Force of Infection is now on the summer schedule, meaning national Outbreak Outlook updates are available only to paid subscribers. The winter schedule, including the free national version, will resume in October. To continue receiving reports during the summer, please upgrade to paid.

Influenza-like illness

Outpatient visits to the doctor for fever and either cough or sore throat, known as influenza-like illness or ILI, rose again this week from 1.1% to 1.3%. Test positivity for influenza is rising as well, and emergency department (ED) visits ticked up slightly from 0.1% to 0.2% at the national level. We remain firmly in the off season and activity is categorized as minimal, but we are definitely seeing the effects of back to school season, with week-over-week increases across several metrics.

The Southern region in particular is seeing increasing activity, with Florida, Georgia, and Texas all over 2% for outpatient ILI. These states often signal new trends.

Children ages 0 to 4 are most affected, with outpatient ILI now at 4.2%, up from a recent low of 3.1%. Seasonal peaks can reach 20%, so we're still in excellent shape, but there is increasing activity. People ages 5 to 24 are at 2.1%, and older age groups are at or below 1.1%.

COVID-19

National Trend

Covid-19 activity continues to rise with emergency department visits now at 0.6%, up from a recent low of 0.1%. However, we remain below last summer's peak, meaning this season is milder than what we saw last year, when ED visits peaked around 1.7%.

CDC's Center for Forecasting and Outbreak Analytics still estimates that Covid-19 activity is rising in nearly every state, with a few exceptions in the South. Activity is stable in Louisiana and Mississippi and likely growing in Tennessee, Alabama and Georgia. Personally, I'm not seeing those signs in the data just yet, but perhaps in the weeks ahead.

South

Force of Infection is now on the summer schedule, meaning national Outbreak Outlook updates are available only to paid subscribers. The winter schedule, including the free national version, will resume in October. To continue receiving reports during the summer, please upgrade to paid.

Influenza-like illness

We remain firmly in the off-season, but the effects of back-to-school are evident in this week's data. Outpatient influenza-like illness, or ILI, ticked up for a second week in a row to 1.1%. This remains far below the 3.1% threshold that would mark the onset of flu season, but nonetheless reflects increased activity from recent summer lows.

All four regions of the country are seeing increases, with the South registering the most notable uptick to 1.3%. Florida, Georgia, and Texas have all seen sizable increases in outpatient ILI over the last week. This fits with previous patterns, as those states tend to register trends first. The Midwest remains in best shape at 0.5% for outpatient ILI. Nonetheless, all fifty states are registering minimal activity, so these differences are mostly academic at this point.

As always, children ages 0-4 have the highest rates of outpatient ILI. This week they saw a sharp increase from 3.2% to 3.8%. Children ages 5-24 also saw a steep increase, from 1.3% to 1.7%. Older age groups remain below 1%.

Severe illness is minimal.

COVID-19

National Trend

Covid-19 activity continues to increase, with no signs of peak just yet. Emergency department visits for Covid-19 are at 0.5% nationwide with substantial variation from region to region. As in previous weeks, the South and West have markedly higher activity than the Midwest and Northeast, which have hardly registered the summer season. 

CDC's Center for Forecasting and Outbreak Analytics estimates growing activity in all 50 states.

South

As I shared in my recent State of the newsletter update, I want to spend more time on immunocompromised (IC) readers, who are often left out or brushed aside in public health updates. So, I put together an IC guide to seasonal vaccinations using information from reputable sources. Most of it summarizes 2025 guidance developed by the Infectious Diseases Society of America, a professional organization of infectious disease doctors. Other sources are linked within. This post is free for everyone, so please share.

Covid-19

Bottom line: Get vaccinated every year. For people who are immunocompromised, a second dose (given at least two months after the first) is likely to make protection last longer. You do not need to show documentation to prove you are eligible for a second dose; self-

Force of Infection is now on the summer schedule, meaning national Outbreak Outlook updates are only available to paid subscribers. The winter schedule, including the free national version, will resume in October. To continue receiving reports during the summer, please upgrade to paid.

Influenza-like illness

We are still in the off season. Outpatient influenza-like illness (ILI), or the percentage of visits to the doctor that are for fever and cough or sore throat, remains minimal at 0.9%. Activity in all four regions of the country is very low. Severe illness is minimal.

