Upper Respiratory Tract Infections
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INFECTIONS OF THE UPPER RESPIRATORY TRACT

General Goal: To know the major cause(s) of these diseases, how they are transmitted, and the major manifestations of each disease.

Specific Educational Objectives: The student should be able to:

1. recite the common cause(s) of these disease.

2. describe the common means of transmission.

3. describe the major manifestations of this infection.

4. describe how you diagnose, treat and prevent this infection.

Reading: MEDICAL MICROBIOLOGY by P.R. Murray, K.S. Rosenthal, G.S. Kobayashi and M.A. Pfaller, 3rd Edition. page number depends on microorganism.

Mosby's Color Atlas and Text of Infectious Diseases by Christopher P. Conlon and David R. Snydman. pp.53-66.

Lecture: Dr. Neal R. Chamberlain

References:

OVERVIEW

The discussion of the respiratory tract is divided into three different sections in this handout: upper respiratory tract infections, respiratory airway infections, and lower respiratory tract infections. This section of the handout will discuss infections of the upper respiratory tract and includes infections of the nasal passages, paranasal sinuses, and the pharynx (Figure R-1). The diseases that are included in this chapter are the common cold, rhinosinusitis, pharyngitis and diphtheria. Viruses are the most common cause of all of these diseases except for diphtheria.

I. The Common Cold

The common cold is caused by a multitude of organisms; about 90% of cases are due to viruses.

Etiology

Most cases of the common cold are caused by rhinoviruses; there are at least 100 immunologically distinct rhinoviruses. Other causes of the common cold are listed in Table URI-1.

Table URI-1. Some Infectious Agents that Cause the Common Cold
Agents*	Human Serotypes
Myxoviruses
Influenza	A, B, C
Parainfluenza	1, 2, 3, 4
Respiratory syncytial virus	1 (possibly 2)
Human metapneumovirus	1
Coronaviruses	1
Picornaviruses
*Rhinoviruses (most common cause)*	> 100 types
Coxsackievirus A	24
Coxsackievirus B	6
Echoviruses	31 (only types 11, 20, and 25 may cause respiratory illnesses)
Adenoviruses	34 (types 1, 2, 3, 5, 7, 14, and 21 are responsible for respiratory illnesses)
*Mycoplasma pneumoniae*	1

*Nonbacterial agents are responsible for > 90% of upper respiratory infections in humans.

Manifestations

Initially, the common cold begins with nasal stuffiness, sneezing, and headache. Rhinorrhea then occurs with increasing severity. General malaise, lacrimation, sore throat, slight fever, and anorexia are common in moderate to severe cases. If organisms enter the trachea and bronchi, a tracheobronchitis develops and there may be a cough and a feeling of substernal discomfort.

Epidemiology

The common cold is worldwide in distribution.
A child younger than 5 years of age can acquire five to seven colds per year, and an adult can acquire one or two colds per year.
The common cold is usually seen in the winter months.
Viruses are spread person to person, usually during hand-to-hand contact (e.g., shaking hands).

Pathogenesis

The rhinovirus infects the nasal passages following direct contact of contaminated surfaces or via inhalation of infectious droplets. It then infects the cells lining the nasal passages and the pharynx following attachment to intercellular adhesion molecule-1 (i.e., ICAM-1) on the host cells. Inflammatory changes occur with hyperemia, edema, and leukocyte inflammation. The ciliated columnar epithelial cells are destroyed and slough off.

The pathology reaches its peak by days 2 to 5. Regeneration of the cells begins rapidly, with new cells formed by about the day 14. The acute phase of the illness begins with a runny nose, when copious amounts of clear, mucoid nasal secretions are produced. After 1 to 2 days, a secondary bacterial infection by the normal flora causes the secretions to become mucopurulent. If severe, blockage of the sinus ostia or the eustachian tubes can occur, resulting in paranasal sinusitis (acute rhinosinusitis) or otitis media. Complications are usually related to the infection extending to the lower respiratory tract and resulting in bronchitis.

Diagnosis

Diagnosis of the common cold is dependent on the patient’s symptoms, localization of the disease process, time of year, and afebrile course. Laboratory culture of the viruses and serologic testing is rarely performed.

Therapy and Prevention

Treatment of the common cold involves supportive therapy to ease the patient’s discomforts. The studies on the use of zinc acetate lozenges and nasal gel containing zinc gluconate are mixed. Some say zinc helps. Others say they are of no help in treating patients with the common cold. Regular intake of large doses of vitamin C (0.2 gm/day) may shorten the duration of the illness and decrease the severity of symptoms of the common cold. However, the effects were so small that many doubt vitamin C’s usefulness in treating the common cold. Regular intake of megadoses of this vitamin did not decrease the number of colds people got and so is not recommended to prevent the common cold. The only study that showed benefit of daily megadoses of vitamin C was in people exposed to severe physical exercise or cold environments for short periods of time. Handwashing and disinfecting contaminated objects can help to avoid acquiring the common cold as well as avoiding contact with others during the cold season.