Influenza Pandemics in Singapore, a Tropical, Globally Connected City

Tan Tock Seng Hospital, Singapore.
Emerging infectious diseases (Impact Factor: 6.75). 08/2007; 13(7):1052-7. DOI: 10.3201/eid1307.061313
Source: PubMed


Tropical cities such as Singapore do not have well-defined influenza seasons but have not been spared from influenza pandemics. The 1918 epidemic in Singapore, which was then already a major global trading hub, occurred in 2 waves, June-July, and October-November, and resulted in > or = 2,870 deaths. The excess mortality rate was higher than that for industrialized nations in the Northern Hemisphere but lower than that for less industrialized countries in Asia and Africa. The 1957 epidemic occurred in May and resulted in widespread illness. The 1968 epidemic occurred in August and lasted a few weeks, again with widespread illness. Tropical cities may be affected early in a pandemic and have higher mortality rates. With the increase in travel and trade, a future pandemic may reach a globally connected city early and spread worldwide. Preparedness and surveillance plans must be developed to include the megacities of the tropical world.

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Available from: Siew-Pang Chan, Sep 08, 2014
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    • "The possibility that the virus could have been introduced into Spain from the southern Spanish border cannot be ruled out although the earliest reports of pandemic influenza in The Strait of Gibraltar did not occur until May 1918, a month after the respiratory disease reports in France [2]. Early pandemic waves associated with low excess mortality rates have been documented in other regions during February-July 1918 including New York City [5], Mexico [7], Geneva [39], Copenhagen [19], the US military [40], the UK [23], and Singapore [11]. These epidemiological findings are in line with virologic evidence of pandemic A/H1N1 influenza infection among US soldiers in May 1918 [41]. "
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    ABSTRACT: Background The impact of socio-demographic factors and baseline health on the mortality burden of seasonal and pandemic influenza remains debated. Here we analyzed the spatial-temporal mortality patterns of the 1918 influenza pandemic in Spain, one of the countries of Europe that experienced the highest mortality burden. Methods We analyzed monthly death rates from respiratory diseases and all-causes across 49 provinces of Spain, including the Canary and Balearic Islands, during the period January-1915 to June-1919. We estimated the influenza-related excess death rates and risk of death relative to baseline mortality by pandemic wave and province. We then explored the association between pandemic excess mortality rates and health and socio-demographic factors, which included population size and age structure, population density, infant mortality rates, baseline death rates, and urbanization. Results Our analysis revealed high geographic heterogeneity in pandemic mortality impact. We identified 3 pandemic waves of varying timing and intensity covering the period from Jan-1918 to Jun-1919, with the highest pandemic-related excess mortality rates occurring during the months of October-November 1918 across all Spanish provinces. Cumulative excess mortality rates followed a south–north gradient after controlling for demographic factors, with the North experiencing highest excess mortality rates. A model that included latitude, population density, and the proportion of children living in provinces explained about 40% of the geographic variability in cumulative excess death rates during 1918–19, but different factors explained mortality variation in each wave. Conclusions A substantial fraction of the variability in excess mortality rates across Spanish provinces remained unexplained, which suggests that other unidentified factors such as comorbidities, climate and background immunity may have affected the 1918–19 pandemic mortality rates. Further archeo-epidemiological research should concentrate on identifying settings with combined availability of local historical mortality records and information on the prevalence of underlying risk factors, or patient-level clinical data, to further clarify the drivers of 1918 pandemic influenza mortality.
    BMC Infectious Diseases 07/2014; 14(1):371. DOI:10.1186/1471-2334-14-371 · 2.61 Impact Factor
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    • "Tropical regions experience influenza all year round, usually with two annual epidemic peaks [1] and an impact comparable to temperate regions [2]. In tropical Singapore, seasonal influenza mortality rates have been shown to be similar to temperate and sub-tropical countries [3], and excess deaths in Singapore from previous pandemics were comparable with global estimates [4]. The 2009 influenza pandemic also affected Singapore, infecting 13% of community-living adults during the first epidemic wave [5]. "
