This document outlines the in-service course module on tuberculosis (TB) and leprosy management, focusing on TB's transmission, risk factors, case definitions, and disease classification. It describes TB as an airborne disease caused by Mycobacterium tuberculosis, emphasizing infection transmission, risk factors including HIV and malnutrition, and the necessity for effective prevention strategies. The document also details various classifications of TB cases based on anatomical site, treatment history, HIV status, and drug resistance, providing essential information for proper patient management and public health initiatives.

1. 1
IN-SERVICE COURSE IN INTEGRATED AND COMPREHENSIVE TB AN
D LEPROSY MANAGEMENT
MODULE 1: UNIT 1.2
TB BASIC FACTS AND CLASSIFICATION

2. 2
Introduction
• This unit describes basic facts about TB regarding its
transmission, risk factors, natural history, TB standard
definitions prevention and TB classification.

3. 3
Unit objectives
The objective of this unit is to have participants be able to:
• Describe basic facts about TB (What is TB, characteristics of M.
TB, TB transmission, fate of droplet nuclei, TB risk factors, TB
natural history and key populations, TB prevention )
• Describe standard TB case definitions and TB disease
classification

4. 4
What is TB?
• Tuberculosis (TB) is caused by a bacterium called
Mycobacterium tuberculosis (M.tb)
• Other species include:
• Mycobacterium bovis,
• Mycobacterium africanum
• Mycobacterium microti
• M. tuberculosis causes infection in the lungs or other part of
the body.
• Tubercle bacilli cause lesions in tissues called tubercles.

5. 5
Characteristics of M. tuberculosis
• Slightly curved rod shaped bacilli
• Size: 0.2-0.5 microns in diameter, 2-4 microns in length.
• Have thick cell wall of lipids, waxes and mycolic acids
• Cell wall protects them from digestion by
macrophage enzymes.
• Cell wall resists decolourization by acid alcohol
(retains a red dye) hence name Acid-Alcohol Fast
Bacilli (AAFB)

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Characteristics of M. tuberculosis
• Multiplies slowly; - every 18-24 hours
• Can remain dormant for decades
• Aerobic
• Non-motile

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How is TB Transmitted?
• From person to person by mucous droplets
(air borne) when the person with TB of the
lungs sneezes, coughs, laughs, spits, sings,
talks, breathes
• Then droplets are inhaled by exposed person
into the lungs and deposited into the alveoli.
• Less frequently transmitted by:
• Ingestion of Mycobacterium bovis found in
unpasteurized milk products
• Not following recommended safety precautions
Airborne TB Transmission

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Ways through which TB is NOT transmitted
• Shaking hands with a TB patient
• Sharing food, sharing cups and plates with a TB patient
• Touching or sharing towels, bed linen and personal clothes
• Sharing toilet seat with a TB patient.

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Number and fate of droplet nuclei
• Number of TB bacteria carrying droplets < 100 microns in diameter
liberated per minute:
• Speaking/talking 0-210
• Coughing 0-3,500
• Sneezing 4,500- 1,000,000
• Size of the droplets is determined by air velocity
• Smaller droplets <100 microns are produced at high velocity (e.g a
violet sneeze)
Source: Duguid 1945

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Transmission depends on
• Concentration of TB germs
• Duration of exposure
• Ventilation
Therefore a close contact of a pulmonary bacteriologically
confirmed TB patient who is not on treatment and is living in
an environment with poor ventilation is more at risk and is
more likely to contract TB than any other person.

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Risk Factors for TB Infection
• Being a close contact with a person with active Pulmonary TB
(PTB) especially bacteriologically confirmed PTB
• Close contacts include schools.
• Living in countries with a high TB burden such as Uganda.
• High HIV rates in the community because people living with HIV
have an increased risk for TB.

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Risk factors for TB Disease
Risk factors for TB Disease
• Young age (especially less than 2 years), are at the highest risk of TB disease
• Human Immune Deficiency Virus (HIV) infection,
• Malnutrition
• Other Immune-suppressive conditions like post measles disease, severe kidney
disease, prolonged use of corticosteroids, and pregnancy.
Risk factors for Severity of TB Disease
• Young age (less than 2 years),
• HIV infection and
• lack of BCG vaccination

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TB Natural history
Exposure
Infection
10%
Risk
factors
Active TB
Disease
10%
Latent TB
Infection
90%
Risk
factors
Continued
Latency
Active TB
disease
Risk
factors
No Infection
90%

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TB Natural history
• Following TB exposure, only 10% of those
exposed to TB become infected
• And in 90% of those who get infected,
immunity develops quickly and body
contains the infection hence infection
remain latent and may never develop
active TB disease.

