Comparison of influenza disease burden in older populations of Hong Kong and Brisbane: the impact of influenza and pneumococcal vaccination.

BACKGROUND: Influenza and pneumococcal vaccine uptake in the older population aged 65 years or over of Hong Kong dramatically increased since the 2003 SARS outbreak. This study is aimed to evaluate the impact of increased coverage of influenza and pneumococcal vaccines by comparing the change of disease burden in the older population of Hong Kong, with the burden in the older population of Brisbane with relatively high vaccine coverage in the past fifteen years. METHODS: Time series segmented regression models were applied to weekly numbers of cause-specific mortality or hospitalization of Hong Kong and Brisbane. Annual excess rates of mortality or hospitalization associated with influenza in the older population were estimated for the pre-SARS (reference period), post-SARS and post-pandemic period, respectively. The rate ratios (RRs) between these periods were also calculated to assess the relative change of disease burden. RESULTS: Compared to the pre-SARS period, excess rates of mortality associated with influenza during the post-SARS period in Hong Kong decreased for cardiorespiratory diseases (RR = 0.90, 95% CI 0.80, 1.01), stroke (RR = 0.74, 95% CI 0.50, 1.09), and ischemic heart diseases (RR = 0.45, 95% CI 0.34, 0.58). The corresponding RRs in Brisbane were 0.79 (95% CI 0.54, 1.15), 0.33 (0.13, 0.80), and 1.09 (0.62, 1.90), respectively. Only the mortality of ischemic heart diseases showed a greater reduction in Hong Kong than in Brisbane. During the post-pandemic period, excess rates of all-cause mortality increased in Hong Kong, but to a lesser extent than in Brisbane (RR = 1.41 vs 2.39). CONCLUSION: A relative decrease (or less of an increase) of influenza disease burden was observed in the older population of Hong Kong after increased coverage of influenza and pneumococcal vaccines in this population, as compared to those of Brisbane where vaccination rates remained stable. The lack of significant findings in some disease categories highlights the challenges of evaluating the benefits of vaccination at the population level.

Urban climate modified short-term association of air pollution with pneumonia mortality in Hong Kong.

BACKGROUND: City is becoming warmer, especially in the process of urbanization and climate change. However, it is largely unknown whether this warming urban climate may modify the short-term effects of air pollution. OBJECTIVES: To test whether warmer urban climates intensify the acute mortality effects of air pollution on pneumonia in Hong Kong. METHODS: Participants who died of pneumonia from a prospective Chinese elderly cohort between 1998 and 2011 were selected as cases. Urban climatic (UC) classes of cases were determined by an established Urban Climatic Map according to their residential addresses. UC classes were first dichotomized into cool and warm climates and case-crossover analysis was used to estimate the short-term association of pneumonia mortality with air pollution. We further classified UC classes into climate quartiles and used case-only analysis to test the trend of urban climate modification on the short-term association of pneumonia mortality with air pollution. RESULTS: Among 66,820 elders (≥65 years), 2208 pneumonia deaths (cases) were identified during the 11-14 years of follow-up. The effects of air pollution for cases residing in the warm climate were statistically significant (p < 0.05) higher than those living in the cool climate. There was an increasing linear trend of urban climate modification on the association of pneumonia mortality with NO2 (nitrogen dioxide) (p for trend = 0.035). Compared to climate Quartile 1 (the lowest), deaths resided in climate Quartile 2, 3, and 4 (the highest) were associated with an additional percent change of 9.07% (0.52%, 17.62%), 12.89% (4.34%, 21.43%), and 8.45% (-0.10%, 17.00%), respectively. CONCLUSIONS: Warmer urban climate worsened the acute mortality effects of pneumonia associated with air pollutants in Hong Kong. Our findings suggest that warmer urban climate introduced by climate change and urbanization may increase the risks of air pollution-related pneumonia.

Seasonal temperature variability and emergency hospital admissions for respiratory diseases: a population-based cohort study.

