Since we call both influenza and the stomach flu by the term "flu," when speaking colloquially, it's easy to conflate the two — but influenza and the stomach flu are two different conditions.
Aside from some overlap in the symptoms, they have different causes, prevention tools, symptoms, treatments, and tips and tricks.
Dr. Christina Johns, a pediatric emergency physician, helps us unpack them.
What Is Influenza?
Influenza, aka "the flu" or "seasonal flu," is a respiratory system infection affecting the nose, throat, windpipe, and lungs.
The strains mutate and change yearly, so some years it may be a relatively mild flu season, while other years, "It's like a total whopper," says Johns.
What Causes the Flu?
The influenza virus — types A, B, C, and D — causes the flu. Type A is more common overall and can cause epidemics. It is also more common in adults, while Type B is more common in babies under the age of five.
What Are the Symptoms of Influenza?
If you have the flu, you might experience congestion and symptoms like runny nose, sneezing, coughing, sore throat, body and muscle aches, headaches, fever, chills, and fatigue.
According to Johns, the hallmark of influenza, and how experts generally differentiate it from other infectious diseases, is that it tends to cause higher sustained fever. "I get up, I'm exhausted, my muscles hurt. And I have that sustained high fever and headache," she says.
How Does the Flu Spread?
The flu is an airborne virus that spreads through the teeny-tiny saliva droplets a person releases into the air when coughing, sneezing, talking, laughing, etc. Inhaling the contaminated air or coming in contact with the droplets that have landed on surfaces and then touching your nose and mouth can result in an infection.
"It's not as contagious as something like measles, but it is definitely in the 'very contagious' category," says Johns. Kids under the age of 5, adults over the age of 65, and immuno-compromised people like people with asthma or diabetes are most at risk of contracting the influenza virus.
When Is Flu Season?
Influenza is common and can be contracted at any time of the year. "There is always some level of circulating influenza, whatever the strain du jour is, right?" says Johns. It's not like there is no flu in August and 100 percent in December, Johns said.
Yet, there is a "seasonality to it," says Johns — "flu season." This is the time of year during fall and winter when influenza is most common in the U.S. It usually starts in October and peaks between December and February, according to the Centers for Disease Control (CDC) data. Influenza viruses are cold-weather viruses — hardier in cold weather. They transmit easier in the winter because we spend more time inside and increase close contact.
How Long Does the Flu Last?
The first 48 to 72 hours of symptoms are when you're most sick and most contagious. After that, your viral load slowly decreases — symptoms such as coughing, sneezing, and feeling congested usually go away in up to a week — but many people still feel like they've been knocked off their feet for seven to 10 days.
Read More: Why Are Viruses More Active In The Winter?
How Severe Is Influenza?
Most people who contract influenza will feel better after a few days without having to do anything special but rest and keep their symptoms in check. Yet, the flu can get serious and lead to sinus and ear infections or severe complications like pneumonia.
What Makes You Most at Risk for Influenza?
Chronic lung issues
Being young (young children)
According to Johns, if you fall under one of the following on the list, you could be at risk for potential organ damage and other complications from the flu.
How To Prevent the Flu
There are vaccines for the flu, and the CDC recommends getting one every year for people over the age of 6 months. You should get the shot as early in "flu season" as possible, like late October.
How Effective Is the Flu Vaccine?
The vaccine might not completely shield you from contracting the infection, but it has been proven to lower your chance of getting it, make symptoms and complications less severe, decrease your chances of ending up in the ICU, and lower the chances of spreading it around.
How To Treat the Flu
Most of the time, the flu will just do its course and resolve on its own. To help alleviate flu symptoms, get plenty of rest, stay hydrated, and take medications like paracetamol or ibuprofen to reduce fever and muscle pain.
Antibiotics have no effect since a virus causes influenza, so that the doctor might prescribe antiviral medication like Tamiflu. You should start these medications within 48 to 72 hours of initial symptoms, or they don't have any added benefit.
Still, they're "a mixed bag," according to Johns, and might not do the trick for everybody — so always speak to your healthcare provider about what they recommend.
What Is the Stomach Flu?
The stomach flu, known to science as gastroenteritis, is an infection of the gastrointestinal system — so your intestines and stomach. You might experience loss of appetite, abdominal cramps, nausea, vomiting, and watery diarrhea.
You might also experience general symptoms from your immune system responding to the infection, including fever, achiness, and fatigue.
What Causes the Stomach Flu?
Unlike influenza, the stomach flu is more of a general term to refer to the irritation and infection of the gastrointestinal tract, so there are multiple causes. Stomach flu can result from unclean food and water parasites and bacteria, such as E. coli, campylobacter, shigella, and Salmonella.
Still, viruses cause almost half of all stomach flu. Viruses that cause the stomach flu include norovirus, rotavirus, cytomegalovirus, adenovirus, and astrovirus. Norovirus is the most common of these viruses, causing up to 21 million illnesses yearly.
A doctor will likely diagnose you according to your symptoms and a physical check.
Read More: How To Avoid Food-Borne Illness
How Does Stomach Flu Spread?
Stomach bugs spread in different ways. Consuming contaminated food or water that carries the illness or touching a contaminated surface results in infection. Or you may come in contact with an infected person — especially their vomit or stool, like by changing a diaper.
Overall, though, the stomach flu is very contagious. That's why it's common for large groups of people in close contact to contract it. "They are all infectious diseases; whether or not some may be slightly more contagious than others, they're all contagious," says Johns.
How Long Does Stomach Flu Last?
Symptoms for the stomach flu usually show up within 48 hours after you've come in contact with the bacteria or virus. From then on, it mostly lasted one to three days and sometimes up to a week. Vomiting usually only lasts for the first 48 hours of the virus, but diarrhea might linger a little longer.
Read More: Why We Feel So Terrible When We Get Sick
How To Prevent Stomach Flu
Unlike influenza, there is no shot against the stomach flu, except for two vaccines against rotavirus for children and infants.
Your best chance to avoid contracting this pesky infection is by keeping your hygiene to the max, always washing your hands for two entire Happy Birthdays, and staying away from anybody who might not be feeling great.
How To Treat Stomach Flu
Most of the time, the stomach flu will just do its course and resolve on its own. In the meantime, get plenty of rest, stay hydrated, and avoid food that could irritate your stomach.
For others around you who might want to stay safe, tips are easy too: "No sharing drinks, carry out frequent hand washing and wipe down of surfaces," says Johns. "If you have the capability, let the sick person use one bathroom and one bathroom only."
How to Avoid the Flu and Stomach Flu
Whether it's the flu or the stomach flu, the guidelines are always the same: try not to get it!
"I always like to do the equation' prevention > treatment,'" says Johns, whether it's staying at home and missing out on some extra tiring activities or something as simple as wearing a mask when you're feeling iffy.
"Don't be a jerk about it, right?" says Johns. "Do it. It is worth it to temporarily hunker down and do the things that we know work to prevent and help decrease the spread of some of this stuff."