Function memintensity is used to calculate the thresholds for influenza activity
using historical records (surveillance rates).
This method is based on the Moving Epidemics Method (MEM) used to monitor influenza
activity in a weekly surveillance system.
Number of epidemic values used to calculate the intensity thresholds.
i.seasons
Maximum number of seasons to use.
Details
Input data is a data frame containing rates that represent historical influenza surveillance
data. It can start and end at any given week (tipically at week 40th), and rates can be
expressed as per 100,000 inhabitants (or per consultations, if population is not
available) or any other scale.
MEM is used to locate the epidemic for each season. Then confidence intervals are
calculated at different levels.
The parameter i.levels, define the three levels of the confidence intervals
used to calculate thresholds.
The i.n.max parameter indicates how many epidemic values to use to calculate
the thresholds. A value of -1 indicates the program to use an appropiate number of
points depending on the number of seasons provided as input.
The i.seasons parameter indicates how many seasons are used for calculating
thresholds. A value of -1 indicates the program to use as many as possible. If there
are less than this parameter, the program used all seasons avalaible.
Intensity thresholds and Epidemic threshold defines 5 levels of intensity:
Medium level - Above low intensity threshold and below medium
intensity threshold.
4
High level - Above medium intensity threshold and below high
intensity threshold.
5
Very high level - Above high intensity threshold.
Value
memintensity returns a list with three objects, two of them are the parameters
used (param.levels and param.seasons) and the third one
(intensity.thresholds) is a matrix 1x4 with the epidemic and intensity thresholds.
1
Epidemic threshold.
2
Low intensity threshold.
3
Medium intensity threshold.
4
High intensity threshold.
Author(s)
Jose E. Lozano Alonso <lozalojo@jcyl.es>.
References
Vega T., Lozano J.E. (2004) Modelling influenza epidemic - can we detect the beginning
and predict the intensity and duration? International Congress Series 1263 (2004)
281-283.
Vega T., Lozano J.E. (2012) Influenza surveillance in Europe: establishing epidemic
thresholds by the Moving Epidemic Method. Influenza and Other Respiratory Viruses,
DOI:10.1111/j.1750-2659.2012.00422.x.
Examples
## Castilla y Leon Influenza Rates data
data(flucyl)
## Finds the timing of the first season: 2001/2002
intensity<-memintensity(flucyl)
intensity