Suggested Citation: Garko, M. G. (2014, September). Cold and flu – Part I: Get informed, not infected. Health and Wellness Monthly. Retrieved (insert month, day, year), from www.letstalknutrition.com.
Cold and Flu – Part I: Get Informed, Not Infected
Michael Garko, Ph.D.
Syndicated Host & Producer of Let’s Talk Nutrition
They’re baaaaack, cold and flu viruses that is. Are you prepared for cold and flu season this year or are you a prime target to become infected with either a cold or flu virus, or both?
The cold and flu season for 2014 – 2015 is upon us. While the timing of flu is unpredictable, in the United States and Northern hemisphere, winter is the time of year for flu season. However, flu season begins as early as October, peaks in January or February but it can continue and persist until May (Centers for Disease Control and Prevention, 2014f). Cold season begins a little earlier than the flu season, beginning during late August, early September and lasting until March or April.
It is estimated that annually in the United States, on average 5%-20% of the population will become infected with seasonal influenza (commonly referred the as “the flu”), with more than 200,000 people being hospitalized from flu-related complications (Centers for Disease Control and Prevention 2014f).
According to the Centers for Disease Control and Prevention (CDC) (2014b), over a period of 30 years (i.e., 1976-2006), flu-associated deaths in the United States ranged annually from approximately 3,000 to about 49,000. For nearly a decade, the CDC reported that 36,000 people on average die annually from flu. After being criticized from different quarters for using inappropriate statistical methods to calculate the annual number of influenza-related-deaths, the CDC seems to have moderated its position and now reports that the “CDC does not know exactly how many people die from seasonal flu each year” (Centers for Disease Control and Prevention, 2014a, p.1). Nevertheless, those who are at especially high risk for flu-related complications are the elderly, pregnant women, those with certain health conditions and young children (Centers for Disease Control and Prevention, 2014b).
With respect to children in public schools in the United States, infectious diseases are responsible for millions of missed school days annually for kindergarten through 12th-grade students. Specifically, approximately 38 million school days are lost annually because of seasonal influenza and 22 million school days are lost annually because of colds (Centers for Disease Control and Prevention, 2011).
The September, 2014, issue of Health and Wellness Monthly, provides information on some basic characteristics of viruses. Specific attention is devoted to important aspects of influenza and the common cold, differences between them, how they are transmitted and symptoms associated with them. Also, a spotlight is put on people who are at high risk for developing common cold- and influenza-related complications.
Basic Characteristics of Viruses
Generally speaking, viruses are among the four major categories of microbes (other three being bacteria, fungi and protozoa). As microbes, they are living organisms capable of being viewed only under a microscopic, and, thus, are referred to as microorganisms. In fact, viruses are so small they cannot be seen with a conventional, light microscope but can be viewed only with an electron microscope. They are approximately one-millionth of an inch (17 to 300 nanometers) in length and are about a thousand times smaller in size than are bacteria.
More specifically, viruses are infectious microorganisms displaying a variety of morphologies or otherwise shapes and sizes (e.g., rod-shaped, sphere-shaped, helical-shaped or multi-sided) and constituted of molecules of genetic material (either DNA or RNA but not both), which contain the genes of the virus. The genes of the virus are surrounded by a durable, protective protein shell or coat. The individual proteins of the coat match-up with and attach to specific receptors located on the surface of a cell. Once attached to the surface of the cell, viruses then enter the cell and hijack its machinery so they can reproduce. It is important to remember that viruses are not cells. Rather, they are pieces of genetic material designed to attack the cells of a host (i.e., animal, plant or bacterium).
Viruses are host-dependent. They can only survive, reproduce and spread by invading a host. They can attack plants, animals (humans included) and even other microbes (i.e., bacteria). In terms of humans, viruses are capable of targeting specific cells of the tissues, organs and systems of the body (e.g., liver, brain, pancreas, respiratory system, blood cells and digestive system).
