Importance: Reported cases of SARS-CoV-2 infection likely underestimate the prevalence of infection in affected communities. Large-scale seroprevalence studies provide better estimates of the proportion of the population previously infected. Objective: To estimate prevalence of SARS-CoV-2 antibodies in convenience samples from several geographic sites in the United States. Design: Serologic testing of convenience samples using residual sera obtained for routine clinical testing by two commercial laboratory companies. Setting: Connecticut (CT), south Florida (FL), Missouri (MO), New York City metro region (NYC), Utah (UT), and Washington State’s (WA) Puget Sound region. Participants: Persons of all ages with serum collected during intervals from March 23 through May 3, 2020. Exposure: SARS-CoV-2 virus infection. Main outcomes and measures: We estimated the presence of antibodies to SARS-CoV-2 spike protein using an ELISA assay. We standardized estimates to the site populations by age and sex. Estimates were adjusted for test performance characteristics (96.0% sensitivity and 99.3% specificity). We estimated the number of infections in each site by extrapolating seroprevalence to site populations. We compared estimated infections to number of reported COVID-19 cases as of last specimen collection date. Results: We tested sera from 11,933 persons. Adjusted estimates of the proportion of persons seroreactive to the SARS-CoV-2 spike protein ranged from 1.13% (95% confidence interval [CI] 0.70-1.94) in WA to 6.93% (95% CI 5.02-8.92) in NYC (collected March 23-April 1). For sites with later collection dates, estimates ranged from 1.85% (95% CI 1.00-3.23, collected April 6-10) for FL to 4.94% (95% CI 3.61-6.52) for CT (April 26-May 3). The estimated number of infections ranged from 6 to 24 times the number of reported cases in each site. Conclusions and relevance: Our seroprevalence estimates suggest that for five of six U.S. sites, from late March to early May 2020, >10 times more SARS-CoV-2 infections occurred than the number of reported cases. Seroprevalence and under-ascertainment varied by site and specimen collection period. Most specimens from each site had no evidence of antibody to SARS-CoV-2. Tracking population seroprevalence serially, in a variety of specific geographic sites, will inform models of transmission dynamics and guide future community-wide public health measures. Key findings: Question: What proportion of persons in six U.S. sites had detectable antibodies to SARS-CoV-2, March 23-May 3, 2020? Findings: We tested 11,933 residual clinical specimens. We estimate that from 1.1% of persons in the Puget Sound to 6.9% in New York City (collected March 23-April 1) had detectable antibodies. Estimates ranged from 1.9% in south Florida to 4.9% in Connecticut with specimens collected during intervals from April 6-May 3. Six to 24 times more infections were estimated per site with seroprevalence than with case report data. Meaning: For most sites, evidence suggests >10 times more SARS-CoV-2 infections occurred than reported cases. Most persons in each site likely had no detectable SARS-CoV-2 antibodies.

Background: Approximately 80 000 Egyptians participate in Hajj pilgrimage annually. The purpose of this study was to estimate influenza virus and MERS‐CoV prevalence among Egyptian pilgrims returning from Hajj.Study: A cross‐sectional survey among 3 364 returning Egyptian pilgrims from 2012 to 2015 was conducted. Nasopharyngeal (NP) and oropharyngeal (OP) swabs were collected from all participants. Sputum specimens were collected from participants with respiratory symptoms and productive cough at the time of their interview. Specimens were tested for influenza viruses, and a convenience sample of NP/OP specimens was tested for MERS‐CoV. Thirty percent of participants met the case definition for influenza‐like illness (ILI), 14% tested positive for influenza viruses, and none tested positive for MERS‐CoV. Self‐reported influenza vaccination was 20%.Conclusions: High prevalence of reported ILI during pilgrimage and confirmed influenza virus on return from pilgrimage suggest a continued need for influenza prevention strategies for Egyptian Hajj pilgrims. An evaluation of the Ministry of Health and Population's current risk communication campaigns to increase influenza vaccine use among pilgrims may help identify strategies to improve vaccine coverage.

