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BACKGROUND: Since 2004, invasive methicillin-resistant Staphylococcus aureus(MRSA) in Tennessee has been reportable to two population-based (PB) surveillance systems, the National Electronic Disease Surveillance System Base System (NBS) and the Emerging Infections Program (EIP) (Davidson County only). Starting July 2010, hospitals were required to report MRSA bloodstream infections (BSI) from emergency departments and inpatient units to the facility-based (FB) National Healthcare Safety Network (NHSN). FB-NHSN data are not direct measures of MRSA at the population level with 10.5% of hospital admissions in Tennessee hospitals from out-of-state residents. We developed a PB-surveillance metric for MRSA-BSIs from NHSN and hospital admissions data contained in the Tennessee Joint Annual Report for comparison to NBS and EIP MRSA surveillance in Tennessee.
METHODS: The case definition of MRSA BSI used for each surveillance measure was a unique positive MRSA result from blood without a prior positive result in the past 30 days. The PB-NHSN metric was calculated by applying the distribution of the patient population by county to the LabID event total for each Tennessee facility. Results were summed for each county at each facility in Tennessee and aggregated to provide regional and state level incidence estimates. The similarity between surveillance metrics was assessed using crude rate ratios and Pearson correlation coefficients.
RESULTS: The PB-NHSN metric identified 4,133 MRSA BSIs in Tennessee from January 2011 through December 2012 in comparison to 4,495 and 3,384 BSIs reported from the FB-NHSN measure and NBS, respectively. Both the FB-NHSN metric (p=0.02) and the PB-NHSN metric (p=0.03) at the state level were significantly correlated with NBS by quarter. The PB-NHSN rate was similar and correlated with the NBS rate in 7 of the 13 regions in Tennessee. In Davidson County residents in 2011, PB-NHSN reported 179 cases versus 177 from EIP. In 2012, PB-NHSN reported 154 cases versus 176 from EIP. Neither NBS nor FB-NHSN was statistically similar to EIP either year.
CONCLUSIONS: Both the FB-NHSN and PB-NHSN metric accurately measure the incidence and trend of MRSA BSIs at the state level and in over half of the regions of Tennessee. The PB-NHSN BSI total and rate were comparable to EIP surveillance in Davidson County by quarter and over the course of an entire year. The availability of the FB-NHSN and PB-NHSN metrics to measure the incidence of MRSA BSI at the state and regional level allowed for the removal of the NBS MRSA reporting requirement starting in 2014.