TUBERCULOSIS AS INFECTIOUS DISEASE

2.  A TB infection doesn’t always mean a person will
get sick. There are two forms of the disease:
• Latent TB: Patient will have the bacteria in the
body, but the immune system keeps them from
spreading. Patient don’t have any symptoms, and
he is not contagious. But the infection is still alive
and can one day become active. If he is at high risk
for re-activation -- for instance, if the patient have
HIV, an infection in the past 2 years, the chest X-
ray is unusual, or the immune system is weakened
-- the doctor will give the patient medications to
prevent active TB.

3. • Active TB. The bacteria multiply and make
the patent sick. Patient can spread the
disease to others. Ninety percent of active
cases in adults come from a latent TB
infection.
 A latent or active TB infection can also
be drug-resistant, meaning certain
medications don’t work against the bacteria.

4.  One quarter of the world's population was thought
to have latent infection with TB. New infections
occur in about 1% of the population each year. In
2018, there were more than 10 million cases of
active TB, resulting in 1.5 million deaths and
making it the number one cause of death from an
infectious disease at that time. Most TB cases
occurred in the regions of South-East Asia (44%),
Africa (24%) and the Western Pacific (18%), with
more than 50% of cases being diagnosed in eight
countries: India (27%), China (9%), Indonesia (8%),
the Philippines (6%), Pakistan (6%), Nigeria (4%)
and Bangladesh (4%). The number of new cases
each year has decreased since 2000.

5.  When people with active pulmonary TB
cough, sneeze, speak, sing, or spit, they
expel infectious aerosol droplets 0.5 to
5.0 µm in diameter. A single sneeze can
release up to 40,000 droplets. Each one of
these droplets may transmit the disease,
since the infectious dose of tuberculosis is
very small (the inhalation of fewer than 10
bacteria may cause an infection).

6.  When a person breathes in TB bacteria, the
bacteria can settle in the lungs and begin to grow.
From there, they can move through the blood to
other parts of the body, such as the kidney, spine,
and brain.
 TB disease in the lungs or throat can be infectious.
This means that the bacteria can be spread to other
people. TB in other parts of the body, such as the
kidney or spine, is usually not infectious.
 People with TB disease are most likely to spread it
to people they spend time with every day. This
includes family members, friends, and coworkers or
schoolmates.

7.  Pulmonary (90% of the active cases)
• Chest pain
• Prolonged cough producing sputum
• Hemoptysis in small amounts
• In rare cases, the infection may erode into
the pulmonary artery or a Rasmussen's
aneurysm (inflammatory pseudo-aneurysmal
dilatation of a branch of pulmonary artery
adjacent to a tuberculous cavity), resulting in
massive bleeding.
• Scarring in the upper lobes of the lungs.

8.  Extra-pulmonary & General (15-20% of active
cases)
• Pain in affected area
• Fever
• Chills
• Night sweats
• Loss of appetite
• Weight loss
• Fatigue.
• Significant nail clubbing may also occur.

11.  TB infection begins when the mycobacteria
reach the alveolar air sacs of the lungs, where
they invade and replicate within endosomes of
alveolar macrophages. Macrophages identify
the bacterium as foreign and attempt to
eliminate it by phagocytosis. During this
process, the bacterium is enveloped by the
macrophage and stored temporarily in a
membrane-bound vesicle called a phagosome.
The phagosome then combines with a
lysosome to create a phagolysosome.

12.  The primary site of infection in the lungs, known as
the "Ghon focus", is generally located in either the
upper part of the lower lobe, or the lower part of
the upper lobe. Tuberculosis of the lungs may also
occur via infection from the blood stream. This is
known as a Simon focus and is typically found in
the top of the lung. This hematogenous
transmission can also spread infection to more
distant sites, such as peripheral lymph nodes, the
kidneys, the brain, and the bones. All parts of the
body can be affected by the disease, though for
unknown reasons it rarely affects the heart, skeletal
muscles, pancreas, or thyroid.

