Abstract

Background and purpose

To characterize the frequency and risk of serious infections in patients with myasthenia gravis (MG) relative to age/sex/area‐matched comparators.

Methods

This was a population‐based cohort study in Ontario, Canada of patients with newly‐diagnosed MG and 1:4 age/sex/area‐matched general population comparators accrued from 1 April 2002 to 31 December 2015. The main outcome was a serious infection, defined by a primary diagnosis code on a hospitalization or emergency department record. We computed crude overall and sex‐specific rates of infection among patients with MG and comparators, and the frequency of specific types of infection. Adjusted hazard ratios and 95% confidence intervals were estimated using Cox regression.

Results

Among 3823 patients with MG, 1275 (33.4%) experienced a serious infection compared with 2973/15 292 (19.4%) of comparators over a mean follow‐up of over 5 years. Crude infection rates among patients with MG were twice those in comparators (72.5 vs. 35.0 per 1000 person‐years, respectively). The most common infection types were respiratory infections, particularly bacterial pneumonia. After adjustment for potential confounders, MG was associated with a 39% increased infection risk (adjusted hazard ratio, 1.39; 95% confidence intervals, 1.28–1.51).

Conclusions

Patients with MG are at a significantly higher absolute and relative risk of serious infections compared with age/sex/area‐matched comparators. This needs to be considered when selecting MG treatments and when planning vaccination/prophylaxis. Determining whether this risk is due to the use of immunosuppressive medications (vs. MG itself) is an important area for future research.