Evaluating West Nile Virus and Saint Louis Encephalitis Surveillance in Harris County, TX, 2010-2014

BACKGROUND:   West Nile Virus (WNV) and Saint Louis Encephalitis (SLE) are endemic in Texas. While most individuals infected with these arboviruses are asymptomatic, WNV and SLE may cause debilitating neuroinvasive symptoms, thus placing significant burden on healthcare systems. Because of this, it is important to conduct surveillance to monitor the spread of these arboviruses in the population. Having a reliable and sensitive surveillance system helps detect outbreaks, determine geographic areas with high infection rates, and inform mosquito control efforts. The Harris County evaluation of the arbovirus surveillance system ensures every step in the process is functioning optimally from data quality assurance and timeliness to meeting important benchmarks.

METHODS:   The evaluation of the surveillance system follows the guidelines presented in the 2001 MMWR“Updated Guidelines for Evaluating Public Health Surveillance Systems.” Analysis for all WNV, SLE, and unspecified arbovirus cases collected from 2010 through 2014 was conducted to determine data quality, usefulness, representativeness, acceptability, and timeliness. Results helped determine the strengths and weaknesses of the current system.

RESULTS:   From 2010-2014, Harris County received 294 arbovirus reports, but only 46.94% of reports were identified as true cases. 56 reports were referred to other jurisdictions, primarily the Houston Department of Health. Evaluation determined that surveillance for these diseases is important since 78.26% of cases required hospitalization, 61.59% were seen in the ER, and 1 case was fatal. Data is generally complete and of high quality, but race and ethnicity fields continue to have missing data despite increased quality assurance methods. The surveillance process for arboviruses is more complicated than for other conditions due to additional laboratory testing, two surveillance forms, and the need for patient interviews. The complexity of the surveillance compromises timeliness, leading to case closure averages around 19.59 days. Even with the complicated process, 78.83% of cases close within 30 days, meeting the Harris County goal. However, there is also a 30-day goal from the date reported to when CDC receives the final report, and only 38.98% of cases met this criteria due to the timeliness complications occurring at the local level.

CONCLUSIONS:   The evaluation shows that the system meets its main objectives while remaining stable and flexible; however, there is some room for improvement at every stage from reporting to submitting the final investigation. Improving the system will allow for greater efficiency and increased data quality, which will give the county a better sense about the spread of arboviruses every year.