10 Common Winter Illnesses: Are You Contagious?

You can be infectious from two days to two weeks.

The season of sharing — cold germs, flu viruses, stomach bugs and more — is upon us. That magical time when your kid brings home every germ in existence from school or daycare and spread the wealth, and your sneezy coworker insists on coming in for that meeting. (Why, just why???)

This season could be a doozy, with respiratory syncytial virus (RSV) now surging — along with the double-whammy of flu and COVID-19 (what medical experts have dubbed “ flurona ”). Family physician Matthew Goldman, MD, explains how to stay safe this winter season.

Why we get sick in the winter
“Illnesses are more common in the winter because contaminated respiratory droplets travel more easily in dry air when an ill person coughs or sneezes,” explains Dr. Goldman. “Plus, people tend to gather indoors when it’s cold outside (and for the holidays), making it easier for germs to spread from person to person.”

It takes a few days for symptoms of a winter illness to appear after you’re infected. This time is called the incubation period — you’re infected but don’t feel sick.

And while you may feel fine, you’re probably unknowingly infecting others. “You’re usually most contagious two to three days after you’re infected, but you can infect others for two weeks or longer while recovering from an illness,” notes Dr. Goldman.

Exactly how long you’re contagious depends on the winter illness. Dr. Goldman shares when it’s safe to be around others.

1. Common cold (rhinovirus)
With more than 200 different cold viruses (rhinoviruses) in circulation, it’s no wonder that most adults catch colds two or three times a year. Kids — with their germy hands, phlegmy coughs and (lack of) sneeze-covering skills — get sick even more frequently.

How long is a cold contagious?
You or your child are contagious during the symptom-free incubation period. But you’re most likely to infect others when cold symptoms are at their worst — usually around day three of feeling lousy.

Cold viruses linger, and you can pass the virus to others for up to two weeks.

2. Flu (influenza)
Flu season runs from October to May, but it’s possible to get sick with an influenza virus any time of the year. The flu sickens millions in the U.S. every year, and thousands die.

The flu vaccine is the best way to protect yourself and your family from this highly contagious virus.

How long is the flu contagious?
By the time you start showing flu symptoms, you’ve probably already given the virus to at least one other person. That’s because you’re infectious before you know you’re sick.

The flu is contagious for a week or longer after you first have symptoms.

3. COVID-19
COVID-19 spawned a still-ongoing pandemic, so you know this coronavirus spreads easily. The COVID-19 vaccine can protect you, your loved ones and the community from infection. While you can still get COVID-19 even after you’ve been vaccinated, you’re likely to experience less severe COVID-19 symptoms.

How long am I contagious with COVID-19?
You’re more likely to infect others with COVID-19 one to two days before symptoms appear and two to three days after you start feeling unwell. How long you’re contagious can also depend on the severity of your illness. If you have:

• Mild or no symptoms (asymptomatic): You’re contagious for about five days.
• Moderate to severe symptoms: You may be infectious for up to 20 days.

4. Respiratory syncytial virus (RSV)
In adults and children who are otherwise healthy, respiratory syncytial virus (RSV) typically causes mild symptoms similar to a cold. But this respiratory infection can cause potentially life-threatening bronchiolitis and pneumonia in infants, adults who are older and people with weak immune systems.

Every year, RSV infections in children lead to 58,000 to 85,000 hospitalizations.

How long is RSV contagious?
You or your child are contagious for a couple of days before symptoms appear and up to eight days afterward. But infants who are infected and people with weak immune systems may be contagious for up to four weeks, even when they no longer have symptoms.

5. Bronchitis (chest cold)
The viruses that cause colds, flu and COVID-19 can all lead to bronchitis. Also known as a chest cold, bronchitis causes the airways to your lungs to swell and fill with mucus. The most common symptom is a chronic cough that lasts three weeks or longer.

How long am I contagious with bronchitis?
Bronchitis isn’t contagious. But the cold, flu or other virus that led to bronchitis is, so you still need to take precautions to prevent infecting others.

