Several cases have occurred in the United States in the past few months.

All six described species occur only in the United States.

Some of the military training would occur in the United States.

But not a single attack has occurred in the United States.

Of course no such change had occurred in the United States at all.

To date, no known cases of dog to human transmission have occurred in the United States.

Thus many security experts believe that it is only a matter of time until another attack occurs in the United States.

This had never occurred anywhere before in the United States.

The crash occurred during the civil rights movement in the United States.

Fewer than ten cases occur annually in the United States.