'High': Map shows how many New Yorkers were sick before Christmas gatherings

(NEXSTAR) – Respiratory illness around the country spiked last week, just as families and friends gathered to celebrate the holidays.

Tracking by the Centers for Disease Control and Prevention shows a 16% jump in people testing positive for influenza last week, plus a substantial rise in reports of other respiratory illnesses like COVID-19 and RSV.

New data released Friday, Dec. 29 shows 13 states, plus New York City, have "very high" levels of respiratory illness. New York and 18 other states are classified as "high."

According to the New York State Influenza Surveillance Report from the week ending in Dec. 23, influenza activity was widespread with 40% of 71,329 specimens tested coming out positive, which is a 34% increase from the previous week.

There was also a 20% increase in hospitalized cases compared with the previous week and no influenza-associated pediatric deaths were reported that week.

The map below shows the severity of respiratory illness in every state as of Dec. 23. The darker the red, the higher the spread of sickness.

Seven states are shaded in purple to indicate they are in the highest tier tracked by the CDC, level 13: Alabama, Georgia, Louisiana, Mississippi, New Mexico, South Carolina, and Tennessee. Just three weeks ago, no states or jurisdictions were in that category. (See more from the CDC's interactive map here.)

The CDC determines each state’s level of flu activity by comparing the current data from healthcare providers to what’s normal for that area outside of flu season.

The data is based on the number of people reporting to a health care facility with flu symptoms – fever, cough, or sore throat. It is not based on lab-confirmed influenza cases.

That means it could include cases that turn out to be other respiratory illnesses, like COVID or RSV. Still, it also could be underreporting cases where people are staying home and fighting the sickness on their own.

The three major viral illnesses listed above – COVID-19, RSV, and influenza – have many overlapping symptoms, making it hard to know what you have without a test. (We compare the symptoms here to help you narrow it down.)

The flu, which is especially dangerous for the elderly, immunocompromised people, and young children, has killed an estimated 4,500 so far this season. Twenty of those deaths were children.

The Associated Press contributed to this report.