Transcript 2.1 Epi, transmission and path.ppt

Module 2:
Overview and Background
Learning Objectives
• Part 1
– Describe TB global epidemiology
– Explain 5-point DOTS strategy for effective TB control
– Understand TB case definitions
• Part II
– Explain how TB is transmitted
– Describe active vs. latent TB
– List risk factors for progression to active TB
Global Epidemiology
Estimated TB Incidence Rates, 2003
per 100 000 pop
< 10
10 - 24
25 - 49
50 - 99
100 - 299
300 or more
No estimate
HIV Prevalence in Adults, 2003
Adult prevalence %
15.0% − 39.0%
5.0% − 15.0%
1.0% − 5.0%
0.5% − 1.0%
0.1% − 0.5%
0.0% − 0.1%
not available
38 million people [range: 35-42 million] living with HIV as of end 2003
UNAIDS Report on the Global HIV/AIDS Epidemic, 2004
Reported Case Rate (per 100,000)
HIV Is Changing Global
TB Epidemiology
700
600
Botswana
500
Zimbabwe
Malawi
Tanzania
Ivory Coast
400
300
200
100
0
700
600
40
500
30
400
20
300
200
10
100
0
0
1975
1980
1985
1990
1995
2000
HIV seroprevalence (%)
TB case rate (per 100,000)
Reported TB Case Rate in Botswana,
1975–2002,
and HIV Prevalence in Antenatal Women,
1992-2003
Strategy and Framework
Botswana and DOTS
TB Treatment--DOTS Strategy
1. Sustained
Government Commitment
to TB control
3. Standardized Short Course
Chemotherapy Under DOT
2. Microscopy-based Case Identification
4. Secure Supply of
5. Case Registry,
Quality Drugs
Monitoring & Evaluation
2HRZE(S)/
4HR
“Enhanced DOTS”
• TB/HIV
• MDR TB
• Community TB
Care
• Private Public Mix
(PPM)
What is the
of DOTS?
CASE DEFINITIONS HOLD THE
PROGRAM TOGETHER
Case Definitions
• Purposes
– Proper patient registration and case notification
– Prioritize treatment of smear-positive cases
(the main source of infection in community)
– Ensure cases on appropriate standardized
regimens
– Evaluate cases according to site of disease,
bacteriology and treatment history
– Permit cohort analysis of treatment outcomes
Matching diagnostic category and
treatment regimens: Why?
• Avoid under-treatment of previously
diagnosed cases
• Maximize cost-effective use of resources and
minimize side effects by avoiding overtreatment
Determining the Case Definition
• Four factors
– Disease Classification (i.e., is site of disease
(pulmonary, extrapulmonary or both?)
– Bacteriology (i.e., smear status)
– Patient Category ( determined by TB history—
i.e., is patient “new” or “retreatment”?)
– Severity of TB disease (cavitary vs. non-cavitary)
First three factors recorded in register
Disease Classification and SmearStatus: PTB+ vs. PTB• PTB+ (Pulmonary TB smear-positive)
–One AFB-positive smear; i.e. any patient with at
least one positive smear result (irrespective of
quantity of AFBs seen on microscopy)
Recommendations to improve the diagnosis of smear negative pulmonary and
extrapulmonary TB among adults in HIV prevalent and resource constrained settings.
Draft for discussion by Strategic and Technical Advisory Group of Stop TB Department of
WHOJune 2006
Site of Disease: PTB+ vs. PTB• PTB- (smear-negative)
Any pulmonary TB case that does not meet the definition
of being smear-positive. This includes:
1. Patients with three negative smear results and
radiological findings and doctor’s decision to treat for TB
2. Patients with negative smear results and a positive
culture result for M. tuberculosis
3. Patients who are unable to produce sputum and with
highly suspicious radiological and clinical findings and
doctor's decision to treat for TB
Severity of Disease
• Determinants include
– Bacillary load
– Extent of disease
– Anatomical site
•
•
•
•
•
Significant acute threat to life (e.g., pericardial dx)
Risk of severe handicap (e.g., spinal TB)
Or both (e.g., meningitis)
Miliary considered severe
EPTB can be “severe” or “less severe”
Registration Category: New
Determined by previous treatment history
NEW: Never had TB treatment or who has taken
anti-TB treatment (ATT) < 1 month
RETREATMENT (3 types): Any patient who has
taken > 1 month of ATT
Registration Category: Retreatment
RETREATMENT CASES
RELAPSE: A patient previously treated for TB who has
been declared cured or treatment completed, and is
diagnosed with bacteriologically-positive TB (smear- or
culture-positive)
FAILURE: Patient started on re-treatment regimen after
failing previous treatment
DEFAULT: A patient who returns to treatment,
bacteriologically-positive, following a treatment
interruption of two-months or more.
