Hospitals motivated to skimp on infection control.

Hospitals fighting the spread of antibiotic-resistant bacteria are engaged in a self-preserving struggle, not only against the bacteria but also quite possibly against each other. A new mathematical model suggests that in urban areas, the presence of other hospitals gives each hospital an economic incentive to relax its infection a person sees control procedures, even though the overall result is bad for society.

In their model, David Smith of the National Institutes of Health in Bethesda, Md., and his coworkers portray infection control as a strategic game in which each hospital chooses to spend a certain amount on measures to prevent infection and thereby save money that it would otherwise have to spend on infected patients. Because a patient may acquire a drug-resistant bug in one hospital and then carry the infection to another, each hospital's choices about how vigilantly to fight infection can affect the success of efforts by other hospitals.

If Hospital A fights infection actively while Hospital B is more lax, the second hospital benefits from the first hospital's vigilance, since patients are unlikely to carry an infection from A to B. By contrast, vigilant Hospital A suffers, since some patients will bring the disease to it from lax Hospital B. Thus, the lax hospital freeloads on the vigilant hospital's investment.

The mathematical model predicts that the more hospitals there are in a given area, the less incentive each has to spend money on infection control, the researchers report in an upcoming Proceedings of the National Academy of Sciences.

The model may indicate one reason why drug-resistant bacteria often emerge first in metropolitan hospitals, which tend to have neighbor hospitals, the investigators suggest. In these areas, they argue, coordinating infection control centrally is probably more effective than leaving decisions to individual hospitals.--E.K.