Self-Study Modules on Tuberculosis
Return to Module 5 Main Menu
This is an archived document. The links
and content are no longer being updated.
Module 5: Infectiousness and Infection Control
Reading Material
Infectiousness
What Factors Affect the Infectiousness of a TB Patient?
The infectiousness of a TB patient is directly related to the
number of tubercle bacilli that he or she expels into the air. Patients
who expel many tubercle bacilli are more infectious than patients
who expel few or no bacilli. The number of tubercle bacilli expelled
by a TB patient depends on the following factors.
What is the site of the disease?
Usually, only people with pulmonary or laryngeal TB (TB of the
larynx) are infectious. This is because these people may be coughing
and expelling tubercle bacilli into the air. People with extrapulmonary
TB only (no pulmonary TB) generally are not infectious. This is
because tubercle bacilli usually cannot be expelled into the air
from an extrapulmonary site.
Does the chest x-ray show that the patient has a cavity in the
lung?
Because there are many tubercle bacilli in a cavity, patients
who have a cavity in the lung may be expelling tubercle bacilli
if they are coughing.
Is the patient coughing? If so, how often and how forcefully?
Patients expel more tubercle bacilli if they have a cough that
produces a lot of sputum. Also, they may expel tubercle bacilli
if they are undergoing medical procedures that cause them to cough
(cough-inducing procedures).
Does the patient cover his or her mouth when coughing?
Patients who do not cover their mouth when they cough are more
likely to expel tubercle bacilli.
Are there acid-fast bacilli on the sputum smear?
The presence of acid-fast bacilli on a sputum smear indicates
that the patient may be expelling tubercle bacilli.
Is the patient receiving adequate treatment?
Patients who have NOT been receiving adequate treatment are much
more likely to be infectious than patients who have been receiving
adequate treatment for 2 to 3 weeks or longer. Patients who have
been receiving adequate treatment usually respond to treatment;
in other words, their symptoms improve and eventually go away.
Also, patients who have drug-resistant TB are more likely to
be infectious than patients who have drug-susceptible TB. This is
because patients with drug-resistant TB may not respond to the initial
drug regimen, and they may remain infectious until they receive
proper drugs.
These factors are summarized in Table 5.1.
Young children with pulmonary or laryngeal TB disease are much
less likely than adults to be infectious. This is because children
generally do not produce sputum when they cough. However, it is
possible for children to transmit TB to others.
Infectiousness appears to decline very rapidly after adequate
treatment is started, but how quickly it declines varies from patient
to patient. Some patients may stop being infectious on the day they
begin treatment. Others may remain infectious for weeks or even
months. Patients with drug-resistant TB may not respond to the initial
drug regimen, and they may remain infectious until they receive
proper drugs.
Patients can be considered noninfectious when they meet
all of the following criteria:
- They have been receiving adequate treatment for 2 to 3 weeks
- Their symptoms have improved (for example, coughing less
and no longer have a fever)
- They have THREE consecutive negative sputum smears from
sputum collected on different days
Study Questions 5.1-5.3
5.1. Why does the site of disease affect the infectiousness
of a TB patient?
5.2. List five other factors that affect the infectiousness
of a TB patient.
5.3. When can a TB patient be considered noninfectious?
List all three criteria.
Answers
|
Case Study 5.1
For each of the following situations, decide whether
the patient should be considered infectious or noninfectious,
and explain why.
- Mr. Lopez started TB treatment 7 days ago. He
still has a cough. Two weeks ago, he had a sputum
smear that was positive; since then no sputum specimens
have been tested.
- Ms. Nguyen, a patient with pulmonary TB, has
been receiving TB treatment for 6 weeks, and she
no longer has symptoms of TB. She has had three
sputum smears done. The first one was positive,
but the last two were negative.
- Mr. Martin started treatment for pulmonary TB
in April. His symptoms went away and his sputum
smears became negative in May. He missed his clinic
appointment in June. When he returned to the TB
clinic at the beginning of August, he was coughing.
Answers
|
Last Reviewed: 05/18/2008 Content Source: Division of Tuberculosis Elimination
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
|