12.5.2  ‘Doubling of cases in a week method’

Doubling of the number of malaria cases in a given week compared to the same week in the previous year is another method used to detect epidemics early. You can use this method when you have less than five years of previous data (see Table 12.3). For example, if you only have data from 2003 that is broken down into weeks, you can compare data from the current year (2004, in this example) with the number of cases in the same week from the previous year, 2003. That is, you should compare Week 1 of 2003 with Week 1 of 2004, and so on.

You declare an epidemic if the number of cases in a particular week is double, or more than double, the number of cases in the same week of the previous year. For example in the data shown in Table 12.3, the data cases are doubled, or more than that, in Weeks 4 and 5.

Table 12.3  The weekly number of malaria cases for 2003 and 2004 (EC).

Week No.2003This year (2004)
Week 12019
Week 22220
Week 33535
Week 43774
Week 53675
Week 63038
Week 72929
Week 83229
...
Week 512033
Week 522531

If you do not have last year’s data, then you can compare last week’s data with this week. If cases become doubled, or more than double, in this week, then you can consider it as an epidemic.

12.5.1  Epidemic monitoring charts using ‘second largest number’ method

12.6  Epidemic control