BACKGROUND: Climate change increases global mean temperature and changes short-term (eg, diurnal) and long-term (eg, intraseasonal) temperature variability. Numerous studies have shown that mean temperature and short-term temperature variability are both associated with increased respiratory morbidity or mortality. However, data on the impact of long-term temperature variability are sparse. OBJECTIVE: We aimed to assess the association of intraseasonal temperature variability with respiratory disease hospitalisations among elders. METHODS: We ascertained the first occurrence of emergency hospital admissions for respiratory diseases in a prospective Chinese elderly cohort of 66 820 older people (≥65 years) with 10-13 years of follow-up. We used an ordinary kriging method based on 22 weather monitoring stations in Hong Kong to spatially interpolate daily ambient temperature for each participant's residential address. Seasonal temperature variability was defined as the SD of daily mean summer (June-August) or winter (December-February) temperatures. We applied Cox proportional hazards regression with time-varying exposure of seasonal temperature variability to respiratory admissions. RESULTS: During the follow-up time, we ascertained 12 689 cases of incident respiratory diseases, of which 6672 were pneumonia and 3075 were COPD. The HRs per 1°C increase in wintertime temperature variability were 1.20 (95% CI 1.08 to 1.32), 1.15 (1.01 to 1.31) and 1.41 (1.15 to 1.71) for total respiratory diseases, pneumonia and COPD, respectively. The associations were not statistically significant for summertime temperature variability. CONCLUSION: Wintertime temperature variability was associated with higher risk of incident respiratory diseases.

Long-term exposure to fine particulate matter air pollution and type 2 diabetes mellitus in elderly: A cohort study in Hong Kong.

BACKGROUND: Evidence for the link between long-term air pollution exposure and occurrence of diabetes is limited and the results are mixed. OBJECTIVES: We aimed to assess the association of long-term residential exposure to fine particulate matter (PM2.5) with the prevalence and incidence of type 2 diabetes mellitus (DM). METHODS: This is a prospective cohort study. We studied 61,447 participants of the Chinese Elderly Health Services cohort in Hong Kong enrolled 1998-2001 and followed participants without DM at baseline to 31 December 2010 to ascertain the first hospital admissions for type 2 DM. Yearly mean residential PM2.5 exposure was predicted based on satellite data. Logistic regression and time-varying Cox regression model were used to evaluate the prevalence and incidence risk of DM associated with PM2.5 while adjusting for potential individual and neighborhood confounders. RESULTS: There were 61,447 participants included in the study of prevalent DM, and in 53,905 participants without DM at baseline we studied incident type 2 DM. Over a mean follow-up of 9.8 years, we ascertained 806 incident cases of type 2 DM. After adjusting for potential confounders, the odds ratio (OR) for every interquartile range (3.2 µg/m3) increase of PM2.5 concentration was 1.06 (95% confidence interval (CI): 1.01-1.11) for prevalent DM, while the corresponding hazard ratio (HR) was 1.15 (95% CI: 1.05-1.25) for incident type 2 DM. CONCLUSIONS: Long-term exposure to high levels of PM2.5 may increase the risk of both prevalence and incidence of type 2 diabetes mellitus in Hong Kong elderly population.

Fine particulate matter exposure and incidence of stroke: A cohort study in Hong Kong.

OBJECTIVE: We aimed to assess the association of long-term residential exposure to fine particulate matter (PM) with aerodynamic diameter less than 2.5 µm (PM2.5) with the incidence of stroke and its major subtypes. METHODS: We ascertained the first occurrence of emergency hospital admission for stroke in a Hong Kong Chinese cohort of 66,820 older people (65+ years) who enrolled during 1998-2001 (baseline) and were followed up to December 31, 2010. High-resolution (1 × 1 km) yearly mean concentrations of PM2.5 were predicted from local monitoring data and US National Aeronautics and Space Administration satellite data using linear regression. Baseline residential PM2.5 exposure was used as a proxy for long-term exposure. We used Cox proportional hazards to evaluate the risk of incident stroke associated with PM2.5 exposure adjusted for potential confounders, including individual and neighborhood factors. RESULTS: Over a mean follow-up of 9.4 years, we ascertained 6,733 cases of incident stroke, of which 3,526 (52.4%) were ischemic and 1,175 (17.5%) were hemorrhagic. The hazard ratio for every 10 µg/m3 higher PM2.5 concentration was statistically significant at 1.21 (95% confidence interval [CI] 1.04-1.41) for ischemic and non-statistically significant at 0.90 (95% CI 0.70-1.17) for hemorrhagic stroke in fully adjusted model 3. The estimates for ischemic stroke were higher in older participants (>70 years), less educated participants, and in men for current smokers. CONCLUSION: Long-term PM2.5 exposure was associated with higher risk of incident ischemic stroke, but the association with incident hemorrhagic stroke was less clear.

