Epidemiology of TB and its control Dr' V' K' Chadha Sr' Epidemiologist National TB Institute Bangalo

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Epidemiology of TBand its controlDr. V. K.
ChadhaSr. EpidemiologistNational TB
InstituteBangalore
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• I. General concepts in TB Epidemiology
• II. Epidemiological indicators of TB and their
  estimation
• III. Global epidemiological trends of TB
• IV. TB situation in South East Asia
• - presentations by Country participants
• V. Prospects of TB control

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Why do we need to study Epidemiology of TB?
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Aims of Epidemiology ?

• To describe natural history of disease
• Describe Distribution and relative importance
• Measure frequency
• To define risk groups
• To evaluate interventions
• To describe trends
• To predict future trends and changes in disease
  presentation.

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What is Epidemiology ?

• Epi - among Demos - People Logos -
  Study
• DEFINITION
• Epidemiology is the study of the -
• Frequency
• Distribution - time, place person
• Determinants - physical, biological, social,
  behavioural cultural
• of health problems health related events and
  application of this study to control health
  problems.

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Risk of exposure ?

• Incidence / prevalence of infectious TB in the
  community
• Duration of infectiousness
• opportunities for case - contact interactions
• -Urban/Rural
• -No. of individuals in the house holds

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Risk of Infection ?

• No. of infectious droplets produced
• Volume of shared air space
• Length of exposure
• Ventilation
• Climatic conditions

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Household transmission of TB- important
epidemiological factor

• Case control study in Malawi

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Each case leads to two cases

-_-_-
1 Infectious case
20 contacts
2 cases
of TB
1 Non-infectious
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What is the most important risk factor for TB?
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Risk factors for disease given that infection has
occurred ?
Relative Risk of remotely acquired infection
1 (0.2 per year)
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Incidence of TB in South Africa per 1000
population
IJTLD,3(9),1999,791-798
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Other High Risk Groups

• Populations in war / civil unrest
• Refugees and migrants
• Slum dwellers
• Homeless people/Foot path dwellers
• Smoking
• Prisoners

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TB in prisons

• Studies in Thailand
• TB incidence 90 times higher in prisons
• High HIV sero-positivity in TB cases
• High levels of drug resistance
• RFLP studies signify role of recent transmission

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Determinants of death?

• Severity of illness
• Smear positivity
• delay in diagnosis
• quality of treatment
• drug susceptibility pattern

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• Epidemiological indicators of TB and their
  estimation

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Enumerate epidemiological indicators of TB you
know of?
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Epidemiological indicators of tuberculosis ?

• Prevalence of infection
• Incidence (average annual risk) of infection
  (ARI)
• Prevalence of disease
• Incidence of disease
• Tuberculosis mortality rates

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How to estimate prevalence of infection?
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• Estimating prevalence of infection
• Study population-sampling
• Registration of eligible age group
• - house-to-house / school based.
• Informed consent.
• Examination for BCG scar.
• Tuberculin testing with 1TU/2TU PPD RT23 with
  tween 80.
• Reading of reaction sizes appx. 72 hours later.

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What is the rationale behind tuberculin surveys
in children ?

• Extent or recent transmission
• Study trends in TB epidemiology
• (Ultimate aim of control programme is to replace
  older more infected cohorts with younger less
  infected cohorts)

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Analysis of tuberculin survey
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Estimation of incidence of infection?
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Dual skin testing at two different periods
-Conversion -Boosting Compute average
annual risk of infection (ARTI) 1-(1-P)1/A
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A RT I

• Key epidemiological indicator in developing
  countries.
• It is the probability of acquiring new
  tuberculosis infection or re-infection over the
  course of one year.

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• A R I expresses the overall impact of various
  factors influencing the transmission of tubercle
  bacilli !
• - Load of infectious cases
• - Efficiency of case finding
• - Efficiency of treatment programme

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• ARI identifies the regions of high transmission
• It provides an indirect estimate of size of
  sources of infection
• Any change in disease burden and programme
  implementation is first reflected in the change
  in ARI
• It holds the key to the study of epidemiological
  trends which are more important than exact
  estimates of disease prevalence

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How to estimate prevalence of disease?
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DISEASE SURVEY METHODOLOGY

• Sampling of representative population
• House to house registration
• Screening
• - MMR X-ray of all above five years of age
• - Symptomatic screening
• X-ray pictures read by two independent readers
  and by an umpire reader
• Sputum specimens (2/3) collected from persons
  with abnormal X-ray shadows / or chest
  symptomatics
• Sputum examination by direct microscopy (and
  culture).

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How to estimate disease incidence?
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Relationship between ARTI and incidence of disease
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Styblo derived the following relationship from
data of pre- chemotherapy

• Every one percent of ARTI corresponds to 50 new
  smear positive cases per 100,000 population per
  year

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Relationship between ARI Incidence of smear
positive cases of Pulmonary Tuberculosis(Indian
studies)
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Relation between ARI and Incidence !

• Situation Disease incidence remains same but
  the risk of infection declines
• Q 1. When is this situation likely?
• Q 2. What is the impact on equation
• (relationship) ?

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What happens to the equation in high HIV settings?
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The equation is dependent more on number of
infections generated per case and not merely on
incidence
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Disease mortality rates !