As always, children ages 0-4 have the highest rates of outpatient ILI at 3.2%, up slightly from the week prior. The 5-24 age group is also up slightly, now at 1.3%. Adults are experiencing minimal activity. 

One point of interest: This marks the first time in many months that outpatient influenza-like illness has increased. Activity is so low that this is not of practical consequence, but I always find it interesting to see evidence of increased transmission during back to school season.

COVID-19

National Trend

Covid-19 activity continues to rise as we move further into the summer season, particularly in the South and West. However, current levels remain below what we saw at this point last year. Both ED visits and wastewater concentration are increasing, and test positivity continues to rise from a recent low of less than 1% to 4.8% during the most recent reporting week. For context, last summer peaked at 12%.

This summer marks Force of Infection's fourth anniversary. I started this publication after returning from a stint at CDC. It began as a way to reflect on emerging infectious disease outbreaks, but I quickly learned that readers wanted news they can use about viruses that keep us out of work and school. Thus Outbreak Outlook was born, bringing weekly reports on flu, Covid-19, and RSV to your inbox year-round. I've published some 600 editions to over 47,000 readers, through data blackouts, holiday seasons, and an ever-changing political landscape.

This year has brought two big changes. Force of Infection moved off Substack and onto forceofinfection.com. It was a leap of faith to move away from a platform with a ready audience, but independence from the algorithm was worth it.

I also launched FOI Clinical, a publication for clinicians and public health practitioners. Whereas Force

Force of Infection is now on the summer schedule, meaning national Outbreak Outlook updates are only available to paid subscribers. The winter schedule, including the free national version, will resume in October. To continue receiving reports during the summer, please upgrade to paid.

Influenza-like illness

Influenza-like illness (ILI) activity is exceptionally low, with just 0.9% of outpatient visits for fever and a cough or sore throat. This is lower than at the same point during any of the last six seasons. Typically, initial increases in ILI coincide with the start of the school year, but I haven't seen that yet. The flu season usually does not start in earnest until October or November.

Although flu shots are becoming available at local drugstores, I suggest holding off for now. Immunity tends to wane after several months, so it is better to time your shot closer to

Influenza-like illness

Seasonal influenza activity remains low. Visits to the doctor for symptoms like fever, cough, and sore throat (outpatient influenza-like illness, or ILI) still account for less than 1% of all visits.

Activity in the West is slightly above the national average. As I mentioned last week, this is partially due to California, where outpatient ILI is on the high side (relatively speaking) at 1.6%. Wyoming has also ticked up to 1.3%. Everywhere else, outpatient ILI is below 1%. The Midwest is in great shape at 0.5%. Severe illness is low across the country.

As always, children ages 0-4 have the highest rates of outpatient ILI at 3%. This past winter the rate hit 20%, so I'll take 3% any day. Older age groups are all at or below 1%. School-age kids will likely see increases soon, now that school is starting in some districts, so be on the lookout.

Covid-19

The summer Covid season is here. Activity is low across the country but rising steadily in all four regions. Test positivity and wastewater concentration are also increasing.

The South, where the season started first, is leading the way. Emergency department (ED) visits in Louisiana, Florida and Texas are higher than other parts of the country at 0.5-0.7% and increasing. Other states in the region are seeing steady increases, with Georgia reporting a noticeable bump this week from 0.2% to 0.4%.

ED visits are also increasing in the West, especially in Hawaii, California, and Nevada, but to a lesser degree than in the South. Wastewater concentration is also rising in the West, including California, Hawaii and Alaska. (Caveat: there are only five wastewater sampling sites for all of Alaska.)

The Midwest and Northeast are in better shape with minimal to low activity according to both ED visits and wastewater concentration. However, activity is increasing, so there might be more to say in a few weeks.

RSV

Force of Infection is now on the summer schedule, meaning national Outbreak Outlook updates are only available to paid subscribers. The winter schedule, including the free national version, will resume in October. To continue receiving reports during the summer, please upgrade to paid.

Influenza-like Illness

Seasonal influenza activity is low. Trips to the doctor for symptoms like fever, cough and sore throat (referred to as outpatient influenza-like illness or ILI) remain steady at 1%. 

Now that school is starting in some regions of the country, I expect we’ll start to see increases in the weeks ahead. However, ILI tends to remain low overall until the season starts in earnest in October or November. Regional editions of Outbreak Outlook, which provide detailed data for each state, begin in October for that reason.

