Facts On Infectious Diseases

Deaths from infectious diseases have declined markedly in the United States during the 20th century. This decline contributed to a sharp drop in infant and child mortality and to the 29.2-year increase in life expectancy. In 1900, 30.4% of all deaths occurred among children aged less than 5 years; in 1997, that percentage was only 1.4%. In 1900, the three leading causes of death were pneumonia, tuberculosis (TB), and diarrhea and enteritis, which (together with diphtheria) caused one third of all deaths. Of these deaths, 40% were among children aged less than 5 years. In 1997, heart disease and cancers accounted for 54.7% of all deaths, with 4.5% attributable to pneumonia, influenza, and human immunodeficiency virus (HIV) infection. Despite this overall progress, one of the most devastating epidemics in human history occurred during the 20th century: the 1918 influenza pandemic that resulted in 20 million deaths, including 500,000 in the United States, in less than 1 year--more than have died in as short a t ime during any war or famine in the world. HIV infection, first recognized in 1981, has caused a pandemic that is still in progress, affecting 33 million people and causing an estimated 14 million deaths. These episodes illustrate the volatility of infectious disease death rates and the unpredictability of disease emergence.

Public health action to control infectious diseases in the 20th century is based on the 19th century discovery of microorganisms as the cause of many serious diseases (e.g., cholera and TB). Disease control resulted from improvements in sanitation and hygiene, the discovery of antibiotics, and the implementation of universal childhood vaccination programs. Scientific and technologic advances played a major role in each of these areas and are the foundation for today's disease surveillance and control systems. Scientific findings also have contributed to a new understanding of the evolving relation between humans and microbes.

Some infectious disease experts wager future epidemics will take a greater toll on human life than those in the past, despite medical advances made over the past century. We are increasingly more vulnerable to infectious diseases, these experts point out, because of the growing proportion of people residing in urban areas, which act as magnets for epidemics. In 1800, less than 2 percent of the world's population lived in urban communities.

Air travel, in addition, allows diseases to spread between cities on opposite ends of the globe in a matter of hours.

Prominent on the list of new or reemerging diseases that have health officials concerned are invasive strep infections, tuberculosis (TB), hantavirus pulmonary syndrome, malaria, and dengue.

Changes in the Streptococcus bacterium that give it more punch are credited with causing recent outbreaks of "flesh-eating" strep and streptococcal toxic shock syndrome (strep TSS).

Both these infections are caused by invasive strep--a type of Streptococcus that more readily spreads in the body than the types that cause strep throat. Studies by Dennis Stevens at the Veterans Affairs Medical Center in Boise, Idaho, suggest invasive strep is armed with two powerful toxins. In the body's furious attempt to rid itself of one of the toxins, the immune system can foster the destruction of infected muscle tissue or the sheath that covers the muscle (the flesh-eating manifestation) or prompt the body to go into shock, which is often fatal, or both. Damage also is wreaked by the other toxin, an enzyme that destroys tissue by breaking down protein.

Invasive strep usually enters the body through minor injuries, such as deep bruises, punctures, or chicken pox blisters. Only rarely is the deadly form of strep acquired through person-to-person contact. People with invasive strep usually don't complain of a sore throat, but rather often have flu-like achiness and fatigue that is followed by a number of symptoms, including pain in one region of the body, cough and difficulty breathing, or painful skin that is red, hot and swollen and gradually purples and forms blisters. This can be accompanied or followed by confusion, low blood pressure, and coma.

The antibiotics penicillin, erythromycin and clindamycin are the drugs of choice for treating invasive strep infections; the earlier treatment is begun, the better the outcome. Surgical removal of infected tissue, possibly including limb amputation, may be necessary. Researchers are currently testing a vaccine for invasive strep.

After a comforting steady decline since the 1950s, TB incidence in the United States began to climb in 1985, setting off alarms in the medical community. According to CDC (Centers for Disease Control and Prevention), in 1994 there were 24,361 cases of TB in the United States--about 2,000 more cases than in 1984.

TB's comeback in this country is tied to the rising numbers of people whose immune systems are weakened by HIV infection, cancer and chemotherapy, or the drugs taken following an organ transplant. A resurgence of the disease is also being fostered by increasing poverty and drug abuse, as well as by increasing numbers of immigrants to this country with TB.

Well-known to the ancient Egyptians, TB is caused by airborne bacteria expelled from the lungs when a person with active TB coughs, sneezes or speaks. Repeated exposure to these droplets can infect another person's lungs.

The immune defenses of healthy people usually prevent TB infection from spreading beyond a small area of the lungs by creating a barricade around the bacteria. This walled-up infection is called latent TB and may be present throughout a person's life. People with latent TB test positive on the TB skin test. About 10 to 15 million people in this country have latent TB.

Other possible resurgent and emerging diseases include a dangerous kind of E. coli infection spread by contaminated meat, drug-resistant cholera, deadly Ebola infection, and a new disease called human granulocytic ehrlichiosis, which is spread by the type of ticks that can also carry Lyme disease.

Experts can't predict if any of these diseases will become a great problem. The best protection is to be aware of the possibility and take precautions to prevent their spread. As a 1992 National Academy of Sciences report on emerging infections points out, "despite a great deal of progress in detecting, preventing, and treating infectious diseases, we are a long way from eliminating the human health threats posed by ... a broad array of microbes."

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