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TB Natural history
• In latent period, the person is not ill, not
contagious, has a normal chest x-ray and
usually has a positive tuberculin skin test
and other newer TB infection tests
• And the TB bacilli are still alive but
surrounded (walled off) by body’s
immune system

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TB natural history
• Exposure to TB risk factors, e.g. in HIV infection, diabetes mellitus,
alcoholism, cancer, and use of immunosuppressive drugs,
malnutrition, and advancing age, leads to progression to TB disease
• In 10% of those infected, the previously dormant germs start
multiplying, causing TB disease (Post-primary TB disease)
• The TB germs may also spread from lymphatic organs and through
blood to other parts of the body, a process that takes 6 – 8 weeks.
• Those who develop TB disease, if untreated die within two years.
Only a small proportion of them get self-cured).

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TB key populations (Most at risk)
Immune suppressed
individuals
• HIV positive clients
• Diabetics
• Children
Occupation exposure
• Health workers
Others
• Males
Congregate settings related
• Prisoners
• Refugees and internally displaced
• Slum dwellers/ urban poor
• Populations in hard to reach villages, lake
showers , Islands and fishing communities
• Miners and Plantation workers
• Close contacts of confirmed TB patients
• Nomadic communities

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TB prevention
• BCG vaccination
• Early detection and treatment of infectious TB patients
• Isoniazid preventive therapy (IPT) for:
• All HIV positive persons irrespective of TB exposures
• Under five-year child contacts of persons with active TB
• Infection control measures

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Purpose of TB case definitions and disease
classification
Uniform criteria to define a TB case are needed for:
• Proper patient registration and case notification
• Selecting appropriate TB treatment regimens
• Standardizing process of data collection for TB control
• Evaluating the proportion of cases according to site, bacteriology and
treatment history
• Cohort analysis of treatment outcomes
• Accurate monitoring of trends and evaluation of the effectiveness of
TB programs within and across districts, countries and global regions.

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Standard TB Case Definition
• Presumptive TB patient: Is any patient who presents with symptoms and
signs suggestive of TB (previously called a TB suspect).
• Bacteriologically confirmed TB patient (BC): A bacteriologically confirmed
TB patient is one from whom a biological specimen is positive for TB by
smear microscopy, culture, Nucleic Acid Amplification Tests e.g. Xpert
MTB/RIF or WHO recommend new diagnostics. These Should be recorded
in the unit TB register and notified, regardless of whether TB treatment
has been started.

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Standard TB Case Definition
Clinically diagnosed TB patient (CD):
• One who does not fulfil the criteria for bacteriological confirmation but has
been diagnosed with active TB by a clinician (doctor, clinical officer, midwife
or nurse) has decided to give the patient a full course of TB treatment
• includes cases diagnosed by X-ray, TB LAM, suggestive histology and extra-
pulmonary (EPTB) cases without laboratory confirmation.
• Clinically diagnosed cases subsequently found to be bacteriologically
positive (before or after starting treatment) should be reclassified as
bacteriologically confirmed.

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BC or CD TB cases are also classified according to:
• Anatomical site of the disease (body organ involved)
• Patient’s history of previous treatment
• Drug susceptibility and resistance to anti TB medicines and
• HIV status

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Classification Based on Site of the Disease
• Pulmonary tuberculosis (PTB): Bacteriologically confirmed(BC) or
clinically diagnosed (CD) case of TB involving the lung parenchyma or the
tracheobronchial tree.
• Extra-pulmonary tuberculosis (EPTB): any BC or CD case of TB involving
organs other than the lungs, e.g. pleura, lymph nodes, abdomen, GIT, skin,
joints bones, and meninges. Mediastinal and/or hilar TB or tuberculous
pleural effusion, without radiographic abnormalities in the lungs,
constitutes a case of extra-pulmonary TB (EPTB).
• A patient with both pulmonary and extra-pulmonary TB should be
classified as a case of PTB.