Activity in the West is highest at around 1%. This is influenced in part by California, where outpatient ILI is 1.6%. Everywhere else, outpatient ILI is below 1% and steady. The Midwest is in the best shape at 0.5%. Severe illness is low and stable in all four regions of the country.

Activity in adults and seniors is up a tick, heading towards 1%. Infants and children are steady at 3%. In the wintertime, outpatient ILI in children can hit 15-20%; enjoy these low numbers while they last.

Covid-19

We are confident the summer season is now in progress. Activity for Covid-19 is low but rising in all four regions of the country.

Force of Infection is now on the summer schedule, meaning national Outbreak Outlook updates are only available to paid subscribers. The winter schedule, including the free national version, will resume in October. To continue receiving reports during the summer, please upgrade to paid.

Influenza-like illness

Seasonal influenza activity is low. Trips to the doctor for symptoms like fever, cough and sore throat (referred to as outpatient influenza-like illness or ILI) account for less than 1% of outpatient visits. 

The West remains slightly above the national average, but lower than last week. The Midwest continues to have the lowest ILI at 0.5% and remains steady. There is a slight uptick in outpatient influenza in the South, driven primarily by increases in Arkansas, Delaware, Kentucky, Texas, and Tennessee. The uptick is small and likely just a temporary blip.

Outpatient ILI for infants and young children under 4 years continues to trend downward toward 3%, while all other age groups are below 2%. 

Covid-19

Activity for Covid-19 remains low across the country, with emergency department (ED) visits hovering just below 0.2%. That said, hospitalization rates related to Covid-19 have ticked up slightly to 0.3 per 100,000. We've been reporting for several weeks about increases in ED visits, wastewater, and test positivity. Increased hospitalizations add to the evidence that the summer season is underway.

Force of Infection is now on the summer schedule, meaning national Outbreak Outlook updates are only available to paid subscribers. The winter schedule, including the free national version, will resume in October. To continue receiving reports during the summer, please upgrade to paid.

Influenza-like illness

Seasonal influenza remains low at this time of the year. The percentage of visits to the doctor for symptoms like fever, cough and sore throat (referred to as ILI) is steady at 1%, which is very low. 

The West sits slightly above the national average at 1.2%, while the Midwest registers the lowest ILI at 0.5%. This week, the South is slightly lower than last week and continues to trend down, below 1%.

Severe illness remains low. Visits to the emergency department (ED) are holding steady at 0.1%. All regions remain steady. The weekly influenza hospitalization rate is very

There is currently a large outbreak of cyclosporiasis, a foodborne illness, that’s making headlines. Here’s a brief look at what you need to know.

There is a very large outbreak of cyclosporiasis underway. Current reports are concentrated in southeast Michigan and northwest Ohio – Michigan has reported over 700 cases since late June, which is approximately 14 times the state's annual average. Cases have been identified in at least 18 states, including New York, North Carolina, Indiana, and Texas, with an unofficial national count (based on state reports) likely exceeding 1,200. It's not yet confirmed whether these state clusters share a common source.

Cyclospora cayetanensis is a microscopic parasite that inhabits the small intestine. Infection begins when someone ingests contaminated food or water. Fresh produce like herbs, leafy greens, fruits, etc. are most commonly implicated. Unlike some other stomach bugs you may be familiar with, like

Force of Infection is now on the summer schedule, meaning national Outbreak Outlook updates are only available to paid subscribers. The winter schedule, including the free national version, will resume in October. To continue receiving reports during the summer, please upgrade to paid.

Respiratory illness

No data was published this week because of the 4th of July holiday. As of last week, influenza was very low and steady, while Covid-19 was also low but showing some early signs of increase in Gulf states. When new data is released, I will be looking for both continued increases and expansion to other states. Those would be signs we are edging into the summer Covid-19 season.

Food Recalls

The following foods are being recalled because they are contaminated and can pose a health risk to you and your family. Please check your cupboards and discard any of these items:

• Oribe Serene Scalp Densifying Shampoo, possible contamination with Pluralibacter gergovia bacteria (More info)

Previously reported

• Ready-to-eat chicken Caesar wrap, possible Listeria contamination (More info)
• La Colonia, Selectos Latinos, Clover Hill, Soft Ricotta Cheese, Mexican Cottage Cheese, possible Listeria contamination (More info)
• TNVitamins, Moringa Capsules & Powder, possible Salmonella contamination (More info)
• Clover Hill Dairy all brand cheeses, potential Listeria contamination (More info)
• Nara Organics Whole Milk Infant Formula, potential botulism contamination (More Info)

In Other News

Force of Infection is now on the summer schedule, meaning national Outbreak Outlook updates are only available to paid subscribers. The winter schedule, including the free national version, will resume in October. To continue receiving reports during the summer, please upgrade to paid.