Different responses of influenza epidemic to weather factors among Shanghai, Hong Kong, and British Columbia.

Weather factors have long been considered as key sources for regional heterogeneity of influenza seasonal patterns. As influenza peaks coincide with both high and low temperature in subtropical cities, weather factors may nonlinearly or interactively affect influenza activity. This study aims to assess the nonlinear and interactive effects of weather factors with influenza activity and compare the responses of influenza epidemic to weather factors in two subtropical regions of southern China (Shanghai and Hong Kong) and one temperate province of Canada (British Columbia). Weekly data on influenza activity and weather factors (i.e., mean temperature and relative humidity (RH)) were obtained from pertinent government departments for the three regions. Absolute humidity (AH) was measured by vapor pressure (VP), which could be converted from temperature and RH. Generalized additive models were used to assess the exposure-response relationship between weather factors and influenza virus activity. Interactions of weather factors were further assessed by bivariate response models and stratification analyses. The exposure-response curves of temperature and VP, but not RH, were consistent among three regions/cities. Bivariate response model revealed a significant interactive effect between temperature (or VP) and RH (P < 0.05). Influenza peaked at low temperature or high temperature with high RH. Temperature and VP are important weather factors in developing a universal model to explain seasonal outbreaks of influenza. However, further research is needed to assess the association between weather factors and influenza activity in a wider context of social and environmental conditions.

An Occupational Therapy Fall Reduction Home Visit Program for Community-Dwelling Older Adults in Hong Kong After an Emergency Department Visit for a Fall.

OBJECTIVES: To investigate the effects of an occupational therapy fall reduction home visit program for older adults admitted to the emergency department (ED) for a fall and discharged directly home. DESIGN: Single-blind, multicenter, randomized, controlled trial. SETTINGS: EDs in three acute care hospitals in Hong Kong. PARTICIPANTS: Individuals aged 65 and older who had fallen (N = 311). INTERVENTIONS: After screening for eligibility, 204 consenting individuals were randomly assigned to an intervention group (IG) and received a single home visit from an occupational therapist (OT) within 2 weeks after discharge from the hospital or a control group (CG) and received a well-wishing visit from a research assistant not trained in fall prevention. MEASUREMENTS: Both groups were followed for 12 months through telephone calls made every 2 weeks by blinded assessors with a focus on the frequency of falls. Another blinded assessor followed up on their status with telephone calls 4, 8, and 12 months after ED discharge. Prospective fall records on hospital admissions were retrieved from electronic databases; 198 individuals were followed for 1 year on an intention-to-treat basis. RESULTS: The percentage of fallers over 1 year was 13.7% in the IG (n = 95) and 20.4% in the CG (n = 103). There were significant differences in the number of fallers (P = .03) and the number of falls (P = .02) between the two groups over 6 months. Significant differences were found in survival analysis for first fall at 6 months (log-rank test 5.052, P = .02) but not 9 or 12 months. CONCLUSION: One OT visit after a fall was more effective than a well-wishing visit at reducing future falls at 6 months. A booster OT visit at 6 months is suggested.

Healthcare seeking behavior of patients with influenza like illness: comparison of the summer and winter influenza epidemics.