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Classification Based on Patient’s History of Previous
Treatment
1. New patients: Patients who have never been treated for TB or
have taken anti-TB drugs for less than 1 month.
2. Previously treated TB patients: Patients who have received one
month or more of anti TB drugs in the past. They are sub
classified as follows:
• Relapse patients: Previously treated for TB, declared cured or treatment
completed at the end of their most recent course of treatment, and are
now diagnosed with a recurrent episode of TB.

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Classification Based on Patient’s History of Previous
Treatment
• Treatment after failure patients: are those who have previously
been treated for TB and whose treatment failed at the end of
their most recent course of treatment.
• Treatment after loss to follow-up patients: have previously been
treated for TB and were declared lost to follow-up at the end of
their most recent course of treatment.
• Other previously treated patients: Previously been treated for TB
but whose outcome after their most recent course of treatment is
unknown or undocumented.

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Classification Based on HIV Infection Status
• HIV-positive TB patient: any BC or CD case of TB with a positive HIV result
from HIV testing conducted at the time of TB diagnosis or other
documented evidence of enrolment in HIV care, such as enrolment in the
pre-ART register or ART register.
• HIV-negative TB patient: any BC or CD case of TB who has a negative result
from HIV testing conducted at the time of TB diagnosis.
• Any HIV-negative TB patient subsequently found to be HIV-positive should
be reclassified accordingly.

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Classification Based on Drug susceptibility to
anti TB medicines
1. Drug Susceptible TB: The MTB germs are susceptible to
FLD anti TB drugs (RHZE)
2. Drug Resistant TB: The MTB germs are resistant to one or
more FLD (RHZE) and SLD (Kanamycin (km), Capreomycin,
Levofloxacin, Ethionamide, Prothionamide, etc)

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Classification Based on Drug Resistance
• Mono resistance: resistance to one first-line anti-TB drug only.
• Poly drug resistance: resistance to more than one first-line anti-TB
drug (other than both Isoniazid and Rifampicin).
• Multidrug resistance (MDR): resistance to at least both Isoniazid and
Rifampicin
• Extensive drug resistance (XDR): resistance to any Fluoroquinolone
and to at least one of three second-line injectable drugs
(Capreomycin, Kanamycin and Amikacin), in addition to multidrug
resistance.

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Classification Based on Drug Resistance
Rifampicin resistance (RR): Resistance to Rifampicin detected
using phenotypic (usual drug susceptibility testing, DST) or
genotypic methods (commonly Xpert MTB/Rif), with or without
resistance to other anti-TB drugs.
• It includes any resistance to Rifampicin, whether mono, poly,
multi, or extensively drug resistance.
• These categories are not all mutually exclusive; when
enumerating Rifampicin resistant TB (RR-TB), for instance,
multi-drug TB (MDR-TB), and Extensively drug resistance
(XDR-TB) are also included.

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Classification Based on Drug Resistance
“Pre-XDR” TB: refers to an isolate that is resistant to either a
fluoroquinolone or a second-line injectable, but not both.
It is a commonly used designation but not officially accepted
terminology by WHO or the global TB community.

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Group Exercise
Working in small groups, answer the following questions:
• How is TB classified?
• What is the importance of TB case definitions and TB disease
classification?

32. 32
Conclusion
• Tuberculosis (TB) is caused by a bacterium called Mycobacterium
tuberculosis (M.tb)
• It is an Acid-Alcohol fast bacillus (AAFB)
• TB is an air borne disease transmitted when the person with TB of the
lungs sneezes, coughs, laughs, spits, sings, talks, breathes
• Transmission depends on concentration of TB germs, duration of
exposure and ventilation
• TB Classification is based on anatomical site of the disease, patient’s
history of previous treatment, susceptibility to anti TB medicines and HIV
status

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References
1. World Health Organization. Global tuberculosis report 2015.
2. Manual of the National Tuberculosis and Leprosy program, Uganda.
3nd
Edition 2017
3. Richeldi L. An Update on the Diagnosis of Tuberculosis Infection.
Am J Respir Crit Care Med. 2006; 174:736-742