Flu Cases Jump in Florida as First Cold Front Arrives, With State Among Three Worst on National Flu Index

Flu is spreading quickly in Florida just as the season's first real cold snap arrives. State health data show positive flu tests and flu-related emergency room visits rising for several weeks in a row. A national pharmacy index ranks Florida among the three worst states for flu activity. Health experts say cooler weather that sends people indoors could speed up the spread, weeks before the usual winter peak.

The Florida Department of Health's latest weekly Florida Flu Review covers Nov. 1 through Nov. 7. It found that the share of flu tests coming back positive and the share of emergency department visits for flu both increased compared with the previous three-week average. The predominant strain is influenza A H1N1, the same lineage behind the 2009 pandemic.

What the state data show

The Department of Health measures flu trends by comparing each week to the average of the three weeks before it, rather than publishing statewide case totals. Individual flu cases are not reportable in Florida, except for novel flu A infections and flu-associated deaths of children. Outbreaks must be reported.

The two most recent reports show the same upward direction:

The state's flu season formally runs through May 22, 2027, though surveillance continues year round. The department says Florida's respiratory activity usually begins to rise around the start of October and that seasons vary in timing, severity and length. The reports say it is not possible to predict what each season will look like.

Florida near the top of the national flu index

WUSF reported on Nov. 13 that Florida's most recent Walgreens Flu Index score was 6.35, compared with a national score of 3.6. Only Washington and Hawaii ranked worse. The index uses a 0-to-10 scale and combines flu testing data, prescriptions and sales of over-the-counter cold and flu medicine.

Florida was already an early hot spot. As of Oct. 31, it was one of seven states reporting moderate to high flu activity, along with California, Louisiana, Oregon, South Carolina, Texas and Washington, according to a TODAY report republished by NBC 6 South Florida.

Why cold weather matters

WUSF reported that temperatures were expected to drop into the 40s over the next few days as the season's first wintry cold blast moved in.

Benjamin Anderson, a professor in the University of Florida's Department of Environmental and Global Health, told WUSF that the rise in cases is tied to cooler weather and more face-to-face contact as people gather indoors. He said flu cases generally start climbing or holding steady in October and November, while "the majority of influenza cases" usually come in late December and early January. The peak varies from year to year.

The national picture

The U.S. Centers for Disease Control and Prevention's FluView report for the week ending Nov. 7, published Nov. 13, shows flu rising across the country:

• 11.3% of specimens tested at clinical labs were positive for flu, up from the week before.
• Flu-like illness made up 3.2% of outpatient visits, above the national baseline of 2.9%.
• Hospitals reported 9,584 flu admissions for the week.
• The CDC estimates at least 2.6 million illnesses, 36,000 hospitalizations and 2,100 deaths from flu so far this season.
• Five children have died of flu nationally this season. Last season's total was 203.

H1N1 accounted for 98.9% of the flu A viruses subtyped nationally that week. The CDC rated the season's severity so far as low for all age groups but noted that could change as activity grows.

A changed H1N1 strain

The dominant virus is an H1N1 strain from subclade D.3.1.1 that has picked up a new mutation, called G155E. It was first identified in Seattle in September, according to the TODAY report. The mutation affects a spot that matters for the body's antibody response, which means the virus may partly slip past existing immunity. Scientists do not yet know whether it spreads more easily or causes more severe illness.

The CDC has said that early-season flu activity is higher than usual for this time of year. It has also cautioned that "an earlier increase in activity does not necessarily lead to a higher seasonal peak" and that "it is too early to know what viruses may predominate."

Andrew Pekosz, a virologist at the Johns Hopkins Bloomberg School of Public Health, said even an imperfect vaccine match still offers protection. "A mismatch is not a black-or-white situation. We may have less immunity, not no immunity," he said in the TODAY report.

Vaccines and prevention

Anderson told WUSF that higher vaccination rates help slow the virus. "When we have higher percentages of the population covered, it helps create disruption in the transmission of the virus," he said. He added that people who already had flu may have some immunity to that strain but should talk with a doctor, because a vaccine after infection can act as a booster.

The CDC recommends avoiding close contact with sick people, covering coughs and sneezes, avoiding touching the eyes, nose and mouth, and washing hands often. The state's flu report repeats CDC guidance that people at higher risk of complications should start antiviral treatment as soon as possible if they have confirmed or suspected flu, ideally within 48 hours of the first symptoms. That group includes children under 2, adults 65 and older, pregnant women and people with underlying medical conditions.

What's next

The Department of Health publishes a new Florida Flu Review each week, and the CDC updates FluView every Friday. The next state report will cover Nov. 8 through Nov. 14, and the reports after that will show whether the cold front and Thanksgiving gatherings push Florida's numbers higher. With Florida already ranking near the top of the national flu index well before the usual late December peak, experts such as Anderson say wider vaccination is the main tool for slowing transmission before the busiest weeks arrive.