The outbreak of polio in Yemen has swelled to 63 cases, making it one of the worst epidemics in the world, the U.N. health agency said today. The number of cases will probably soon exceed 100, as many more suspected cases are still being investigated, said Oliver Rosenbauer, a spokesman for the World Health Organization's polio eradication campaign. Before the first polio cases in the Middle Eastern country surfaced last month, The Associated Press said Yemen was believed to be to be free of the disease.