TABLE 1.

Analysis of association between loci in 59 H. pylori isolates from family members^a

Isolate group	Isolates				PCR-RFLP types only
	No.	X	IA	P	No.	X	IA	P
vacA s1 type	44	6.83	0.61	<0.001	16	7.67	1.64	<0.001
vacA s2 type	10	4.02	0.78	>0.05	3	6.00	0	>0.05
vacA m1 type	34	6.05	0.99	<0.001	11	7.58	2.52	<0.001
vacA m2 type	25	6.51	0.24	>0.05	10	7.00	1.36	0.001
cagA positive	34	6.78	0.36	>0.05	13	7.89	1.66	<0.001
cagA negative	25	5.88	1.59	<0.001	9	6.64	2.92	<0.001
From antrum	27	7.13	0.74	<0.001	19	7.60	1.14	<0.001
From corpus	26	6.90	0.22	>0.05	16	7.44	0.50	>0.05
All	59	6.80	0.43	<0.01	21	7.58	1.42	<0.001

^aX, mean number of allelic mismatches between pairs of H. pylori isolates or between PCR-RFLP types; I_A, index of association between loci; P, probability based on the Monte Carlo procedure. Values of I_A that differ significantly from zero indicate a clonal structure in bacterial populations, with rare or absent recombination. In contrast, values of I_A that do not differ significantly from zero indicate a panmictic structure, with frequent recombination.