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Leading Indicators and the Evaluation of the Performance of Alerts for Influenza Epidemics.

Schanzer DL, Saboui M, Lee L, Domingo FR, Mersereau T - PLoS ONE (2015)

Bottom Line: However, the difference in timing exceeded 1 week and was statistically significant at the significance level of 0.01 in 5 out of 28 regional seasons.After allowing for a reporting delay of 2 weeks, the alert period included 80% of all influenza-confirmed hospitalizations.Though differences in timing were statistically significant, neither time-series consistently led the other.

View Article: PubMed Central - PubMed

Affiliation: Centre for Communicable Diseases and Infection Control, Infectious Disease Prevention and Control Branch, Public Health Agency of Canada, Ottawa, Ontario, Canada.

ABSTRACT

Background: Most evaluations of epidemic thresholds for influenza have been limited to internal criteria of the indicator variable. We aimed to initiate discussion on appropriate methods for evaluation and the value of cross-validation in assessing the performance of a candidate indicator for influenza activity.

Methods: Hospital records of in-patients with a diagnosis of confirmed influenza were extracted from the Canadian Discharge Abstract Database from 2003 to 2011 and aggregated to weekly and regional levels, yielding 7 seasons and 4 regions for evaluation (excluding the 2009 pandemic period). An alert created from the weekly time-series of influenza positive laboratory tests (FluWatch, Public Health Agency of Canada) was evaluated against influenza-confirmed hospitalizations on 5 criteria: lead/lag timing; proportion of influenza hospitalizations covered by the alert period; average length of the influenza alert period; continuity of the alert period and length of the pre-peak alert period.

Results: Influenza hospitalizations led laboratory positive tests an average of only 1.6 (95% CI: -1.5, 4.7) days. However, the difference in timing exceeded 1 week and was statistically significant at the significance level of 0.01 in 5 out of 28 regional seasons. An alert based primarily on 5% positivity and 15 positive tests produced an average alert period of 16.6 weeks. After allowing for a reporting delay of 2 weeks, the alert period included 80% of all influenza-confirmed hospitalizations. For 20 out of the 28 (71%) seasons, the first alert would have been signalled at least 3 weeks (in real time) prior to the week with maximum number of influenza hospitalizations.

Conclusions: Virological data collected from laboratories was a good indicator of influenza activity with the resulting alert covering most influenza hospitalizations and providing a reasonable pre-peak warning at the regional level. Though differences in timing were statistically significant, neither time-series consistently led the other.

No MeSH data available.


Related in: MedlinePlus

a) Weekly number of influenza positive tests and influenza admissions to hospital for the Ontario, 2010/11 season. b) Corresponding cumulative distribution functions (CDF).In this example, influenza admissions peaked in the last week of 2010 and first week of 2011, a time when resource planning can be more critical. The alert set based on laboratory data for the week of Nov 21 and available operationally the week of Dec 5, would have provided a 3 week notice of peak influenza activity.
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pone.0141776.g006: a) Weekly number of influenza positive tests and influenza admissions to hospital for the Ontario, 2010/11 season. b) Corresponding cumulative distribution functions (CDF).In this example, influenza admissions peaked in the last week of 2010 and first week of 2011, a time when resource planning can be more critical. The alert set based on laboratory data for the week of Nov 21 and available operationally the week of Dec 5, would have provided a 3 week notice of peak influenza activity.

Mentions: The alert was set for week t if at least 15 influenza positive tests were observed for week t and the corresponding positivity rate was at least 5% (i.e. at least 300 specimens were tested in week t and 15 or 5% or more were positive). At any point in time, the most current influenza surveillance report is usually available for the period dated 2 weeks earlier. To allow for this delay in reporting and processing, a 2 week operational delay was assumed. That is, if the first alert was set based on laboratory reports for week 1, we assumed that the alert would be announced early in week 3, and preparations could begin in week 3. As gaps were more likely to occur at the beginning or end of the alert period when numbers were small, we waited one week before turning the alert off in order to improve the continuity of the alert period. The influenza hospitalizations for week t+2 (date of admission) were considered to be included in the alert period if the alert was set based on the virological data for week t or t-1. The length of the alert period is the time from the first to last alerted week (including any gaps). The length of the pre-peak period was calculated from the presumed week of first announcement (week of the first alert +2) to the week with the seasonal maximum number of hospitalizations by week of admission. All statistics were calculated based on the alert status as would have been reported in the most recent surveillance report available at the time of hospitalization. As well, the alerted weeks flagged in Figs 1–6 were adjusted for this 2 week operational delay. The first and last alerted weeks do not necessarily correspond to the beginning and end of the epidemic period as generally defined elsewhere to be periods in excess of what is normally expected (usually in reference to ILI surveillance). In using virological data for the alert, the ultimate objective is to provide some advanced warning of an emerging epidemic prior to observing an excess case load.