Schoolchildren are commonly linked to influenza transmission. Handwashing with soap has been shown to decrease infections; however, improving handwashing practices using soap and water is difficult in low-resource settings. In these settings, alternative hygiene options, such as hand sanitizer, could improve handwashing promotion to reduce influenza virus infections. We conducted a cluster randomized control trial in 24 primary schools in Dhaka to assess the effectiveness of hand sanitizer and a respiratory hygiene education intervention in reducing influenza-like illness (ILI) and laboratory-confirmed influenza during June–September 2015. Twelve schools were randomly selected to receive hand sanitizer and respiratory hygiene education, and 12 schools received no intervention. Field staff actively followed children daily to monitor for new ILI episodes (cough with fever) through school visits and by phone if a child was absent. When an illness episode was identified, medical technologists collected nasal swabs to test for influenza viruses. During the 10-week follow-up period, the incidence of ILI per 1,000 student-weeks was 22 in the intervention group versus 27 in the control group (P-value = 0.4). The incidence of laboratory-confirmed influenza was 53% lower in the intervention schools (3/1,000 person-weeks) than in the control schools (6/1,000 person-weeks) (P-value = 0.01). Hand sanitizer and respiratory hygiene education can help to reduce the risk of influenza virus transmission in schools.

Influenza burden estimates help provide evidence to support influenza prevention and control programs at local and international levels. Through a systematic review, we aimed to identify all published articles estimating rates of influenza-associated hospitalizations, describe methods and data sources used, and identify regions of the world where estimates are still lacking. We evaluated study heterogeneity to determine if we could pool published rates to generate global estimates of influenza-associated hospitalization. We identified 98 published articles estimating influenza-associated hospitalization rates from 2007-2018. Most articles (65%) identified were from high-income countries, with 34 of those (53%) presenting estimates from the United States. While we identified fewer publications (18%) from low- and lower-middle-income countries, 50% of those were published from 2015-2018, suggesting an increase in publications from lower-income countries in recent years. Eighty percent (n = 78) used a multiplier approach. Regression modelling techniques were only used with data from upper-middle or high-income countries where hospital administrative data was available. We identified variability in the methods, case definitions, and data sources used, including 91 different age groups and 11 different categories of case definitions. Due to the high observed heterogeneity across articles (I2>99%), we were unable to pool published estimates. The variety of methods, data sources, and case definitions adapted locally suggests that the current literature cannot be synthesized to generate global estimates of influenza-associated hospitalization burden.

Background: Influenza burden estimates help provide evidence to support influenza prevention and control programs. In this study, we estimated influenza‐associated respiratory hospitalization rates in Bhutan, a country considering influenza vaccine introduction.Methods: Using real‐time reverse transcription‐polymerase chain reaction laboratory results from severe acute respiratory infection (SARI) surveillance, we estimated the proportion of respiratory hospitalizations attributable to influenza each month among patients aged <5, 5‐49, and ≥50 years in six Bhutanese districts for 2015 and 2016. We divided the sum of the monthly influenza‐attributed hospitalizations by the total of the six district populations to generate age‐specific rates for each year.Results: In 2015, 10% of SARI patients tested positive for influenza (64/659) and 18% tested positive (129/736) in 2016. The incidence of influenza‐associated hospitalizations among all age groups was 50/100 000 persons (95% confidence interval [CI]: 45‐55) in 2015 and 118/100 000 persons (95% CI: 110‐127) in 2016. The highest rates were among children <5 years: 182/100 000 (95% CI: 153‐210) in 2015 and 532/100 000 (95% CI: 473‐591) in 2016. The second highest influenza‐associated hospitalization rates were among adults ≥50 years: 110/100 000 (95% CI: 91‐130) in 2015 and 193/100 000 (95% CI: 165‐221) in 2016.Conclusions: Influenza viruses were associated with a substantial burden of severe illness requiring hospitalization especially among children and older adults. These findings can be used to understand the potential impact of seasonal influenza vaccination in these age groups.

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, the inadequate availability of nationally representative, robust estimates of influenza‐associated hospitalizations limits 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 to 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 WHO methods, adjusted for a 6‐day‐a‐week enrollment schedule, selective testing of specimens from children under five, and healthcare‐seeking behavior, based on the proportion of symptomatic community participants seeking healthcare within the past week. 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 during 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.