BACKGROUND: Influenza often causes winter and summer epidemics in subtropical regions, but few studies have investigated the difference in healthcare seeking behavior of patients with influenza-like illness (ILI) between these two epidemics. METHODS: Household telephone surveys were conducted using random digit dialing in Hong Kong during July-August 2014 and March-April 2015. One adult from each household was interviewed for ILI symptoms and associated healthcare seeking behaviour of themselves and one child in the household (if any), during the preceding 30 days. Healthcare seeking behavior of respondents with self-reported ILI was compared between summer and winter influenza. Logistic regression was used to explore the factors associated with healthcare seeking behavior. RESULTS: Among 516 and 539 adult respondents in the summer and winter surveys, 22.6 and 38.0 % reported ILI symptoms, and 40.9 and 46.8 % of them sought medical care, respectively. There was no significant difference in healthcare seeking behavior between the summer and winter epidemics, except a higher proportion of self-medication in summer in the adult respondents. Among 155 and 182 children reported by the adults in both surveys, the proportion of self-reported ILI was 32.9 and 40.1 % in the summer and winter surveys, respectively. Of these children, 47.1 and 56.2 % were brought for medical consultation in summer and winter, respectively. Women, adults with diabetes and those with symptoms of cough, shortness of breath, and runny nose were more likely to seek medical consultations for ILI symptoms. The factors associated with seeking medical consultations in children with ILI symptoms included being female, age under 10 years, and with symptoms of sore throat or vomiting. Those older than 60 years were less likely to self-medicate, whereas regular smokers and those with symptom of sore throat were more likely to do so. CONCLUSION: Healthcare seeking behavior of the general public was not significantly different between these two epidemics. However ILI was associated with increased healthcare utilization in both winter and summer epidemics in Hong Kong.

Age-specific genetic and antigenic variations of influenza A viruses in Hong Kong, 2013-2014.

Age-specific genetic and antigenic variations of influenza viruses have not been documented in tropical and subtropical regions. We implemented a systematic surveillance program in two tertiary hospitals in Hong Kong Island, to collect 112 A(H1N1)pdm09 and 254 A(H3N2) positive specimens from 2013 to 2014. Of these, 56 and 72 were identified as genetic variants of the WHO recommended vaccine composition strains, respectively. A subset of these genetic variants was selected for hemagglutination-inhibition (HI) tests, but none appeared to be antigenic variants of the vaccine composition strains. We also found that genetic and antigenicity variations were similar across sex and age groups of ≤18 yrs, 18 to 65 yrs, and ≥65 yrs. Our findings suggest that none of the age groups led other age groups in genetic evolution of influenza virus A strains. Future studies from different regions and longer study periods are needed to further investigate the age and sex heterogeneity of influenza viruses.

Cancer Mortality Risks from Long-term Exposure to Ambient Fine Particle.

BACKGROUND: Few studies have assessed long-term effects of particulate matter (PM) with aerodynamic diameter < 2.5 µm (PM2.5) on mortality for causes of cancer other than the lung; we assessed the effects on multiple causes. In Hong Kong, most people live and work in urban or suburban areas with high-rise buildings. This facilitates the estimation of PM2.5 exposure of individuals, taking into account the height of residence above ground level for assessment of the long-term health effects with sufficient statistical power. METHODS: We recruited 66,820 persons who were ≥65 in 1998 to 2001 and followed up for mortality outcomes until 2011. Annual concentrations of PM at their residential addresses were estimated using PM2.5 concentrations measured at fixed-site monitors, horizontal-vertical locations, and satellite data. We used Cox regression model to assess the HR of mortality for cancer per 10 µg/m(3) increase of PM2.5 RESULTS: PM2.5 was associated with increased risk of mortality for all causes of cancer [HR, 1.22 (95% CI, 1.11-1.34)] and for specific cause of cancer in upper digestive tract [1.42 (1.06-1.89)], digestive accessory organs [1.35 (1.06-1.71)] in all subjects; breast [1.80 (1.26-2.55)] in females; and lung [1.36 (1.05-1.77)] in males. CONCLUSIONS: Long-term exposures to PM2.5 are associated with elevated risks of cancer in various organs. IMPACT: This study is particularly timely in China, where compelling evidence is needed to support the pollution control policy to ameliorate the health damages associated with economic growth. Cancer Epidemiol Biomarkers Prev; 25(5); 839-45. ©2016 AACR.

STROBE-Long-Term Exposure to Ambient Fine Particulate Air Pollution and Hospitalization Due to Peptic Ulcers.

