Anthony S. Fauci is director of the National Institute of Allergy and Infectious Diseases
The ancient scourge of tuberculosis kills someone every 15 seconds, amounting to 5,000 deaths each day worldwide and nearly two million each year. More than 16 million people have the active form of TB, and two billion - about one third of the world's population - are carriers of TB bacteria. About 20 percent of cases resist treatment with the two mainstay TB drugs.
Recently, even more dangerous strains of TB bacteria - resistant to most or all drugs currently used - have emerged. These bacteria, which cause a sometimes incurable form of TB, have been documented in at least 20 countries, and additional undocumented cases likely have occurred. Clearly, this extensively drug-resistant TB - known as "XDR-TB" - is a frightening menace.
So far, XDR-TB accounts for an estimated 2 percent of all TB cases. But in infectious diseases, almost all crises start out small. We now have an opportunity to act quickly and prevent XDR-TB from becoming a global health crisis.
The emergence of XDR-TB should have been predicted. Drug resistance is a common problem with nearly all infectious diseases. While tuberculosis is usually curable, the drugs used to treat it must be taken every day for six months. Many patients stop therapy once they begin to feel better because of inconvenience or side effects. Such intermittent use, along with the high prevalence of TB in people with HIV infection whose immune systems are compromised, has led to the emergence of XDR-TB.
The most important action we can take is to make certain that TB-control programs function effectively and ensure that all TB patients receive appropriate drugs and keep taking them for the entire duration of therapy. In the past, as resistant strains of TB have emerged, newer drugs and more complex regimens were developed - but then XDR-TB strains emerged that resist even these second-line therapies. To prevent XDR-TB from becoming even more prevalent, it is crucial to administer second-line TB drugs under very tightly controlled conditions so they retain their potency.
Another important step is to develop and implement rapid, easy-to-use diagnostic tests. Drug-resistant TB is often identified only when patients fail to respond to first-line therapy, at which time they are shifted to second-line drugs. But all along, patients continue to spread TB bacteria, which are often already drug-resistant. Improved diagnostic tests will help ensure that patients are treated with effective drugs from the outset, and will help prevent treatment failures and the spread of drug-resistant bacteria.
We also need to accelerate drug-development efforts. For the first time in decades, TB researchers are making substantial progress. Last year, two promising new TB drugs entered clinical trials. These drugs may potentially reduce the long duration of treatment now required. More than 10 new drug candidates are being tested in animals.
A vaccine against TB has been available for several decades, but it does not reliably prevent TB in adults. More effective vaccines are desperately needed.
It is also important to recognize that most TB infections occur in people who already suffer from other diseases, such as HIV/AIDS, parasitic diseases, hepatitis or diabetes. Scientists tend to study one disease at a time, examining individual microbes in isolation. We need to expand laboratory investigations to examine the co-infections seen together with TB in the real world.
We have a limited window of opportunity to deal with XDR-TB. We can avert the threat if we address it in a timely and appropriate manner. If we fail to act now, XDR-TB could develop into an enormous problem with fatal consequences throughout the world.