EPIDEMIOLOGY OF TUBERCULOSIS

SANTOSH KUMAR YADAVGSVM MEDICAL COLLEGE KANPUR

ROLL NO.- 128PARA- G2

EPIDEMIOLOGY “The study of the distribution and

determinants of health-related states or events in specified populations, and the application of this study to the control of health problems”

TUBERCULOSIS Tuberculosis is a specific infectious

disease caused by M. tuberculosis. The disease primarily affects lungs and causes pulmonary tuberculosis.

TB is spread person to person through the air via droplet nuclei

M. tuberculosis may be expelled when an infectious person:– Coughs– Sneezes– Speaks – Sings

Transmission occurs when another person inhales droplet nuclei

TB TRANSMISSION

TB TRANSMISSION

Transmission is defined as the spread of an organism, such as M. tuberculosis, from one

person to another.

• Probability that TB will be transmitted depends on:Infectiousness of person with TB diseaseEnvironment in which exposure occurredLength of exposureVirulence (strength) of the tubercle bacilli

• The best way to stop transmission is to:Isolate infectious personsProvide effective treatment to infectious

persons as soon as possible

INCUBATION PERIOD

• The time from receipt of infection to the development of a +ve tuberculin test ranges from 3-6 weeks

• Incubation period may be week, month or year

• Until mid-1800s, many believed TB was hereditary

• 1865 Jean Antoine-Villemin proved TB was contagious

• 1882 Robert Koch discovered M. tuberculosis, the bacterium that causes TB

Mycobacterium tuberculosisImage credit: Janice Haney Carr

HISTORY OF TB

1840 19201860 1900 1940 1960 1980 20001880

1993: TB cases decline 1993: TB cases decline due to increased funding due to increased funding and enhanced TB control and enhanced TB control

effortsefforts

1884: 1884: First TB First TB

sanatorium sanatorium established established

in U.S.in U.S.

1865: 1865: Jean-Jean-

Antoine Antoine Villemin Villemin

proved TB is proved TB is contagiouscontagious

1943: 1943: Streptomycin Streptomycin

(SM) a drug used (SM) a drug used to treat TB is to treat TB is discovereddiscovered

1882: 1882: Robert Koch discoversRobert Koch discovers

M. tuberculosisM. tuberculosis

Mid-1980s: Mid-1980s: Unexpected rise in Unexpected rise in

TB casesTB cases

1943-1952: 1943-1952: Two more drugs are Two more drugs are discovered to treat discovered to treat TB: INH and PASTB: INH and PAS

TB HISTORY TIMELINE

EPIDEMIOLOGICAL INDICES• Indices or parameters are needed to

measure the tuberculosis problem in a community

• For planning and evaluation of control measures

• Indices are also required for international comparison

Following epidemiological indices are generally used in TB :

a) Prevalence of infection:- It is the percentage of individual who show a

positive reaction to the standard tuberculin test.

b) Incidence of infection (Annual infection rate):- It is the percentage of population under study

who will be newly infected by M. tuberculosis. It reflects the annual risk of being infected in a

given community.

c) Prevalence of disease (Case rate) :- It is the percentage of individuals who’s

sputum is positive for tubercle bacilli on microscopic examination.

It is the best available practical index to estimate the number of infectious cases or case load in a community.

d) Indices of new cases :- It is the percentage of new tuberculosis

cases per 1000 population occurring during one year.

e) Prevalence of suspect cases :- It is based on X- Ray examination of chest. Drawback of this index is that radiography

cannot reveal with any certainty. That’s why it has no epidemiological

significance.

f) Case detection rate :- no. of new and relapse cases in a year estimated incidence of such cases in same year

g) Prevalence of new drug resistance cases :-

The patients resistance to anti- tuberculosis drugs.

• Mortality rate :- The no. of deaths from TB per lakh

population was used as the index of the TB problem in a community.

At present time it has no significance.

SOME DEFINATIONS OF TB CASES

• NEW CASES – A patient with sputum +ve PTB who has never treated for TB or has taken anti- tuberculosis drug for less than 4 week.

• RELAPSE – A patient who return smear +ve having previously been treated for TB and cured.

• Return after default- A patient who return sputum smear +ve after having left treatment for at least 2 months.

• TRANSFER IN- A patient recorded in another administrative area register and transferred into another area to continue treatment.

• TRANSFER OUT- A patient who has been transfer to another area registered and treatment result are not known.

• CURED– Initially smear +ve positive patient who completed treatment and had –ve smear result on at least two occasions.

