When Antibiotics Become Ineffective

Inappropriate Drug Use Has Led to Resistant Bacterial Infections in a Major Hospital and Threatens Public Health

by Patricia McBroom

A dangerous rise in antibiotic-resistant bacterial infections has been documented in a large New York hospital by a Berkeley professor of public health.

His study suggests that drug-resistant enterococci, which cause blood infections, are "rapidly becoming endemic in an increasing number of hospitals in the United States."

Nearly one in five patients in the 988-bed teaching hospital was infected with enterococci bacteria that had become resistant to the antibiotic vancomycin.

"This is a major disaster," said Lee W. Riley, a microbiologist and epidemiologist here.

"Vancomycin is one of the drugs of last resort. If we see this happening with enterococci, it's not too long before it will happen with staphylococci."

These two classes of bacteria account for the great majority of infections contracted by patients in hospitals. Even when treatable with antibiotics, they carry high mortality rates. Bacteremia, caused by the organism Enterococcus faecium, is quite dangerous whether or not it is susceptible to vancomycin, said Riley.

This is the largest study of drug-resistant infections in a hospital setting and it documents the magnitude of the problem, said Riley. Resistant enterococci first appeared in the U.S. in 1989 and by 1993 had shown a 20-fold increase. The Riley study, conducted between 1990 and 1992, found 183 cases in the one hospital -- almost a fifth of the total number of beds.

"This is far more prevalent than we realized," said Riley. "Other major referral hospitals may well be suffering from the same problem."

It also appeared from the Riley study that the drug-resistant bacteria was more lethal than the vancomycin-susceptible form, particularly among subgroups of patients older than 50. Mortality data, however, presented a complicated picture and the death rate was not different between experimental and control groups when age and length of hospital stay were controlled.

In rough terms, mortality was twice as high among the 145 patients with resistant infections, as compared to the 145 control patients whose infections responded to antibiotics.

On the optimistic side, the study also identified several ways that hospitals could reduce the risk of infection and the transmission of drug-resistant bacteria.

Riley's study, published in the October issue of the journal Clinical Infectious Diseases, was co-authored by Nadia G. Tornieporth, Richard B. Roberts, Joylene John and Alice Hafner of Cornell University Medical College. Riley, who has recently become a professor of public health here, was formerly at Cornell.

At Berkeley, Riley has joined a new program at the School of Public Health to study drug-resistant infectious diseases which are expected to become an ever-more important public health threat.

"In the past five years, we have recognized that this is a major public health issue, even in developed countries like the United States," said Riley.

He said that new diseases are emerging such as AIDS, hantavirus infections, hemorrhagic colitis and Lyme disease.

Old ones, such as tuberculosis, are becoming drug-resistant at an increasing pace. He added that stories of a future plague may not be far off the mark.

On the other hand, drug resistance can be reversed, said Riley.

He pointed out that after a program of extremely close monitoring of antibiotic use in New York, where medical aides went to homes and directly observed patients taking medication, the prevalence of drug-resistant tuberculosis strains there have declined for three straight years. Riley believes that observation enforced the proper use of the antibiotics.

The same could happen in hospitals with drug-resistant bacterial infections, said Riley.

Heavy use of antibiotics was strongly associated with appearance of the resistant strain, and Riley is convinced that if hospitals applied antibiotics very carefully, the bacteria would begin to lose molecular protection against the drugs.

Other risks associated with the appearance of the resistant strain were long hospital stays and multiple transfers between floors.

The mortality rate among older patients in the intensive care unit tripled when the people with the resistant strain were compared to patients whose bacteremia still responded to vancomycin.

Also at increased risk of death were older patients in hemodialysis.

Riley is convinced that the resistant bacteria are more lethal, even though differences in mortality disappeared when the total group was compared and matched by age and length of hospital stay.


Copyright 1997, The Regents of the University of California.
Produced and maintained by the Office of Public Affairs at UC Berkeley.
Comments? E-mail berkeleyan@pa.urel.berkeley.edu.