Determining the Case Definition
Bacteriology
History of TB
Site of Disease
Smear-negative
NO
Pulmonary
New
Smear-positive
TB CASES
Extra-pulmonary
Return after
default
YES
Relapse
Failure
Severity of Disease
Progress towards 70% case detection
Cases notified under DOTS (%)
80
70
WHO target 70%
60
accelerated progress:
target 2005
50
40
30
20
DOTS begins
1991
average rate of
progress: target 2013
10
0
1990
WHO, 2000
1995
2000
2005
2010
2015
2003 Case Detection and Treatment Success Rates
(WHO)
100
Malta
Target zone
Cambodia
Treatment success (%)
Tonga
Solomon Is
90
Cuba
Viet Nam
Maldives
Peru
Tunisia
Fiji
Jamaica
Bosnia & Hezegovina
Hong Kong
Samoa
Uruguay
Mongolia
Marshall Is Nicaragua
Kyrgyzstan
St Lucia
80
Guatemala
Kenya
El Salvador
Latvia
70
Chile
Morocco
Kazakhstan
Venezuela
Slovenia
BOTSWANA
Tanzania
Oman
Qatar
Djibouti
Sri Lanka
French Polynesia
South Africa
Lebanon Portugal
Italy
USA
Turks & Caicos Is
DR Congo
50
60
70
80
90
DOTS detection rate (%)
100
110
120
Transmission and Pathogenesis
Transmission of M. tuberculosis
• Expelled when person with infectious TB
coughs, sneezes, speaks, or sings
• Spread by droplet nuclei
• Close contacts at highest risk
• Transmission occurs from person with
infectious (active) TB disease, not latent
TB infection
It’s all about VELOCITY
Cough: 100 km/hr!!!
Sneeze 150 km/hr!!!
TB in the Lungs
Once TB bacilli is inhaled some bacilli reach the
alveoli, where they are ingested by macrophages.
Infection begins with the multiplication of tubercle
bacilli within these alveolar macrophages.
Some of the bacilli spread through the bloodstream
when the macrophages die; however, the immune
system response usually contains the bacilli and
prevents the development of disease.
Probability TB Will Be Transmitted
• Environment in which exposure occurred
• Infectiousness of person with TB
• Duration of exposure
• Virulence of the organism
Annual Risk of Infection (ARI)
ARI is defined as a calculated average from an observed prevalence
of infection, approximating the incidence of infection.
•
Methodology
-Sample of school-age children
-Tuberculin skin tested (Mantoux test)
• Used to estimate the percentage of new TB
infections each year
-Accounts for responses to non-tuberculous
mycobacterium and BCG
• TST+ prevalence in Botswana in 1989 7.7%
among 6-10 y.o
H. Rieder: Annual risk of infection with Mycobacterium tuberculosis. Eur Respir J 2005; 25:181-185
Pathogenesis
•
10% of infected persons with normal immune
systems will develop TB (lifetime risk)
HIV strongest risk factor for development of TB
- HIV infection increases the risk of developing TB
disease 7% to 10% each year
In addition to HIV there are other health conditions that
increase the risk of developing TB disease.
Other Conditions That Increase
Risk of Progression to TB Disease
• Recent infection
• Substance abuse (alcohol and recreational
drugs)
• Diabetes mellitus
• Silicosis
• Malnutrition
• Smoking
• Some malignancies
• Prolonged corticosteriod therapy
• Other immunosuppressive therapy
• Chest radiograph suggestive of previous TB
disease
Conditions That Increase the Risk of
Progression to TB Disease (cont.)
•
Cancer of the head and neck
•
Hematologic and reticuloendothelial diseases
•
End-stage renal disease
•
Intestinal bypass or gastrectomy
•
Chronic malabsorption syndromes
•
Low body weight (10% or more below the ideal)
Latent TB Infection vs. Active TB Disease
TB Types
Patient has
symptoms
Patient
infectious to
others
Diagnosis
Latent TB
Infection
No
No
Tuberculin
skin test
(TST)
Active TB
Disease
Yes
Yes – when in
Sputum
the lungs