Both colds and the flu are contagious and are caused by viruses. However, the viruses that cause colds (for example, rhinoviruses) are not the same as those that cause the flu (influenza viruses).
Although the typical incubation period for influenza is about one to four days, some adults can be contagious from about one day before the onset of symptoms for up to two weeks. Other people who develop complications, such as pneumonia, may extend the contagious period for a week or two.
For colds, most individuals become contagious about a day before cold symptoms develop and remain contagious for about five to seven days. Some children may pass the flu virus for longer than seven days (occasionally for two weeks).
Colds are considered upper respiratory infections. The flu may also cause lower respiratory infections.
How do you know if I have a cold or the flu?
For both the cold and the flu, early symptoms may be similar. Symptoms and signs include a cough, runny nose, and feeling tired. If you know you have had contact with someone with a cold or the flu in the past few days, you should suspect you may have become infected. However, flu symptoms generally are more intense than cold symptoms.
People with flu can develop fever, body aches, chills, and headaches, and some develop nausea and vomiting. Cold symptoms are much milder and usually do not require medical care. However, if you suspect you have the flu, you should seek medical care.
The flu often can be diagnosed with rapid tests available to most physicians.
How are cold and flu viruses spread?
A common cold and the flu are easily spread from person to person, the flu most often by droplets produced by coughing and sneezing. Cold viruses in droplets are spread mainly hand to hand. These droplets contain infectious viruses.
Occasionally, these droplets land on various surfaces and, depending on the survivability of the virus type, can be transferred when an uninfected individual touches the contaminated surface and subsequently touches his/her mouth or nose.
How do you know if the flu or cold is gone?
In most instances, individuals with a cold will resolve their symptoms without medical intervention in about one week, although sometimes the cough may last longer. However, at this point, the cough is not spreading a contagious virus. When cold symptoms and signs resolve, a person is cured of the cold. The flu is similar except that the symptoms are more severe and, in some individuals, medical intervention may be required (for example, antiviral medications). However, depending upon the influenza strain and the severity of the infection, some individuals may require hospitalization. The cure for these individuals occurs when symptoms resolve and the patient is discharged from the hospital.
The stomach flu is not caused by cold or by flu viruses. The term stomach flu is a nonspecific term that describes symptoms of nausea, vomiting, and diarrhea. Although these symptoms may occur with the flu, the flu is a respiratory infection. In most individuals with only stomach flu, the causes are usually non-flu-type viruses. Similarly, cold sores are not caused by cold viruses but by herpes viruses.
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When should someone seek medical care for a cold or the flu?
Unless the person has medical problems, such as a depressed immune system, most individuals do not need to seek medical care for a cold. However, individuals with the flu may need to seek medical care under the following conditions:
- Fever that is continual or becomes high
- Shaking chills
- Coughing that produces bloody sputum and/or a greenish-yellow color
- Difficulty breathing
- Chest pain or chest pressure
- Repeated nausea and vomiting
- Facial pain
If there is any question as to whether or not you have a cold or the flu, especially during flu season, you should seek medical care.
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