Table 3. Comparison of the performance of detection algorithms following Seasonal Autoregressive-Integrated Moving-Average (SARIMA) smoothing (resulting in fitted and residuals) using gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV) polymerase chain reaction (PCR)-negative submissions from January 1st, 2012, through February 1st, 2014, to monitor porcine delta coronavirus (PDCoV) PCR-positive submissions.
| Alarm algorithms | Model parameters | # monitored weeks | Total alarms | False alarms (%)a | Number of true alarms (starting at June 1st 2013)b | Time (Weeks) to detect PDCoV emergence (February 1st, 2014)c |
|---|---|---|---|---|---|---|
| CUSUM fitted | Initial value of standard error = 0; Number of standard errors to be considered out of control = 5; Number of shifts to be detected = 1 | 51 | 17 | 0 (0%) | 17 | 17 |
| CUSUM residuals | Initial value of standard error = 0; Number of standard errors to be considered out of control = 5; Number of shifts to be detected = 1 | 51 | 0 | NA | NA | NA |
| EARS C1 fitted | Method = C1; Lambda = 0.5; Alpha = 0.001; Baseline = 7 weeks | 51 | 1 | 1 (50%) | 1 | 18 |
| EARS C1 residuals | Method = C1; Lambda = 0.5; Alpha = 0.001; Baseline = 7 weeks | 51 | 3 | 1 (33%) | 2 | 18 |
| EARS C3 fitted | Method = C3; Lambda = 0.5; Alpha = 0.001; Baseline = 11 weeks | 51 | 5 | 0 (0%) | 5 | 17 |
| EARS C3 residuals | Method = C3; Lambda = 0.5; Alpha = 0.001; Baseline = 11 weeks | 51 | 1 | 1 (100%) | NA | NA |
| EWMA fitted | Baseline = 1 years; Lambda = 0.4; Sigma = 3 | 51 | 17 | 0 (0%) | 17 | 17 |
| EWMA residuals | Baseline = 1 years; Lambda = 0.4; Sigma = 3 | 51 | 0 | NA | NA | NA |
| Farrington fitted | Baseline = 1 year; Weeks before and after current week = 3 weeks; Past week weight = 1; Number of past weeks not included = 3; Alpha = 0.05 | 51 | 5 | 0 (0%) | 5 | 5 |
| Farrington Flexible fitted | Baseline = 1 year; Weeks before and after current week = 1 weeks; Weight of past week = 2.58; Number of past weeks not included = 3; Alpha = 0.05 | 51 | 6 | 0 (0%) | 6 | 6 |
a False alarm rate referred to the frequency of incorrect alarms (false positive) divided by the total number of monitored weeks. For PDCoV emergence, given that the true alarms were expected to begin after June 1st, 2013 (8 months earlier than the first PDCoV disease cases on February 1st, 2014), any alarms generated in any weeks between January 2012 and June 2013 were considered false alarms.
b True alarms referred to alarms generated when there was a true increase in weekly negative submissions within the period of monitoring. For PDCoV emergence, the true alarms were expected to begin after June 1st.
c Time to detect an outbreak refers to the number of weeks between the first alarm and the week reporting PDCoV emergence (February 1st, 2014).