Tracking Flu in a Large Urban Area…A Complicated Matter

Tracking flu is no easy task, especially in Harris County, Texas; millions of residents, dozens of acute care hospitals, countless physicians’ offices, and collaboration with many public health partners. Adding to this complexity, only pediatric fatal flu cases and novel influenza are notifiable in Texas. Our solution, approach schools for voluntary reporting. The result, priceless!

Influenza, more commonly referred to simply as “the flu,” is a viral respiratory illness that occurs seasonally. The disease spreads via respiratory droplets generated when an infected individual coughs or sneezes. Transmission to others may occur before the infected person even knows that they are ill. The illness can range in severity from mild to very severe, and may result in fatalities. In the United States, influenza season generally ranges from October to May. Laboratories and healthcare providers in the United States are not required to report to public health departments. As a result, public health departments only have a partial picture of the impact of the disease. In order to begin to estimate influenza activity, voluntary reporting of influenza-like illness (ILI) occurs at some health departments throughout the United States from a variety of sources, including hospitals, private physician’s offices, and public health clinics; Harris County Public Health & Environmental Services (HCPHES) is one such health department. This passive surveillance activity, accomplished via the reporting of individuals who exhibit a specific clinical syndrome, is a simple form of syndromic surveillance.

The approach at HCPHES is innovative in that the majority of these voluntary reports come from nurses affiliated with the local independent school districts in the form of daily absenteeism and absenteeism due to ILI counts for both students and staff. This data, combined with a sample of rapid flu test results from acute care hospitals, provide a way for Epidemiologists at HCPHES to examine trends in ILI activity during the school year. Those who report daily absenteeism counts to HCPHES do so online using a secure, credentialed reporting system called the “Flu Portal.” The “Flu Portal” was developed using freeware, a software platform that is available free of charge, but usually requires a programmer to customize the basic application to conform to a specific set of needs and preferences. The Epidemiology Program at HCPHES spent several months working with a contract programmer to customize the forms needed for ILI data collection from school nurses and hospital infection prevention staff. Each week, an Epidemiologist exports the data into Excel for analysis. The system requires a user account and password for access, and is secure and encrypted.

“Analysis conducted with data collected through the Flu Portal when overlaid to the Texas ILINet data shows that it is a good representation of flu activity in Harris County during Flu Season,” says Dr. Diana Martínez, Program Manager for the Epidemiology Program at HCPHES. While the data does not provide the total impact of influenza on the residents of Harris County, HCPHES is able to compare the weekly ILI activity with data reported by the school nurses for previous school years to determine if a given week in the current season is comparatively more or less active. HCPHES currently has daily absenteeism data for five complete flu seasons; online reporting began with the 2009-2010 flu season. We have been able to maintain high reporting rates from schools in Harris County. Each year we invite all schools to participate in the school-based surveillance system, utilizing the Flu Portal. The percentage of schools reporting consistently has remained high, ranging from 58% to 74% with a five-year average of 66%, through the continued commitment of the school districts in Harris County. Good reporting was defined as schools that reported at least three days for at least 16 weeks out of the Flu Season.

Some lessons learned by HCPHES staff related to the development, implementation and maintenance of this innovative approach to influenza-like-illness reporting, the “Flu Portal” are: 1) Data collected from the school nurses provides a good estimate of influenza activity in Harris County; 2) Median estimates are a better measure to use than means when enough data is available to calculate them reliably; 3) Freeware platforms are a reasonably-priced solution for health departments wishing to develop online reporting capabilities –a) The product is not ready to use - “out of the box;” a programmer is required to initially customize the application according to the specific needs and preferences; b) Additional functionality can be built on as a necessity, although the ability to customize the final application is limited to the constraints of the individual freeware platform being used; 4) Strong, established relationships with school districts and their school nurses is a huge asset to disease surveillance; 5) The “Flu Portal” can be expanded to include the collection of other notifiable conditions; 6) Maintain a maintenance agreement with contact programmer. We are very pleased with the consistent participation of schools in this surveillance system. With this data, HCPHES has a clearer picture of influenza illness among Harris County residents each flu season. Given the vast geographic area our department covers, it is important to have representation from all areas of Harris County.