Table 1. Comparison of performance indicators for measles case-based surveillance in Viet Nam before and after the mass measles immunization campaign.

Performance indicator by zone	Before the campaigna	After the campaignb	P-value from provincal analysisc	P-value from regional and nationwide analysesd
Case investigation ratee (%)
North	686 of 9 365 (7)	196 of 228 (86)	0.002	< 0.001
South	1418 of 4 736 (30)	435 of 696 (63)	0.036	< 0.001
Nationwide	2104 of 14 101 (15)	631 of 924 (68)	< 0.001	< 0.001
Specimen collection ratef (%)
North	317 of 9 365 (3)	157 of 228 (69)	< 0.001	< 0.001
South	746 of 4 736 (16)	392 of 696 (56)	< 0.001	< 0.001
Nationwide	1063 of 14 101 (8)	549 of 924 (59)	< 0.001	< 0.001
Febrile rash cases reported but discarded as non-measles per 100 000 populationg
North	0.20	0.41	0.112	NA
South	0.19	1.01	< 0.001	NA
Nationwide	0.20	0.74	< 0.001	NA
Proportion of silent provincesh (%)
North	1 of 28 (4)	9 of 28 (32)	NA	0.005
South	4 of 33 (12)	4 of 33 (12)	NA	1.000
Nationwide	5 of 61 (8)	13 of 61 (21)	NA	0.041

NA, not applicable.
^a 2001 in the north of Viet Nam and 2002 in the south of Viet Nam.
^b 2003 in the north of Viet Nam and 2004 in the south of Viet Nam.
^c P-value derived using the Wilcoxon signed-rank test for the difference between the median values of the indicators before and after the campaign in each province.
^d P-value derived using Fisher’s exact test for the difference in indicator values recorded before and after the campaign.
^e Proportion of cases investigated among the total number of suspected measles cases reported.
^f Proportion of cases for which a serum specimen was collected among the total number of suspected measles cases reported.
^g The figures do not include suspected cases that were reported but not classified because there was no case investigation.
^h Proportion of provinces that did not report even one suspected measles case.