Background: Global influenza-associated acute respiratory infections contribute to 3-5 million severe illnesses requiring hospitalization annually, with 90% of hospitalizations occurring among children <5 years in developing countries. In Bangladesh, limited availability of nationally representative, robust estimates of influenza-associated hospitalizations limit allocation of resources for prevention and control measures. Methods: This study used data from the Hospital Based Influenza Surveillance (HBIS) system in Bangladesh from 2010-2019 and Healthcare Utilization Surveys to determine hospital utilization patterns in the catchment area. We estimated annual influenza-associated hospitalization numbers and rates for all age groups in Bangladesh using methods outlined by the World Health Organization and adjusted for enrolment, laboratory testing practices, and healthcare seeking behavior. We then estimated national hospitalization rates by multiplying age-specific hospitalization rates with the corresponding annual national census population. Results: Annual influenza-associated hospitalization rates per 100,000 population for all ages ranged from 31 (95% CI: 27-36) in 2011 to 139 (95% CI: 130-149) in 2019. Children <5 years old had the highest rates of influenza-associated hospitalization, ranging from 114 (95% CI: 90-138) in 2011 to 529 (95% CI: 481-578) in 2019, followed by adults aged ≥65 years with rates ranging from 46 (95% CI: 34-57) in 2012 to 252 (95% CI: 213-292) in 2019. The national hospitalization estimates for all ages from 2010-2019 ranged from 47,891 to 236,380 per year. Conclusions: The impact of influenza-associated hospitalizations in Bangladesh may be considerable, particularly for young children and older adults. Targeted interventions, such as influenza vaccination for these age groups, should be prioritized and evaluated.

Background: Recent evidences reported that co-infection with SARS-CoV-2 and Influenza virus is common. We explored hospital-based influenza surveillance (HBIS) data during the COVID-19 pandemic. Methods: We analyzed data from March to December 2020 among patients admitted with severe acute respiratory infections (SARI) defined as subjective or measured fever of ≥ 38 C° and cough with onset within the last ten days. Physicians recorded patients’ demographic, clinical, and laboratory information and obtained nasopharyngeal and oropharyngeal swabs to test for influenza virus and SARS-CoV-2 by rRT-PCR. Results: We enrolled 1,986 SARI case-patients with median age of 28 years (IQR: 1.2 ­ 53 years), and 67.6% were male. Among SARI case-patients, 285 (14.3%) were infected with SARS-CoV-2 and 175 (8.8%) infected with influenza virus. Only five (0.3%) SARI patients were co-infected with SARS-CoV-2 and influenza virus. Difficulty breathing (83% vs. 77%, p=0.024) and sore throat (26% vs. 17%, p<0.001) were more likely to be present in SARS-CoV-2-infected SARI patients. SARI case-patients with diabetes and hypertension were more likely (14% vs. 6%, p<0.001 and 27% vs. 12%, p<0.001 respectively) to be infected with SARS-CoV-2 virus than those without co-morbidities. Influenza virus remained undetectable during the first 14 weeks of the 20 weeks (May to September) of peak influenzacirculation period in Bangladesh. Conclusions: Our findings suggest that co-infection with SARS-CoV-2 and influenza virus was not very common together with nonappearance of the influenza virus during most of the peak influenza period in Bangladesh during COVID-19 pandemic. Future studies are warranted for further exploration.

Background We explored whether hospital-based surveillance is useful in detecting severe acute respiratory infection (SARI) clusters and how often these events result in outbreak investigation and community mitigation. Methods During May 2009– December 2020, physicians at 14 sentinel hospitals prospectively identified SARI clusters (i.e., ≥2 SARI cases who developed symptoms ≤10 days of each other and lived <30 minute walk or <3 km from each other). Oropharyngeal and nasopharyngeal swabs were tested for influenza and other respiratory viruses by rRT-PCR. We describe the demographic of persons within clusters, laboratory results, and outbreak investigations. Results Physicians identified 464 clusters comprising 1,427 SARI cases (range 0–13 clusters per month). Sixty percent of clusters had three, 23% had 2, and 17% had ≥4 cases. Their median age was 2 years (interquartile [IQR] 0.4–25) and 63% were male. Laboratory results were available for the 464 clusters a median 9 days (IQR = 6–13 days) after cluster identification. Less than one in five clusters had cases that tested positive for the same virus: RSV in 58 (13%), influenza viruses in 24 (5%), HMPV in 5 (1%), HPIV in 3 (0.6%), adenovirus in 2 (0.4%). While 102/464 (22%) had poultry exposure, none tested positive for influenza A(H5N1) or A(H7N9). None of the 464 clusters led to field deployments for outbreak response. Conclusions For 11 years, none of the hundreds of identified clusters led to emergency response. The value of this event-based surveillance might be improved by seeking larger clusters, with stronger epidemiologic ties or decedents.