RESPIRATORY TRACT

I. Incidence of infections

II. Economic impact

III. Severity of infections

IV. Exposure

V. Sites of infection

VI. Agents of infection

 

 

RESPIRATORY TRACT - General Comments

1. Common site of infection

2. Usually mild - taken for granted as one of the `vicissitudes' of life

3. Represent a huge disease burden on society - thus has MAJOR economic impact

4. URIs account for more visits to physician than any other diagnosis

In US influenza-like illnesses responsible for < 400 million days of restricted activity each yr.

5. Some respiratory infections have severe consequences (esp. in people compromised by other diseases)

Pneumonia still accounts for large no. of deaths in US population

6. Respiratory tract in direct contact with environment

7. Continuously exposed to MOs suspended in the air (Figure 1)

Some highly virulent

May infect normal person even in small numbers

Most don't cause infection unless other factors have interfered with host defenses

8. Infections at different levels of the RT (Figure 2, Figure 3, Figure 4)

Infections of conjunctive, middle ear, and paranasal sinuses included because they are continuous with RT and lined by respiratory epithelium

VIRUSES: important in upper RT - account for most cases of pharyngitis

BACTERIA: Important cause of otitis media, sinusitis, pharyngitis, epiglottitis, bronchitis, and pneumonia

FUNGI & PROTOZOA: Rarely cause serious RT infection in normal person but are important causes of pneumonia in immunocompromised individuals

Some MOs show predilection for certain sites in RT (trophics or selective survival)

e.g. reason common cold occurs in nose and not further down is that cold viruses grow best at 33C (temperature found in nose not lungs)