PRELIMINARY REPORT AND OBSERVATIONS ON THE 1956 POLIOMYELITIS OUTBREAK IN CHICAGO: WITH AN EVALUATION OF THE LARGE-SCALE USE OF SALK VACCINE, PARTICULARLY IN THE FACE OF A SHARPLY RISING INCIDENCE

This is a report on Chicago's 1956 poliomyelitis out-break, in which 1,111 cases of poliomyelitis (835, or 75.2%, confirmed paralytic cases and 276, or 24.8%, confirmed nonparalytic cases), including 36 deaths, were reported in Chicago residents in the city of Chicago. The outbreak lasted 16 weeks, and, on the basis of the date of onset of the disease, it started during the week ending June 21, reached its peak during the week ending Aug. 2, and ended during the week ending Oct. 4. (fig. 1). (The terms "outbreak" and "upsurge" are used throughout this report instead of "epidemic," inasmuch as the yardstick that we followed defined an epidemic as "a rate of 35 or more cases per 100,000" population. 1 ) Of the 1,111 cases, virology reports have been received on 651. Of these 651 cases, a poliomyelitis virus has been successfully isolated from 412, and 99% of the viruses isolated