• Community based prospective studies
• Death certification

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• ESTIMATION OF ANNUAL RISK OF TUBERCULOUS
  INFECTION IN DIFFERENT ZONES OF INDIA
• A CROSS SECTIONAL STUDY
• 2000-2003

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Districts selected for National Sample Survey -ARI
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Does higher ARTI in urban areas indicate higher
incidence of smear positive cases
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Programme inputs

• The survey findings provide baseline estimates of
  ARI for
• - evaluation of TB Control Measures.
• - Study of epidemiological trends in years to
• come
• High rate of ARI indicates high load of
  infectious cases of TB in most parts of India.
  Prolonged and sustained efforts required to
  control TB.
• There are significant inter-regional differences
  in tuberculosis situation.
• Intensification of TB control services in urban
  areas with higher ARI rates to be taken up
  on priority basis.
• Case finding expectations cannot be applied
  uniformly all over the country

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Other Epidemiological indicators of Tuberculosis

• Ratio of prevalence and incidence
• Age distribution of cases
• Case fatality rates
• Force of MDR cases
• TBM notification rates
• Disability adjusted life years (DALY)

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• Epidemiological trends of TB

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TB trends in EuropeMedian age in Finland
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TB trends in EuropeNetherlands
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Global drug resistance surveillance
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Trends in ARI-Chingleput

• At intake in 1969 1.8
• After 4 years in 1973 1.8
• After 10 years 1.9
• After 15 years 1.7

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How does HIV pandemic influence TB epidemic
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• Higher rate of progression from latent infection
  to disease (5-10 per year compared to 10 per
  year among HIV negative)
• Previously HIV infected persons when exposed to
  TB rapidly develop the disease.
• Excess cases due to the above lead to increased
  transmission of infection
• Higher case fatality due to HIV infection

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Evidence of association between HIV and TB

• Increase in TB in areas worst affected by HIV
• Higher increase in age group affected by HIV.
• 50 to 70 AIDS cases develop TB in SEAR.
• HIV positivity higher among TB cases than general
  population.
• -Northern Thailand HIV positivity in TB cases
  40
• Malawi 75

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20 of all patients in Russia have MBR TB
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Increase in CFR attributable to increase in drug
resistance cases
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Average - 3.4 (3.6 for smear pos)
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In your opinion, what should be the practical
methods of monitoring epidemiological trends in
any given community
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Global picture

• 3rd largest cause of death (2.8) and loss of
  DALYs in 15-59 year age group
• Incidence all cases - 8.8 million
  (2002)-141/100000
• in 22 HBCs - 7.0 million (80)
• Smear - 3.9 (63/100000) million
• Case notifications of smear positive cases
  increasing _at_ 4 per year- 5 in eastern Europe
  and 7 in high HIV African countries.

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Epidemiological situation of TB in South East
Asian countries
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Format for Country presentations
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TB in South-East Asia
Incidence 3 mill Deaths 1 mill (1500/day)
India, Bangladesh, Indonesia, Myanmar Thailand
contribute 95 of regional burden
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HIV-TB in SEAR

• Second largest number of HIV positives after SSA
• SSA60 SEAR30
• 6 million HIV positives in SEAR
• India 4 mill
• Thailand 1 mill
• Myanmar 0.5 mill
• Low sero-positivity in Bangladesh, Maldives,
  Bhutan, Indonesia and Sri lanka
• Nepal Low in antenatal women, high among IDUs.

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TB situation in India
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Prevalence of sputum positive pulmonary TB
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INCIDENCE OF PULMONARY TUBERCULOSIS IN INDIA
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HIV Sero-prevalence among TB Cases
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Multi Drug Resistance in new TB cases
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Multi Drug Resistance in previously treated TB
cases
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ARI in other countries
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Country wise Epidemiology situation
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Country wise Epidemiology situation - Continued
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Progress of DOTS in high burdened countries
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What is meant by control ?

• To move from high to low endemicity or
  elimination

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Objectives of TB control programmes

• Decrease transmission of infection by-
• - Rapidly identifying cases
• - Adequate treatment
• Decrease deaths due to TB.
• Cure of maximum number of cases.
• To prevent relapse.
• To prevent emergence of drug resistance.
• To reduce TB in children by preventive treatment.
• IEC - Purpose ?

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Each case leads to two cases

-_-_-
1 Infectious case
20 contacts
2 cases
of TB
1 Non-infectious
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How does DOTS strategy help control TB?
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DOTS

• Decreases deaths
• Decreases duration of infectiousness
• Increased case detection plus high cure rate
  decreases transmission of infection that will
  ultimately lead to decline in incidence.
• Prevents emergence of MDR

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A good programme like DOTS reduces disease burden

• Case fatility rate reduced to lt5 compared to
  60-70 in a few years among untreated cases.
• Cure of every case under DOTS with about 4 months
  diagnostic delay prevents 0.7 new smear positive
  cases.(further prevention possible by reducing
  diagnostic delay)
• Preventive treatment to each child prevents 0.03
  new case and 0.007 deaths.

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How does a poor programme worsen the TB situation
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• Poor programme with low cure rate (lt50) and low
  detection rate worsen TB situation by decreasing
  case fatility rates leading to increased
  prevalence and transmission of infection.

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HIV prevention and control is of major importance
towards TB control
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Priority to smear positive cases

• To reduce transmission of infection. A good DOTS
  programme would reduce transmission of infections
  by about 73
• Cost per DALY highest for treating smear positive
  cases.

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The Cuba example
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• Very low levels of MDR in Cuba
• Cuba is a low HIV country

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• Increased case detection will decrease
  transmission rapidly provided cure rates are
  high.
• It has been estimated that achievement of 70
  case detection and 85 cure rate by 2010 will
  result in greatest benefits in cases and deaths
  averted in regions with highest burden - South
  East Asia, Africa and Western Pacific.
• Longer the time taken to reach targets, incidence
  will decrease more slowly.
• The proportion of deaths averted by DOTS would be
  greater than the proportion of cases
• Non curative treatment can prevent death without
  eliminating infectiousness.
• Programme will treat non-infectious cases also

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• Control TB since every breadth counts (World TB
  day 2004 theme)
• Business as usual will not eliminate TB
• It is time for business unusual