The (potentially) worst flu season in nearly a decade, mapped

The United States' current influenza season is poised to be the worst in nearly a decade, as tens of thousands of patients seek care for flulike symptoms at U.S. hospitals and at least 37 U.S. children have died from the flu, according to the latest CDC data.

Traveling this winter? How to avoid the flu when you fly.

CDC's Weekly Influenza Surveillance Report, which the agency updated Friday, includes data reported through Jan. 20.

Flu activity

CDC said as of Jan. 20, every state had reported evidence of the flu virus. Hawaii and the District of Columbia have reported "local" flu activity, while the rest of the country has reported widespread activity, according to CDC.

Below is a map of report flu activity in the United States for the week ending in Jan. 20:

According to CDC, the percentage of patients who visited the doctor for flu-like symptoms increased to 6.6%, which is the highest level of activity recorded since the 2009 pandemic year, when such visits peaked at 7.7%, MedPage Today reports.

In addition, the data show a total of 11,965 U.S. residents have been hospitalized with laboratory-confirmed cases of the flu between Oct. 1, 2017, and Jan. 20. That amounts to an overall hospitalization rate of 41.9 per 100,000 population—which is comparable to the hospitalization rate of the swine-flu pandemic in 2009 and the 2014-2015 flu season, the Washington Post's "To Your Health" reports.

According to the data, hospitalization rates for the flu are highest among U.S. residents over the age of 65, while those between ages 50 to 64 have the second-highest hospitalization rate so far this season.

CDC officials said there have been 37 reported pediatric deaths from the flu so far this flu season, but added that the total number of pediatric flu deaths could be twice that number due to reporting delays.  CDC officials said the pediatric death count for this season is likely to reach—or possibly exceed—the 148 deaths recorded during the 2014-2015 flu season.

Overall, Dan Jernigan, who lead's CDC's flu division, said influenza-related deaths for this season have risen above the epidemic threshold, increasing to 9.1% of all reported deaths in the United States, MedPage Today reports.

Why is this flu season so bad?

Jernigan said this year's flu season is distinct from others because it reached nearly all U.S. states at the same time and has remained at a high level nationally for three consecutive weeks. The flu in previous years appeared in different regions of the United States at varying times. Jernigan said the rise in flu cases in January probably is linked to children returning to school and spreading the virus.

CDC officials said other factors contributing to the rise in flu cases include this season's flu strains and vaccination rates. Officials said vaccination rates among U.S. adults younger than 65 are lower than vaccination rates among those 65 and older.

According to "To Your Health", public health experts are continuing to remind U.S. residents that it is not too late to receive a flu vaccination to protect against the three most prevalent strains—H1N1, H3N2, , and an influenza B strain—this season. CDC is recommending that all U.S. residents six months or older receive an injectable flu vaccine as soon as possible.

Flu season strains providers

The flu season has strained various health care providers, who are working to treat influxes of patients seeking care for flu symptoms, Becker's Clinical Leadership & Infection Control reports.

For example, as of Jan. 23, Cleveland Clinic and its regional hospitals had admitted more than 930 patients with flu symptoms, which is the largest number of inpatients the hospital has had for flu since the 2014-15 influenza season. As result, the health system is advising patients with nonemergency flu symptoms to use the system's telemedicine services, Cleveland Clinic Express Care Online, for care. Cleveland Clinic has treated more than 190 patients with flu symptoms over telemedicine services this flu season.

Meanwhile, Lehigh Valley Health Network set up tents with 12 beds each, outside of its main emergency department (ED) at both its Allentown and Bethlehem campuses in Pennsylvania to serve as a mobile point of care for patients with flu symptoms.

SSM Health St. Clare Hospital in Missouri opened its emergency overflow wing, outpatient centers, and surgical holding centers to treat patients with flu symptoms. The hospital also had nurses from various floors of the hospital come and care for flu patients. Caregivers were offered an increased hourly rate for overtime work, but the hospital remains short-staffed as many nurses have gotten the flu, Becker's Clinical Leadership & Infection Control reports.

Other hospitals are implementing visitor restrictions to contain the spread of the flu. For instance, Kaiser Permanente Los Angeles Medical Center is temporarily placing restrictions on patient visits from children ages 14 and under or anyone with flu symptoms.

Some say flu season might be peaking

Experts have said it is difficult to predict the length and severity of this—or any—flu season, but they often look at previous flu seasons with similar flu strains to make estimates, "To Your Health" reports. Flu activity in previous H3N2-dmoniated seasons remained active for an average of nearly 16 weeks, but in some instances, lasted 20 weeks. Jernigan said, "By that measure, we are about halfway there, but it means we have several more weeks of flu to go."

Adam Leisy—head of the ED at the West Boca Medical Center in Florida, which recently has seen a rise in patients—said this flu season "may be peaking, but who knows what the next few weeks will bring." Leisy said the hospital has seen a particular  increase in elderly patients who already have chronic conditions, but now are dealing with fevers and wheezing from coughs  (Walker, MedPage Today, 1/26; Painter, USA Today, 1/26; Grayson/Stein, "Shots," NPR, 1/26; AP/Modern Healthcare, 1/26; Sun/Wan, "To Your Health," Washington Post, 1/26; Bean, Becker's Clinical Leadership & Infection Control, 1/26).

Traveling this winter? How to avoid the flu when you fly.

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