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How contagious are you when you have a cold or flu?

photo of young woman blowing her nose | Johns Creek Family MedicineFeeling a bit under the weather? Thinking of taking a sick day? Understanding some of the basics of cold and flu can help make it clear when to stay home to help keep contagions at bay.

Cold and flu: 101

The common cold is caused by a group of viruses called rhinoviruses, named as such because of their propensity for the nasal cavity. Due to this location, most of the symptoms of the common cold – sniffling, sneezing, sore throat and cough – are localized to the nose and upper respiratory tract.

The flu is caused by the influenza virus, of which there are numerous subtypes and strains. Influenza has a greater affinity than cold viruses for parts of the lower respiratory tract, increasing the risk for subsequent pneumonia. The flu can also more often include systemic symptoms such as fevers, chills, body aches and fatigue.

Some strains of rhinovirus can be associated with more severe symptoms and involvement of the lower respiratory tract. Such “chest colds” may resemble the flu and can also increase the risk for later infections, such as bronchitis.

Distinguishing cold, flu and flu-like symptoms

In most cases, infections with flu-like symptoms are caused by a cold virus. This is because the cold virus is more prevalent than the flu virus. That does not mean, however, that influenza is uncommon. In fact, most communities experience at least a small epidemic of influenza infections during the winter months each year. Influenza can be a serious health risk to certain people, such as the young and the elderly, making the use of a flu shot in these and other vulnerable groups an important part of health maintenance.

When am I contagious?

Most rhinoviruses are contagious for the period from about a day before until five or seven days after symptoms have started. The ability of a cold virus to spread before an infection is even apparent makes habits such as good hand hygiene and covering all coughs and sneezes with a disposable tissue always important.

During the symptomatic period, the capacity for a rhinovirus to spread is significantly increased by the symptoms themselves: sneezing and runny nose promote the spread of the cold virus to other surfaces and people. This makes the symptomatic period the most important part of the cycle of contagion. Help prevent further spread of a rhinovirus by continuing to observe good hand hygiene during the symptomatic phase of the infection.

The flu is generally contagious for a longer period of time than the common cold. Flu may be spread up to four day prior to symptom onset and during the course of the symptomatic period, which is often around two weeks. Influenza that is complicated by additional infection such as pneumonia may remain contagious an additional week or two longer. The same habits of covering sneezes and regular hand washing that help prevent the spread of a rhinovirus also apply to influenza.

Calling in sick

While this article is intended to informative, it cannot take the place of professional medical advice. If you are feeling under the weather or are otherwise concerned about preventing the spread of cold or flu, please consider contacting Dr. Zack Charkawi, M.D. at Johns Creek Family Medicine or another healthcare professional in your area.

Johns Creek Family Medicine is located in Johns Creek near the Peachtree Parkway (Highway 141) and McGinnis Ferry Road intersections, directly across from Emory Johns Creek Hospital on Hospital Parkway. Dr. Zack Charkawi, M.D. is accepting new patients from South Forsyth, Gwinnett and North Fulton counties and the surrounding North Atlanta areas including Alpharetta, Cumming, Roswell, Suwanee, Johns Creek, Duluth, and Dawsonville.

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