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UPPER RESPIRATORY TRACT INFECTIONS
OVERVIEW
The upper respiratory tract includes the sinuses, nasal passages, pharynx, and larynx. These structures direct the air we breathe from the outside to the trachea and eventually to the lungs for respiration to take place.
An upper respiratory tract infection, or upper respiratory infection, is an infectious process of any of the components of the upper airway.
Upper respiratory infections are one of the most frequent causes for a doctor visit with varying symptoms ranging from a runny nose, sore throat, cough, to breathing difficulty, and lethargy. In the United States, upper respiratory infections are the most common illness leading to missing school or work.
Although upper respiratory infections can happen at any time, they are most common in the fall and winter months, from September until March. This may be explained because these are the usual school months when children and adolescents spend a lot of time in groups and inside closed doors. Furthermore, many viruses of upper respiratory infection thrive in the low humidity of the winter.
TRANSMISSION
Most upper respiratory tract infections are due to self-limited viral infections. Occasionally, bacterial infections may cause upper respiratory infections. Most often, upper respiratory infection is contagious and can spread from person to person by inhaling respiratory droplets from coughing or sneezing. The transmission of respiratory infections can also occur by touching the nose or mouth by hand or another object exposed to the virus.
CAUSES
An upper respiratory tract infection is generally caused by the direct invasion of the inner lining (mucosa or mucus membrane) of the upper airway by the culprit virus or bacteria. For the pathogens (viruses and bacteria) to invade the mucus membrane of the upper airways, they must fight through several physical and immunologic barriers.
The hair in the lining of the nose acts as a physical barrier and can potentially trap the invading organisms. Additionally, the wet mucus inside the nasal cavity can engulf the viruses and bacteria that enter the upper airways. There are also small hair-like structures (cilia) that line the trachea which constantly moves any foreign invaders up towards the pharynx to be eventually swallowed into the digestive tract and into the stomach.
In addition to these intense physical barriers in the upper respiratory tract, the immune system also does its part to fight the invasion of the pathogens or microbes entering the upper airway. Adenoids and tonsils located in the upper respiratory tract are a part of the immune system that helps fight infections. Through the actions of the specialized cells, antibodies, and chemicals within these lymph nodes, invading microbes are engulfed within them and are eventually destroyed.
Despite these defense processes, invading viruses and bacteria adopt various mechanisms to resist destruction. They can sometimes produce toxins to impair the body's defense system or change their shape or outer structural proteins to disguise from being recognized by the immune systems (change of antigenicity). Some bacteria may produce adhesion factors that allow them to stick to the mucus membrane and hinder their destruction.
Different pathogens have varying abilities to overcome the body's defense system and cause infection.
It is also important to note that different pathogens have varying abilities both viruses and bacteria can cause acute upper respiratory tract infections:
Viruses
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rhinovirus
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adenovirus
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coxsackievirus
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parainfluenza virus
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respiratory syncytial virus
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human metapneumovirus
Bacteria
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group A beta-hemolytic streptococci
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group C beta-hemolytic streptococci
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Corynebacterium diphtheriae (diphtheria)
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Neisseria gonorrhoeae (gonorrhea)
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Chlamydia pneumoniae (chlamydia)
to overcome the body's defense system and cause infection.
TYPES
Infection of the specific areas of the upper respiratory tract can be named specifically. Examples of these may include:
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Rhinitis -- inflammation of the nasal cavity
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Sinusitis or rhinosinusitis -- inflammation of the sinuses located around the nose
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Nasopharyngitis -- inflammation of the nares, pharynx, hypopharynx, uvula, and tonsils
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Pharyngitis -- inflammation of the pharynx, uvula, and tonsils
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Epiglottitis -- inflammation of the upper portion of the larynx or the epiglottis
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Laryngitis -- Inflammation of the larynx
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Laryngotracheitis -- inflammation of the larynx and the trachea
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Tracheitis -- inflammation of the trachea
SYMPTOMS
Symptoms of upper respiratory infection include:
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cough,
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sneezing,
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nasal discharge,
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nasal congestion,
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runny nose,
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fever,
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scratchy or sore throat, and
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nasal breathing
Some common risk factors for upper respiratory infection are:
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physical or close contact with someone with an upper respiratory infection.
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poor hand washing after contact with an individual with an upper respiratory infection.
RISK FACTORS
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close contact with children in a group setting, schools, or daycare centers.
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contact with groups of individuals in a closed setting, such as traveling, tours, cruises.
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smoking or second-hand smoking (may impair mucosal resistance and destroy the cilia).
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health care facilities, hospitals, nursing homes.
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immunocompromised state (compromised immune system) such as HIV, organ transplant, congenital immune defects, long term steroid use;
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anatomical abnormalities as in facial trauma, upper airway trauma, nasal polyps.
Most cases of upper respiratory tract infections are caused by viruses.
DIAGNOSIS
In evaluating people with a suspected upper respiratory infection, other alternative diagnoses need to be considered. Some of the common and important diagnoses that can resemble upper respiratory infection are:
The diagnosis of upper respiratory tract infections is typically made based on a review of symptoms, physical examination, and occasionally, laboratory tests.
TREATMENT
As described above, most cases of upper respiratory tract infections are caused by viruses and therefore, require no specific treatment and are self-limited. People with upper respiratory infections typically diagnose themselves and treat their symptoms at home without requiring a doctor's visit or prescription medications.
Rest is an important step in treating upper respiratory infections. Usual activities, such as working and light exercising may be continued as much as tolerated. Increased intake of oral fluids is also generally advised to keep up with the fluid loss from a runny nose, fevers, and poor appetite associated with upper respiratory infections. Treatment of the symptoms of upper respiratory infection is usually continued until the infection has resolved.
PREVENTION
There are several measures that can reduce the risk of infections in general. Smoking cessation, reducing stress, an adequate and balanced diet, and regular exercise are all measures that can improve the immune system and reduce the overall risk of infections. Breastfeeding also helps strengthen the immune system of infants by transferring the protective antibodies from the mother's milk to the baby.
Other preventive measures to diminish the risk of spread of upper respiratory infections are:
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handwashing is especially encouraged during the cold seasons (fall and winter) or handling others with the infection.
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reducing contact with people who may have the infection (people may carry and spread the virus a few days before they have symptoms and a few days after their symptoms have resolved).
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proper cleaning of common objects that are touched by individuals who may be infectious such as, telephones, refrigerator door, computers, stair railings, door handles, etc.
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covering mouth and nose when coughing or sneezing
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vaccination with flu vaccine as recommended for certain people (elderly, people with chronic medical conditions, health care workers, etc.).
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asthma,
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pneumonia,
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H1N1 (swine) flu,
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influenza,
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allergic reactions,
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seasonal allergies,
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chronic (long-standing) sinusitis,
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acute HIV infection, and
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bronchitis