Tougher Bugs, Few New Drugs
Tuberculosis, or TB, stubbornly refuses to be relegated to historical footnotes. WHO estimates that as much as a third of the world's population is infected with the organism that causes TB. With the development of effective treatment and improved public health measures, disease incidence in the United States steadily declined during the 20th century, only to surge in the late 1980s and early 1990s. Many of these new cases manifested in a virulent form that was resistant to isoniazid, one of the first-line and most effective anti-tubercular drugs.
While the number of new cases of TB has decreased nationwide since the mid-1990s, some parts of the country have not seen such a dip. The Washington area saw an increase of cases in 2002 from the previous year.
Increased TB incidence "is definitely a problem in the D.C. area," said Poretz, president-elect of the Bethesda-based National Foundation of Infectious Diseases and a clinical professor of medicine at Georgetown University School of Medicine. "We have had patients at Fairfax Hospital in the past six months with drug-resistant TB."
One patient, he said, showed marked resistance both to isoniazid and rifampin, the other first-line treatment for TB. Other medications are less effective and far more toxic to the patient. People using these drugs also take longer to treat: Instead of the conventional six-month course of therapy, multi-drug-resistant strains require treatment for up to two years.
Poretz said he has seen an occasional patient with infections that defied every drug available. While this phenomenon is unusual at Fairfax Hospital, where he sees the bulk of his patients, it's less so at other institutions.
"The organisms are completely resistant to everything," he said. "This has the potential for major problems."
Rates of syphilis and gonorrhea are also climbing, with the emergence of drug-resistant strains. As many as a third of gonorrhea strains found in the United States are resistant to penicillin and tetracycline. Syphilis also appears to be developing resistance to azithromycin, one of the drugs used to treat it. Officials in San Francisco documented eight cases in 2002 and 2003 in which the antibiotic failed to cure the infection.
A New Kind of Staph
One bug that greatly concerns Poretz is methicillin-resistant Staphylococcus aureus, better known as MRSA. S. aureus is responsible for a wide range of ailments, including pneumonia, skin, blood and bone infections, and is one of the primary causes of hospital-acquired infections.
Calling the organism methicillin-resistant is somewhat misleading: While the name implies resistance to only one antibiotic, MRSA organisms, which first appeared in the 1960s, are generally resistant to all antibiotics in the penicillin group, as well as to aminoglycosides, cephalosporins and other classes of antibiotics. MRSA accounts for 45 to 50 percent of all staph infections, said Poretz.
For the most part, MRSA infections can still be treated with other antibiotics, notably vancomycin. Once used by physicians only after other antibiotics had failed, it is increasingly becoming a first-line defense. And as anticipated, reports of staph infections with reduced susceptibility to vancomycin have begun to surface over the past few years.
In 2002, another chapter in antibiotics history was written: The first documented U.S. case appeared of an S. aureus infection that was completely resistant to vancomycin. (The patient was treated with aggressive wound care and another antibiotic.)
Linezolid, the first of a new class of antibiotics called oxazolidinones, was approved in 2000 and has proven effective against MRSA, among other pathogens. But only a year after its entry into the marketplace, a strain of linezolid-resistant MRSA was isolated found in a patient.
Even more worrisome is MRSA's entry into the community. Once confined to the hospital setting, it is being diagnosed increasingly in patients who have never been hospitalized and who have had no contact with anyone associated with health care facilities. Known as community-acquired MRSA, it is a completely separate strain from the hospital type.
Said Bartlett, "It's different in two ways. The way it causes resistance is unique, but more importantly, it has a unique virulence factor. It can cause a very virulent disease in some patients."
© 2004 The Washington Post Company