Influenza transmission during extreme indoor conditions in a low-resource tropical setting
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Influenza transmission occurs throughout the planet across wide-ranging environmental conditions. However, our understanding of the environmental factors mediating transmission is evaluated using outdoor environmental measurements, which may not be representative of the indoor conditions where influenza is transmitted. In this study, we examined the relationship between indoor environment and influenza transmission in a low-resource tropical population. We used a case-based ascertainment design to enroll 34 households with a suspected influenza case and then monitored households for influenza, while recording indoor temperature and humidity data in each household. We show that the indoor environment is not commensurate with outdoor conditions and that the relationship between indoor and outdoor conditions varies significantly across homes. We also show evidence of influenza transmission in extreme indoor environments. Specifically, our data suggests that indoor environments averaged 29 °C, 18 g/kg specific humidity, and 68 % relative humidity across 15 transmission events observed. These indoor settings also exhibited significant temporal variability with temperatures as high as 39 °C and specific and relative humidity increasing to 22 g/kg and 85 %, respectively, during some transmission events. However, we were unable to detect differences in the transmission efficiency by indoor temperature or humidity conditions. Overall, these results indicate that laboratory studies investigating influenza transmission and virus survival should increase the range of environmental conditions that they assess and that observational studies investigating the relationship between environment and influenza activity should use caution using outdoor environmental measurements since they can be imprecise estimates of the conditions that mediate transmission indoors.
KeywordsInfluenza Indoor Environment Specific Humidity Transmission Efficiency Outdoor Temperature
This publication was developed under Assistance Agreement No. (RD No. 83574901) awarded by the US Environmental Protection Agency to Christopher K. Uejio. It has not been formally reviewed by the EPA. The views expressed in this document are solely those of the authors and do not necessarily reflect those of the Agency. EPA does not endorse any products or commercial services mentioned in this publication. This work was also supported by an Old Gold Fellowship form the College of Liberal Arts and Sciences at the University of Iowa (JT); the US Environmental Protection Agency RD No. 83574901 (JT, CU); and the National Institute of Allergy and Infectious Diseases, National Institutes of Health, under grant number U01AI088654 (AG), and was funded through a career development award from the John E. Fogarty International Center, National Institutes of Health (K02 TW009483; AG).
Compliance with ethical standards
Written informed consent or parental proxy was obtained for all participants. In addition, verbal assent was obtained from children aged 6 years and older. This study was approved by the Institutional Review Boards at the Ministry of Health, Nicaragua, the University of Michigan, and the University of California, Berkeley.
Conflict of interest
The authors declare that they have no conflict of interest.
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