The new strep A bacteria, like all streptococcal organisms, are typically inhaled, but they can also enter the body through a cut or scrape. The infection they provoke once inside the body is especially insidious: its early symptoms are easily mistaken for signs of the flu. In several cases, the bacteria have overwhelmed their host with pneumonia, and in others, with kidney and liver damage before the infected person has sought treatment. So advanced, the infection is extremely difficult to treat. Even if massive doses of penicillin succeed in killing the bacteria, there are no means available to counter the effects of the deadly toxin they produce—which actually causes the pneumonia and tissue damage.

Although reports of the first cases of fatal infection with the new strep A appeared in the medical literature in 1989 (Stevens et al., 1989), health problems associated with the streptococcus family of bacteria are not new. In the days before antibiotics, they were responsible for widespread outbreaks of scarlet fever and rheumatic fever. Nor are these bacteria rare. Strep throat is so common an ailment among children that it could almost be considered a rite of passage.

Much about the new strep A remains a mystery. Some scientists—noting the similarity between the toxin secreted by the new strep A and the toxin once seen with scarlet fever—believe that this bacterium is an old microbe making a comeback. Others consider this highly virulent form of strep the result of a recent bacterial mutation.

Whatever its origin, the new strep A deserves attention. Experts strongly encourage people to seek immediate medical care if they become very ill (high fever, sore throat) in a sudden fashion, especially if they have recently suffered a cut or burn.

Although cases of infection with this new, deadly microbe remain quite rare, their increasing incidence in the past two years is cause for concern. A vaccine for streptococcal infections is in development, but researchers estimate that it will not be ready for public use for at least another three years. In the meantime, the Centers for Disease Control is working to track the new strep A more closely, with the hope of learning more about the bacterium and how to stop it.

Table 2-1 is a list of emerging infectious agents, categorized by type of organism. Appendix B provides more detailed information on each of these agents. The committee recognizes that this list is continually expanding, mainly as a result of the growing numbers of immunocompromised individuals. Therefore, it may not contain all organisms that fit the definition above.

Once a new pathogen has been introduced into a human population, its ability to spread becomes a critical factor in emergence. The same is true for agents that are already present in a limited or isolated human population:



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