Master mixes were prepared at room temperature for each reaction immediately before use with either 6.25 or 10 μl, respectively, of the WarmStart Colorimetric RT-LAMP 2X Master Mix (M1800, New England Biolabs) and 1.25 or 2 μl, respectively, of the 10× primer mix, filled up to 11.5 or 19 μl with nuclease-free water (AM9937, Ambion).