14.  Chest X-ray
 Multiple sputum cultures for acid-fast
bacilli are typically part of the initial
evaluation
 The Mantoux tuberculin skin test is often
used to screen people at high risk for
TB. Those who have been previously
immunized with the Bacille Calmette-Guerin
vaccine may have a false-positive test result.

15.  The Mantoux test or Mendel–Mantoux test
(also known as the Mantoux screening test,
tuberculin sensitivity test, Pirquet test, or
PPD test for purified protein derivative) is a
tool for screening for tuberculosis (TB) and
for tuberculosis diagnosis.

16.  In the Mantoux test, a standard dose of 5
tuberculin units (TU - 0.1 ml) is injected
intradermally on the flexor surface of the left
forearm, mid-way between elbow and wrist. The
injection should be made with a tuberculin
syringe, with the needle bevel facing upward.
Alternatively, the probe can be administered by
a needle-free jet injector. When placed
correctly, injection should produce a pale wheal
of the skin, 6 to 10 mm in diameter. The result
of the test is read after 48-96 hours but 72
hours (3rd day) is the ideal.

17.  POSITIVE
The results of this test must be interpreted carefully.
The person's medical risk factors determine at
which increment (5 mm, 10 mm, or 15 mm) of
induration the result is considered positive. A
positive result indicates TB exposure.
 5 mm or more is positive in
› An HIV-positive person
› Persons with recent contacts with a TB patient
› Persons with nodular or fibrotic changes on chest X-ray
consistent with old healed TB
› Patients with organ transplants, and other
immunosuppressed patients

18.  10 mm or more is positive in
› Recent arrivals (less than five years) from high-prevalence
countries
› Injection drug users
› Residents and employees of high-risk congregate settings (e.g.,
prisons, nursing homes, hospitals, homeless shelters, etc.)
› Mycobacteriology lab personnel
› Persons with clinical conditions that place them at high risk
(e.g., diabetes, prolonged corticosteroid therapy, leukemia, end-
stage renal disease, chronic malabsorption syndromes, low
body weight, etc.)
› Children less than four years of age, or children and
adolescents exposed to adults in high-risk categories
 15 mm or more is positive in
› Persons with no known risk factors for TB[

19.  FALSE POSITIVE
 TST/PPD in a person who has received BCG
vaccine is interpreted as latent TB infection
(LTBI). Due to the test's low specificity, most
positive reactions in low-risk individuals are
false positives.A false positive result may be
caused by nontuberculous mycobacteria or
previous administration of BCG vaccine.
Vaccination with BCG may result in a false-
positive result for many years after vaccination.

20.  False positives can also occur when the
injected area is touched, causing swelling
and itching. If the swelling is less than 5 mm,
it is possibly due to error by the healthcare
personnel causing inflammation to the area.
 Another source of false positive results can
be allergic reaction or hypersensitivity.

21.  FALSE NEGATIVE
 Reaction to the PPD or tuberculin test is
suppressed by the following conditions:
 Recent TB infection (less than 8–10 weeks)
 Infectious mononucleosis
 Live virus vaccine - The test should not be
carried out within 3 weeks of live virus
vaccination (e. g. MMR vaccine or Sabin
vaccine).
 Sarcoidosis

22.  Hodgkin's disease
 Corticosteroid therapy/steroid use
 Malnutrition
 Immunological compromise
(This is because the immune system needs to
be functional to mount a response to the protein
derivative injected under the skin. A false
negative result may occur in a person who has
been recently infected with TB, but whose
immune system hasn't yet reacted to the
bacteria.)
 Upper respiratory virus infection

23.  Tuberculosis prevention and control efforts rely
primarily on the vaccination of infants and the
detection and appropriate treatment of active
cases. The World Health Organization (WHO)
has achieved some success with improved
treatment regimens, and a small decrease in
case numbers.
Vaccines
 Tuberculosis vaccines and BCG vaccine
 The only available vaccine as of 2011 is Bacillus
Calmette-Guérin (BCG). In children it decreases
the risk of getting the infection by 20% and the
risk of infection turning into active disease by
nearly 60%.