Table 5.

Serological follow-up of cases and controls

Possible chronic Q fever			Possible chronic Q fever
Antibody titers on the 24 thmonth after acute Q fever diagnosis	IgG phase I	IgG phase II	Antibody titers on the 36 thmonth after acute Q fever diagnosis	IgG phase I	IgG phase II
<1:32	0 (0.0%)	0 (0.0%)	<1:32	0 (0.0%)	0 (0.0%)
1:32 - 1:128	2 (7.4%)	0 (0.0%)	1:32 - 1:128	1 (4.8%)	0 (0.0%)
1:256 - 1:512	7 (25.9%)	2 (7.4%)	1:256 - 1:512	7 (33.3%)	3 (14.3%)
1:1,024 - 1:2,048	12 (44.4%)	13 (48.1%)	1:1,024 - 1:2,048	10 (47.6%)	12 (57.1%)
≥1:4,096	6 (22.2%)	12 (44.4%)	≥1:4,096	3 (14.3%)	6 (28.6%)
IgG phase I			IgG phase II
Antibody titers on the 48 th month after acute Q fever diagnosis	Possible chronic Q fever	No chronic Q fever †	Antibody titers on the 48 th month after acute Q fever diagnosis	Possible chronic Q fever	No chronic Q fever †
<1:32	1 (2.9%)	55 (51.0%)	<1:32	0 (0.0%)	3 (2.8%)
1:32 - 1:128	6 (17.6%)	47 (43.9%)	1:32 - 1:128	0 (0.0%)	31 (29.0%)
1:256 - 1:512	11 (32.4%)	5 (4.7%)	1:256 - 1:512	5 (14.7%)	51 (47.7%)
1:1,024 - 1:2,048	10 (29.4%)	0 (0.0%)	1:1,024 - 1:2,048	19 (55.9%)	19 (17.8%)
≥1:4,096	6 (17.6%)	0 (0.0%)	≥1:4,096	10 (29.4%)	3 (2.8%)
p-value =0.001*			p-value =0.001*

*Chi-square test is used to calculate the p-value.

^†There were three patients without chronic Q fever of which serological data of four years after acute Q fever diagnosis was missing.