Little is known about the effect of air pollution on the gastrointestinal (GI) system. We investigated the association between long-term exposures to outdoor fine particles (PM2.5) and hospitalization for peptic ulcer diseases (PUDs) in a large cohort of Hong Kong Chinese elderly.A total of 66,820 subjects aged ≥65 years who were enrolled in all 18 Government Elderly Health Service centers of Hong Kong participated in the study voluntarily between 1998 and 2001. They were prospectively followed up for more than 10 years. Annual mean exposures to PM2.5 at residence of individuals were estimated by satellite data through linkage with address details including floor level. All hospital admission records of the subjects up to December 31, 2010 were retrieved from the central database of Hospital Authority. We used Cox regression to estimate the hazard ratio (HR) for PUD hospitalization associated with PM2.5 exposure after adjustment for individual and ecological covariates.A total of 60,273 subjects had completed baseline information including medical, socio-demographic, lifestyle, and anthropometric data at recruitment. During the follow-up period, 1991 (3.3%) subjects had been hospitalized for PUD. The adjusted HR for PUD hospitalization per 10 µg/m of PM2.5 was 1.18 (95% confidence interval: 1.02-1.36, P = 0.02). Further analysis showed that the associations with PM2.5 were significant for gastric ulcers (HR 1.29; 1.09-1.53, P = 0.003) but not for duodenal ulcers (HR 0.98; 0.78 to 1.22, P = 0.81).Long-term exposures to PM2.5 were associated with PUD hospitalization in elder population. The mechanism underlying the PM2.5 in the development of gastric ulcers warrants further research.

The influence of pre-existing health conditions on short-term mortality risks of temperature: Evidence from a prospective Chinese elderly cohort in Hong Kong.

BACKGROUND: Both cold and hot temperatures are associated with adverse health outcomes. Less is known about the role of pre-existing medical conditions to confer individual's susceptibility to temperature extremes. METHODS: We studied 66,820 subjects aged ≥65 who were enrolled and interviewed in all the 18 Elderly Health Centers of Department of Health, Hong Kong from 1998 to 2001, and followed up for 10-13 years. The distributed lag nonlinear model (DLNM) combined with a nested case-control study design was applied to estimate the nonlinear and delayed effects of cold or hot temperature on all natural mortality among subjects with different pre-existing diseases. RESULTS: The relative risk of all natural mortality associated with a decrease of temperature from 25th percentile (19.5°C) to 1st percentile (11.3°C) over 0-21 lag days for participants who reported to have an active disease at the baseline was 2.21 (95% confidence interval (CI): 1.19, 4.10) for diabetes mellitus (DM), 1.59 (1.12, 2.26) for circulatory system diseases (CSD), and 1.23 (0.53, 2.84) for chronic obstructive pulmonary disease (COPD), whereas 1.04 (0.59, 1.85) for non-disease group (NDG). Compared with NDG, elders with COPD had excess risk of mortality associated with thermal stress attributable to hot temperature, while elders with DM and CSD were vulnerable to both hot and cold temperatures. CONCLUSIONS: Elders with pre-existing health conditions were more vulnerable to excess mortality risk to hot and/or cold temperature. Preventative measures should target on elders with chronic health problems.

Who is more vulnerable to death from extremely cold temperatures? A case-only approach in Hong Kong with a temperate climate.

The short-term effects of ambient cold temperature on mortality have been well documented in the literature worldwide. However, less is known about which subpopulations are more vulnerable to death related to extreme cold. We aimed to examine the personal characteristics and underlying causes of death that modified the association between extreme cold and mortality in a case-only approach. Individual information of 197,680 deaths of natural causes, daily temperature, and air pollution concentrations in cool season (November-April) during 2002-2011 in Hong Kong were collected. Extreme cold was defined as those days with preceding week with a daily maximum temperature at or less than the 1st percentile of its distribution. Logistic regression models were used to estimate the effects of modification, further controlling for age, seasonal pattern, and air pollution. Sensitivity analyses were conducted by using the 5th percentile as cutoff point to define the extreme cold. Subjects with age of 85 and older were more vulnerable to extreme cold, with an odds ratio (OR) of 1.33 (95 % confidence interval (CI), 1.22-1.45). The greater risk of extreme cold-related mortality was observed for total cardiorespiratory diseases and several specific causes including hypertensive diseases, stroke, congestive heart failure, chronic obstructive pulmonary disease (COPD), and pneumonia. Hypertensive diseases exhibited the greatest vulnerability to extreme cold exposure, with an OR of 1.37 (95 % CI, 1.13-1.65). Sensitivity analyses showed the robustness of these effect modifications. This evidence on which subpopulations are vulnerable to the adverse effects of extreme cold is important to inform public health measures to minimize those effects.