Another feature of viruses is that they can adapt and change by altering their genetic make-up. For example, they have the ability to develop resistance to drugs and vaccines. They can also jump from one type of host to another (e.g., pigs to humans, birds to humans). The ability of viruses to reproduce, adapt and move from one host to another is what makes them such a threat.
As it turns out, there are more than 400 different viruses which cause an infection and create a variety of known human illnesses. The influenza (flu) virus and its various subtypes is just one type of virus.
Influenza as a Disease
Technically, influenza viruses cause the flu (i.e., influenza), which is a contagious respiratory illness. Once infected with an influenza virus, a person can experience mild to severe symptoms and in some cases even death.
Types of Influenza Viruses
Influenza A, B and C are the three types of influenza viruses. Influenza type A and B viruses are responsible for the seasonal flu epidemics affecting tens of thousands of people and taking place nearly every winter. Influenza C virus infections can cause a mild respiratory illness but it is not considered to cause flu epidemics (Centers for Disease Control and Prevention, 2014g).
Based on two proteins, hemagglutinin (H) and the neuraminidase (N), located on its surface coat, Influenza A virus can be categorized into 18 different hemagglutinin subtypes referred to as H1 through H18 and 11 different neuraminidase subtypes referred to as N1 through N11. Without getting too complicated, suffice it to say that Influenza A viruses can be broken down further into different types of strains. There are two subtypes of Influenza A infecting people. They are influenza A (H1N1) and influenza A (H3N2) (see Centers for Disease Control and Prevention, 2014g).
Unlike influenza type A and B viruses, influenza type B viruses do not have subtypes but can be divided into different lineages (i.e., B/Yamagata and B/Victoria) and strains. Compared to influenza A, influenza B viruses cause milder symptoms and do not raise pandemic flu concerns (see Centers for Disease Control and Prevention, 2014g).
Two Ways Influenza Viruses Change
During flu season Influenza A and influenza B and subtypes of influenza A circulate and can change genetically. They change in two basic ways, antigenic drift and antigenic shift. Antigenic means possessing the properties of an antigen, which is a toxin or other foreign substance to the body that evokes the production of antibodies by the immune system.
Antigenic drift. This occurs by way of the slow accumulation of mutations occurring within the antibody-binding sites of viruses, protecting them from the antibodies developed from previous strains. Influenza viruses changing by antigenic drift occurs frequently. Antigenic drift occurs in Influenza A and Influenza B viruses. An important implication of antigenic drift is that a person infected with a particular influenza virus and who has built up antibodies against that virus may become infected with an antigenically different and newer virus. Hence, “[g]enetic changes that result in a virus with different antigenic properties is the main reason why people can get the flu more than one time. This is also why the flu vaccine composition must be reviewed each year, and updated as needed to keep up with evolving viruses” (Centers for Disease Control and Prevention, 2014d, p.1).
Antigenic shift. This a process whereby there is a sudden and major change/shift in the antigenic properties of a virus stemming from the combining of the surface antigens of the two or more original viral strains, which results in a new viral subtype. Specifically, “[s]hift results in a new influenza A subtype or a virus with a hemagglutinin or a hemagglutinin and neuraminidase combination that has emerged from an animal population that is so different from the same subtype in humans that most people do not have immunity to the new (e.g. novel) virus” (Centers for Disease Control and Prevention, 2014b, p.1). An example of an antigenic shift took place in the spring of 2009. At that time, an H1N1 virus possessing a new combination of genes emerged in the population infecting people. It spreads quickly, causing a pandemic and leaving people with little or no immune protection against the newly formed virus (see Centers for Disease Control and Prevention, 2014d).
There is a reason why the phrase “common cold” is used to refer to colds. People in the United States suffer one billion colds annually (see A.D.A.M. Medical Encyclopedia, 2013). Adults average 2-4 colds annually, with children experiencing far more colds a year. Children tend to catch a lot of colds because of their close contact with one another in daycare centers and schools.
