A simulation framework to characterize the effect of ventilation control on airborne infectious disease transmission in schools

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2019-05

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Kumar, Sangeetha

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This study provides a detailed methodology for assessing the impact of ventilation control strategies on airborne infectious disease, specifically influenza, in schools. The probability of influenza infection in a classroom was approximated by the Rudnick and Milton (2003) model using inputs from a field campaign in Central Texas schools and reported influenza epidemiological data. The model is highly dependent on the quanta generation rate or the infectivity of an infector; therefore, a fractional removal term was developed to correct for filtration and depositional losses of the infectious quanta generated by the infector. Energy requirements for ventilation and associated outdoor air conditioning were estimated using air exchange rates and environmental quality conditions indoors (from the field study) and outdoors. To assess the variability in input parameters, Monte Carlo simulations were performed for different mechanical system types – split system and variable air volume (VAV) systems—and varying fractional removal terms. Assuming one infected student enters the school each day during the three-month period, the probability of infection ranges from 0.51% (9.5%) to 4.4% (6.3%). The corresponding number of secondary infections in a flu season range from ~400 to ~1100, which is in line with typical influenza-like-illness absence rates of ~1% a day. The modeling framework considers five control strategies, increasing the ventilation rate by 20%, 40%, 60%, 80%, and 100% during the peak flu season of December to February. The largest benefit-to-cost ratios (BCR) due to reduced absenteeism were from increasing ventilation by 20% or increasing energy expenditures by $0.25/student for a single flu season. The greatest net benefits (NB) per student were from increasing ventilation by 100% (for some classrooms maintaining minimum ASHRAE standards for fresh air requirements) or increasing energy expenditures by $1.25/student for one flu season. Given the relatively low cost of energy for Central Texas, a hot and humid climate, increasing ventilation rates to adequate levels may prove beneficial for the well-being of students and staff. School systems may strongly benefit from this analysis to make better decisions on ventilating classrooms to reduce financial losses due to sickness related absences during the flu season.

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