This had not always been the case, he said, and has led officials to speculate that heterosexual transmission was increasing as a source of infection.

He later quoted the odds of heterosexual vaginal transmission at 1 in 5 million.

"They want the story on heterosexual transmission and transmission at or before birth."

"In that sort of environment, we can have effective heterosexual transmission," he said.

The incidence of heterosexual transmission is rising in some European countries.

They have persisted in reporting a low rate of heterosexual transmission, month after month.

Almost all were infected through heterosexual transmission, and a majority, he estimates, came to him with a history of sexually transmitted disease.

The new definition does not affect the rate of increase by heterosexual transmission.

However, there is clear evidence of a significant rise in heterosexual transmission.

Three-quarters of all the cases would have resulted from heterosexual transmission.