WASHINGTON - At least 28 US states are not following US Centers for Disease Control and Prevention (CDC) guidelines on reporting new COVID-19 cases, half of which saw the trend of new cases increasing in the last week, CNN reported on Tuesday.

Those states are not reporting probable cases, according to the daily case count listed on the CDC's website.

Probable cases are those in which a patient either meets "clinical criteria" and "epidemiological evidence" for an infection but was not tested for COVID-19, meets one of those criterion along with "presumptive laboratory evidence" or meets "vital records criteria" without being tested, according to the CDC.

Some of the most populous states - including California, Florida, New York and Texas - are among those the CDC does not have data from.

This comes as 26 states see an increased or steady rate of new cases, according to the CNN report.

An update on the CDC website on Tuesday said 17,598 new confirmed cases and 550 new deaths were reported in the United States from Monday.