Flu By the Numbers: December 3, 2022

The CDC has started reporting influenza activity in the United States. In any flu season, the data that is reported each week are preliminary and can change as new information becomes available.

Flu activity in the U.S. is very high and increasing. As of December 3, almost every state is reporting high to very high influenza-like illness (ILI) activity.

Some of these cases may not be the flu. There are also respiratory illnesses going around, including COVID-19 and respiratory syncytial virus (RSV).

The number of specimens being tested in clinical labs for the flu, as well as the percentage that are testing positive, is also different compared to last year. Here's an example:

• At the end of week 39 in 2021, clinical labs in the U.S. had tested 41,539 specimens for the flu and about 0.1% tested positive.
• At the end of week 39 in 2022, clinical labs in the U.S. had tested 40,709 specimens for the flu and about 2.5% had tested positive.
• Last year at this time, the percentage of positive flu tests was split almost equally between influenza A and B. This year, almost all of the positive flu tests have been for influenza A.

Centers for Disease Control and Prevention

Flu Testing

For the week ending November 26, clinical laboratories in the U.S. tested 130,584 specimens for flu viruses, of which 25.1% were positive. Among the positive results, 99.6% were for influenza A.

Public health laboratories in the U.S. also reported data about specimen testing to the CDC. Of the 7,447 samples tested, 1,264 were positive for the flu. Influenza A accounted for 99.9% of positive flu cases.

Influenza patterns vary according to the specific flu virus strains that are circulating in a given year, as well as human behavior. For example, some of the changes that the pandemic brought about—such as mask wearing and social distancing—slowed down the flu spread last year.

Another factor that affects flu patterns is vaccination. Annual flu vaccines are a safe and effective way to help curb the spread of the flu and to prevent hospitalizations and deaths.

What Information Do States Report?

The CDC tracks LIL activity levels in each state and presents a weekly flu surveillance report. LIL activity levels are defined as the following:

• Minimal (levels 1-3)
• Low (levels 4-5)
• Moderate (levels 6-7)
• High (levels 8-10)
• Very High (levels 11-13)

State health departments track flu data provided by hospitals, clinics, clinical laboratories, and healthcare organizations. These reports can include information like the number of flu tests conducted, positivity rates, and the number of flu-like illnesses that providers saw in the patients they treated.

What Can The Data Tell Me About Flu Activities In My State?

Data on ILI activity can give you a sense of how many people have respiratory symptoms in your state.

If the ILI activity level where you live is high, it can be a sign that the flu is "going around" in your community. Having this information, you can take preventive steps, such as washing your hands frequently and getting a flu shot, to help reduce your risk of getting sick.

If you have flu-like symptoms, call your provider to see if you should have a test. They might want you to take antiviral medications such as Tamiflu to help reduce your symptoms. While you are sick, wear a mask and stay at home to help keep other people from catching the flu from you.

How Is Flu Data Different From COVID-19 Data?

The flu and COVID-19 are different illnesses, caused by different viruses, that may need different treatments. That said, the flu and COVID can have similar symptoms and can be hard to tell apart without a test.

Some specimens tested for the flu can be tested for COVID at the same time. If a flu test is negative, a person might need to have a COVID test. It's also possible for someone to have both COVID and the flu at the same time.

Testing people who are sick helps providers care for them, but it also helps us get a sense of how the viruses are circulating in our communities and how effective the vaccines for the viruses are.