Methods for Determing Viral Transmission in New York City (NYC) Schools During a Novel H1N1 Influenza Outbreak
Keywords: school closure, influenza, H1N1
During the spring 2009 novel H1N1 influenza outbreak in New York City (NYC), the health department instituted a policy of selectively closing schools thought to exhibit high rates of viral transmission. School closure as a non-pharmaceutical intervention (NPI) strategy in mitigating pandemic influenza has been in use since at least 1918. Closing schools early in an outbreak is thought to lower the incident peak, delay the exponential increase in incidence and reduce overall morbidity and mortality in a community.
We outline methods for determining influenza transmission in NYC schools for the 2009-2010 school year from multiple time series, including clinical data from school nurses and grade-specific rates of absenteeism. Visits to school nurses for NYC public schools are reported electronically to the New York City Department of Health and Mental Hygiene (NYC DOHMH) through the Automated School Health Reporting System (ASHR). These daily time series data include a child’s symptoms and measured temperature. An additional online reporting system tracking influenza-like illness in NYC private schools, as well as schools not reporting through ASHR, was initiated in the Fall of 2009. Rates of absenteeism are reported to the NYC DOHMM from the New York City Department of Education on a daily basis for all 1,533 public schools.
Several challenges exist in estimating the temporal pattern of influenza transmission in NYC schools, including changes in the reporting systems over time, incomplete data and interrupted time series due to weekend closure. Furthermore, due to the highly non-linear transmission dynamics of influenza, all increases in reported illness due not represent true outbreaks. We discuss methods of dealing with these challenges while monitoring changes in influenza transmission and identifying NYC schools that warrant further investigation. Results of this work could be used to inform policy aimed at mitigating influenza transmission in schools.