Colds and flu

Updated 11 October 2017

Flu and colds: are you still contagious?

Check out this guide to knowing when you’re most likely to be contagious for the most common flu and cold viruses.

Check out this guide to knowing when you’re most likely to be contagious for the most common flu and cold viruses.

The common cold

You’re contagious: from one day before your first symptom to eight days after it
You can catch the common cold from over 200 different viruses, which lurk in the air and on common surfaces. You can be contagious before telltale symptoms, such as sneezing, stuffy or runny nose, sore throat and coughing, even begin. That means stellar hygiene is key 24/7, not just when you feel under the weather. And remember that a cold must run its course there is no cure for this common respiratory infection.

Seasonal flu

You’re contagious: from one day before your first symptom to up to seven days after it
Both types of the flu hitch rides on sneeze and cough droplets. “You’re most infectious during the first three days that you’re sick with the flu, because that’s when you experience the most nasal secretions,” says Linda Meloy, M.D., a professor in the division of general pediatrics at Virginia Commonwealth University Children’s Medical Center in Richmond, Virginia. This period also usually corresponds to when your fever is highest. An antiviral medication may shorten the stretch that you’re contagious, so see your doctor at the first sign of symptoms fever, headache, muscle pain, fatigue, runny nose or sore throat.

Strep throat

You’re contagious: from the first day of symptoms to 24 hours after you start taking antibiotics
The streptococcal bacteria is the culprit behind the classic symptoms: sudden sore throat, pain when you swallow, fever over 101 degrees Fahrenheit, swollen tonsils, swollen lymph nodes, and white or yellow spots on the back of the throat. Unlike when you have a cold or the flu, you need an antibiotic to get well, so it’s crucial to visit your doctor for a strep test and a treatment plan that includes prescription antibiotics. Although you’re typically not contagious after a full day on the medication, it’s important to complete the entire course of treatment to eradicate the infection completely.


You’re contagious: from the first day of your first symptom to up to 7 days after it
A virus is usually to blame for this inflammation of the bronchial tubes, and the infection takes about a week to leave your system. Key symptoms include a cough that produces mucus, wheezing, low fever and chest tightness. Once in a while, bronchitis is caused by bacteria (your doctor can check) and you’ll need an antibiotic to kick it.


You’re contagious: from the first day of your first symptom to 24 hours after you start taking antibiotics
This infection of the lungs is most often caused by bacteria called pneumococcus, so you won’t recover until you treat it with antibiotics. The most common symptoms are cough, fever, chills, wheezing and shortness of breath. That said, in rare cases, pneumonia is caused by a virus, so medications won’t wipe out the infection (and it will take about a week to stop being contagious).


You’re contagious: never
Many hay fever symptoms sneezing, stuffy nose, headache, wheezing copycat the symptoms of the common cold. However, you can’t spread or catch allergies, because they’re not infectious illnesses, says Charles Ericsson, M.D., head of clinical infectious disease at the University of Texas Medical School at Houston. So why do you and your spouse get hay fever at the same time? Probably because you’ve been exposed to the same environmental triggers such as pollen, mold and dust.

(Ella Brooks for Sniffle Solutions)

(Photo: Young man with cold from Shutterstock)


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Flu expert

Dr Heidi van Deventer completed her MBChB (Bachelor of Medicine and Bachelor of Surgery) degree in 2004 at the University of Stellenbosch.
She has additional training in ACLS (Advanced Cardiac Life Support) and PALS (Paediatric Advanced Life Support) as well as biostatistics and epidemiology.

Dr Van Deventer is currently working as a researcher at the Desmond Tutu Tuberculosis Centre at the University of Stellenbosch.

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