Modelo dinámico del VE

Hospitals always have been places where people risk picking up an infection. As an inevitable side effect of having large numbers of ill or injured people in such a confined area, disease microbes travel from host to host and establish colonies within any machinery that allows them to live and multiply. Even in the largest medical centers with the most sophisticated filtering systems and sanitation procedures, a lot of time and effort goes to preventing and combating infections.

The disinfectants that perfume hospital corridors and rooms hold down the microbes that can be deposited by a patient’s sneeze or along with a fingerprint. Though bacterial infections can spring up in patients following surgery, antibiotics have been able to keep them in check. But it is not possible to eliminate all the infectious disease microbes within a hospital building. Physicians and nurses travel from

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3) Over time, microbes such as bacteria and viruses evolve an immunity to the most commonly prescribed drugs.

1) Patients with different maladies enter a hospital. The enclosed conditions provide a perfect place for germs to spread, even with rigorous sanitation and disease control practices.

2) Hospital staff administers standard antibiotics and other antimicrobial drugs both to patients who come in sick and to patients who pick up diseases after arriving.

4) The drug-resistant microbes work their way into the hospital population, infecting patients, visitors, and health care workers. Not everyone will come down with a resistant disease, but some will act as carriers.

5) As more patients fall ill to drug-resistant diseases, physicians have to turn to more powerful drugs. Over time the process repeats until, some people fear, it reaches the point where there are no drugs left to fight one or more diseases.

DEVELOPING DRUG RESISTANCE IN THE HOSPITAL

patient to patient at all hours, and new patients arrive with new diseases all the time. Patients die from postoperative infections or from diseases such as pneumonia that they contract during their stay. A late-1990s estimate showed that of the 2 million or so hospital patients who come down with an infection during their stay, about 5 percent—90,000 peo-ple—succumb to the new disease. But these deaths, though tragic, are not unexpected, and modern hospitals usually have been able to keep these diseases under control. That is, unless the microbes manage to outwit the medicines.

Almost as soon as World War II ended, people began benefiting from the sudden flood of antibiotics that followed the penicillin revo-lution. Vaccination, antiviral drugs, and drugs to combat parasitic infections played equally effective roles in raising lifespans and expec-tations of good health. Hidden among these medical success stories, though, were signs of trouble for the future. During his experiments with penicillin, Sir Alexander Fleming noticed that some Staphylococcus bacteria seemed to adapt to and live with the drug. Before the end of the 1940s, hospitals around the world experienced outbreaks of bacte-rial infections that seemed to ignore some antibiotics. Such resistance to the effects of penicillin, streptomycin, and similar drugs was unusual, however, and the public neither noticed nor seemed to care about the wonder drugs’ sudden vulnerability.

During the next two decades, microbes and medicine ran a close race to see which side would dominate the other. For the most part, healing drugs kept ahead of diseases. Then, things began tipping in the microbes’ favor. Two types of bacteria—Haemophilus influenzae, which causes some respiratory infections, and Neisseria gonorrhaeae, the source of the venereal disease gonorrhea—developed strains that essentially ate penicillin in the mid-1970s. With both bacteria, the invulnerable strain appeared in people who were taking penicillin as a way to prevent disease, rather than to cure it. The resistant gonorrhaeae, in particular, developed during the Vietnam War in South Vietnamese prostitutes who were taking penicillin precisely to avoid coming down with gonorrhea.

As with earlier drug-resistant germs, physicians were able to treat these strains with stronger antibiotics or with drugs that boosted the immune system. However, using more powerful drugs created other problems. Antibiotics do not just target microbes that cause disease.

Once the drugs reach the bloodstream, they can kill any bacterium in their path, even ones that have no effect on the body. These bugs do a valuable service for the people they inhabit: by taking up space in the body, they deny diseases a place to grow. Eliminating these harmless

germs opens up living space for harmful microbes. Other bacteria, such as Escherichia coli, aid digestion, and killing them off wreaks havoc in the intestines until new E. coli move in.

Using more powerful antibiotics also leads to the development of more powerful germs. For the rest of the 1970s and throughout the 1980s, hospitals and physicians reported that previously simple infec-tions were resisting standard drugs. Soon, bacteria began developing the ability to fight off a spectrum of progressively stronger drugs.

Microbiologists created a new term to describe these bacteria, as well as other microbes that were becoming immune to many medicines: the multiple-drug-resistant, or MDR, microbe. MDR bacteria are the most common of this new class of microbes. They are the ones that resist most antibiotics except for drugs such as vancomycin, which is so potent that it has been used as a “drug of last resort.” One of the great-est public-health fears is that a widespread vancomycin-resistant dis-ease might appear one day.