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EPIDEMIOLOGY OF TUBERCULOSIS:

EPIDEMIOLOGY OF TUBERCULOSIS Dr. Babita Assistant Professor Community Medicine

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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.

Global burden:

Global burden Globally In 2015, an estimated 10.4 million people developed TB 5.9 million males 56% 3.5 million females 34% 1 million children 10% 4.8 lacs – MDR tuberculosis 1.4 million TB deaths

Burden in India:

Burden in India India is the second-most population country in the world one fourth of the global incident TB cases occur in India annually. WHO statistics for 2014 giving an estimated incidence figure of 2.2 million cases of TB for India out of a global incidence of 10.4 million. India’s TB control programme is on track as far as reduction in disease burden is concerned. There is 42% reduction in TB mortality rate by 2012 as compared to 1990 level. Similarly there is 51% reduction in TB prevalence rate by 2012 as compared to 1990 level

Burden of Tuberculosis in India:

Burden of Tuberculosis in India TB burden 2014 Prevalence – 195/100000 population Incidence – 167/100000 population Mortality – 17/100000 population Percentage of TB cases with MDR-TB New – 2.2% Retreatment – 15% Notification rate of bacteriologically confirmed cases - 68/100000 population Notification rate of all new and relapse cases– 124/100000 population

TB TRANSMISSION:

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:

TB TRANSMISSION Transmission is defined as the spread of an organism, such as M. tuberculosis , from one person to another.

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Probability that TB will be transmitted depends on: Infectiousness of person with TB disease Environment in which exposure occurred Length of exposure Virulence (strength) of the tubercle bacilli The best way to stop transmission is to: Isolate infectious persons Provide effective treatment to infectious persons as soon as possible

INCUBATION PERIOD:

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

HISTORY OF TB:

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 tuberculosis Image credit: Janice Haney Carr HISTORY OF TB

TB HISTORY TIMELINE:

1840 1920 1860 1900 1940 1960 1980 2000 1880 1993: TB cases decline due to increased funding and enhanced TB control efforts 1884: First TB sanatorium established in U.S. 1865: Jean-Antoine Villemin proved TB is contagious 1943: Streptomycin (SM) a drug used to treat TB is discovered 1882: Robert Koch discovers M. tuberculosis Mid-1980s: Unexpected rise in TB cases 1943-1952: Two more drugs are discovered to treat TB: INH and PAS TB HISTORY TIMELINE

EPIDEMIOLOGICAL INDICES:

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

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Following epidemiological indices are generally used in TB : Prevalence of infection:- It is the percentage of individual who show a positive reaction to the standard tuberculin test. 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.

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Prevalence of disease (Case rate) :- Number of TB cases at a given point in time It is the best available practical index to estimate the number of infectious cases or case load in a community. Indices of new cases :- It is the percentage of new and relapse tuberculosis cases occurring during one year.

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Case notification rate New and recurrent episodes of TB notified to WHO for a given year expressed per 100000 population Case detection rate :- no. of notification of new and relapse cases in a year estimated incidence of such cases in same year

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Mortality rate :- The no. of deaths from TB in HIV negative patients per lakh population used as the index of the TB problem in a community.

Revised definitions of tuberculosis cases and treatment:

Revised definitions of tuberculosis cases and treatment Case definitions Bacteriologically confirmed case – bacteriological specimen positive by smear microscopy, culture or WRD (WHO endorsed Rapid Diagnostics) such as Xpert MTB/RIF Clinically diagnosed TB case – does not fulfill criteria for bacteriological confirmation but has been diagnosed with active TB by a clinician or other medical practitioner who has been decided to give the patient full course of TB treatment

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Classification according to Anatomical site of disease History of previous treatment Drug resistance HIV Status

Anatomical site of disease :

Anatomical site of disease Pulmonary tuberculosis (PTB) refers to any bacteriologically confirmed or clinically diagnosed case of TB involving the lung parenchyma or the tracheobronchial tree. Miliary TB is classified as PTB because there are lesions in the lungs. Extrapulmonary tuberculosis (EPTB) refers to any bacteriologically confirmed or clinically diagnosed case of TB involving organs other than the lungs, e.g. pleura, lymph nodes, abdomen, genitourinary tract, skin, joints and bones, meninges. A patient with both pulmonary and extrapulmonary TB should be classified as a case of PTB.

History of previous treatment :

History of previous treatment New patients have never been treated for TB or have taken anti-TB drugs for less than 1 month. Previously treated patients have received 1 month or more of anti-TB drugs in the past. They are further classified by the outcome of their most recent course of treatment

Previously treated patients:

Previously treated patients Relapse patients have previously been treated for TB, were 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 (either a true relapse or a new episode of TB caused by reinfection). 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.

Previously treated patients:

Previously treated patients 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. (These were previously known as treatment after default patients.) Other previously treated patients are those who have previously been treated for TB but whose outcome after their most recent course of treatment is unknown or undocumented .

Classification based on HIV status :

Classification based on HIV status HIV-positive TB patient refers to any bacteriologically confirmed or clinically diagnosed case of TB who has a positive 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 in the ART register once ART has been started. HIV-negative TB patient refers to any bacteriologically confirmed or clinically diagnosed case of TB who has a negative result from HIV testing conducted at the time of TB diagnosis

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HIV status unknown TB patient refers to any bacteriologically confirmed or clinically diagnosed case of TB who has no result of HIV testing and no other documented evidence of enrolment in HIV care.

Classification based on drug resistance :

Classification based on drug resistance Monoresistance: resistance to one first-line anti-TB drug only. Polydrug resistance : resistance to more than one first-line anti-TB drug (other than both isoniazid &rifampicin). Multidrug resistance : resistance to at least both isoniazid and rifampicin. Extensive drug resistance : resistance to any fluoroquinolone and to at least one of three second-line injectable drugs (capreomycin, kanamycin and amikacin), in addition to multidrug resistance. Rifampicin resistance : resistance to rifampicin detected using phenotypic or genotypic methods, with or without resistance to other anti-TB drugs.

Treatment outcome definitions :

Treatment outcome definitions Cured - A pulmonary TB patient with bacteriologically confirmed TB at the beginning of treatment who was smear- or culture-negative in the last month of treatment and on at least one previous occasion. Treatment completed -A TB patient who completed treatment without evidence of failure BUT with no record to show that sputum smear or culture results in the last month of treatment and on at least one previous occasion were negative, either because tests were not done or because results are unavailable. Treatment failed- A TB patient whose sputum smear or culture is positive at month 5 or later during treatment.

Treatment outcome definitions :

Treatment outcome definitions Died - A TB patient who dies for any reason before starting or during the course of treatment. Lost to follow-up - A TB patient who did not start treatment or whose treatment was interrupted for 2 consecutive months or more. Not evaluated - A TB patient for whom no treatment outcome is assigned. This includes cases “transferred out” to another treatment unit as well as cases for whom the treatment outcome is unknown to the reporting unit. Treatment success - The sum of cured and treatment completed.

SOME DEFINATIONS OF TB CASES:

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.

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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:

NATURAL HISTORY OF TB

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