Definition of Cold
The common cold known simply as cold, is a self-limiting acute viral infection of the upper respiratory tract.
Different viruses are responsible for cold syndromes, rhinoviruses being the most common, accounting for 30 to 50 % of all colds. The second most common causing pathogens are coronaviruses accounting for 10 to 15 % of colds.
Cold viruses are spread by direct contact with secretions from a sick person. They can also spread through aerosol of secretions, when a person coughs or sneezes.The viral contraction is followed by a 1 to 2 days incubation period during which the virus replicates its genome.
Cold symptoms peak at 1 to 3 days of infection and last 7 to 10 days, occasionally for up to three weeks. They include sore throat, nasal discharge, mild cough, and malaise.
The severity of the symptoms varies according to the virus type and between individuals. Fever is common in children and rare or mild in adults. The incidence and frequency of the common cold decline with age. Children under two years have an average of six infections per year, whereas adults about two to three only.
Diagnosis of common cold is usually clinical, even though it is impossible to identify the virus based on the symptoms, since the same symptoms are caused by different viruses.
The treatment is typically symptomatic with analgesic drugs to alleviate pain. Patients are advised to rest and drink a lot of fluids.
While a common cold infection cannot be completely prevented, physical hygiene measures such as frequent hand washing can considerably lower the risk of contracting and spreading the virus.
Definition of Flu
The term flu stands for influenza, an acute respiratory illness caused by influenza viruses A, B, and C. Influenza viruses are transmitted by aerosol of the secretions following sneezing and coughing, and by direct contact.
Depending on the type of flu virus and on the host immunity, an influenza infection can stay asymptomatic, or provoke a severe illness.
After a 1 to 2 days incubation period, sudden and severe systemic symptoms appear. They are characterized by high fever reaching 41°C in some cases, chills, headache, myalgia, malaise, and anorexia. These symptoms last from 3 to 8 days.
Moreover, an influenza illness provokes respiratory and ocular symptoms. Respiratory symptoms include coughing, nasal discharge, and sore throat. Ocular symptoms are characterized by conjunctivitis, lacrimation, photophobia, and painful eye movement.
Cough and malaise can persist for up to two weeks after the resolution of fever.
While it is mostly clinical, an influenza diagnosis is difficult because symptoms overlap with those caused by other respiratory viruses. An appropriate diagnosis is often made when symptoms are severe with high fever and cough. The patients present in this case a higher risk of developing complications. The presence of a flu epidemic in the population can also help guide the diagnosis.
Laboratory tests are used to confirm the clinical diagnosis and help choosing the right treatment, thus avoiding the inappropriate use of antibiotics.
Following a sure laboratory diagnosis, treatment with oral or intravenous antiviral drugs is recommended. The clinical symptoms are relieved with the use of analgesics, high fluid intake, and rest.
Vaccination is the most effective method to prevent an influenza infection with seasonal vaccines being updated annually. Hygiene habits like hand washing can also help prevent the spreading of the virus but are not enough on their own.
In the case of unvaccinated individuals at high risk of developing complications after a contact with the virus, the antiviral agents are recommended as prophylaxis for at least two weeks.
Difference between Cold and Flu
- Infecting agent
Rhinoviruses and coronaviruses are the most common viruses behind a cold infection, whereas Influenza A, B, and C viruses are responsible for a flu infection.
They are both spread by direct contact with secretions from a patient or by aerosol of secretions through coughing and sneezing.
- Clinical symptoms
Common cold and influenza, both infect the upper respiratory tract. The common cold presents mild symptoms including occasional fever, sore throat, nasal discharge, and malaise.
Flu symptoms are sudden and severe, with high fever reaching 41°C, chills, myalgia, general malaise, and anorexia. Respiratory symptoms are similar to the cold symptoms with a severe cough, nasal discharge, and sore throat. Ocular symptoms such as conjunctivitis, lacrimation, photophobia, and painful eye movement can also be present.
The clinical differential diagnosis between cold and flu is hard with both presenting overlapping symptoms.
Influenza is more severe with high fever and severe cough. The patients show a higher risk for complications. The presence of a population flu epidemic and laboratory tests help confirm the diagnosis.
Treatment of cold is mostly symptomatic with analgesics, fluid intake and rest. In the case of a confirmed influenza infection, oral and intravenous antiviral drugs are administered.
Hygiene measures like frequent hand washing can help prevent the spreading of cold and influenza viruses, but are not enough on their own.
Anti Influenza vaccines are annually updated and produced. They constitute the most effective method to prevent and control flu infections. Antiviral drug prophylaxis is recommended for unvaccinated patients in contact with the virus.
Cold vs Flu
Cold and flu are two different viral infections of the upper respiratory tract, caused by different viruses. They present overlapping respiratory symptoms making the proper clinical diagnosis hard.
The severity of an influenza infection combined with laboratory tests can help guide the choice of treatment.
Both diseases can be controlled and prevented through hygiene measures and vaccination.
Author: Lyne Chahine
Lyne Chahine holds a Master’s Degree in Biomedical Sciences from the Free University of Brussels in Belgium, and a Master’s Degree in Cellular and Molecular Physiopathology from the Paul Sabatier University in Toulouse, France.