Multiple sclerosis (MS) patients have a greater risk of infections, particularly urinary and kidney infections, around the time of their diagnosis, compared with individuals without MS, a large Swedish population-based study found.
Rates of serious and non-serious infections, as well as infections caused by bacteria, virus, and fungus, also were higher in these patients, researchers reported.
The study, “Infections in patients with multiple sclerosis: A national cohort study in Sweden,” was published in the journal Multiple Sclerosis and Related Disorders.
Compared to the public at large, MS patients are thought to be at increased risk of infections because MS disease-modifying therapies used to lower relapse rates act by dampening the immune system.
But studies investigating the rates of incident infections in MS patients are rare.
Researchers in Sweden now have conducted a large population-based study to determine the rates of infections before and after an MS diagnosis, compared with matched individuals without MS. Their analysis was categorized by age and sex.
In total, the study included 6,602 adult MS patients, diagnosed from 2008 to 2016, and 61,828 controls without MS, who were matched to patients in terms of age, sex, and region (county) of residence at the time of MS diagnosis. For each patient, about 10 matched controls were included in the analysis.
Results showed that in the year before their diagnosis, MS patients already had a significantly higher rate of infections, including those of the urinary tract and kidneys, respiratory and throat infections, meningitis and encephalitis, bacterial infectious diseases, and herpes virus infections.
Among MS patients, urinary and kidney infections were more common in women and in patients age 60 or older. Respiratory and throat infections also were more common in women.
Investigators then assessed the rate of first infections occurring after the MS diagnosis, and whether some specific infections were more common in MS patients. This last assessment was done via the incidence rate ratio (IRR), which compares incidence rates in two distinct populations.
Of note, an IRR of 1 means an identical incidence rate in both populations; greater than 1 means the incidence is greater in MS patients, and lower than 1 defines a greater incidence in controls.
Like in the year prior to their diagnosis, MS patients also had significantly more first infections after their diagnosis compared with controls. The incidence of serious infections was 2.5 times higher in patients than in controls, and non-serious first infections were 1.6 times more common in patients.
MS patients had a greater incidence of many kinds of first infections, including skin, respiratory and throat infections, pneumonia and influenza, bacterial, viral, and fungal infections. The greatest difference in incidence, however, was seen for urinary and kidney infections, which were 2.44 more common in patients.
All the aforementioned infections, except skin infections, had higher IRR in men than in women with MS. Meningitis and encephalitis, two inflammations of the brain, were greater only in MS patients younger than 60.
The cumulative incidence — essentially the proportion of patients who developed an infection within a certain period of time — of urinary and kidney infections, skin infections, respiratory and throat infections, pneumonia and influenza, meningitis and encephalitis, bacterial and viral infections, also was greater for MS patients in the first five years within their diagnosis and in the five years that followed, compared to controls.