• COHORT- A group of patients in whom TB has been diagnosed and who were registered for treatment during a specified time period.

NATURAL HISTORY OF TB

AGENT FACTORS

AGENTM. TUBERCULOSISIS A FACULTATIVEINTRACELLULAR

PARASITE

SOURCE OF INFECTION

(TWO SOURCES)

COMMUNICABILITYPATIENTS ARE REMAIN

INFECTIVE AS LONG AS THEY REMAIN

UNTREATED

HUMAN SOURCEMOST COMMON

SOURCE

BOVINE SOURCEINFECTION USUALLY BY INFECTED MILK

HOST FACTORS

AGE- TB AFFECTS ALL THE AGES

SEX- MORE PREVALENT IN MALES

HERIDITY- TB IS NOT A HERIDITARY DISEASE

NUTRIENT- MALNUTRITION IS WIDELY PREDISPOSE TO TB

IMMUNITY- MAN HAS NO INHERITED IMMUNITY AGAINST TB

SOCIAL FACTORS

POOR QUALITY OF LIFE

POOR HOUSING

OVERCROWDING

POPULATION EXPLOSION

UNDERNUTRITION

LACK OF EDUCATION

LARGE FAMILIES

EARLY MARRIAGES etc.

GLOBAL BURDEN OF TB • 2 billion infected, i.e. 1 in 3 of global population• 9.4 million (139/lakh) new cases in 2008, 80% in

22 high-burden countries • About 5.7 million cases were notified through

DOTS programme during 2010• Global incidence of TB has peaked in 2004 and is

declining• 1.77 million deaths in 2007, 98% in low-income

countries• 1.4 million deaths in 2010• MDR-TB -prevalence in new cases around 3.6%

GLOBAL SITUATION• Since 1995, over 21 million patients have

been diagnosed and treated in DOTS programmes.

• In 2007, 5.5 million new and relapse TB cases were initiated on treatment under DOTS strategy.

• Of 2.5 million new smear positive patients registered in 2006, 85% were successfully treated under DOTS.

TUBERCULOSIS IN INDIA• Estimated incidence

1.96 million new cases annually0.8 million new smear positive cases annually75 new smear positive PTB cases/lakh population per

year • Estimated prevalence of TB disease

3.8 million bacillary cases in 2000 1.7 million new smear positive cases in 2000

• Estimated mortality 330,000 deaths due to TB each yearOver 1000 deaths a day2 deaths every 3 minutes

• Prevalence of TB infection40% (~400 million) infected with M.

tuberculosis (with a 10% lifetime risk of TB disease in the absence of HIV)

• Estimated Multi-drug resistant TB< 3% in new cases12% in re-treatment cases

• TB-HIV~2.31 million people living with HIV

(PLWHA)10-15% annual risk (60% lifetime risk) of

developing active TB disease in PLWHAAbout 80% of TB patients are between 15-54

year of age, while two- third of the cases are male.

India is the highest TB burden country accounting for more than one-fifth of the global incidence

Indonesia6%

Nigeria5%

Other countries20%

Other 13 HBCs16% China

14%

South Africa5%

Bangladesh4%

Ethiopia3%

Pakistan3%

Phillipines3%

India21%

Source: WHO Geneva; WHO Report 2009: Global Tuberculosis Control; Surveillance, Planning and Financing

Global annual incidence = 9.4 million

India annual incidence = 1.96 million

India is 17th among 22 High Burden

Countries (in terms of TB incidence rate)

MCQ’S1. National tuberculosis institute is

located at:A. New DelhiB. ChingelputC. BangaloreD. Chennai

2. Decrease in which of the following parameters indicate the decrease in tuberculosis problem in India ?

A. Incidence of infectionB. Prevalence of infectionC. Incidence of diseaseD. Prevalence of disease

3. Mycobacterium tuberculosis infection in humans is most because of :

A. ContactB. InhalationC. InfiltrationD. Inoculation

4. By WHO best criteria for TB diagnosis is ?

A. Sputum +veB. Chest painC. Cough- 3 weeksD. X-ray finding

5. The number of sputum +ve cases of TB per lakh in India is ?

A. 75B. 50C. 40D. 10

6. Which of the following is not false about the annual risk of TB ?

A. ARI of 1%= 75 new casesB. Current ARI in India is 1.7%C. It represents new cases of TBD. It is assessed by tuberculin conversion

in previously non-vaccinated children

REFRENCES

• Internet and Wikipedia• K. Park• Vivek Jain