| Travel, Demographics, and Susceptibility |
Bacteria move readily from person to person; global travel has contributed significantly to the dissemination of novel pathogens, including drug-resistant strains. Stuart Levy refers to antibiotics as "societal drugs." They not only affect the bacteria in a treated individual, but also produce long-lasting changes in the kinds and proportions of bacteria in the environment and in human populations at large. For example, the multidrug resistant Streptococcus pneumonia (a bacterium that causes pneumonia and meningitis) has migrated from Spain to the United Kingdom, the United States, and South Africa.
Crowding also contributes to the dissemination of novel pathogens. Hospitals and nursing homes are particularly ideal environments for the exchange of microbes, including drug-resistant strains. Every year two million people acquire infections while hospitalized and 77,000 people die. Healthy caregivers and visitors can be unwitting carriers, but the scenario is worsened by the compromised status of patients. Cancer treatments and other immunosuppressives, such as those used for transplant patients, contribute to the problem. So does HIV. But any procedure, such as surgery or catheterization, that breaches the protective barrier of the skin increases the risk of infection. In crowded cities, especially in third world countries where adequate sanitation may be lacking, microbes arrive by immigrants from diverse locations. These bacteria can spread rapidly, particularly when immunizations and health care are unavailable.