Probably the two most frequently abused words in the health and medical dictionary are 'cold' and 'flu', which are incidentally the two most common illnesses to plague mankind. Because very few of us actually know the difference between the two, and even fewer have shared that knowledge, most of us go through life using the two words indiscriminately and getting confused when the doctor tells us we have one condition or the other.

Now, we are all aware that the common cold and influenza are severely debilitating illnesses that take only one infected person and a poorly ventilated room to spread. The question is: is there any difference between the two?

You bet.

What Causes the Common Cold and Influenza?

Both the cold and the 'flu are caused by viruses. The common cold is caused by a wide variety of them. Rhinoviruses are responsible for 30-35% of all adult colds, but most other adult cold cases are caused by coronaviruses, especially those that occur in winter or early spring. Influenza, on the other hand, is caused by three types of influenza viruses¹: influenza type A, B and C. The Type A virus tends to cause more severe illness than the other two, and it has been reported that a new strain of Type A influenza virus emerges every ten years or so to replace the pre-existing strain.

How Common Are the Cold and the 'Flu?

According to a report from the US National Institute of Allergy and Infectious Disease (NIAID), children catch cold as often as twelve times a year; adults commonly catch cold three to four times a year. The National Centre for Health Statistics (NCHS) also claims that there were 62 million cases in 1996, causing '45 million days of restricted activity and 22 million days lost from school'. Influenza affects perhaps 10-20% of the people, and the American Lung Association reported over 95 million cases in 1996 alone.

How Severe are these Infections?

The common cold rarely poses a severe threat to one's health, and even when it does, its damage is usually social. The degree of infection varies from subclinical infection (no symptoms) to mild sneezing to full-blown common cold (acute, self-limiting upper respiratory tract infection), depending on the type of pathogen at work. It may be of interest to note that 10-15% of adult colds are caused by families of viruses that do not cause too much trouble as cold pathogens, but are perfectly capable of wreaking havoc under other circumstances. One example is the coronavirus, which is responsible for the highest number of common cold cases, and yet was reported recently as being the causative agent of Sudden Acute Respiratory Syndrome (SARS), which has caused up to 404 deaths worldwide at the time of writing.

On the other hand, influenza viruses are unpredictable. Influenza cases may be moderately severe even if the infected individual is healthy to begin with, although the victim usually recovers fully within a week or so. However, for those who are not healthy to begin with, influenza can be fatal, causing an average 36,000 deaths and 114,000 hospitalisations per year in the US alone. And then there are the 'flu pandemics²: the Spanish Flu of 1918-19, which caused 20-50 million deaths worldwide; the 1957-58 Asian Flu, which killed over 70,000 Americans; and more recently, the Avian Flu in Hong Kong (1997) which was mercifully contained before it could kill more than six people.

Who Is at risk?

Practically everybody, no matter how healthy, will come down with a cold at least once during his or her lifetime. However, people who have asthma and underlying respiratory diseases such as bronchitis or Chronic Obstructive Pulmonary Disease (COPD) face the risk of additional complications with viral respiratory diseases.

As with the common cold, everybody will catch the 'flu sooner or later. Those who are healthy to begin with will simply suffer a week or so of debilitation. However, influenza can become severe, even fatal for those who fall into the high-risk group. This group includes those who suffer from chronic lung diseases such as asthma, emphysema, chronic bronchitis, bronchiectasis, tuberculosis, or cystic fibrosis; those with heart or chronic kidney disease, or chronic metabolic disorder such as diabetes; anaemics; those who are immunocompromised because of disease or medical treatment; and senior citizens, especially those residing in health care facilities.

How Do You Know if You Have a Cold or Influenza?

Here is a list of symptoms of cold and 'flu.

How Are These Two Infections Different?

Both the cold and 'flu infection start out the same way. The causative virus enters the human body, penetrates target cells and establishes command of the cell's protein-making mechanism to make more copies of itself.

Medical researchers hypothesise that the symptoms for the common cold are the result of the body's immune response to viral invasion. When infected, cells lining the nasal passage broadcast signals that recruit specialised white blood cells to the site of infection, where these blood cells secrete immune system chemicals such as kinin. It is speculated that these chemicals cause cold symptoms by inducing swelling and inflammation of the nasal membranes, leakage of proteins and fluid from capillaries and lymph vessels, as well as increasing mucus production.

The influenza virus, on the other hand, infects endothelium cells in the lower respiratory tract. It takes over the cell machinery to produce new RNA segments, which will enable production of virus particles, which, when assembled, will bud out of the host cell, causing the cell to die several hours later. This allows it to spread through the mucosal lining of the respiratory tract, causing destruction in its wake. Secondary infection by bacteria sometimes follows because the infected endothelium cells are incapable of proper cilial movement or phagocytic activity; also, their exudates make perfect nourishment for bacteria.

How Are These Two Illnesses Cured?

