Colds and influenza are both respiratory illnesses and many people use the terms interchangeably. However, they are both caused by different viruses. Charmaine Gauci, director, Health Promotion and Disease Prevention Directorate, spots the differences.

Symptoms of common cold v influenza

Influenza is more serious than a common cold. With a cold, the symptoms are centered on the nose and throat. But influenza tends to make the whole body ache and the patient is sick all over.

The symptoms of a cold include a runny or blocked nose, sneezing, throat irritation, mild fever, a sore throat (in 40 per cent of cases), a cough (in 50 per cent of cases), blocked ears and coloured mucus or nasal discharge.

Symptoms of influenza usually start suddenly with a high fever, and one may feel sick enough to go to bed. Other symptoms include irritation in the throat or lungs, a dry cough, high fever, shivering, sweating and severe muscle aches.

Tests are available to diagnose influenza but there are no such tests for colds. Most of the time, the doctor does not do any tests but recommends treatment based on the diagnosis made from symptoms. If a patient needs hospitalisation, then further tests are done as required.

Infection mechanism

Both the common cold and the influenza viruses are transmitted by the airborne route and by direct contact.

The incubation period (time from contact with virus to development of symptoms) for influenza is one to four days, with an average of two days.

Persons can be infectious starting the day the symptoms begin through approximately three to five days from clinical onset but children may be infectious for a longer period. The incubation period for the common cold is even shorter and may be 12 hours.

The most common way to catch influenza or a cold is to inhale droplets from coughs or sneezes of an infected person. The infectious period (time during which an infected person can infect others) begins about one day before symptoms start, and continues for the first five days of the illness.

Symptoms, however, are not necessary for viral shedding or transmission as a percentage of asymptomatic subjects exhibit viruses in nasal swabs, likely controlling the virus at concentrations too low for them to have symptoms.

Another common way of getting the viruses is by direct contact. When an infected person touches an object such as a door handle, shopping trolley or another human, they leave the virus behind. The next person to touch the object takes on the virus.

All that's needed to trigger an infection is a dozen virus particles. If the person who has picked up the cold virus touches their own nose or eyes, they deposit it in a warm, moist environment, where it can thrive and start off an infection.

Prevention

Another difference between the common cold and influenza is that the flu is preventable by means of a vaccine.

Every season, only a few strains of the influenza virus cause most of the flu across the world. Hence a vaccine is available.

On the other hand, the common cold is caused by a large variety of viruses, which change very frequently, resulting in constantly changing virus strains. Vaccines cannot be developed for the common cold.

In Malta, the influenza vaccination campaign kicks off in October to offer immunity to people by the time the viruses are around.

It is offered free of charge to people over 55, children under five, people who are more susceptible to complications and some work categories, such as health care workers.

The uptake over the years has been good with over 75,000 vaccinations every year.

The best way to avoid a cold is to avoid close contact with people who are sick, to wash hands thoroughly and regularly; and to avoid touching the mouth and face. These principles apply for influenza too.

Treatment

Common cold treatment: There is no cure for the common cold.

Treatment is limited to symptomatic supportive options, maximising the comfort of the patient and limiting complications and harmful sequelae. The most reliable treatment is a combination of fluids and plenty of rest. The common cold is self-limiting. In healthy people, it resolves in seven days on average.

Antibiotics are not at all effective in treating common cold because colds are caused by a virus, not by bacteria.

Influenza treatment: People with influenza are advised to get plenty of rest, drink a lot of liquids, avoid using alcohol and tobacco and, if ­necessary, take medications such as paracetamol to relieve the fever and muscle aches.

Antibiotics have no effect on the infection unless a doctor prescribes them for secondary infections such as bacterial pneumonia. Antiviral ­medication is sometimes effective but this too should be taken following doctor’s advice.

Comparing cold and flu