The US has said it had confirmed 2,532 cases of swine flu, as officials warned more cases and fatalities would come.
With 278 new cases, the Centers for Disease Control and Prevention (CDC) said 44 of the nation's 50 states as well as the capital, Washington, have seen cases of swine flu.
The number of confirmed A(H1N1) cases has spiked dramatically in recent days, with around 600 new cases reported on Friday and Saturday.
The United States has now surpassed Mexico as the world's most affected nation, although the death toll in the United States is significantly lower than that across its southern border.
Mexico has reported 48 deaths from the virus, while the United States' third death was reported on Saturday in northwestern state of Washington. He was a man in his 30s with an underlying heart condition.
The two other victims on US soil were a Mexican child who had traveled to Texas and a woman who had chronic health problems.
Canada and Costa Rica have also reported one death each due to swine flu.