COVID-19 cases began to rise this summer across the United States, including in Pennsylvania. Now, flu activity is picking up, with the respiratory virus climbing more quickly than it typically has in previous years.
While viral levels are lower in Pennsylvania than they are nationwide, Allegheny County is already reporting more flu infections than it did this time last year. And cases are expected to continue to rise as we move into the colder months.
Here's what we know about flu cases in Allegheny and Pennsylvania.
Flu infections projected to rise nationwide
Flu cases began to take off in early fall this year, reaching an activity level in October not usually seen until December or January, according to wastewater data.
As of Oct. 7, CDC projections found that flu infections were on the
rise in 50 states. The highest activity is occurring on the West Coast, specifically the regions that cover Arizona, California, Hawaii, Nevada, Alaska, Idaho, Oregon and Washington.
Flu activity detected from wastewater was still categorized as "very low" nationwide as of Oct. 3, according to the CDC. The CDC noted that wastewater data tracking is experiencing a "brief gap" in updates due to a new contract with a testing company. It did not clarify how long this gap would last.
CDC data through Oct. 3 also showed that about 3.6% (1,435) of the 39,317 flu tests administered that week were reported positive to the National Respiratory and Enteric Virus Surveillance System. The vast majority of these confirmed illnesses (97%) were influenza A, the most common form of the flu. Hospitalizations remained low.
Wastewater data maintained by WasteWaterSCAN, a Stanford University-led tool for tracking the spread of disease, categorized flu activity as "high" nationally, meaning higher concentrations of the virus have been detected in the wastewater of more communities nationwide.
The same data shows the earliest onset of flu in at least the last four years; samples positive for influenza A were at 60% for the month as of Oct. 13, compared to just 20% in October 2025.
The CDC likewise noted that seasonal flu activity began increasing around late August to early September.
Is the flu spreading in Pittsburgh? Cases in Allegheny County
In Allegheny County, reported cases of flu are increasing — and trending above last year's count around the same time.
While there were only a handful of flu cases reported during the summer months, cases are gradually increasing, with 107 infections reported during the week of Oct. 4, according to the county's respiratory virus dashboard. Last year, during the week of Oct. 5, there were just six infections reported.
Last season's cases peaked on Dec. 21, 2025, when the county reported 1,763 flu cases.
Because not every infection is reported, the county also tracks influenza levels in wastewater. Wastewater data showed that viral activity was has remained "very low" since mid-January. Last year, levels didn't jump until December.
Data from WasteWaterSCAN shows that across the Northeast, Influenza A levels are still low, though they've increased throughout the region since late August. Last year, levels rose very slightly in September, though there wasn't a steadier increase until mid-October.
Where flu cases are on the rise: map
Flu activity is growing in Pennsylvania, according to data from the CDC.
What is the most prominent flu strain?
Currently, influenza A is dominant as the No. 1 strain. Influenza A is the most common type of flu that circulates seasonally and causes symptoms most often associate with being "flu-like," such as fever, cough and runny nose. Influenza B also shows up during flu season, but it typically doesn't account for as many cases.
The subclade (a subtype or group of an illness) A(H1N1)pdm09 has been the most detected by the CDC this season. It's the same strain that caused the "swine flu" pandemic in 2009, back when it was a new virus. Now, it is part of a typical flu season.
Influenza A mutates faster than other types, which is why it has many subtypes and is best known for causing outbreaks and major illness clusters. Influenza A's ability to rapidly change is a driving factor behind why the flu shot is reformulated each season to target the year's strains and subtypes.
Last year, for example, a newly mutated influenza A type known as subclade K caused a stir as it drove cases and evaded the season's target shot.
What are the symptoms of flu?
According to Mayo Clinic and CDC, symptoms of flu, including the most common influenza A, include:
- Fever
- Body aches and chills
- Cough
- Runny or stuffy nose and sneezing
- Sore throat
- Headache
- Fatigue
- Loss of appetite and upset stomach
How does flu spread?
The flu is most commonly spread through droplets when someone who is sick with the virus coughs, sneezes or talks, according to the CDC. These droplets can be inhaled into the mouth, nose or lungs of those nearby, and they can also land on nearby surfaces.
It's less common but still possible to get sick from touching a surface with the virus on it.
People who are sick with the flu are typically contagious one day before symptoms start and up to five to seven days after becoming sick, though they're most contagious during the first three days of the illness, according to the CDC.
How to protect yourself from flu
There are numerous steps you can take to protect yourself from catching or spreading the flu, according to the CDC. These include:
- Getting a yearly flu vaccine
- Avoiding close contact with people who are sick, and limiting contact with others if you are sick
- Cleaning high-touch surfaces
- Covering coughs and sneezes
- Wearing a mask or respirator (like an N95) to protect others from your germs and to protect you from inhaling other people's germs
- Washing your hands with soap and water, or using alcohol-based hand sanitizer when soap and water aren't available
- Avoiding touching your eyes, nose and mouth
- Improving air quality by gathering outdoors, opening windows or using an air purifier
If you do get sick with the flu, your healthcare provider can prescribe antiviral medication to make your illness milder and shorter.
Who is eligible for the flu shot?
The Trump administration limited COVID vaccine recommendations in 2025 and issued a memo in January 2026 removing universal recommendations for some childhood vaccines. While a federal judge blocked some of these changes in March, parents will need to check with their pediatrician and local pharmacy to make sure all requirements are met before they get their children vaccinated.
People over the age of 18 can walk into their local pharmacy and get vaccinated at their discretion.
The flu vaccine is the most effective way to previous serious complications from the flu, including encephalitis, myocarditis, pneumonia and Guillain-Barré syndrome, according to the World Health Organization, CDC and other leading medical institutions.
Finch Walker is the Pittsburgh Connect Reporter for the USA TODAY Network. Contact Walker at FWalker@usatodayco.com. Instagram: @finchwalker_. X: @_finchwalker.
This article originally appeared on USA TODAY: Flu levels climb in Allegheny County. See cases, symptoms, prevention
