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(Reuters) - The World Health Organization on Tuesday reported that extensively drug-resistant tuberculosis (XDR-TB), a lethal strain of the contagious lung disease, has spread to 55 countries and territories worldwide.
The emergence and spread of drug-resistant germs makes it harder and more expensive to treat, and increases the likelihood that people infected with tuberculosis will die.
Here are the main public health issues involved.
Although antibiotics can cure "normal" tuberculosis, many patients have failed to take the full six- to nine-month treatment course of existing drugs, leading germs to develop resistance. Doctors prescribing the wrong medicines and shortages of drugs in low-income countries have exacerbated these problems.
Multi-drug-resistant tuberculosis fails to respond to two or more of the most potent tuberculosis drugs, and can take two years or more to treat. Extensively-drug-resistant -- or XDR -- strains are even less responsive, defying nearly all existing tuberculosis drugs. A recent South Korean study found that half of the people infected with XDR-TB die as a result.
While tuberculosis is found predominantly in developing countries, the XDR-strain has been reported in both rich and poor nations, partly because developed economies have better screening and diagnostic technology to identify it.
To date, XDR-TB has been found in: Argentina, Armenia, Austria, Azerbaijan, Bangladesh, Botswana, Brazil, Canada, Chile, Colombia, Czech Republic, Ecuador, Estonia, France, Georgia, Germany, Hong Kong, India, Iran, Ireland, Israel, Italy, Japan, Kenya, Latvia, Lesotho, Lithuania, Mexico, Moldova, Mozambique, Myanmar, Namibia, Nepal, Netherlands, Norway, Oman, Peru, the Philippines, Poland, Portugal, Qatar, Romania, Russia, Slovenia, South Africa, South Korea, Spain, Swaziland, Sweden, Thailand, Ukraine, United Arab Emirates, United Kingdom, United States, Uzbekistan, and Vietnam.
World Health Organization experts say people with weakened immune systems face the biggest risks from highly drug-resistant tuberculosis, making its presence in southern Africa and other areas with high HIV/AIDS rates a particular concern.
The mingling of tuberculosis patients and immune-suppressed HIV sufferers in health clinics and hospital waiting rooms, as well as other crowded areas such as refugee camps and prisons, could prove especially lethal.
The U.S. Centers for Disease Control and Prevention said that although XDR-TB cases have been identified in the United States, it remains quite rare, while the WHO says the deadly strain is currently most common in Russia and former Soviet republics, India, China and South Africa.
U.S. researchers said last month that AstraZeneca's MERREM I.V., an intravenous antibiotic also called meropenem, used together with clavulanate, sold by GlaxoSmithKline in combination with amoxicillin as the drug Augmentin, killed laboratory-grown strains of XDR-TB. Those researchers plan to launch clinical trials using the drugs in South Korea and in South Africa.
Reporting by Laura MacInnis