Epidemiology of Tuberculosis

Prof. Ashry Gad MohamedMBChB, MPH, DrPH

Objectives

1. To perceive the magnitude of global tuberculosis problem.

2. To understand the cycle of infection of tuberculosis.

3. To understand methods of prevention and control of tuberculosis.

Magnitude of the problem • Globally, 9.2 million new cases

• 1.7 million deaths from TB, 2006

• of which 0.7 million cases and 0.2 million deaths were in HIV-positive people.

• 95% from developing countries• 19-43% of world population is infected• Between 2000-2020 G. One billion will get infection 200 million get sick 35 million will die

• Tuberculosis (TB) remains one of the world’s deadliest communicable diseases. In 2013, an estimated 9.0 million people developed TB and 1.5 million died from the disease, 360 000 of whom were HIV-positive.

TB is present in all regions of the world

Of the estimated 9 million people who developed TB in 2013, more than half (56%) were in the South-East Asia and Western Pacific Regions. A further one quarter were in the African Region, which also had the highest rates of cases and deaths relative to population. India and China alone accounted for 24% and 11% of total cases, respectively.

TB is slowly declining each year and it is estimated that 37 million lives were saved between 2000 and 2013 through effective

diagnosis and treatment.

About 60% of TB cases and deaths occur among men

• Almost 60 per cent of TB cases worldwide are now detected, and out of those, the vast majority are cured. Over the past decade, 26 million patients have been placed on effective TB treatment thanks to the efforts of governments and a wide range of partners. But the disease still kills 4400 people every day."

TB in Saudi Arabia

• During the period 2000-2013 there were a total of 64,345 reported TB cases. Of these 48% were Non-Saudis.

• TB annual incidence rate ranged between 14 and 17/100,000. For Saudis, the rate ranged between 8.6 and 12.2/100,000.

• Non-Saudis had 2-3 times higher incidence. Disease trend was rising over the first 10 years(2000-2010) then it started to fall slightly.

• The incidence increased with age, but only people older than 45 years showed a declining trend.

• Regional variations were observed. Makkah and Jazan regions had the highest incidence rates. Disease trends were rising over the last 10 years in Makkah and Central regions.

Factors contributing to rise of TB occurrence • HIV/AIDS 15% of deaths among AIDS patients

due to TB.• Poorly managed TB programs Wrong treatment regimen and

inconsistent or partial treatment lead to multidrug resistant TB (MDR-TB).

• Movement of people Global trade, traveling and migration

Agent

Mycobacterium tuberculosis complex

• M. Tuberculosis

• M. bovis

• M. africanum

• M. microti

• M. canetti

Tuberculosis Tuberculosis BacillusBacillus• Bacillus is thin, somewhat curved,

from 1 to 4 microns in length, with a complex cellular wall (lipid core) responsible for its characteristic coloration (acid-alcohol-resistant).

• Susceptible to sunlight, heat and dryness.

• Strictly parasitic and airborne; slow multiplier.

Reservoir

• Human

• Cattle

Modes of transmission

• 1-Air-borne droplet nuclei 1-5 μ m in diameter. remain airborne for long times.• Factors determining the probability of

infection No. of organisms expelled Conc. of organisms in air Length of exposure Immune status of exposed person

• 2-Ingesion of raw milk & diary products.

• 3-Direct invasion through wounds

Immune System Response

• Bacteria invades lung tissue

• White cells surround the invaders and try to destroy them.

• Body builds a wall of cells and fibers around the bacteria to confine them, forming a small hard lump.

• Bacteria cannot cause more damage as long as the confining walls remain unbroken.

• Most infected individuals never progress to active TB.

• Most remain latently-infected for life.

• Infection progresses and develops into active TB in less than 10% of the cases.

Incubation period: 4-12 weeks.

Diagnosis:

No single test is diagnostic in all situations, but complementary techniques should be used to generate complete & rapid information.

• 1-tuberculin test to identify infection*• 2-Acid fast bacilli smear• 3-Culture• MMR & X-ray• Genotype (DNA fingerprinting)*

Tuberculin test

0.1ml intradermal. • 48-72 hours• false negative poor nutrition poor general health overwhelming acute illness Immunosuppression• False positive BCG vaccination Other mycobacteria infection

Interpretation:

• On the basis of sensitivity, specificity and the prevalence of TB in different groups three cut points have been recommended for defining positive tuberculin reaction.

• 5mm. 10 mm. 15 mm.

Classification of tuberculosis

Based on exposure history, infection & disease.

• Class 0: No history of exposure

Negative tuberculin test (no

infection)

• Class 1: History of exposure

Negative tuberculin

• Class 2: Positive tuberculin (latent infection)

Negative X-ray

Negative bacteriology & radiol.• Class 3: Patients with clinically active TB

Whose diagnostic procedures

were completed (positive clinical,

bacteriological or/and radiological

of current TB).

• Remain in this stage until treatment is completed

• Pulmonary• Pleural• Lymphatic• Bone and/or joint• Genitourinary• Miliary• Meningeal• Peritonial • Others

• Class 4:

-Not clinically active TB

-Receiving treatment for latent infection

-Completed previously prescribed

-course of chemotherapy

-Abnormal stable radiol. With negative

bacteriology and positive tuberculin

• Class 5: Tuberculosis suspect

-Clinically active disease has not

been ruled out.

-Persons not adequately treated

in the past.

-Patient should not remain in this

stage more than 3 months

Prevention and control

Prevention:

• Case finding

• Vaccination

• Chemoprophylasis

• Environmental

Control:

• Reporting

• Isolation

• Concurrent disinfect ion

• Contact measures

• Treatment

Elements of the DOTS Strategy

• Political commitment

• Bacteriological diagnostic capacity

• Regular supply ofmedications and supplies

• Directly Observed Treatment Strategy

• Information system Registries

Two potential barriers

The first is multidrug-resistant tuberculosis (MDR-TB),Given limited laboratory and treatment capacity, countries project they will provide treatment only to an estimated 10% of people with MDR-TB worldwide in 2008.

The second threat to continued progress is the lethal combination of TB and HIV, particularly in Africa