Common Cold As A Disease
The common cold is an upper respiratory system infection caused by a virus. The virus can attack the nose, throat, sinuses, Eustachian tubes, trachea, larynx, and bronchial tubes of the respiratory system. There are more than 200 different viruses which can cause a cold. Over 200 viruses can cause the common cold. However, the rhinovirus is the most common type of virus causing colds (Centers for Disease Control and Prevention, 2013).
The CDC provides a good description of how cold viruses cause an infection:
When germs that cause colds first infect the nose and sinuses, the nose makes clear mucus. This helps wash the germs from the nose and sinuses. After two or three days, the body’s immune cells fight back, changing the mucus to a white or yellow color. As the bacteria that live in the nose grow back, they may also be found in the mucus, which changes the mucus to a greenish color. This is normal and does not mean you or your child needs antibiotics (Centers for Disease Control and Prevention, 2013, p.1).
Transmission of Common Cold and Flu Viruses
Influenza and cold viruses spread primarily from person to person by way of respiratory droplets from coughs or sneezes. When an infected person coughs or sneezes, respiratory droplets are propelled in the form of an aerosol through the air and come in contact with another person’s mouth or nose. They can also be transmitted when a person touches or comes in contact with the infected respiratory droplets on another person or contaminated object (e.g., table, desk top, restaurant counter, computer keyboard, telephone, doorknob, clothing, bedding, etc.) and then touches his/her mouth or nose or another person’s mouth or nose. The risk of getting a cold or flu increases when people find themselves in highly populated areas, such as in crowded living conditions and schools.
Differences Between the Common Cold and Flu
Since the common cold and flu are respiratory illnesses caused by viruses, they share a number of symptoms. Thus, it is sometimes difficult for people to determine whether they have a cold or flu.
Health Consequences and Complications
Typically, the flu is worse in its health impact on people than the common cold. It is worse in terms of the severity of symptoms and how it makes people feel. It is also worse in terms of its potential complications.
Generally speaking, the symptoms of the common cold are milder. Also, people with a cold are less likely to experience serious health consequences such dying, being hospitalized or suffering from dehydration, bacterial pneumonia, ear and sinus infections and a worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes (see CDC, 2007c).
It is not uncommon for the flu “knocks people off their feet.” The most common flu symptoms include the following:
- Fever (usually high) and chills
- Fatigue/tiredness (often extreme)
- Coughing (dry cough)
- Sore throat
- Nasal congestion (i.e., runny or stuffy nose)
- Muscle aches and pains (frequently intense)
- Stomach symptoms (e.g., nausea, vomiting & diarrhea) can occur but tend to affect children more than adults (Centers for Disease Control and Prevention, 2014c)
While it may not be as severe as the flu, the common cold can create a lot of discomfort for people and be quite distracting. Symptoms of the common cold usually begin 2 to 3 days after infection and often include:
- Sore or scratchy throat
- Stuffy and runny nose
- Watery eyes
- Headache (mild)
- Muscle aches and fatigue (not usually as intense as when inflected by the flu and more characteristic of influenza)
- Loss of appetite (Centers for Disease Control and Prevention, 2013).
People At High Risk For Developing Common Cold and Flu Complications
While most people who become infected with a seasonal cold or flu virus will experience uncomfortable symptoms, they will not require medical care and attention and will be on the road to recovery within less than two weeks. However, there are other individuals who are at higher risk for developing complications (e.g., pneumonia, bronchitis, sinus and ear infections & dehydration) requiring them to be hospitalized, especially when suffering from seasonal flu. Furthermore, seasonal cold and flu can exacerbate or otherwise worsen chronic medical conditions, such as congestive heart failure, asthma, or diabetes (see Centers for Disease Control and Prevention, 2014e).
According to the CDC (2014e), children who are younger than five years of age and particularly children who are younger than two years of age, adults who are 65 years of age and older and pregnant women are groups of people who are at high risk of developing complications, especially when infected with the flu virus. The CDC (2014e) also identifies several specific medical conditions which put people at higher risk for complications. The CDC’s list of risk-related medical conditions is as follows:
- Neurological and neurodevelopmental conditions [including disorders of the brain, spinal cord, peripheral nerve, and muscle such as cerebral palsy, epilepsy (seizure disorders), stroke, intellectual disability (mental retardation), moderate to severe developmental delay, muscular dystrophy, or spinal cord injury].
