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:

I. The Common Cold

ETIOLOGY and EPIDEMIOLOGY

The common cold is caused by a multitude of organisms. 90 percent of the cases of the common cold are due to viruses. Table 21-1 contains a list of the organisms that cause the common cold.

The common cold is worldwide in it's distribution and is spread person-to-person. Most commonly the viruses are spread during hand-to-hand contact (shaking hands, etc.). The average child (less than 5 years of age) will get 5-7 colds per year and the average adult will get 1-2 colds per year.

The common cold is seen mostly in the winter months. More infections in these months occur due to more person-to-person contact during this time of year. The most common cause of the common cold is the rhinoviruses (10 to 25%).

Table 21-1. Nonbacterial Agents that Cause Upper Respiratory Tract Infections of Man

Agents	Human Serotypes	Nucleic Acid Types	Date of Discovery
Myxoviruses
Influenza	A, B, C	RNA	1933-1949
Parainfluenza	1, 2, 3, 4	RNA	1953
Respiratory Syncytial Virus	1 (maybe 2)	RNA	1956
Coronaviruses	1	RNA	1965
Picornaviruses
Rhinoviruses- most common cause.	> 100 types	RNA	1960s
Coxsackie virus A	24 (perhaps only A₂₁ causes respiratory illnesses)	RNA	1948
Coxsackie virus B	6 (perhaps only B₄, B₅ cause respiratory illnesses)	RNA	1948
Echoviruses	31 (perhaps only types 11, 20, 25 cause respiratory illnesses)	RNA	1950s
Adenoviruses	34 (types 1, 2, 3, 5, 7, 14, 21 are responsible for respiratory illnesses)	DNA	1953
*Mycoplasma pneumoniae*	1	DNA + RNA	1944

*Nonbacterial agents are responsible for more than 90% of the upper respiratory infections in man.

Rhinoviruses

These viruses are responsible for 25% of the colds seen in the U.S. There are at least 100 immunologically distinct rhinoviruses. This makes vaccine production virtually impossible. 80% of these bind to ICAM-1on the human epithelial cells. These viruses are picornaviruses labile to pH of 3 therefore they are not present in the gastrointestinal tract as one would see the poliovirus. These viruses also grow optimally at 33° C which is the temperature of the nasal mucosa of humans. Coronaviruses

These viruses are enveloped RNA viruses. More than 20 strains of coronaviruses have been obtained from humans. In adults coronaviruses can cause from 10 to 24% of common colds. Coxsackieviruses and Echoviruses

Both these viruses are picornaviruses which are placed in the enterovirus category due to their residence in the intestines. Coxsackieviruses are grouped into groups A and B. Each group consists of several serotypes. Echoviruses are not grouped but several types exist. Usually these viruses cause aseptic meningitis and pleurodynia (pain in the intercostal muscles due to irritation of pleural surfaces) but occasionally they have been found to cause the common cold. Myxoviruses

This group of viruses contains Influenza viruses, Parainfluenza viruses, and Respiratory Syncytial virus; all of which can cause the common cold. Influenza viruses (types A, B, and C) typically cause influenza, which we will discuss later, however it can also cause the common cold. In adults the four types of parainfluenza viruses can cause the common cold, however, in children these viruses can cause severe disease including croup, bronchitis, and pneumonia. Respiratory syncytial virus causes the common cold in adults. In children it is associated with severe lower respiratory tract infections.

Adenoviruses

Only a few of the 34 types of adenoviruses cause the common cold. These infections are particularly a problem in military recruits.

Mycoplasma pneumoniae

This organism is not a virus but rather a cell-wall deficient bacterium. This organism can cause respiratory infections that range from the common cold to bronchopneumonia.

PATHOLOGY and PATHOGENESIS

The suspectable person acquires the virus by direct contact or via inhalation of droplets. The cells lining the nasal passages and the pharynx are infected by the virus. Rhinovirus attaches itself to the cells lining the nasal region by binding to ICAM-1 (InterCellular Adhesion Molecule-1). Inflammatory changes occur with hyperemia, edema, and leukocyte inflammation. The ciliated columnar epithelial cells are destroyed and slough off.

The destruction reaches its peak by day 2 to 5. Regeneration of the cells begins quite quickly with new cells formed by about the 14th day.

The acute phase of the illness presents with a runny nose. Large amounts of material is produced that is clear and mucoid. After 1 to 2 days secondary bacterial infection by the normal flora causes the secretions to become mucopurulent.

If severe blockage of the sinus ostia and the eustachian tube occurs it may lead to paranasal sinusitis or otitis media.

MANIFESTATIONS

Initially, the patients experiences nasal stuffiness, sneezing, and headache. Rhinorrhea then occurs with increasing severity. General malaise, lacrimation (secretion and discharge of tears), sore throat, slight fever, and anorexia are common in moderate to severe cases.

If the organisms get into the trachea and bronchi then a tracheobronchitis develops and the patients may start coughing and feeling substernal discomfort.

DIAGNOSIS

This is largely dependent on the patients symptoms, the localization of the disease process, the time of year, and an afebrile course. Laboratory culture of the viruses has been done but is very impractical. Serology is also unnecessary but is available.

Prognosis: Usually, the patient totally recovers in 1 week. Complications are usually related to extension of infection to the lower respiratory tract resulting in bronchitis, or inflammation of the nasal ostia/eustachian tube resulting in paranasal sinusitis/otitis media.

THERAPY

Supportive therapy to ease the patients discomforts. Zinc acetate lozenges shorten the duration and lowered the severity of syptoms of the common cold (Prasad, A.S. et.al., Duration of symptoms and plasma cytokine levels in patients with the common cold treated with zinc acetate. A randomized, double-blind, placebo-controlled trial. Ann Intern Med 2000 Aug 15;133(4):245-52).

PREVENTION Researchers are working with ICAM-1 receptor have used a soluble ICAM-1 called tremacamra to see if infection with Rhinoviruses can be prevented. Preliminary results are promising (Turner RB, Wecker MT, Pohl G, Witek TJ, McNally E, St George R, Winther B, Hayden FG, Efficacy of tremacamra, a soluble intercellular adhesion molecule 1, for experimental rhinovirus infection: a randomized clinical trial. JAMA 1999 May 19;281(19):1797-804).

WASH your hands and disinfect contaminated objects. Avoiding hand contact with other people during the cold season. No vaccine is available.