The smoke-free legislation in Hong Kong: its impact on mortality.

OBJECTIVES: To examine trends in deaths for conditions associated with secondhand smoke exposure over the years prior to and following the implementation of a smoke-free policy in Hong Kong. DESIGN: Time-series study. SETTING: Death registration data from Hong Kong Special Administrative Region (SAR) Government Census and Statistics Department. PARTICIPANTS: All deaths registered from 1 January 2001 to 31 December 2011. MAIN OUTCOME MEASURES: Deaths for conditions associated with passive smoking include cardiovascular disease (CVD), respiratory disease and other causes. RESULTS: There was a decline in the annual proportional change for ischaemic heart disease (IHD), acute myocardial infarction (AMI) and CVD mortality in the year after the intervention for all ages and those aged 65 years or older. There were also clear declines in the cool season peaks for these three conditions in the first postintervention year. There was a further drop in the cool season peak for AMI among all ages in the year after the exemptions ceased. No declines in annual proportional change or changes in seasonal peaks of mortality were found for any of the control conditions. CONCLUSIONS: The findings in this study add to the evidence base, as summarised in the Surgeon General's report, extending the impact of effective smoke-free legislation to those aged 65 years or older and to cerebrovascular events in younger age groups. They also reinforced the need for comprehensive, enforced and effective smoke-free laws if the full extent of the health gains are to be achieved.

Milk consumption in relation to incidence of nasopharyngeal carcinoma in 48 countries/regions.

BACKGROUND: Decreasing trends of nasopharyngeal carcinoma (NPC) incidence have been consistently reported in endemic populations but the etiology of NPC remains unclear. The objective of our study was to assess the international and local (Hong Kong) correlations of milk and dairy products per capita consumption with NPC incidence. METHODS: We conducted an ecological study in 48 countries/regions. Age standardized incidence rates of NPC were obtained from the Cancer Incidence in Five Continents. Dairy product consumption and Human Development Index were obtained from the Food and Agriculture Organization of the United Nations and the United Nations Development Programme. Spearman correlation, multivariate analysis and time-lagged analysis were performed. RESULTS: The negative correlations between milk consumption and decreased age standardized incidence rates of NPC were observed in the 48 countries/regions adjusting for Human Development Index in endemic countries/regions. In Hong Kong, multivariate analysis, after adjusting for other potential confounders, including salted fish, cigarette, vegetable consumption and socioeconomic status, showed consistently negative and significant correlations between milk consumption and NPC incidence (The strongest coefficient (ß) was observed at 10-year lag in males [ß = -0.439; P < 0.01] and in females [ß = -0.258; P < 0.01]). CONCLUSIONS: Our study showed the correlations on milk consumption per capita and against lower risk of NPC in 48 countries/regions and in Hong Kong. These hypothesis-generating results could support further studies on individual exposures and the disease.

Temperature as a modifier of the effects of fine particulate matter on acute mortality in Hong Kong.

Interactions between particulate matter with aerodynamic diameter less than or equal to 2.5 µm (PM2.5) and temperature on mortality have not been well studied, and results are difficult to synthesize. We aimed to assess modification of temperature on the association between PM2.5 and cause-specific mortality by stratifying temperature into low, medium, and high stratum in Hong Kong, using data from 1999 to 2011. The mortality effects of PM2.5 were stronger in low temperature stratum than those in high. The excess risk (%) per 10 µg/m(3) increase in PM2.5 at lag 0-1 in low temperature stratum were 0.94% (95% confidence interval: 0.65, 1.24) for all natural, 0.88% (0.38, 1.37) for cardiovascular, and 1.15% (0.51, 1.79) for respiratory mortality. We found statistically significant interaction of PM2.5 and temperature between low and high temperature stratum for all natural mortality. Our results suggested that temperature might modify mortality effects of PM2.5 in Hong Kong.

Age and Sex Differences in Rates of Influenza-Associated Hospitalizations in Hong Kong.

