Seasonal variation of multiple sclerosis exacerbations in Arizona

We studied 178 MS patients and 82 controls for 5 years. A monthly pattern in in the frequency of exacerbations in Arizona differed from the patterns seen in other regions of the world. Exacerbations were most common in warmer months. No explanation for this was found. In this prospective study, the frequency of viral infections in the MS patients was lower than in the controls.