Surveillance Evaluation of Methicillin-Resistant Staphylococcus Aureus Reporting through the National Electronic Disease Surveillance System Base System in Tennessee

BACKGROUND:  Invasive Methicillin-resistant Staphylococcus aureus (MRSA) is the third-most frequently reported condition in Tennessee.  Since 2004, invasive MRSA has been reportable in Tennessee through the National Electronic Disease Surveillance System Base System (NBS).  In July 2010, positive MRSA blood cultures from Tennessee hospitals were made reportable to the National Healthcare Safety Network (NHSN).  The purpose of the surveillance evaluation was to determine the extent to which invasive MRSA reporting to NBS provides useful and actionable information in addition to NHSN.

METHODS:  Data quality, completeness, and representativeness of key variables were compared between NBS and NHSN.  The case definition for a unique MRSA blood culture was standardized for both surveillance systems to be a patient with a positive MRSA blood culture with no prior positive result in the past 30 days.  Gender, date of birth, and event date were used for a direct case to case comparison between NBS and NHSN. Statewide incidence rates were calculated using U.S. Census data and analyzed for trend using the Pearson correlation coefficient.  Timeliness was compared from specimen collection date to report date in both systems. A convenience sample was used to determine the reporting burden of invasive MRSA to NBS in Tennessee.

RESULTS:  From July 2010 to June 2013, 3,875 unique MRSA blood isolates were reported to both NBS (n=5,126) and NHSN (n=6,626).  NBS had more complete patient name information (100.0% versus 77.4%) but less complete specimen source information (70.1% versus 100.0%) in comparison to NHSN.  Gender, date of birth, and facility name were over 99% complete in both systems. With the exception of the race variable in NBS, other individual MRSA risk factors were not captured in either system.  The median report time for invasive MRSA was 11 days in NBS versus 35 days for all infection events reported to NHSN.  The NBS incidence rate for Tennessee was correlated with the NHSN rate by quarter through January 2011 to June 2013 (p=0.02).  An estimated 400 hours were spent completing invasive MRSA case investigations at the regional health department level.

CONCLUSIONS:  Invasive MRSA surveillance is comparable between NBS and NHSN with regards to variable completeness and the reported incidence over time in Tennessee.  The comparability and reporting burden identified through the surveillance evaluation resulted in the removal of the NBS MRSA reporting requirement and the continuation of the NHSN MRSA reporting requirement in Tennessee.