An unusual concentration of whooping cough cases has been reported in the Iowa counties of Black Hawk, Clinton, Dallas, Iowa, Keokuk, Linn, Madison, and Polk, where 11 cases have been reported so far. However, health officials say there is not yet any indication that this year's outbreak will grow to be as bad as last year's incident when whooping cough hit 120 people in Johnson County alone. Physicians who suspect whooping cough in their patients are being urged to send samples to the University of Iowa Hygienic Laboratory for testing.