S. J. Carlson, C. B. Dalton, M. T. Butler, J. Fejsa, E. Elvidge, and D. N. Durrheim, “Flutracking weekly online community survey of influenza-like illness annual report 2011 and 2012”, Commun Dis Intell (2018), vol. 37, pp. 398–406, Dec. 2013.