Risk factors for multiple sclerosis: a case-control study in Israel.

This case-control study was aimed at identifying environmental risk factors for multiple-sclerosis (MS). Ninety-three Israeli-born MS patients identified in country-wide studies and 94 age- and sex-matched controls were interviewed. The questionnaire covered a large span of factors at ages 0, 10 and onset of the disease, with particular emphasis on socioeconomic status (SES) and sanitary conditions (SAN). A significantly larger percentage of patients reported frequent respiratory educational levels than controls. The SES and SAN at age 10 were also systematically higher among patients, but significance was reached only when the frequencies of conditions indicating extremely low values of SES or SAN were compared. It is possible that the protective effect of low SES or SAN on risk of MS can be detected only when living conditions are well below average, as is frequent in developing countries.