TABLE 5.

Weighted rate of a positive anti-PT IgG result^a by selected characteristics among individuals aged 6 to 49 years, NHANES III, 1991 to 1994

Characteristic	Sample size (no. of individuals)	Estimated population size (in millions)	Weighted rate of a positive anti-PT IgG result (95% CI)b	P valuec
Age (yr) at interview
6-9	621	10.2	6.50 (3.71-10.4)	0.384
10-14	858	14.9	3.16 (1.52-5.74)
15-19	628	10.6	4.42 (1.68-9.26)
20-24	755	16.0	2.76 (1.29-5.11)
25-29	719	16.5	1.86 (0.15-7.41)
30-34	741	18.9	2.28 (0.65-5.64)
35-39	680	18.4	2.68 (0.85-6.27)
40-44	640	18.3	3.94 (1.73-7.58)
45-49	388	11.7	2.34 (0.32-7.87)
Race or ethnicity
Non-Hispanic white	1,672	97.5	3.11 (1.89-4.82)	0.291
Non-Hispanic black	2,127	16.1	3.36 (2.35-4.65)
Mexican-American	1,926	9.2	2.28 (1.63-3.10)
Other	305	12.8	3.80 (0.41-13.6)
Gender
Male	2,666	66.9	3.81 (2.57-5.41)	0.086
Female	3,364	68.7	2.52 (1.95-3.19)
Metro residenced
Yes	3,150	66.8	2.44 (1.72-3.35)	0.053
No	2,880	68.8	3.85 (2.85-5.06)
Poverty indexe
< poverty level	1,754	21.0	3.54 (1.35-7.42)	0.855
≥ poverty level	3,862	108.7	3.22 (2.18-4.58)
No. of persons living in household
1-2	1,092	34.6	3.20 (1.71-5.42)	0.830
3-4	2,527	63.0	2.89 (1.67-4.64)
≥5	2,411	38.0	3.55 (1.83-6.15)
Month of clinical exam
July to September	1,491	47.0	4.31 (2.79-6.32)	0.101
Other	4,539	88.5	2.54 (1.78-3.51)

^aData are for 6,030 serum samples that had valid results by the PT assay.

^bA positive anti-PT IgG result was defined by the cutoff point derived from the mixture model (specificity = 99%), ≥94 EU. The exact binomial CI modified for the NHANES III sampling design (22).

^cWald test for the null hypothesis of no difference in the rate of a positive anti-PT IgG result across subgroups.

^dResidence in central counties of metropolitan areas of more than 1 million population.

^eData on poverty index were missing for 6.9% of the sample.