Table 6. Median, the 25th and 75th percentile of weekly cases per sentinel medical institution before and after the issuing of a pre-epidemic warning.

		Weekly cases per sentinel medical institution
						Onset week					Other weeks*
		4weeks	3weeks	2weeks	1week		1week	2weeks	3weeks	4weeks
Influenza-like illness	median	0.5	1.1	2.8	6.3	13.6	19.0	20.7	18.0	12.7	0.0
	25th percentile	0.0	0.3	1.3	4.3	11.5	12.6	12.3	8.9	5.9	0.0
	75th percentile	1.4	2.6	4.8	8.2	17.1	27.4	32.5	30.0	23.0	0.1
	number of observation	1,333	1,333	1,333	1,333	1,333	1,332	1,325	1,317	1,308	79,626
Chickenpox	median	2.0	2.0	2.5	2.0	4.5	2.7	3.4	2.7	2.9	0.9
	25th percentile	1.0	1.0	1.7	1.3	4.1	1.7	2.3	1.7	1.8	0.3
	75th percentile	3.0	3.0	3.3	3.0	5.1	3.8	4.9	4.0	4.3	1.8
	number of observation	2,239	2,239	2,239	2,239	2,239	2,220	2,205	2,191	2,184	72,190
Rubella	median	0.0	0.0	0.0	0.0	1.0	0.0	0.0	0.0	0.0	0.0
	25th percentile	0.0	0.0	0.0	0.0	1.0	0.0	0.0	0.0	0.0	0.0
	75th percentile	0.0	0.0	0.0	0.0	1.5	0.3	0.2	0.0	0.0	0.0
	number of observation	154	154	154	154	154	151	150	149	148	90,185
Measles	median	0.0	0.0	0.0	0.0	0.6	0.2	0.2	0.0	0.0	0.0
	25th percentile	0.0	0.0	0.0	0.0	0.5	0.0	0.0	0.0	0.0	0.0
	75th percentile	0.2	0.2	0.3	0.2	0.8	0.5	0.5	0.4	0.5	0.0
	number of observation	1,818	1,818	1,818	1,818	1,818	1,803	1,787	1,779	1,772	75,926
Mumps	median	1.5	1.7	1.7	1.5	3.3	2.0	2.0	2.3	2.0	0.4
	25th percentile	0.8	1.0	1.0	1.0	3.0	1.1	1.3	1.5	1.0	0.0
	75th percentile	2.1	2.3	2.3	2.0	3.8	2.8	3.0	3.3	3.0	1.0
	number of observation	1,444	1,444	1,444	1,444	1,444	1,435	1,421	1,408	1,395	79,159

The data are expressed as median, the 25th and 75th percentile of cases per week per sentinel medical institution.

The number of observations represents the total number of weeks in which indices fall into the various categories.

The period from the beginning of week in April 1999 till the end of week in March 2002 are used for the analysis.

*Other weeks: weeks that exclude the week of onset and before and after the onset of a pre-epidemic warning.