It seldom takes medication to cure the common cold. It is generally recommended that the patient get plenty of rest and fluids, and that he or she gargle with warm salt water and apply petroleum jelly to their raw nose. In the event of a headache or fever, these can be kept under control with generic aspirin³ or acetaminophen. Some may choose to alleviate their conditions by using decongestants and cough suppressants; however, these will do nothing to shorten the period of infection. Although a prescribed cytokine called interferon-alpha has been known to prevent infection and illness, it nevertheless produces undesirable side effects such as nosebleeds, and is consequently not recommended for therapy.

The standard cure for influenza is similar, the golden rule being to stay in bed at home for as long as the illness persists. Fever, aches and pains, as in the case of the cold, are treated with acetaminophen. In the event that somebody comes down with the more severe influenza A, he or she may be given an antiviral drug (amantadine or rimantadine). Two new drugs, Zanamivir and Oseltamivir, have also been shown to ameliorate 'flu conditions if taken at the onset of the 'flu. Please bear in mind, however, that all these drugs are perfectly capable of causing undesirable side effects such as insomnia, depression and stomach upsets, and should only be taken if prescribed by the doctor.

Please also take note that since both the cold and influenza are caused by viruses, there would be no use in taking antibiotics either as a prophylactic or cure, unless of course one is suffering from secondary bacterial infection as a complication.

Are There Any Preventive Measures I Can Take?

Where the common cold is concerned, the best preventive action that works is avoidance of the virus. Because cold viruses are transmitted by droplets or respiratory secretion, therefore hand-washing is probably one of the most effective ways of keeping the cold at bay. When in the company of someone who has a cold⁴, avoid touching your eyes or nose - there might be infective droplets on your hands - and if possible, clean possibly contaminated surfaces with a virus-killing disinfectant. Avoid sharing easily contaminated things with an infected person⁵, and keep your personal hygiene items far away - or make sure they can be cleaned properly. (These are all just common sense measures) Maintenance of a healthy immune system is also important if you are to avoid a cold. There is currently no vaccine for the common cold because there are just too many viruses to target, and the said viruses have a tendency to evolve over a short period of time.

There are influenza shots on the market that prevent influenza with a high degree of success; however, new vaccines have to be made yearly to accommodate variation in the strains of virus causing influenza⁶. Even then, the efficacy of the vaccine will vary from year to year, depending on the influenza strains. The good news, however, is that people who do still get influenza despite their shots tend to get milder infections, and are less likely to get hospitalised. The bad news is that some people are mildly allergic to the vaccine.

Influenza shots are generally recommended for people over 65 years of age, those who are immunocompromised, healthcare workers who might transfer the 'flu to their high-risk patients and pregnant women in their second or third trimester during the flu season.

If, however, you do not want to get a 'flu shot or are unable to have one, and yet wish to protect yourself because you are in a high-risk area, then the best solution is to use a mask. However, be aware of the fact that there are many types and grades of masks for different purposes, and that there are some that will not offer proper protection. When procuring masks, make sure they are of the N95 variety. Don't share your mask with anybody, and don't try to scrimp and save by trying to wash and recycle them. It doesn't work that way.

An Aside - Common Fallacies About the Cold and 'Flu

We've all heard myths about influenza and the cold. Stuff about how influenza shots actually cause the 'flu, and how taking Vitamin C will keep the rhinovirus at bay. Here is a list of facts dispelling those warped notions:

1. Influenza shots do not cause influenza. The viruses used to make the vaccines are attenuated⁷ or killed⁸.

2. Yes, you do need to get a 'flu shot every year, no matter what others say. This is because new influenza virus strains emerge every year, and old vaccines may not work efficiently against them.

3. Vitamin C does not necessarily protect you from a cold, or cure you should you catch one⁹. If you wish to try this cure, however, please check with your physician first on the appropriate dosage.

4. While steam inhalation therapy may temporarily clear one's nasal passages, it does nothing to inhibit viral replication.

5. Cold weather does not cause common cold. Exposure to cold weather, getting chilled or overheated have not been found to contribute to the development or severity of a cold. However, conditions such as psychological stress, allergic disorders affecting the nasal passages or throat, and menstrual cycles may make one more susceptible to infection by a cold-causing virus¹⁰.

6. And most importantly: influenza isn't just a pain in the neck/back/head. It is most capable of causing serious harm to whoever falls into the high-risk group.

Swine Flu Links

• BBC Health Conditions: Swine Flu
• NHS Swine Flu Information
• Government Flu Pandemic Page

References

Barbaree, JM, RF Breiman, AP Dufour (Editors) (1993) Legionella: Current Status and Emerging Perspectives - American Society for Microbiology, Washington DC

Madigan, MT, JM Martinko and J Parker. 1997. Brock Biology of Microorganisms, 8th ed. Prentice-Hall International, Inc, New Jersey.

Please Note: h2g2 is not a definitive medical resource. If you have any health concerns you must always seek advice from your local GP. You can also visit NHS Direct or BBC Health Conditions.