Influenza-like illness

Seasonal influenza remains low at this time of year. Trips to the doctor for symptoms like fever, cough, and sore throat (referred to as outpatient influenza or ILI) are at 1.2%, which is about as low as it gets. 

The West, which is slightly above the national average, is still trending downward and is now at 1.4%, from 1.6% a few weeks ago. The Northeast is holding steady at 1.1%. The Midwest is experiencing the least ILI, below 1%. 

Severe illness remains low. Visits to the emergency department (ED) continue to hover around 0.2%. The West is at 0.3%, but still trending down. The weekly influenza hospitalization rate continues to be low at 0.1 per 100,000. The Midwest is the region experiencing the least percentage of severe illness, with hospitalizations nearing zero. Michigan and Minnesota contributed to this improvement.

Outpatient ILI for infants and young children under the age of 4 years is trending down towards 4%, while older kids and young adults remain steady at 2%. Activity for older adults (50+ years) is staying below 1%.

Covid-19

Activity for Covid-19 remains low across the country, with emergency department (ED) visits at 0.1% and hospitalizations are minimal. 

Force of Infection is now on the summer schedule, meaning national Outbreak Outlook updates are only available to paid subscribers. The winter schedule, including the free national version, will resume in October. To continue receiving reports during the summer, please upgrade to paid.

Influenza-like illness

Seasonal influenza remains very low in this off-season period. Trips to the doctor for symptoms like fever, cough, and sore throat (referred to as outpatient influenza-like illness or ILI) dropped a further notch and are now at 1.4% (from 1.6% last week). 

The West, which remains above the national average at 1.8%, experienced the most noticeable drop in ILI. All other regions also trended downward, with the Midwest lower than 1%.

Force of Infection is now on the summer schedule, meaning national Outbreak Outlook updates are only available to paid subscribers. The winter schedule, including the free national version, will resume in October. To continue receiving reports during the summer, please upgrade to paid.

Influenza-like illness

Seasonal influenza remains steady in this off-season phase. Trips to the doctor for symptoms like fever, cough, and sore throat (referred to as outpatient influenza-like illness or ILI) are holding at 1.6%, which is the same as last week.

At the regional level, the West is a touch higher at 2% ILI, while the Midwest is the lowest at 1%. 

Force of Infection is now on the summer schedule, meaning national Outbreak Outlook updates are only available to paid subscribers. The winter schedule, including the free national version, will resume in October. To continue receiving reports during the summer, please upgrade to paid.

Influenza-like illness

Seasonal influenza activity continues to trend down during this off-peak period. Trips to the doctor for symptoms like fever, cough and sore throat (referred to as influenza-like illness or ILI) have decreased slightly to 1.6% (down from last week’s 1.8%). 

At the national level, just 0.2% of visits to the emergency department (ED) are for influenza. ED visit rates are highest for young people between the ages of 5 and 17 years (0.7%) and lowest for adults 65 and older (0.1%). The weekly hospitalization rate last week was 0.1 per 100,000 people, down from 0.3 per 100,000 the previous week. 

Among infants and young children (ages 0–4), 5.2% of doctor visits are for fever, cough, and sore throat (influenza-like illness). For older children and young adults (ages 5–24), that figure is 2.3%. Both percentages have decreased slightly compared to last week.

Two influenza-associated deaths were reported this past week, for a total of 174 deaths this season. (Note: death reporting is often delayed, so these deaths may not necessarily be recent). Approximately 85% of reported pediatric deaths this season, according to the Centers for Diseases Control and Prevention, have occurred in either unvaccinated or not fully vaccinated children. 

Covid-19

There are some very early and preliminary indications of increased activity in a few Southern states (e.g., Florida, Texas). Activity is very low, so small increases are of little consequence. I mention it only because this time of year I begin to monitor for the first signs of the summer wave, and it's those states that typically tick up first. It could just be normal fluctuation. To 'call' the start of the wave, I need to see a few consecutive weeks of increase, over an expanding geographic area. We're not there yet.