Leading Indicators and the Evaluation of the Performance of Alerts for Influenza Epidemics.

Schanzer DL, Saboui M, Lee L, Domingo FR, Mersereau T - PLoS ONE (2015)

a) Weekly number of influenza positive tests and influenza admissions to hospital for the Ontario, 2010/11 season. b) Corresponding cumulative distribution functions (CDF).In this example, influenza admissions peaked in the last week of 2010 and first week of 2011, a time when resource planning can be more critical. The alert set based on laboratory data for the week of Nov 21 and available operationally the week of Dec 5, would have provided a 3 week notice of peak influenza activity.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4626042&req=5

pone.0141776.g006: a) Weekly number of influenza positive tests and influenza admissions to hospital for the Ontario, 2010/11 season. b) Corresponding cumulative distribution functions (CDF).In this example, influenza admissions peaked in the last week of 2010 and first week of 2011, a time when resource planning can be more critical. The alert set based on laboratory data for the week of Nov 21 and available operationally the week of Dec 5, would have provided a 3 week notice of peak influenza activity.
Mentions: The alert was set for week t if at least 15 influenza positive tests were observed for week t and the corresponding positivity rate was at least 5% (i.e. at least 300 specimens were tested in week t and 15 or 5% or more were positive). At any point in time, the most current influenza surveillance report is usually available for the period dated 2 weeks earlier. To allow for this delay in reporting and processing, a 2 week operational delay was assumed. That is, if the first alert was set based on laboratory reports for week 1, we assumed that the alert would be announced early in week 3, and preparations could begin in week 3. As gaps were more likely to occur at the beginning or end of the alert period when numbers were small, we waited one week before turning the alert off in order to improve the continuity of the alert period. The influenza hospitalizations for week t+2 (date of admission) were considered to be included in the alert period if the alert was set based on the virological data for week t or t-1. The length of the alert period is the time from the first to last alerted week (including any gaps). The length of the pre-peak period was calculated from the presumed week of first announcement (week of the first alert +2) to the week with the seasonal maximum number of hospitalizations by week of admission. All statistics were calculated based on the alert status as would have been reported in the most recent surveillance report available at the time of hospitalization. As well, the alerted weeks flagged in Figs 1–6 were adjusted for this 2 week operational delay. The first and last alerted weeks do not necessarily correspond to the beginning and end of the epidemic period as generally defined elsewhere to be periods in excess of what is normally expected (usually in reference to ILI surveillance). In using virological data for the alert, the ultimate objective is to provide some advanced warning of an emerging epidemic prior to observing an excess case load.

Bottom Line: However, the difference in timing exceeded 1 week and was statistically significant at the significance level of 0.01 in 5 out of 28 regional seasons.After allowing for a reporting delay of 2 weeks, the alert period included 80% of all influenza-confirmed hospitalizations.Though differences in timing were statistically significant, neither time-series consistently led the other.

View Article: PubMed Central - PubMed

Affiliation: Centre for Communicable Diseases and Infection Control, Infectious Disease Prevention and Control Branch, Public Health Agency of Canada, Ottawa, Ontario, Canada.

ABSTRACT

Background: Most evaluations of epidemic thresholds for influenza have been limited to internal criteria of the indicator variable. We aimed to initiate discussion on appropriate methods for evaluation and the value of cross-validation in assessing the performance of a candidate indicator for influenza activity.

Methods: Hospital records of in-patients with a diagnosis of confirmed influenza were extracted from the Canadian Discharge Abstract Database from 2003 to 2011 and aggregated to weekly and regional levels, yielding 7 seasons and 4 regions for evaluation (excluding the 2009 pandemic period). An alert created from the weekly time-series of influenza positive laboratory tests (FluWatch, Public Health Agency of Canada) was evaluated against influenza-confirmed hospitalizations on 5 criteria: lead/lag timing; proportion of influenza hospitalizations covered by the alert period; average length of the influenza alert period; continuity of the alert period and length of the pre-peak alert period.

Results: Influenza hospitalizations led laboratory positive tests an average of only 1.6 (95% CI: -1.5, 4.7) days. However, the difference in timing exceeded 1 week and was statistically significant at the significance level of 0.01 in 5 out of 28 regional seasons. An alert based primarily on 5% positivity and 15 positive tests produced an average alert period of 16.6 weeks. After allowing for a reporting delay of 2 weeks, the alert period included 80% of all influenza-confirmed hospitalizations. For 20 out of the 28 (71%) seasons, the first alert would have been signalled at least 3 weeks (in real time) prior to the week with maximum number of influenza hospitalizations.

Conclusions: Virological data collected from laboratories was a good indicator of influenza activity with the resulting alert covering most influenza hospitalizations and providing a reasonable pre-peak warning at the regional level. Though differences in timing were statistically significant, neither time-series consistently led the other.

No MeSH data available.


Related in: MedlinePlus