In how many districts was the incumbent Estes Kefauver? 
CREATE TABLE "table1_1342270_42" (
  "district" text,
  "incumbent" text,
  "party" text,
  "first_elected" real,
  "result" text,
  "candidates" text
);
SELECT COUNT("district") FROM "table1_1342270_42" WHERE "incumbent"='Estes Kefauver';