BackgroundLow absolute humidity (AH) has been associated with increased influenza virus survival and transmissibility and the onset of seasonal influenza outbreaks. Humidification of indoor environments may mitigate viral transmission and may be an important control strategy, particularly in schools where viral transmission is common and contributes to the spread of influenza in communities. However, the variability and predictors of AH in the indoor school environment and the feasibility of classroom humidification to levels that could decrease viral survival have not been studied.MethodsAutomated sensors were used to measure temperature, humidity and CO2 levels in two Minnesota grade schools without central humidification during two successive winters. Outdoor AH measurements were derived from the North American Land Data Assimilation System. Variability in indoor AH within classrooms, between classrooms in the same school, and between schools was assessed using concordance correlation coefficients (CCC). Predictors of indoor AH were examined using time-series Auto-Regressive Conditional Heteroskedasticity models. Classroom humidifiers were used when school was not in session to assess the feasibility of increasing indoor AH to levels associated with decreased influenza virus survival, as projected from previously published animal experiments.ResultsAH varied little within classrooms (CCC >0.90) but was more variable between classrooms in the same school (CCC 0.81 for School 1, 0.88 for School 2) and between schools (CCC 0.81). Indoor AH varied widely during the winter (range 2.60 to 10.34 millibars [mb]) and was strongly associated with changes in outdoor AH (p < 0.001). Changes in indoor AH on school weekdays were strongly associated with CO2 levels (p < 0.001). Over 4 hours, classroom humidifiers increased indoor AH by 4 mb, an increase sufficient to decrease projected 1-hour virus survival by an absolute value of 30% during winter months.ConclusionsDuring winter, indoor AH in non-humidified grade schools varies substantially and often to levels that are very low. Indoor results are predicted by outdoor AH over a season and CO2 levels (which likely reflects human activity) during individual school days. Classroom humidification may be a feasible approach to increase indoor AH to levels that may decrease influenza virus survival and transmission.

Influenza is a global problem infecting 5–10% of adults and 20–30% of children annually. Non-pharmaceutical interventions (NPIs) are attractive approaches to complement vaccination in the prevention and reduction of influenza. Strong cyclical reduction of absolute humidity has been associated with influenza outbreaks in temperate climates. This study tested the hypothesis that raising absolute humidity above seasonal lows would impact influenza virus survival and transmission in a key source of influenza virus distribution, a community school. Air samples and objects handled by students (e.g. blocks and markers) were collected from preschool classrooms. All samples were processed and PCR used to determine the presence of influenza virus and its amount. Additionally samples were tested for their ability to infect cells in cultures. We observed a significant reduction (p < 0.05) in the total number of influenza A virus positive samples (air and fomite) and viral genome copies upon humidification as compared to control rooms. This suggests the future potential of artificial humidification as a possible strategy to control influenza outbreaks in temperate climates. There were 2.3 times as many ILI cases in the control rooms compared to the humidified rooms, and whether there is a causal relationship, and its direction between the number of cases and levels of influenza virus in the rooms is not known. Additional research is required, but this is the first prospective study suggesting that exogenous humidification could serve as a scalable NPI for influenza or other viral outbreaks.

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Background Despite the fact infectious diseases can spread readily in grade schools, few studies have explored prevention in this setting. Additionally, we lack valid tools for students to self-report knowledge, attitudes, and behaviors. As part of an ongoing study of a curriculum intervention to promote healthy behaviors, we developed and evaluated age-appropriate surveys to determine students’ understanding of influenza prevention. Methods Surveys were adapted from adolescent and adult influenza surveys and administered to students in grades 2–5 (ages 7–11) at two Rochester public schools. We assessed student understanding by analyzing percent repeatability of 20 survey questions and compared percent “Don’t Know” (DK) responses across grades, gender, and race. Questions thought to be ambiguous after early survey administration were investigated in student focus groups, modified as appropriate, and reassessed. Results The response rate across all surveys was > 87%. Survey questions were well understood; 17 of 20 questions demonstrated strong pre/post repeatability (> 70%). Only 1 question showed an increase in DK response for higher grades (p <.0001). Statistical analysis and qualitative feedback led to modification of 3 survey questions and improved measures of understanding in the final survey administration. Conclusions Grade-school students’ knowledge, attitudes and behavior toward influenza prevention can be assessed using surveys. Quantitative and qualitative analysis may be used to assess participant understanding and refine survey development for pediatric survey instruments. These methods may be used to assess the repeatability and validity of surveys to assess the impact of health education interventions in young children.