Stress and infection and the risk of an exacerbation Certain types of psychological stress can suppress immune reactions, leading to an increased susceptibility to infections. 23 This would confound the positive association we found between stress and exacerbations. However, we found no evidence of an increase in infections after stressful events in this study. Stress and infection were independently associated with the risk of exacerbation. It will not be easy to tackle these factors in

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... ual patients, because infections and stressful events cannot simply be eradicated from patients' lives. The knowledge that stressful events are associated with disease activity adds important information to the limited insight that patients and their caregivers have on this unpredictable disease. We thank the late Monica van der Hoven, who performed secretarial and organisational tasks for this study, and to D Dippel for critical reading of the manuscript. Funding: Stichting Vrienden MS Research, the "Preventiefonds," and Erasmus MC Rotterdam. Competing interests: None declared. Ethical approval: The medical ethical committee of Erasmus MC approved the study.