Table 3.

Multivariate analysis of the risk of occurrence of exacerbation with respect to the presence of stress and infection

			No of exacerbations/No of weeks of follow up
Exacerbation	Risk factor	Relative risk (95% CI)	At high risk	At low risk	P value
First (n=55)	Stress*	2.2 (1.2 to 4.0)	40/1143	15/984	0.014
	Infection**	2.9 (1.6 to 5.1)	20/365	36/1866	<0.001
Second (n=32)	Stress	2.7 (1.2 to 6.0)	20/762	12/1130	0.015
	Infection	2.7 (1.1 to 6.3)	8/253	24/1705	0.023
Third (n=23)	Stress	1.0 (0.4 to 2.5)	12/337	10/352	0.99
	Infection	3.2 (1.3 to 8.1)	9/157	14/568	0.014

Owing to missing diary data weeks could occasionally not be classified for stress (high or low risk). The number of weeks is therefore not always the same for both risk factors (stress and infection).

^*Reported at least once during the preceding four weeks.

^**Week is part of period at risk for infection. Each time a stressful event occurs a period with high risk starts that lasts four weeks. With respect to infections, a period with high risk starts two weeks before the onset of an infection and ends five weeks after the infection. Relative risk represents the relative risk of an exacerbation during these high risk periods.