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    ABSTRACT: Limited information is available about pandemic H1N1-2009 influenza vaccine effectiveness in tropical communities. We studied the effectiveness of a pandemic H1N1 vaccination program in reducing influenza cases in Singapore. A surveillance study was conducted among military personnel presenting with febrile respiratory illness from mid-2009 to mid-2010. Consenting individuals underwent nasal washes, which were tested with RT-PCR and subtyped. A vaccination program (inactivated monovalent Panvax H1N1-2009 vaccine) was carried out among recruits. A Bayesian hierarchical model was used to quantify relative risks in the pre- and post-vaccination periods. An autoregressive generalised linear model (GLM) was developed to minimise confounding. Of 2858 participants, 437 (15.3%), 60 (2.1%), and 273 (9.6%) had pandemic H1N1, H3N2, and influenza B. The ratio of relative risks for pandemic H1N1 infection before and after vaccination for the recruit camp relative to other camps was 0.14 (0.016,0.49); for H3N2, 0.44 (0.035,1.8); and for influenza B, 18 (0.77,89). Using the GLM for the recruit camp, post-vaccination weekly cases decreased by 54% (37%,67%, p<0.001) from that expected without vaccination; influenza B increased by 66 times (9-479 times, p<0.001); with no statistical difference for H3N2 (p = 0.54). Pandemic vaccination reduced H1N1-2009 disease burden among military recruits. Routine seasonal influenza vaccination should be considered.
    PLoS ONE 10/2011; 6(10):e26572. DOI:10.1371/journal.pone.0026572 · 3.23 Impact Factor
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    • "A better understanding of these patterns is essential to better prepare for future influenza pandemics. Quantitative analyses in North America (US [4] [5], Canada [6] [7], Mexico [8]), Europe (Denmark [9], Spain [10], France [10]) and Asia (Japan [11], Singapore [12] Taiwan [13]) have revealed characteristic features of the 1918–1920 influenza pandemic, including increased mortality rates in young adults relative to seasonal epidemics and the occurrence of multiple pandemic waves over 0264-410X/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. "
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    ABSTRACT: Increasing our knowledge of past influenza pandemic patterns in different regions of the world is crucial to guide preparedness plans against future influenza pandemics. Here, we undertook extensive archival collection efforts from three representative cities of Peru-Lima in the central coast, Iquitos in the northeastern Amazon region, Ica in the southern coast-to characterize the temporal, age and geographic patterns of the 1918-1920 influenza pandemic in this country. We analyzed historical documents describing the 1918-1920 influenza pandemic in Peru and retrieved individual mortality records from local provincial archives for quantitative analysis. We applied seasonal excess mortality models to daily and monthly respiratory mortality rates for 1917-1920 and quantified transmissibility estimates based on the daily growth rate in respiratory deaths. A total of 52,739 individual mortality records were inspected from local provincial archives. We found evidence for an initial mild pandemic wave during July-September 1918 in Lima, identified a synchronized severe pandemic wave of respiratory mortality in all three locations during November 1918-February 1919, and a severe pandemic wave during January 1920-March 1920 in Lima and July-October 1920 in Ica. There was no recrudescent pandemic wave in 1920 in Iquitos. Remarkably, Lima experienced the brunt of the 1918-1920 excess mortality impact during the 1920 recrudescent wave, with all age groups experiencing an increase in all cause excess mortality from 1918-1919 to 1920. Middle age groups experienced the highest excess mortality impact, relative to baseline levels, in the 1918-1919 and 1920 pandemic waves. Cumulative excess mortality rates for the 1918-1920 pandemic period were higher in Iquitos (2.9%) than Lima (1.6%). The mean reproduction number for Lima was estimated in the range 1.3-1.5. We identified synchronized pandemic waves of intense excess respiratory mortality during November 1918-February 1919 in Lima, Iquitos, Ica, followed by asynchronous recrudescent waves in 1920. Cumulative data from quantitative studies of the 1918 influenza pandemic in Latin American settings have confirmed the high mortality impact associated with this pandemic. Further historical studies in lesser studied regions of Latin America, Africa, and Asia are warranted for a full understanding of the global impact of the 1918 pandemic virus.
    Vaccine 07/2011; 29 Suppl 2:B21-6. DOI:10.1016/j.vaccine.2011.02.048 · 3.62 Impact Factor
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