The prevalence of multiple sclerosis in Israel based on validation of a health care organization database

In Israel there is no registry of multiple sclerosis (MS), thus the prevalence of MS is unknown. Clalit Health Services (CHS) is Israel's largest health care organization. We have developed an algorithm to identify people with MS (PwMS) using CHS database and validated it against a gold-standard diagnosis by expert neurologists. People with a possible diagnosis of MS were identified in CHS database according to ICD-9 code or dispense of MS specific disease modifying treatment (DMT). The electronic medical records (EMRs) of a random sample of 25% of this population, stratified by age and sex were examined to determine positive predictive value (PPV). Another age- and sex- stratified random sample of 15% of pwMS under our care were searched in CHS database to determine database sensitivity (Sn). Finally, a random sample of 40% of people without MS were searched in CHS database to evaluate database specificity (Sp). The best case definition to retrieve pwMS was ICD-9 code 340 as an established diagnosis or at least one dispense of a DMT (PPV = 87%, Sn = 92%, Sp = 90%). Using this definition the prevalence of MS in Israel was 68, 82 and 95 per 100,000 population by the end of 2011, 2016 and 2021, respectively. The prevalence of MS in Israel is rising, in line with the worldwide trend.