Point-of-Care Testing as an Influenza Surveillance Tool: Methodology and Lessons Learned from Implementation

Figure 1

Full-season charting of ILI cases and positive rapid influenza tests using statistical process control* of daily proportions in the UUPCRN population for the 2007-08 influenza season. *Solid horizontal lines define the center line, and dashed lines define the upper control limit. Letters on the chart denote particular events: “A” is 1 point above 3 sigma; “C” is 9 points in a row above the center line; “D” is 9 points in a row below the center line; “E” is 6 points in a row that are increasing (or decreasing); “F” is 14 points in a row alternating up and down. ^†7-day smoothed graphs have 2 gaps of 7 days each, corresponding to single day clinic closures for Thanksgiving (Nov 22) and Christmas (Dec 25). ^‡Early alert (Jan 19) was the date of the modeled real-time surveillance alert for positive rapid tests; epidemic onset (Feb 3) was the date when 4 of 5 consecutive days exceeded 1 sigma for positive rapid tests.

(a) Smoothed curve^† for ILI cases (top) and positive rapid influenza tests (bottom)

(b) Full-season charting of daily ILI cases, noting the dates^‡ of the rapid test early alert and epidemic onset

(c) Full-season charting of daily positive influenza rapid test results, noting the dates^‡ of the rapid test early alert and epidemic onset