Powepoint On Epidemiological INDICES OF TB Suitable For Community Medicine Students - KUHS KERALA MEDICAL BOARD Prepared By A Student from Mount Zion Medical College , Chayalode Adoor

1. EPIDEMIOLOGICAL
INDICES OF TB
Presented By: Ahamed Faris

2. EPIDEMIOLOGICAL INDICES
 Indices or Parameters – They are factors needed to measure the TB problems in a community, as well
as to plan and to evaluate control measures.
 Indices are also required for international comparison.
These following epidemiological indices are generally used in TB problem measurement and programme
strategy.
1. INCIDENCE
2. PREVALENCE
3. MORTALITY
4. CARE FATALITY RATE
5.CASE NOTIFICATION RATE
6. CASE DETECTION RATE
7. PREVALENCE OF DRUG-RESISTANT CASES
8. INCIDENCE OF INFECTION
9. PREVALENCE OF INFECTION

3. 1. INCIDENCE
It is defined as number of new and recurrent (relapse) episodes of all forms
of TB occuring in a given year.
Recurrent episodes- defined as new episode of TB in people, who have had TB
in the past and for whom there was bacteriological confirmation of cure or
documentation that treatment was completed.
Relapse cases are referred to add recurrent cases because that term is more
useful in explaining estimation of TB incidence.
Recurrent cases maybe True Relapses or new episode of TB caused by
reinfection
But people with a continuing episode of TB that requires a treatment
change are considered as PREVALENCE, not incident cases.
In current case definitions, both relapse cases and patient who require a
chamge in treatment are considered as “RETREATMENT CASES”.

4. 2. Prevalence
Prevalence is defined as the number of all forms of TB cases at a given
point in time.
It is the best available practical index to estimate the case load in a
community.
Age specific Prevalence – Of patients is considered as the best and most
relevant Index.

5. 3. Mortality
Mortality from TB is defines as number of deaths caused by TB in HIV-
negative people, according to the latest revision of International
Classification of Diseases(ICD-10).
HIV Negative people are considered, because HIV positive people’s
deaths are considered as HIV deaths in (ICD-10).
For this reason, estimate of death in HIV negative people are seperately
measured from those in HIV positive.
It is calculated in unit deaths/lakh population.

6. 4. Case fatality rate
It is defined as risk of death due to TB from people with active TB
disease.

7. 5. Case Notification Rate
It refers to new and recurrent episodes of TB notified to WHO for a
given year., expressed per 1 lakh population.
The case notification rate for new and recurrent TB is important for
estimation of TB incidence.
However, in some countries, information on treatment history maybe
missing in some cases.
Im such condition, recurrent cases cant be distinguished from cases
whose treatment was changed.
Since both are registered and reported in category “RETREATMENT”.
Patients reported in the unknown history category are considered in
incident TB episodes (new or relapse).

8. 6. Case detection Rate
It is calculated as number of notinfication of new and relapse cases in a
year divided by the estimated incidence of such cases in a same year.

9. 7 Prevalence of Drug-Resistant Cases
 It is the prevalence of patients excreting tubercle bacilli resistant to anti-TB drugs.
 This index is directly related to chemotherapy.
 (a) Prevalence Of Infection
 . It is % of individuals who show a postive reaction to the STANDARD TUBERCULIN TEST.
 When the same test is done in defined age-groups, it yields age specific prevalence,which
is a far more superior indicator.
 It must be noted that Tuberculin test interpretation has become much complicated in
countries with high BCG vaccination coverage at birth, because all vaccines become positive
reactors to Tuberculin test.
 This becomes a problem in identifying true prevalence of infection.
 Further cross-sensitivity to an atypical mycobacteria, where it occurred had also caused the
prevalence index to be overestimated.
 Even though these disadvantages, Tuberculin test is widely used for estimating prevalence of
TB infection in a population.

10. (b) Incidence Of Infection
Also known as annual infection Rate.
It is the % of population under study, who will be infected by M. tuberculosis,
among the non-infected of the preceding survey, during the course of one
year.
It reflects the ANNUAL RISK OF being infected (or reinfected) in a
community.
Simply, it expresses the attacking force of TB pathogen in a community.
Also known as Tuberculin Conversion Index, this parameter is considered one
of the best indicators for evaluating tuberculosis problem and its trend.
Higher the rate, larger is the problem.
In a good treatment programme, lowers the risk of TB infection in a
community