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Asymptomatic influenza virus infection occurs but may vary by factors such as age, vaccination status, or season. We examined the frequency of influenza virus infection and symptoms using data from two case-ascertained household transmission studies (2017-2023) with prospective, systematic collection of respiratory specimens and symptoms. From the 426 influenza virus infected household contacts that met our inclusion criteria, 8% were asymptomatic, 6% had non-respiratory symptoms, 23% had acute respiratory symptoms, and 62% had influenza-like illness symptoms. Understanding the prevalence of asymptomatic and mildly symptomatic influenza cases is important for implementing effective influenza prevention strategies and enhancing symptom-based surveillance systems., (Published by Oxford University Press on behalf of Infectious Diseases Society of America 2024.)

Background: Whether acute respiratory illnesses (ARIs), often associated with virus detection, are associated with lower risk for subsequent ARI remains unclear. We assessed the association between symptomatic ARI and subsequent ARI in young children.Methods: In a prospective cohort of Peruvian children <3 years, we examined the impact of index ARI on subsequent ARI risk. Index ARI were matched with ≤3 asymptomatic observations and followed over 28 days. We compared risk of subsequent ARI between groups using conditional logistic regression adjusting for several covariates, accounting for repeat observations from individual children.Results: Among 983 index ARI, 339 (34%) had an ARI event during follow-up, compared with 876/2826 (31%) matched asymptomatic observations. We found no significant association of index ARI and subsequent ARI risk during follow-up overall (adjusted odds ratio [aOR], 1.10; 95% confidence interval [CI], .98-1.23) or when limited to index ARI with respiratory viruses detected (aOR, 1.03; 95% CI, .86-1.24). Similarly, when the outcome was limited to ARI in which viruses were detected, no significant association was seen (aOR, 1.05; 95% CI, .87-1.27).Conclusions: ARIs were not associated with short-term protection against subsequent ARI in these children. Additional longitudinal studies are needed to understand drivers of recurrent ARI in young children. [ABSTRACT FROM AUTHOR]

Background Ambient environmental factors have been associated with respiratory infections in ecological studies, but few studies have explored the impact of indoor environmental factors in detail. The current study aimed to investigate the impact of indoor environment on the risk of acute respiratory illness (ARI) in a subtropical city. Method A prospective cohort study was conducted in 285 community-dwelling older adults from December 2016 through May 2019. Individual household indoor environment data and ARI incidence were continuously collected. A time-stratified case-crossover analysis was conducted to estimate the excess risk of ARI associated with per-unit increase of daily mean indoor temperature, relative humidity, and absolute humidity (AH). Result In total, 168 episodes of ARI were reported with an average risk of 36.8% per year. We observed a negative association of ARI with indoor AH up to 5 lag days in cool seasons, with a 6-day cumulative excess risk estimate of −9.0% (95% confidence interval, −15.9% to −1.5%). Negative associations between household temperature or relative humidity and ARI were less consistent across warm and cool seasons. Conclusions Lower indoor AH in household was associated with a higher risk of ARI in the community-dwelling older adults in Hong Kong during cold seasons. [ABSTRACT FROM AUTHOR]

In an observational study of 582 patients with laboratory-confirmed influenza virus infections and their household contacts, we found that the initiation of oseltamivir within 24 hours was associated with shorter duration of self-reported illness symptoms (56% reduction in duration; 95% confidence interval, 41%-67%). However, we did not find any association of oseltamivir treatment with duration of viral shedding by polymerase chain reaction or with the risk of household transmission. [ABSTRACT FROM AUTHOR]

Background: The Influenza Incidence Surveillance Project (IISP) monitored outpatient acute respiratory infection (ARI; defined as the presence of ≥ 2 respiratory symptoms not meeting ILI criteria) and influenza-like illness (ILI) to determine the incidence and contribution of associated viral etiologies.Methods: From August 2010 through July 2011, 57 outpatient healthcare providers in 12 US sites reported weekly the number of visits for ILI and ARI and collected respiratory specimens on a subset for viral testing. The incidence was estimated using the number of patients in the practice as the denominator, and the virus-specific incidence of clinic visits was extrapolated from the proportion of patients testing positive.Results: The age-adjusted cumulative incidence of outpatient visits for ARI and ILI combined was 95/1000 persons, with a viral etiology identified in 58% of specimens. Most frequently detected were rhinoviruses/enteroviruses (RV/EV) (21%) and influenza viruses (21%); the resulting extrapolated incidence of outpatient visits was 20 and 19/1000 persons respectively. The incidence of influenza virus-associated clinic visits was highest among patients aged 2-17 years, whereas other viruses had varied patterns among age groups.Conclusions: The IISP provides a unique opportunity to estimate the outpatient respiratory illness burden by etiology. Influenza virus infection and RV/EV infection(s) represent a substantial burden of respiratory disease in the US outpatient setting, particularly among children. [ABSTRACT FROM AUTHOR]

Background. Respiratory syncytial virus (RSV) is a major cause of acute respiratory illness (ARI). Little is known about RSV disease among older children and adults in Central America.Methods. Prospective surveillance for ARI among hospital patients and clinic patients was conducted in Guatemala during 2007–2012. Nasopharyngeal and oropharyngeal swab specimens were tested for RSV, using real-time reverse-transcription polymerase chain reaction.Results. Of 6287 hospitalizations and 2565 clinic visits for ARI, 24% and 12%, respectively, yielded RSV-positive test results. The incidence of RSV-positive hospitalization for ARI was 5.8 cases/10 000 persons per year and was highest among infants aged <6 months (208 cases/10 000 persons per year); among adults, the greatest incidence was observed among those aged ≥65 years (2.9 cases/10 000 persons per year). The incidence of RSV-positive clinic visitation for ARI was 32 cases/10 000 persons per year and was highest among infants aged 6–23 months (186 cases/10 000 persons per year). Among RSV-positive hospital patients with ARI, underlying cardiovascular disease was associated with death, moribund discharge, intensive care unit admission, or mechanical ventilation (odds ratio, 4.1; 95% confidence interval, 1.9–8.8). The case-fatality proportion among RSV-positive hospital patients with ARI was higher for those aged ≥5 years than for those aged <5 years (13% vs 3%; P < .001).Conclusions. The incidences of RSV-associated hospitalization and clinic visitation for ARI were highest among young children, but a substantial burden of ARI due to RSV was observed among older children and adults. [ABSTRACT FROM AUTHOR]