To Örebro University

Background and purpose: Multiple sclerosis (MS) patients are at increased infection risk. Here the influences of susceptibility, severity and surveillance bias on infection-related hospital admission are assessed.

Methods: Swedish registers identified 20 276 patients with MS, matched with 203 951 people from the general population without MS. Risk of first hospital admission for infection and mortality over 36 years was estimated by Poisson regression.

Results: Multiple sclerosis was associated with an increased hospital admission risk for all infections, with an adjusted relative risk (and 95% confidence interval) of 4.26 (4.13-4.40). A proportion of this raised risk was probably due to surveillance and referral bias, although a raised risk remained when MS was compared with other immune-mediated diseases. The 1-month mortality rate following hospital admission for infection was higher in MS patients than in the comparison cohort, with a relative risk of 4.69 (4.21-5.22). There was no clear temporal trend in the results, and risks were higher in males and varied by MS phenotype.

Conclusions: Higher hospital admission rates among MS patients for infection are likely to be due to a combination of surveillance bias, cautious medical management and greater susceptibility to severe infections. MS-related functional limitations may increase infection risk and this should be considered in MS management.