- Chronic lung disease (such as chronic obstructive pulmonary disease [COPD] and cystic fibrosis)
- Heart disease (such as congenital heart disease, congestive heart failure and coronary artery disease)
- Blood disorders (such as sickle cell disease)
- Endocrine disorders (such as diabetes mellitus)
- Kidney disorders
- Liver disorders
- Metabolic disorders (such as inherited metabolic disorders and mitochondrial disorders)
- Weakened immune system due to disease or medication (such as people with HIV or AIDS, or cancer, or those on chronic steroids)
- People younger than 19 years of age who are receiving long-term aspirin therapy
- People with Chronic Obstructive Pulmonary Disease (COPD)
- People who are morbidly obese (Body Mass Index, or BMI, of 40 or greater) (Centers for Disease Control and Prevention, 2014e, p. 1).
The unpredictable and infectious nature of cold and flu viruses, along with their prevalence, ability to mutate and be transmitted throughout the population, underscores the importance of becoming informed and not infected this cold and flu season. The intention of the September, 2014, issue of Health and Wellness Monthly was to provide information that would help readers not become a prime target for a cold or flu virus by providing a general understanding of viruses, along with some specific insight into influenza and cold viruses in terms of how they behave and change, their differences, their transmission and who would be at high risk for medical complications once infected with them. While not specifically focusing on how to prevent from becoming infected with a cold or flu virus, an assumption underlying the article is that if informed about the sorts of issues explored in the article, then there is less of chance to be misinformed about and infected with a flu or cold virus. This assumption will be carried over into an upcoming issue where attention will be given to prevention and treatment of the flu and common cold.
A.D.A.M. Medical Encyclopedia, 2013. Common cold. Retrieved August 4, 2014 from http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001698/.
Centers for Disease Control and Prevention (2014a). Cold vs flu. Retrieved August 15, 2014 from http://www.cdc.gov/flu/about/qa/coldflu.htm.
Centers for Disease Control and Prevention (2014b). Estimating seasonal influenza-associated deaths in the United States: CDC study confirms variability of flu. Retrieved August 4, 2014 from http://www.cdc.gov/flu/about/disease/us_flu-related_deaths.htm
Centers for Disease Control and Prevention (2014c). Key facts about influenza (flu) & flu vaccine. Retrieved August 15, 2014 from http://www.cdc.gov/flu/keyfacts.htm.
Centers for Disease Control and Prevention (2014d). How the flu virus can change: “Drift” and “shift.” Retrieved August 4, 2014 from http://www.cdc.gov/flu/about/viruses/change.htm.
Centers for Disease Control and Prevention (2014e). People at high risk for developing flu-related complications. Retrieved August 15, 2014, from http://www.cdc.gov/flu/about/disease/high_risk.htm.
Centers for Disease Control and Prevention (2014f). Seasonal influenza Q&A. Retrieved August 4, 2014 from http://www.cdc.gov/flu/about/qa/disease.htm.
Centers for Disease Control and Prevention (2014g). Types of Influenza Viruses. Retrieved August 4, 2014, from http://www.cdc.gov/flu/about/viruses/types.htm.
Centers for Disease Control and Prevention (2014h). What you should know for the 2014-2015 influenza season. Retrieved August 4, 2014 from http://www.cdc.gov/flu/about/season/flu-season-2014-2015.htm.
Centers for Disease Control and Prevention (2013). Common cold and runny nose. Retrieved August 15, 2014, from http://www.cdc.gov/getsmart/antibiotic-use/URI/colds.html.
Centers for Disease Control and Prevention (2011). Infectious diseases at school. Retrieved August 4, 2104 from http://www.cdc.gov/healthyyouth/infectious/index.htm