A company making “smart thermometers” that upload body temperatures to its website claims to be tracking this year’s flu season faster and in greater geographic detail than public health authorities can.

This year’s flu season — which the Centers for Disease Control and Prevention considers “moderately severe” — has left Missouri and Iowa the “sickest states in the country,” said Inder Singh, the founder of Kinsahealth.com.

California has had its worst outbreak in five years, with nearly 1 percent of the state exhibiting flu symptoms on Jan. 2, he added. By contrast, New York, New England and the Southeast have had relatively mild seasons so far, but cases are rising and should peak in two weeks.

Mr. Singh’s data paints a different picture from that of the C.D.C., which held a news conference Friday to announce that flu activity was “widespread” across the continental United States, which is unusual. (Hawaii’s outbreak is smaller, the agency said.)