Bacteria and Viruses

Bacteria and viruses surround us all the time. Yet only rarely do individuals be- come infected, and even more rarely do these infections lead to deaths. Under what conditions do these deaths occur?

First, individuals won’t develop fatal diseases if they are vaccinated against them. Virtually all U.S. children are vaccinated before they begin school—but not nec- essarily by the recommended ages.

Second, even in the absence of vaccinations, individuals exposed to micro- organisms may not become infected unless they already are physically weakened. For example, a significant percentage of all persons admitted to hospitals—a pop- ulation that obviously is already physically vulnerable—develop infections while in the hospitals, some of them life threatening. Similarly, individuals are far more susceptible to infection if age, malnutrition, poor housing, insufficient clothing, or other difficulties weaken their bodies. This explains why American tourists rarely contract tropical diseases when they travel to countries where disease is endemic, even if they don’t get vaccinated and don’t take drugs to prevent infection.

Third, the same factors that leave some people susceptible to infection help explain why, among those who do become infected with a given disease, some die whereas others experience only minor health problems. Measles, for example, is a minor childhood disease in the United States but a major killer in poorer countries.

Fourth, among those who become ill, death or long-term disability may not occur if individuals have ready access to good health care. For example, doctors can cure most bacterial infections in otherwise healthy individuals, and simply providing intravenous nutrition and fluids can save the lives of many infants who experience life-threatening diarrhea.