Objective: The present study was undertaken to determine the incidence of MS in a health maintenance organization from Buenos Aires, the largest populated area in Argentina.
Methods: Population was all members of a hospital-based health maintenance organization who were affiliated since January 1992 up to December 2007. Each person was followed contributing time at risk since January 1992 or enrollment date to the final date. Patients with definite diagnosis according to Poser's criteria were included. Incidence density was calculated with 95% confidence intervals.
Results: A total of 145,000 patients were followed for a total of 1,021,515 person-years, of whom 18 developed the disease. Incidence density (ID): 1.76 /100 000 person-years (95% CI: 1.1-2.8/100,000 person-years).
Conclusion: The incidence density of 1.76 per 100,000 suggests a low-median risk area for MS. This study constitutes the first of its kind to cover data of MS incidence in Argentina.