How Long Is A Cold Or A Flu Contagious?

The falling leaves and cooler temperatures get many people worried, as colds and flu are more common during this time of the year. A common question many ask is this: how long is a cold or the flu contagious? Although the common cold and flu share similar symptoms, it is important to differentiate one from another, because these two infections are slightly different in terms of the period they can be transmitted to others. 

What are the symptoms of the common cold? How long is a cold infectious to others?

The symptoms of the common cold begin after 1-3 days after the virus enters the body. The symptoms develop gradually with a scratchy or sore throat, followed by a runny nose, sneezing, nasal congestion, and fatigue. The temperature is usually normal, although children may get a fever. Nasal discharge is clear in the first few days then becomes mucoid. Mild cough can be experienced in the first week and may even last into the second week. An uncomplicated cold usually resolves within 10 days.

Individuals with a cold are most contagious during the first 2-3 days after the symptoms develop. However, they can be infectious to others a few days before the symptoms start until the symptoms are gone, or up to two weeks. 

What are the symptoms of flu? How long are you contagious when you catch the flu?

Generally speaking, symptoms of flu begin 1 to 4 days  (usually within 2 days) before the influenza virus enters the body. It may start as a common cold with a runny nose and sneezing, but symptoms tend to come on suddenly and are more severe. Fever and chills, muscle aches, headaches, dry persistent cough, and fatigue are common symptoms of the flu. Some may experience eye pain and shortness of breath.

 As per the Centers for Disease Control and Prevention (CDC), people who have flu are most contagious in the first 3-4 days after the symptoms develop. It is possible to be contagious and thus infect others one day before the onset of symptoms and up to 5-7 days after becoming sick. 

Children and older adults with a weakened immune system may be able to transmit the virus for a few more days.  Still, flu is contagious for a shorter period of time compared with the common cold, which can be transmitted to others for up to 2 weeks.

Is there a risk of transmitting the flu if you are asymptomatic (don’t have symptoms at all)? This is unlikely, based on an extensive review of research studies regarding flu transmission, which was published in 2009 in Public Health Reports-SAGE Journals.  

Both common cold and flu are highly contagious

Both the common cold and flu are highly contagious and spread easily from person to person. Personal contact with someone infected such as a handshake,  breathing in droplets from a cough or sneeze, and kissing are the most common ways these viruses spread.

 In very rare cases, some researchers suggest it is possible to get a cold or the flu after coming in contact with different objects and surfaces. For example, if someone is infected,  sneezes or coughs up on doorknobs, TV remotes, computer keyboard, mouse, and telephones. Surfaces and personal items that are frequently used should be disinfected on a regular basis.  According to Mayo Clinic experts, cold and flu virus-filled droplets can remain infectious for several hours. These viruses tend to stay active for a longer period of time on plastic, stainless steel, and other hard surfaces and have a shorter life on soft surfaces and fabric. For how long the cold and flu viruses are active also depends on the environment such as humidity or temperature. 

Since the COVID pandemic started, many people are taking extra precautions to prevent the spread of viruses including increased use of hand sanitizers, social distancing, and masks. A doctor may recommend taking the COVID test. There are specific tests available including polymerase chain reaction (PCR) tests for both the common cold and flu. However, these tests are rarely done, as the diagnosis of colds and flu is based on clinical symptoms.  

When to stay at home 

The CDC recommends that everyone who is sick should stay at home until at least 24 hours after the fever is gone ( a temperature of 100F or 37.8C).  The body temperature should be checked without using medicines that reduce fever-like Tylenol or Advil. Even in case there is no fever, but flu is suspected, a person should remain at home for 4-5 days after the symptoms develop. If an individual develops flu symptoms at work they should isolate themselves from co-workers, go home and stay home for at least 24 hours until the fever subsides or after the symptoms improve. People who have asthma, COPD, or other chronic conditions should take extra precautions to avoid complications of cold and flu.  The CDC also recommends employers to review leave policies and offer schedule flexibility to allow employees to stay at home if they are sick, or if they need to take care of the children or other members of the family.  

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