Table 6. Incidence of active tuberculosis in household contacts and IFNγ production levels at baseline.

IFNγ production*	N	Cases	Percentage of TB cases	Incidence Proportion	Person-years	Incidence Rate (#/1000 person-years)
Negative	666	7	21.2	1.05	1686.9	4.1
Low	338	6	18.2	1.78	857.9	7.0
Medium	688	12	36.4	1.74	1798.1	6.7
High	281	8	24.2	2.85	703.5	11.4
Total Positive †	1307	26	78.8	1.99	3359.6	7.7

*Negative: <22pg/mL, Low: 22–99 pg/mL Medium: 100–999 pg/mL, High: ≥1000 pg/mL.

†Total positive: (Negative + Low + Medium + High).