Table 4

Treatment effect of doxycycline compared with placebo for chronic seronegative or reactive arthritis on pain and functional change scores (AIMS2) by chlamydia and streptococcus status

		n		AIMS2 scale^4-150		Change Scores		F test	p^4-151
		n		AIMS2 scale^4-150		Doxycycline	Placebo	F test	p^4-151	Mean difference (95% CI)
CT^4-152positive	11	Pain (3 m)	3.3	1.3	2.1 (−2.7 to 6.8)		0.35
CT unknown	26	Pain (3 m)	2.5	1.1	1.5 (−2.1 to 5.1)		0.41
CT interaction^4-153	37	Pain (3 m)				0.02	0.90
CT positive	11	Functional^4-154 (3 m)	2.3	6.6	−4.3 (−19.9 to 11.1)		0.55
CT unknown	26	Functional (3 m)	3.4	−0.2	3.6 (−3.8 to 10.9)		0.33
CT interaction	37	Functional (3 m)				0.13	0.72

Strep^4-160 positive	6	Pain (3 m)	3.0	0.2	2.8 (−12.6 to 18.2)		0.64
Strep unknown	31	Pain (3 m)	2.7	1.4	1.2 (−1.7 to 4.1)		0.39
Strep interaction	37	Pain (3 m)				0.11	0.74
Strep positive	6	Functional (3 m)	10.0	−0.4	10.4 (−12.3 to 33.1)		0.27
Strep unknown	31	Functional (3 m)	2.7	3.3	−0.6 (−7.8 to 6.7)		0.87
Strep interaction	37	Functional (3 m)				0.98	0.33

↵4-150 AIMS2 = Arthritis Impact Measurement Scales version 2 questionnaire (n=37).
↵4-151 Change score mean difference and 95% confidence interval from unpaired t test.
↵4-152 CT = Chlamydia trachomatis positive by serology (IgA or IgA) or clinical history.
↵4-153 Interaction term analysed in a full factorial ANCOVA model (SPSS).
↵4-154 Composite functional score consists of sum of mobility, walking and bending, self care, and household tasks AIMS2 scales.
↵4-160 Strep = Streptococcus pyogenes antibody positive by slide agglutination.