong Kong, kindergartens and primary schools were closed when local transmission of pandemic (H1N1) 2009 was identified. Secondary schools closed for summer vacation shortly afterwards. By fitting a model of reporting and transmission to case data, we estimated that transmission was reduced approximately 25% when secondary schools closed.

The 2002-2003 Severe Acute Respiratory Syndrome (SARS) outbreak infected 8,422 individuals leading to 916 deaths around the world. However, there have been few epidemiological studies of SARS comparing epidemiologic features across regions. The aim of this study is to identify similarities and differences in SARS epidemiology in three populations w...

Ribavirin and corticosteroids were used widely as front-line treatments for severe acute respiratory syndrome; however, previous evaluations were inconclusive. We assessed the effectiveness of ribavirin and corticosteroids as the initial treatment for severe acute respiratory syndrome using propensity score analysis. We analyzed data on 1755 patien...

Influenza surveillance systems provide important and timely information to health service providers on trends in the circulation of influenza virus and other upper respiratory tract infections. Online dissemination of surveillance data is useful for risk communication to health care professionals, the media and the general public. We reviewed natio...

We applied time-series methods to multivariate sentinel surveillance data recorded in Hong Kong during 1998-2007. Our study demonstrates that simultaneous monitoring of multiple streams of influenza surveillance data can improve the accuracy and timeliness of alerts compared with monitoring of aggregate data or of any single stream alone.

Optimizing Use of Multistream Influenza Sentinel Surveillance Data

Given the apparent greater use of health care services by smokers and predictions of higher costs for a never-smoking population, we aimed in this study to determine whether the acute hospital costs in the last years of life of never- and ever-smokers differed before death using a database of the decedents in 1 year in Hong Kong. To compare the acu...

Second-hand smoke (SHS) exposure is a modifiable cause of ill health. Despite the smoking ban in public places introduced in Hong Kong in 2007, infants and children continue to be exposed within the home. To determine the critical windows of SHS exposure and the duration of its impact on serious infectious morbidity in the first 8 years of life. Th...

To investigate the association between birth weight, infant growth rate, and childhood adiposity as a proxy for adult metabolic or cardiovascular risk in a Chinese population with a history of recent and rapid economic development. Prospective study in a population-representative birth cohort. Hong Kong Chinese population. Six thousand seventy-five...

Elective cesarean delivery is increasingly common. The potential effects of surgical delivery in an unselected sample of infants beyond the immediate neonatal period remain poorly defined. We carried out an 18-month follow-up of a population-based cohort of 8327 Hong Kong Chinese infants born in 1997. The main outcome measures were utilization of o...

For diseases with some level of associated mortality, the case fatality ratio measures the proportion of diseased individuals who die from the disease. In principle, it is straightforward to estimate this quantity from individual follow-up data that provides times from onset to death or recovery. In particular, in a competing risks context, the cas...

Accurate and precise estimates of the incubation distribution of novel, emerging infectious diseases are vital to inform public health policy and to parameterize mathematical models. We discuss and compare different methods of estimating the incubation distribution allowing for interval censoring of exposures, using data from the severe acute respi...

A variety of Serfling-type statistical algorithms requiring long series of historical data, exclusively from temperate climate zones, have been proposed for automated monitoring of influenza sentinel surveillance data. We evaluated three alternative statistical approaches where alert thresholds are based on recent data in both temperate and subtrop...

The use of discrete-choice contingent valuation (CV) to elicit individuals' preference, expressed as maximum willingness-to-pay (WTP), although primarily developed in environmental economics, has been popular in the economic evaluation of health and healthcare. However, a concern with this method is the potential for 'over-estimating' WTP values du...

To assess the predictors of smoking cessation and intention to quit among the Chinese elderly smokers. A cross-sectional survey of elderly smokers. Setting: Shamsuipo district, Hong Kong. Subject: A total of 1,318 elderly were interviewed (response rate = 83%). Measures: A structured questionnaire was used for data collection. The questionnaire sou...

An accurate prognostic model for patients with severe acute respiratory syndrome (SARS) could provide a practical clinical decision aid. We developed and validated prognostic rules for both high- and low-resource settings based on data available at the time of admission. We analyzed data on all 1755 and 291 patients with SARS in Hong Kong (derivati...

Background: Costs of tobacco-related disease can be useful evidence to support tobacco control. In Hong Kong we now have locally derived data on the risks of smoking, including passive smoking. Aim: To estimate the health-related costs of tobacco from both active and passive smoking. Methods: Using local data, we estimated active and passive s...

This study tests whether socio-economic status (SES), at either the individual or ecologic levels, exerts a direct impact on non-attendance or an indirect impact on attendance through longer waiting time for appointments and/or doctor-shopping behavior at four public specialist outpatient centers in Hong Kong. We collected information through three...