It is that time of the year again! In the United States, Memorial Day weekend marks the unofficial start of the summer. That means longer days, beach trips, kids splashing in pools, picnics, barbecues, and lots of time outdoors. But staying safe is just as important as having fun, which is why every year I share a few first aid videos to remind readers of the basics. I specifically chose these videos because they are only 2-5 minutes long, so you can get through the entire set in about 15 minutes.

When an emergency happens, many of us freeze. It is a natural response. Our brains are hard-wired for the “fight, flight, freeze” response, an automatic reaction to perceived threats that can make it hard to think clearly. But learning a few basic skills ahead of time, can help you stay calm and feel more prepared if something

Force of Infection is now on the summer schedule, meaning national Outbreak Outlook updates are only available to paid subscribers. The winter schedule, including the free national version, will resume in October. To continue receiving reports during the summer, please upgrade to paid.

Influenza-like illness

We continue to navigate this off-season as expected. Trips to the doctor for fever, cough and sore throat (known as influenza-like illness, or ILI) are stable at 1.8%. 

At the regional level, the Midwest is reporting the lowest levels of ILI at 1%, which is nevertheless a slight notch higher than last week (0.9%; this is not a meaningful difference). The West continues to be a tad higher than the national average, but holds steady at 2.1%. 

Force of Infection is now on the summer schedule, meaning national Outbreak Outlook updates are only available to paid subscribers. The winter schedule, including the free national version, will resume in October. To continue receiving reports during the summer, please upgrade to paid.

Influenza-like illness

The off-season is in full swing. Trips to the doctor for fever, cough and sore throat (known as influenza-like illness, or ILI) remain steady at 1.8%. 

At the regional level, the Midwest is reporting the lowest levels of ILI at 0.9%, while the West continues to decline

This is the second installation in a series about respiratory viruses and their complexities. The first essay explained less common viruses like human metapneumovirus and adenovirus. Today, we're taking a deeper look at disease surveillance.

Why don’t I know what I have?

If you go to the doctor or hospital with what feels like a “cold,” there’s a set of decisions happening behind the scenes about whether to test you, and for what.

In most outpatient settings, testing is usually “targeted.” This means you might get a single test (for example, just for influenza), or a small “triplex” panel that checks for the most common viruses: SARS-CoV-2, flu, and RSV. These are the pathogens where a diagnosis can directly affect care or

A new Covid-19 variant has been making headlines lately, and this one has an unusual name. BA.3.2, nicknamed "cicada", has been detected in at least 25 U.S. states and 23 countries. Here's what we know so far.

Why "cicada"?

Cicadas are famous for spending years underground before emerging in enormous numbers, sometimes after 13 or 17 years of dormancy. BA.3.2 follows a loosely similar pattern: it was first identified in South Africa in November 2024, circulated at very low levels for over a year largely under the radar, and then emerged more forcefully in Europe last fall before

Force is growing, and so is the team. I'm excited to welcome Gage Moreno, PhD, as a contributing writer. Like our upcoming move to a standalone website, expanding the team is part of the plan to make this publication more valuable to you over the long term. This is the first explainer in a two-part series; Part II will cover how epidemiologists track these pathogens, and what future technologies might improve surveillance. -Caitlin

If you’ve ever been sick with “a cold,” yet tested negative for flu and Covid-19, you’ve already bumped up against a hidden world of viruses.

“A cold” isn’t a single illness it’s a label used for dozens of respiratory pathogens that circulate every year, most of which are rarely tested for. Even though they are largely invisible to patients, these viruses cause real illness, drive outbreaks, and shape

Yesterday, the U.S. CDC issued a Health Alert Network (HAN) advisory about New World screwworm cases on the Mexico side of the Texas-Mexico border. New World screwworm is primarily a disease of livestock, though humans can become infected. There are currently no human or animal cases in the United States, though it is an encroaching threat.

Against the backdrop of resurgent pertussis and measles, a recent infant botulism outbreak, and a changing vaccine schedule, screwworm feels like a distant concern. Yet clinicians have not received a HAN on these more pressing issues. The last advisory covering a disease with U.S. cases was in March, three HANs ago.

This is the gap I want to close with FOI Clinical, a new outbreak monitoring service I’m launching. There is no quick, easy way for front-line clinicians like pediatricians, family doctors, or emergency physicians to get a recurring,