[Narrator:] Tuberculosis is communicated from one person to another, almost always through the air.
This film will show how airborne infection takes place, how the pattern was verified, and how such spread of infection can be controlled.
Until a few years ago, we did not know the actual mode of transmission of the germ.
There were several notions, however: through direct contact with germs on the bedding of tuberculosis patients, on their clothing,
in dust that accumulated in their rooms, or carried in moist droplets coughed or sneezed into the air.
The droplet theory was nearest the truth, even though particles as large as droplets, dust, or lint
actually cannot reach the depths of the lung necessary for infection.
Transmission begins at the source, usually a person with open, untreated tuberculosis.
To understand how it happens one, must know the particular mechanics involved.
Strong expiration such as sneezing or coughing
[Coughing] blasts forth air from the lungs.
[Cough] At the same time, it shears off droplets from the secretions lining the respiratory tract.
Once outside the body these droplets, the larger of which we see as mist, evaporate rapidly.
There is solid residue, called the droplet nucleus, may contain one or more tubercle bacilli.
These tiny nuclei are light enough to remain floating about until vented to the outdoors. They follow wherever the air currents lead.
If this contaminated air is enclosed in a hospital room or a home, it carries the threat of infection to all susceptible people within the area.
At some moment in this exposure, the susceptible person inhales an infectious particle, drawing it into his lungs.
Usually it must reach the alveoli to take effect. To do so the particle must pass all the natural traps in a respiratory tract.
The size required to accomplish this feat is estimated to be no more than five microns in diameter.
Droplet nuclei range from one to five microns in diameter. Using the vehicle of droplet nuclei, virulent tubercle bacilli reach the alveoli where they are implanted on susceptible tissue and later initiate infection.
To demonstrate this pattern of transmission and infection, a four-year study of tuberculus infection
beginning in 1956 was made under the direction of Dr. Richard L. Riley at the VA Hospital in Baltimore.
Professor William F. Wells, who originated the droplet nucleus theory in 1934, and conceived the tuberculosis study in Baltimore, was a member of the study group.
The study was carried out in a six-room pilot ward with a penthouse overhead.
An independent air conditioning system moved air through the patients' rooms, then exhausted it through animal exposure chambers in the penthouse.
The study sought to answer two questions.
First, whether animals, if placed at a reasonable distance, can be infected by breathing air contaminated with droplet nuclei produced by patients with open TB.
And second, if so, whether such airborne infection can be eliminated by disinfecting the air.
When an average of 156 animals were exposed continuously to ward air during the first two years of the study,
71 infections resulted.
Out of an average of 120 exposed continuously during the second two years, 63 infections resulted.
This test leaves no doubt that infectious droplet nuclei were present in the air of the tuberculosis ward.
The test also demonstrated that there is a wide range of infectious potential among patients.
In a case involving laryngeal tuberculosis, one patient infected 14 animals in three days,
a rate of contagion estimated to be greater than that of measles.
Although some cases did not infect any animals, those patients showing a high infectious potential were invariably open, untreated cases.
The study showed that the ward air harbored approximately one unit of contagion per 12,500 cubic feet of air.
This is roughly the amount of air a hospital ward worker will breathe during duty hours in six months to a year.
Although this is a remarkably low concentration of infective units, it is in keeping with previous observations
that household contacts of people with active TB often require prolonged exposure before acquiring infection.
It seems probable that the droplet nucleus mechanism is of predominant importance
in the spread of tuberculosis in the community.
If tuberculosis is transmitted largely through the air, we face the question, how can infection be blocked?
The pilot study data indicate that three different methods may provide defense.
The first and simplest is by mere ventilation sufficient to dilute the amount of contamination in the air.
This means leaving doors and windows open for free ventilation insofar as possible.
The second is disinfection of the air.
In a controlled unit of the study, air from the pilot ward was irradiated with ultraviolet light before passing into the control chamber.
No animal in this study developed infection. The finding indicates that disinfection is effective when practicable.
The third method is through effective drug treatment.
In the study, it was found that a patient's capacity to infect is virtually blocked within days or a few weeks after receiving effective drug treatment.
This loss of infectious potential becomes apparent before smears and culture turn negative.
In curbing infection, quick and effective treatment is an important tool.