Estimates of seasonal influenza‐associated mortality in Bangladesh, 2010‐2012

Abstract

BackgroundSeasonal influenza‐associated mortality estimates help identify the burden of disease and assess the value of public health interventions such as annual influenza immunization. Vital registration is limited in Bangladesh making it difficult to estimate seasonal influenza mortality.ObjectivesOur study aimed to estimate seasonal influenza‐associated mortality rates for 2010‐2012 in Bangladesh.MethodsWe conducted surveillance among hospitalized patients with severe acute respiratory illness (SARI) for persons aged ≥5 years and severe pneumonia for children <5 years in 11 sites across Bangladesh. We defined the catchment areas of these sites and conducted a community survey in 22 randomly selected unions (administrative units) within the catchment areas to identify respiratory deaths. We multiplied the proportion of influenza‐positive patients at our surveillance sites by the age‐specific number of respiratory deaths identified to estimate seasonal influenza‐associated mortality.ResultsAmong 4221 surveillance case‐patients, 553 (13%) were positive for influenza viruses. Concurrently, we identified 1191 persons who died within 2 weeks of developing an acute respiratory illness within the catchment areas of the surveillance hospitals. In 2010‐2011, the estimated influenza‐associated mortality rate was 6 (95% CI 4‐9) per 100 000 for children <5 years and 41 (95% CI 35‐47) per 100 000 for persons >60 years. During 2011‐2012, the estimated influenza‐associated mortality rate was 13 (95% CI 10‐16) per 100 000 among children <5 years and 88 (95% CI 79‐98) per 100 000 among persons aged >60 years.ConclusionsWe identified a substantial burden of influenza‐associated deaths in Bangladesh suggesting that the introduction of prevention and control measures including seasonal vaccination should be considered by local public health decision‐makers.

Reply to Alonso et al. “Bangladesh and Rwanda: Cases of high burden of influenza in tropical countries?”

“…While we noted that there is substantial burden from influenza virus infection in Bangladesh in 2010‐2012,2 our estimates are not higher than other estimates published from neighboring countries (reviewed in detail here4). Estimates from Kenya,5 South Africa,6 and Thailand7 are comparable to our estimates, and in some instances, higher than estimates for Bangladesh.…”

“…We thank Dr. Alonso et al for their commentary1 on our articles, “Estimates of Seasonal Influenza‐Associated Mortality in Bangladesh, 2010‐2012”2 and “The National Burden of Influenza‐Associated Severe Acute Respiratory Illness Hospitalization in Rwanda, 2012‐2014.”3 In their commentary, they described three assumptions that we would like to address: (1) their use of “substantial” burden compared to “high” burden, (2) the comparability of influenza burden in tropical climate countries, and (3) the impact of the influenza A(H1N1)pdm09 virus on mortality. In addition, they describe three concerns about our estimates, which we would also like to clarify, specifically: (4) a mismatch in the timing of respiratory deaths and the influenza virus circulation period, (5) mortality attribution, and (6) the comparison with Institute of Health Metrics and Evaluation (IHME) estimates.…”

“…In our methods, we calculated the influenza‐associated mortality incidence using monthly ARI death counts and the monthly proportion of samples that tested positive for influenza viruses. As stated on page 67 of our article (the equation),2 the monthly mortality rates were derived by multiplying the proportion of ARI deaths ( D / P ) by the monthly proportion of influenza‐positive specimens ( F ) and then added for a consecutive 12‐month period to produce the annual estimates. If for a given month, the proportion of samples testing influenza positive was zero (ie F  =   0), ARI deaths ( D / P ) from that month would not be attributed to influenza nor contribute to the annual mortality rate estimates as multiplying the ARI deaths by 0% influenza positive ( D / P  *  F ) would also be zero.…”

Evaluating Hospital-Based Surveillance for Outbreak Detection in Bangladesh: Analysis of Healthcare Utilization Data

“…We demonstrate the application of the proposed evaluation strategy by using it to assess the capacity of hospital-based surveillance for severe infectious diseases in Bangladesh, which is based on tertiary care hospitals located throughout the country. We used data from two surveys carried out in catchment areas of some of these hospitals that investigated the healthcare utilization behavior of individuals with severe neurological infectious disease or fatal respiratory infectious disease (Fig 2A) [14,15]. These disease types are of great public health relevance in Bangladesh (e.g., Japanese encephalitis and influenza) but also represent symptoms typical of other emerging infectious diseases (e.g., Nipah and severe acute respiratory syndrome).…”

“…A first survey collected data between 10 June 2008 and 30 March 2009 about cases with symptoms of severe neurological infection that occurred within the previous 12 mo in 60 small administrative units (mean population size of 28,000 people) in the catchment areas of three surveillance hospitals [14]. A second survey collected data between 3 April 2012 and 22 February 2013 about acute respiratory infection (ARI)-related deaths that occurred within the previous 24 mo in 22 administrative units in the catchment areas of 11 surveillance hospitals [15]. We considered ARI-related deaths as a proxy for respiratory disease of sufficient severity to require medical attention.…”