Few studies have explored age and sex differences in the disease burden of influenza, although men and women probably differ in their susceptibility to influenza infections. In this study, quasi-Poisson regression models were applied to weekly age- and sex-specific hospitalization numbers of pneumonia and influenza cases in the Hong Kong SAR, People's Republic of China, from 2004 to 2010. Age and sex differences were assessed by age- and sex-specific rates of excess hospitalization for influenza A subtypes A(H1N1), A(H3N2), and A(H1N1)pdm09 and influenza B, respectively. We found that, in children younger than 18 years, boys had a higher excess hospitalization rate than girls, with the male-to-female ratio of excess rate (MFR) ranging from 1.1 to 2.4. MFRs of hospitalization associated with different types/subtypes were less than 1.0 for adults younger than 40 years except for A(H3N2) (MFR = 1.6), while all the MFRs were equal to or higher than 1.0 in adults aged 40 years or more except for A(H1N1)pdm09 in elderly persons aged 65 years or more (MFR = 0.9). No MFR was found to be statistically significant (P < 0.05) for hospitalizations associated with influenza type/subtype. There is some limited evidence on age and sex differences in hospitalization associated with influenza in the subtropical city of Hong Kong.

Impact of the 2009 H1N1 Pandemic on Age-Specific Epidemic Curves of Other Respiratory Viruses: A Comparison of Pre-Pandemic, Pandemic and Post-Pandemic Periods in a Subtropical City.

BACKGROUND: The 2009 H1N1 influenza pandemic caused offseason peaks in temperate regions but coincided with the summer epidemic of seasonal influenza and other common respiratory viruses in subtropical Hong Kong. This study was aimed to investigate the impact of the pandemic on age-specific epidemic curves of other respiratory viruses. METHODS: Weekly laboratory-confirmed cases of influenza A (subtypes seasonal A(H1N1), A(H3N2), pandemic virus A(H1N1)pdm09), influenza B, respiratory syncytial virus (RSV), adenovirus and parainfluenza were obtained from 2004 to 2013. Age-specific epidemic curves of viruses other than A(H1N1)pdm09 were compared between the pre-pandemic (May 2004-April 2009), pandemic (May 2009-April 2010) and post-pandemic periods (May 2010-April 2013). RESULTS: There were two peaks of A(H1N1)pdm09 in Hong Kong, the first in September 2009 and the second in February 2011. The infection rate was found highest in young children in both waves, but markedly fewer cases in school children were recorded in the second wave than in the first wave. Positive proportions of viruses other than A(H1N1)pdm09 markedly decreased in all age groups during the first pandemic wave. After the first wave of the pandemic, the positive proportion of A(H3N2) increased, but those of B and RSV remained slightly lower than their pre-pandemic proportions. Changes in seasonal pattern and epidemic peak time were also observed, but inconsistent across virus-age groups. CONCLUSION: Our findings provide some evidence that age distribution, seasonal pattern and peak time of other respiratory viruses have changed since the pandemic. These changes could be the result of immune interference and changing health seeking behavior, but the mechanism behind still needs further investigations.

Age-specific epidemic waves of influenza and respiratory syncytial virus in a subtropical city.

Both influenza and respiratory syncytial virus (RSV) are active throughout the year in subtropical or tropical regions, but few studies have reported on age-specific seasonal patterns of these viruses. We examined the age-specific epidemic curves of laboratory-confirmed cases of influenza A (subtyped into seasonal A(H1N1), A(H3N2), and pandemic virus A(H1N1)pdm09), influenza B and respiratory syncytial virus (RSV), in subtropical city Hong Kong from 2004 to 2013. We found that different types and subtypes of influenza showed similar two-peak patterns across age groups, with one peak in winter and another in spring/summer. Age differences were found in epidemic onset time and duration, but none could reach statistical significance (p > 0.05). Age synchrony was found in epidemic peak time for both cool and warm seasons. RSV showed less clear seasonal patterns and non-synchronized epidemic curves across age. In conclusion, age synchrony was found in influenza seasonal epidemics and the 2009 pandemic, but not in RSV. None of the age groups consistently appear as the driving force for seasonal epidemics of influenza and RSV in Hong Kong.