Infection and transmission

Tuberculosis (TB) is a contagious disease. Like the common cold, it spreads through the air.
Only people who are sick with TB in their lungs are infectious.
When infectious people cough, sneeze, talk or spit, they propel TB germs, known as bacilli, into the air.
A person needs only to inhale a small number of these to be infected.

Left untreated, each person with active TB disease will infect on average between 10 and 15 people every year. But people infected with TB bacilli will not necessarily become sick with the disease.
The immune system “walls off” the TB bacilli which, protected by a thick waxy coat, can lie dormant for years.
When someone’s immune system is weakened, the chances of becoming sick are greater.
·        Someone in the world is newly infected with TB bacilli every second.
·        Overall, one-third of the world’s population is currently infected with the TB bacillus. ·        5-10% of people who are infected with TB bacilli (but who are not infected with HIV)          become sick or infectious at some time during their life.

HIV and TB
HIV and TB form a lethal combination, each speeding the other’s progress.
HIV weakens the immune system.
Someone who is HIV-positive and infected with TB is many times more likely to become sick with TB than someone infected with TB who is HIV-negative.
TB is a leading cause of death among people who are HIV-positive.
It accounts for about 13% of AIDS deaths worldwide.
In Africa, HIV is the single most important factor determining the increased incidence of TB in the past 10 years.
WHO and its international partners have formed the TB/HIV Working Group, which develops global policy on the control of HIV-related TB and advises on how those fighting against TB and HIV can work together to tackle this lethal combination.

Drug-resistant TB
Until 50 years ago, there were no medicines to cure TB.
Now, strains that are resistant to a single drug have been documented in every country surveyed; what is more, strains of TB resistant to all major anti-TB drugs have emerged. Drug-resistant TB is caused by inconsistent or partial treatment, when patients do not take all their medicines regularly for the required period because they start to feel better, because doctors and health workers prescribe the wrong treatment regimens, or because the drug supply is unreliable.
A particularly dangerous form of drug-resistant TB is multidrug-resistant TB (MDR-TB), which is defined as the disease caused by TB bacilli resistant to at least isoniazid and rifampicin, the two most powerful anti-TB drugs.
Rates of MDR-TB are high in some countries, especially in the former Soviet Union, and threaten TB control efforts.

From a public health perspective, poorly supervised or incomplete treatment of TB is worse than no treatment at all.
When people fail to complete standard treatment regimens, or are given the wrong treatment regimen, they may remain infectious.
The bacilli in their lungs may develop resistance to anti-TB medicines.
People they infect will have the same drug-resistant strain.
While drug-resistant TB is generally treatable, it requires extensive chemotherapy (up to two years of treatment) that is often prohibitively expensive (often more than 100 times more expensive than treatment of drug-susceptible TB), and is also more toxic to patients.

WHO and its international partners have formed the DOTS-Plus Working Group, which develops global policy on the management of MDR-TB, and facilitates access to second-line anti-TB drugs for approved projects.

TB in refugees and migrants
According to UNHCR, there were an estimated 20 million refugees and displaced and needy people in 2003.
Many refugees originate from countries with high TB incidence rates.
Poor nutrition and health mean that refugees are at particularly high risk of developing TB.
Untreated TB spreads quickly in crowded refugee camps and shelters.
It is difficult to treat mobile populations, as treatment takes at least six months and should ideally be supervised.

In many western European countries, and in the USA, over 50% of TB cases notified in 2001 were among people who were not born in the country and/or were not citizens of the country.

Effective TB control - DOTS
The internationally recommended approach to TB control is DOTS, an inexpensive strategy that could prevent millions of TB cases and deaths over the coming decade. The DOTS strategy for TB control consists of five key elements:
·        government commitment to sustained TB control;
·        detection of TB cases through sputum smear microscopy among people with symptoms
·        regular and uninterrupted supply of high-quality anti-TB drugs;
·        6–8 months of regularly supervised treatment (including direct observation of drug-taking for at least the first two months);
·        reporting systems to monitor treatment progress and programme performance;

Once patients with infectious TB (bacilli visible in a sputum smear) have been identified using microscopy services, health and community workers or trained volunteers observe patients swallowing the full course of the correct dosage of anti-TB medicines.
The most common anti-TB medicines are isoniazid, rifampicin, pyrazinamide, streptomycin and ethambutol.

Sputum smear testing is repeated after two months, to check progress, and again at the end of treatment.
The recording and reporting system ensures that the patient’s progress can be followed throughout treatment.
It also allows assessment of the proportion of patients who are successfully treated, giving an indication of the quality of the programme.

·        The DOTS strategy produces cure rates of up to 95% even in the poorest countries.
·        The DOTS strategy prevents new infections by curing infectious patients.
·        The DOTS strategy prevents the development of drug resistance by ensuring that the full course of treatment is followed.
·        A six-month supply of drugs for treatment under the DOTS strategy costs as little as US$ 10 per patient in some parts of the world.
·        The World Bank has ranked the DOTS strategy as one of the “most cost-effective of all health interventions”.

Implementation of DOTS worldwide
Since its introduction in 1991, more than 17 million patients have received treatment under the DOTS strategy.

By the end of 2002, all 22 of the countries with the highest number of TB cases, which together have 80% of the world’s estimated incident cases, had adopted the DOTS strategy.
By the end of 2003, 182 countries were implementing the DOTS strategy, and 77% of the global population was living in parts of countries where the DOTS strategy was in place. In India alone, 740 million people (almost 70% of the total population) were living in parts of the country where the strategy had been implemented.

In 2001, the Global DOTS Expansion Plan was published.
The two pillars of the plan are the development of medium-term (at least 5-year) plans for TB control in all countries, and the establishment of national interagency coordination committees (NICCs).
All 22 countries with the highest number of cases had formulated plans by the end of 2003, and all but two had NICCs that met regularly.

Global and regional incidence
The table below shows the estimated TB incidence (the number of new cases arising each year) and mortality in each of the WHO regions.
The incidence of all forms of TB, the incidence of infectious (smear-positive) cases, and mortality are shown both as the total number of cases and as the rate per 100 000 population.

The largest number of cases occurs in the South-East Asia Region, which accounts for 33% of incident cases globally.
However, the estimated incidence per capita in sub-saharan Africa is nearly twice that of the South-East Asia, at 350 cases per 100 000 population.

It is estimated that 1.75 million deaths resulted from TB in 2003.
As with cases of disease, the highest number of estimated deaths is in the South-East Asia Region, but the highest mortality per capita is in the Africa Region, where HIV has led to rapid increases in the incidence of TB and increases the likelihood of dying from TB

Estimated TB incidence and mortality, 2003
	Number of cases (thousands)		Cases per 100 000 population		Deaths from TB (including TB deaths in people infected with HIV)
WHO region	All forms (%)	Smear-positive	All forms	Smear-positive	Number (thousands)	Per 100 000 population
Africa	2372 (27)	1013	345	147	538	78
The Americas	370 (4)	165	43	19	54	6
Eastern Mediterranean	634 (7)	285	122	55	144	28
Europe	439 (5)	196	50	22	67	8
South-East Asia	3062 (35)	1370	190	85	617	38
Western Pacific	1933 (22)	868	112	50	327	19
Global	8810 (100)	3897	140	62	1747	28

Redactie: info(at)rijskamp.com                         
Cagayan de Oro September 28, 2005

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