In previous literature, the stability and temporal evolution of psychobehavioral responses to an outbreak remained undefined, because of the exclusively cross-sectional nature of such study designs. Using random-digit dialing, we sampled 4481 Hong Kong residents in 6 population-based surveys that were conducted at different times during and after t...

The evidence on whether breast-feeding reduces health services use in nonwhite infants is scant. We examined the effects of breast-feeding on health services utilization in Hong Kong Chinese infants. We followed a population-based cohort of 8327 infants born in 1997 for 18 months. The main outcome measures were higher (above the sample mean) utiliz...

This article is available at http://dx.doi.org/10.1086/502340 ABSTRACT To compare the public's knowledge and perception of SARS and the extent to which various precautionary measures were adopted in Hong Kong and Singapore. Cross-sectional telephone survey of 705 Hong Kong and 1,201 Singapore adults selected by random-digit dialing. Hong Kong respo...

As yet, no one has written a comprehensive epidemiologic account of a severe acute respiratory syndrome (SARS) outbreak from an affected country. To provide a comprehensive epidemiologic account of a SARS outbreak from an affected territory. Epidemiologic analysis. The 2003 Hong Kong SARS outbreak. All 1755 cases and 302 deaths. Sociodemographic ch...

Improving response rates, particularly among physicians, is important to minimize nonresponder bias and increase the effective sample size in epidemiologic research. We conducted a randomized trial to examine the impact of prepayment vs. postpayment incentives on response rates. Self-completion postal questionnaires were mailed to 949 physicians wh...

Recognizing the suboptimal public health effects of a complete cessation strategy for parents and child caregivers who smoke, some researchers have called for a harm reduction approach; however, the evidence remains scanty and controversial. To examine the effects of secondhand smoke and smoking hygiene on infant health and related health care cost...

Handheld computers (PDAs) uploaded with clinical decision support software (CDSS) have the potential to facilitate the adoption of evidence-based medicine (EBM) at the point-of-care among undergraduate medical students. Further evaluation of the usefulness and acceptability of these tools is required. All 169 Year 4 undergraduate medical students a...

We evaluated factors associated with physicians' perceptions towards the effects of computers on health care and on current levels of computerization in their practice. We also performed a contingent valuation to quantify physicians' perceived benefits from computerization in a hypothetical ambulatory, solo clinic. We surveyed 949 representative ph...

Most evidence-based practice (EBP) educational assessment tools evaluated to date have focused on specific knowledge components or technical skills. Other important potential barriers to the adoption of EBP, such as attitudinal, perceptual and behavioural factors, have yet to be studied, especially in the undergraduate setting. Therefore, we develo...

To assess the educational effectiveness on learning evidence based medicine of a handheld computer clinical decision support tool compared with a pocket card containing guidelines and a control. Randomised controlled trial. University of Hong Kong, 2001. 169 fourth year medical students. Factor and individual item scores from a validated questionna...

We present an analysis of the first 10 weeks of the severe acute respiratory syndrome (SARS) epidemic in Hong Kong. The epidemic to date has been characterized by two large clusters-initiated by two separate "super-spread" events (SSEs)-and by ongoing community transmission. By fitting a stochastic model to data on 1512 cases, including these clust...

Health authorities worldwide, especially in the Asia Pacific region, are seeking effective public-health interventions in the continuing epidemic of severe acute respiratory syndrome (SARS). We assessed the epidemiology of SARS in Hong Kong. We included 1425 cases reported up to April 28, 2003. An integrated database was constructed from several so...

Low breastfeeding rates are an issue of international public health concern. Anecdotal reports suggest very low breastfeeding rates in Asia, but no population-based studies have been conducted in the region. To determine the secular trend in breastfeeding practice in an Asian postindustrialized metropolitan community, we examined data from two popu...

Low response rates, especially among physicians, are a common problem in mailed survey research. We conducted a randomized trial to examine the effects of cash and lottery incentives on response rates. A total of 4,850 subjects were randomized to one of three interventions accompanying a mailed survey-no incentive (n = 1,700), cash payment [three l...

The effects of environmental tobacco smoke (ETS) on breast-feeding patterns are poorly understood, while those of parental smoking on breast-feeding initiation vs. duration have not been clearly delineated. We conducted a prospective, population-based birth cohort study to examine the independent effects of maternal, paternal and ETS on breast-feed...

To examine the effects of cesarean and forceps or vacuum delivery and parental smoking habits on the initiation and duration of breast-feeding. We conducted a prospective, population-based birth cohort study in 1997. Data were collected on breast-feeding history, household smoking habits, method of delivery, and other demographic, obstetric, behavi...

To identify the prevailing attitudes among physicians to use of computers in the clinical setting and specifically those attitudes that may be associated with the adoption of computers in practice. A self-completed, 20-question postal questionnaire sent to 4850 randomly selected physicians. The questionnaire focused on details of the physicians' pr...