Influenza, commonly known as "the flu" is a serious, acute respiratory illness that can lead to pneumonia. It is caused by a virus.
- Who is at risk of catching the flu and how long does it last?
- What are the symptoms?
- What is the difference between a cold and the flu?
- How does the flu virus spread?
- How long can someone with the flu infect someone else?
Who is at risk of catching the flu and how long does it last?
People of any age can get the flu, and illness usually lasts two to seven days, sometimes longer in the elderly and in people with chronic diseases. Most people who get the flu are ill for only a few days. However, some people can become very ill, possibly developing complications and requiring hospitalization.
What are the symptoms of the flu?
Symptoms of the flu include:
- fever
- chills
- cough
- runny eyes
- stuffy nose
- sore throat
- headache
- muscle aches
- extreme weakness and fatigue
- ear aches (children)
- nausea (children)
- vomiting (children)
- diarrhea (children)
Symptoms may vary from person to person. For example, the elderly may not have a fever, while children can have symptoms like earaches or stomach problems.
The cough and fatigue can persist for up to several weeks, making the return to personal and work activities difficult.
If you or a family member have the flu, use this Flu Assessment Tool to help you decide what to do next.
What is the difference between the cold and the flu?
The common cold and flu symptoms are often very similar. Use the chart below to help you determine if what you have is a simple cold or the flu.
| Symptom | Cold | Influenza |
| Fever | Rare | Usual; high fever (102 ° F/39 ° C - 104 ° F, 40 ° C), sudden onset, lasts 3 to 4 days. |
| Headache | Rare | Usual; can be severe |
| Muscle aches and pains | Sometimes, generally mild | Usual; often severe |
| Tiredness and weakness | Sometimes, generally mild | Usual; severe, may last up to 2 to 3 weeks |
| Extreme tiredness | Unusual | Usual; early onset, can be severe |
| Runny, stuffy nose | Common | Common |
| Sneezing | Common | Sometimes |
| Sore throat | Common | Common |
| Chest discomfort, coughing | Sometimes, mild to moderate | Usual, can become severe. |
| Complications | Can lead to sinus congestion or infection, and ear aches.* | Can lead to pneumonia and respiratory failure, and become life-threatening. Can worsen a chronic condition. |
| Prevention | Frequent hand washing | Annual immunization and frequent hand washing |
*Colds do not generally result in serious health problems such as pneumonia or bacterial infections.
NOTE: Children may also experience the croup, ear infections, nausea, vomiting and diarrhea when they have influenza - these symptoms are not common in adults.
How does the flu virus spread?
The influenza virus spreads mainly from person to person through coughing or sneezing. People can become infected by touching objects or surfaces with flu viruses on them and then touching their eyes, mouth or nose.
How long can someone with the flu infect someone else?
People with the flu may be able to infect others one day before symptoms develop and up to seven days after becoming sick.
That means that you may be able to pass on the flu to someone else before you know you are sick, as well as while you are sick. Children, especially younger children, might be contagious for longer periods.
For More Information
For information about fluCall the ServiceOntario INFOline at 1-877-844-1944
TTY 1-800-387-5559
TTY (Toronto) 416-327-4282
Hours of operation : 8:30am - 5:00pm
Visit Telehealth Ontario or call 1-866-797-0000
TTY: 1-866-797-0007
Hours of operation : 24 hours, 7 days a week
Visit ontario.ca/healthcareoptions or call 1-866-330-6206.
To find a health care providerIf you don’t have a health care provider, you can register for the Health Care Connect program. Visit ontario.ca/healthcareconnect or call 1-800-445-1822.
