TABLE 2.

Frequencies of positive pertussis cases in different age groups by culture and/or RT-PCR and serology (PT-ELISA)

Characteristic	Group 1 (<1 yr)	Group 2 (1–6 yr)	Group 3 (≥7 yr)
No. of pertussis-positive cases/total no. of cases	101/260	31/81	94/162
No. (%) of positive cases by culture and/or RT-PCR	61 (60.4)a	2 (6.4)	3 (3.2)
No. (%) of positive cases by PT-ELISA	18 (17.8)	25 (80.6)	81 (86.2)
No. (%) of positive cases by combined assaysb	22 (21.8)	4 (13)	10 (10.6)
No. of seronegative cases	150	47	62
Pc	<0.0001	<0.0001	<0.0001

^aPercentages were calculated with positive specimens by at least one test.

^bCombined assays: culture and/or RT-PCR and PT ELISA.

^cCulture and/or RT-PCR versus PT-ELISA.