Norovirus cases have risen in the United States in recent weeks, according to data from the Centers for Disease Control and Prevention.

Nearly 14% of tests for the illness came back positive during the week that ended on Nov. 15, according to CDC data . Over 2,700 tests were conducted that week, according to the CDC, meaning that about 380 cases of norovirus were diagnosed in that period.

That's more than double the percentage of positive tests recorded about three months ago, when test positivity in the U.S. this year was at its lowest. The week that ended on Aug. 9 saw a 6.53% positivity rate of more than 4,240 tests conducted during that period, according to CDC data.

Test positivity is an imperfect metric because it can vary based on the number of tests conducted. The CDC's data i

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