OBJECTIVES: We evaluated the implementation of three commercially available 
neuraminidase inhibition assays in a public health laboratory (PHL) setting. We 
also described the drug susceptibility patterns of human influenza A and B 
circulating in Maryland during the 2011-2012 influenza season.
METHODS: From January to May 2012, 169 influenza virus isolates were tested for 
phenotypic susceptibility to oseltamivir, zanamivir, and peramivir using 
NA-Fluor(TM), NA-Star®, and NA-XTD(TM) concurrently. A 50% neuraminidase 
inhibitory concentration (IC50) value was calculated to determine drug 
susceptibility. We used the standard deviation based on the median absolute 
deviation of the median analysis to determine the potential for reduced drug 
susceptibility. We evaluated each assay for the use of resources in high- and 
low-volume testing scenarios.
RESULTS: One of the 25 2009 influenza A (H1N1) pandemic isolates tested was 
resistant to oseltamivir and peramivir, and sensitive to zanamivir, on all three 
platforms. Eighty-two influenza A (H3N2) and 62 B isolates were sensitive to all 
three drugs in all three assays. For a low-volume scenario, NA-Star and NA-XTD 
took 120 minutes to complete, while NA-Fluor required 300 minutes to complete. 
The lowest relative cost favored NA-Star. In a high-volume scenario, NA-Fluor 
had the highest throughput. Reagent use was most efficient when maximizing 
throughput. Cost efficiency from low- to high-volume testing improved the most 
for NA-Star.
CONCLUSIONS: Our evaluation showed that both chemiluminescent and fluorescent 
neuraminidase inhibition assays can be successfully implemented in a PHL setting 
to screen circulating influenza strains for neuraminidase inhibitor resistance. 
For improved PHL influenza surveillance, it may be essential to develop 
guidelines for phenotypic drug-resistance testing that take into consideration a 
PHL's workload and available resources.