A/H1N1 flu had killed nearly 4, 000 Americans including 540 children since April, the U. S. Centers for Disease Control and Prevention (CDC) said on Thursday.

The flu has infected about 22 million Americans and put 98,000 in the hospital since April, according to the CDC. Children account for eight million of the infected, 36,000 of those hospitalized.

The new estimates are extrapolations based on detailed data for April-October from 10 states, the CDC said, adding that the new figures didn't mean H1N1 flu suddenly got worse.

The CDC also stressed that the estimated ranges of case, hospitalizations and deaths generated by this method provide a sense of scale in terms of the burden of disease caused by H1N1. However, the methodology was "not a predictive tool and cannot be used to forecast the number of cases, hospitalizations and deaths that will occur going forward over the course of the pandemic because they are based on actual surveillance data."