6. Pneumonia
Bacteria — as well as the viruses that cause COVID-19 and RSV — can cause pneumonia. Both viral and bacterial pneumonia are contagious, but not everyone who’s exposed gets sick.

Children younger than two, adults over 65 and people with weak immune systems should get the pneumococcal (pneumonia) vaccine to prevent severe complications.

How long is pneumonia contagious?

• Viral pneumonia: You’re contagious until your fever breaks and then you’re fever-free for several days.
• Bacterial pneumonia: You’re contagious until you’ve taken at least two days of antibiotics and no longer have a fever.

7. Pink eye (conjunctivitis)
Bacteria, as well as viruses that cause colds and COVID-19, can cause pink eye (conjunctivitis). This eye infection swells blood vessels in the tissues (conjunctiva) that line your eyelids and outer eye. The swollen blood vessels make the white part of an infected eye look pink.

How long am I contagious with pink eye?
You can spread viral pink eye during the incubation period and while you have symptoms. Bacterial pink eye is contagious until you’ve taken antibiotics for at least 24 hours — or until the symptoms go away.

8. Sinus infection (sinusitis)
Colds and seasonal allergies can cause sinus infections. Also known as acute sinusitis, this infection occurs when your sinuses, which make mucus, fill with fluids. Bacteria sometimes grow in this mucus, causing bacterial sinusitis.

How long is a sinus infection contagious?
A bacterial sinus infection isn’t contagious, but you can spread the cold that caused a sinus infection to others.

9. Strep throat
Colds and other viruses tend to cause sore throats, but it’s highly contagious group A streptococcus (strep) bacteria that causes strep throat. This bacterial infection inflames the throat and tonsils, making it painful to swallow. You or your child may also have a fever and swollen lymph nodes.

Left untreated, some children with strep throat will develop a bumpy red rash known as scarlet fever.

How long am I contagious with strep throat?
You’re infectious until the fever is gone and you’ve taken antibiotics for at least 12 hours.

10. Stomach bugs (norovirus)
Norovirus is a stomach bug that causes diarrhea, vomiting and stomach cramps. Some people call it a “stomach flu”— but a flu strain doesn’t actually cause this illness.

Still, noroviruses (there are many types) are highly contagious and difficult to kill. Noroviruses can linger for weeks on surfaces like countertops and doorknobs.

How long am I contagious with a stomach bug (norovirus)?
You’re most contagious when you’re throwing up, experiencing diarrhea or in the few days after symptoms ease. Unfortunately, you can infect others for two weeks or longer, even when you feel better.

How to stop the spread of common winter illnesses
If you or your child are sick, these steps can help avoid spreading viruses to others: 

• Cough and sneeze into the crook of your elbow, not your hands.
• Disinfect high-touch areas like countertops, doorknobs and remotes.
• Don’t share utensils, cups, food, toothbrushes, clothing, towels or other personal items.
• Stay home (isolate or quarantine) until symptoms improve and you’re no longer infectious.
• Wash hands often with warm water and soap or use hand sanitizers.
• Wear a mask in public and consider wearing a mask at home around family members.

When to see a provider about common winter illnesses
Depending on the illness, you or your child may need treatments like antibiotics or antivirals. See a healthcare provider if these symptoms occur:

• Any fever in infants younger than 3 months or a fever between 99 degrees Fahrenheit (37.22 degrees Celsius) and 100.4 degrees F (38 C) in a child older than 3 months.
• High fever above 102 F (38.88 C) in an adult that lasts more than four days.
• Difficulty breathing, wheezing or chest pain.
• Extreme fatigue or lethargy.
• Signs of dehydration like dark-colored urine, confusion, dizziness or a sunken soft spot (fontanelle) in infants.

With some preventive measures (vaccinate!), plenty of soap and water, and lots of common sense (don’t be the sneezy colleague), we can all work together to weather the sick season better.