Results of a study of adults with relapsing remitting multiple sclerosis point to a significant association between viral and bacterial infections and increased risk of relapse.

Investigators, in a report in the journal Neurology, note that published epidemiologic environmental observations point to infection as a possible causative factor or trigger in the onset of MS.

“Microorganisms induce strong immune responses specific for their own antigens, but microbial infections can also trigger responses against self-antigens, promoting inflammatory responses,” they point out.

“Since no single microorganism has been identified as a clear etiologic agent in MS, a more likely explanation for the epidemiologic environmental observations is that infections introduce a proinflammatory bias in immune responsiveness in MS patients that is capable of triggering disease activity and exacerbations.”

Dr. Jorge Correale from Raul Carrea Institute for Neurological Research in Buenos Aires, Argentina, and colleagues say their study supports this line of thinking.

The researchers followed 60 MS patients who were instructed to report as soon as they experienced symptoms of an infection.

The team found a threefold increase in the rate of MS exacerbations during the “at-risk period” ranging from 2 weeks prior to 5 weeks after the onset of symptoms of infection, compared with time periods outside this window.

Any MS attack during the at-risk period was considered temporally related to the infection.

When a narrower “at-risk” time window was considered around infection (2 weeks prior to 2 weeks after symptom onset), the risk of MS exacerbation was elevated fourfold.

“Viral and bacterial infections were equally associated with exacerbations,” Dr. Correale and colleagues note.

The researchers also observed a significant increase in disease activity on magnetic resonance imaging among 20 patients who underwent serial imaging studies, as well as increased T cell activation and proinflammatory cytokine concentrations during infection-related MS exacerbations.

Relapses temporally linked to systemic infection caused more severe and sustained deficit than exacerbations with onset outside the at risk window, the researchers also report.

SOURCE: Neurology, August 22, 2006.